Neuromuscular adaptations after 12 weeks of light‐ vs. heavy‐load power‐oriented resistance training in older adults

This study aimed to determine the specific adaptations provoked by power‐oriented resistance training using light (LL‐PT, 40% 1‐RM) vs. heavy (HL‐PT, 80% 1‐RM) loads in older adults. Using a randomized within‐subject study design, 45 older adults (>65 years) completed an 8‐week control period (CTR) followed by 12 weeks of unilateral LL‐PT vs. HL‐PT on a leg press. The 1‐RM, theoretical force at zero velocity (F0), maximal unloaded velocity (V0), and maximal muscle power (Pmax) were determined through a force‐velocity relationship test. Isometrically, the rate of force development (RFD) and the corresponding muscle excitation of the knee extensor muscles were assessed. In addition, muscle cross‐sectional area (CSA) and architecture of two quadriceps muscles were determined. Changes after CTR, LL‐PT and HL‐PT were compared using linear mixed models. HL‐PT provoked greater improvements in 1‐RM and F0 (effect size (ES) = 0.55‒0.68; p < 0.001) than those observed after LL‐PT (ES = 0.27−0.47; p ≤ 0.001) (post hoc treatment effect, p ≤ 0.057). By contrast, ES of changes in V0 was greater in LL‐PT compared to HL‐PT (ES = 0.71, p < 0.001 vs. ES = 0.39, p < 0.001), but this difference was not statistically significant. Both power training interventions elicited a moderate increase in Pmax (ES = 0.65‒0.69, p < 0.001). Only LL‐PT improved early RFD (ie, ≤100 ms) and muscle excitation (ES = 0.36‒0.60, p < 0.05). Increased CSA were noted after both power training programs (ES = 0.13‒0.35, p < 0.035), whereas pennation angle increased only after HL‐PT (ES = 0.37, p = 0.004). In conclusion, HL‐PT seems to be more effective in improving the capability to generate large forces, whereas LL‐PT appears to trigger greater gains in movement velocity in older adults. However, both interventions promoted similar increases in muscle power as well as muscle hypertrophy.

| INTRODUCTION
The aging process is associated with progressive losses of muscle strength and power, which are mainly explained by changes of the neuromuscular system. 1 One of the most effective countermeasures against this age-related functional decline is resistance training. 2 Current resistance exercise recommendations for older adults suggest including power-oriented exercises (ie, concentric movements performed as fast as possible) into training programs, since muscle power is most critical to physical performance in daily tasks. [2][3][4] Moreover, muscle power declines at a faster rate than both muscle mass and strength, making it the main target of resistance training in older adults. 5,6 In power-oriented resistance training, commonly called power training, subjects aim to perform concentric contractions as fast as possible, in order to maximize mechanical power output and the demands on the neuromuscular system. 7,8 As previous studies have shown, power training is more effective in improving muscle power and physical function of older adults than traditional resistance training. [8][9][10] Furthermore, a recent metaanalysis has demonstrated the benefits of power training in improving the muscle mass of older adults. 11 Since mechanical power is the product of force and velocity, it can be increased through both gains in strength and movement velocity. For example, gains in muscle power can be obtained through plyometric exercise 12,13 (high-velocity demands) and maximal strength training (high-force demands) 14 in older adults, although different mechanisms may underlie the functional gains. While plyometric exercise is assumed to increase fascicle length and the effectiveness of the stretch-shortening cycle (favoring high-velocity adaptations), 12,13 maximal strength training typically augments muscle size and neural drive (favoring high-force adaptations). 14 For this reason, several studies have attempted to determine the optimal training loads (ie, intensities) to maximize power development in older adults. [15][16][17] A respective systematic review suggested that a wide range of intensities-from light-moderate (≤50% 1-RM) to heavy (≥80% 1-RM) loads-may be used to improve muscle power and physical function. 18 However, the low number of studies directly comparing the effect of power training using different loads precluded the authors of this study from performing a meta-analysis, thus limiting its significance. Furthermore, it should be noted that earlier studies mostly failed to equate the prescribed volume load (ie, the number of repetitions × external load) of the implemented power training programs, which complicates the comparison of training effects. 19 In consequence, it is still unknown whether completing progressive systematic resistance training targeting the high-force or high-velocity end of the force-velocity spectrum would be preferable to increase muscle power. This knowledge might help to optimize the prescription of power training programs for older adults. 20 Therefore, the present study aimed to evaluate the effects of volume load-equated light-vs. heavy-load power training on (1) the force-velocity relationship and maximal dynamic strength, (2) maximal isometric force and rate of force development and (3) muscle size and architecture in the lower limbs of older adults. According to the specificity principle of exercise training, we hypothesized that heavier loads would provoke larger increases in the high-force, low-velocity portion of the force-velocity profile whereas lighter loads would be more beneficial in improving performance in low-force, high-velocity contractions. On the other hand, both power training interventions would improve rate of force development since in both cases the repetitions are performed at maximal intended velocity, which would maximize neural drive adaptations, a major determinant of rapid force performance. 21 Finally, maximal isometric force might increase in connection with the expected hypertrophy response, 11 which could be similar in both interventions due to the equal volume load. 19

| Study design
The present investigation addressed the objective I of a randomized controlled trial previously described and registered in clinicaltrials.gov (ID: NCT03724461, October 30th, 2018). 22 The study was performed as a within-person randomized controlled trial with repeated measures and included an 8-week control period (CTR) followed by 12 weeks of power training targeting the lower limbs. By using a control period (ie, a longitudinal study design) rather than a parallel control group we aimed to minimize bias related to biological variability and learning effects during testing, thus increasing statistical power. 23 For the training period, participants were randomized to one of the three following study arms: (i) one leg performed light-load power training (LL-PT) and the contralateral leg did not perform any exercise; (ii) one leg performed heavy-load power training (HL-PT) and the contralateral leg did not perform any exercise; and (iii) one leg performed LL-PT and the contralateral performed HL-PT ( Figure 1). Within each group, the treatment assigned to each leg was randomized. Detailed information about the study design has been previously provided in a respective methods paper. 22 Briefly, the rationale for this three-arm unilateral training design was based on the advantages that unilateral exercise models confer in terms of reducing inter-individual variability and increasing statistical power, 24 and also on the possibility to investigate crosseducation effects, which is the objective II of the abovementioned project. Accordingly, the data acquired in the non-exercised contralateral legs are not directly pertinent to the scope of this report and, therefore, not presented.

| Participants
Older adults (≥65 years old) were recruited through advertisements and community newsletters. Those who accepted to participate were examined by a geriatrician and screened for the following exclusion criteria: frailty or lowlevel of physical function (ie, SPPB score ≤7 points), history of regular resistance exercise training in the last 3 years or undergone knee arthroplasty. A flow chart showing the process of participant selection and allocation, as well as the reasons for dropouts, is shown in Figure 1. Finally, 45 participants (ie, 90 legs) completed the CTR period, and 31 participants (ie, 62 legs) completed the power training period. Further details concerning the a priori sample size calculation, participant recruitment and exclusion criteria are provided in the original study protocol. 22 All subjects were informed about the potential risk and benefits associated with participation in this study before giving written informed consent. The study was performed in accordance with the Helsinki Declaration and approved by the Clinical Research Ethics Committee of the Complejo Hospitalario de Toledo (Spain).

| Interventions
Detailed descriptions of all interventions are provided in the original study protocol. 22 To summarize, the participants were asked to maintain their lifestyle during the CTR period, particularly regarding physical activity, diet and to inform study administrators about any changes in their medication. Regarding the exercise interventions, unilateral power training targeting the lower limbs was performed on a horizontal leg press device (Selection MD, Technogym, Italy) twice a week, for 12 weeks with a minimum of 48 hours between sessions. LL-PT consisted of 6 sets of 12 repetitions with a load equivalent to 40% 1-RM, whereas HL-PT consisted of 6 sets of 6 repetitions with a load equivalent to 80% 1-RM. Thus, both power training programs had the same volume load (ie, number of repetitions × external load relative to 1-RM). Participants were requested to perform F I G U R E 1 Participant selection, allocation and dropouts the concentric phase of each repetition as fast as possible, independently of the load used. A 2-min passive recovery was allowed between sets. The 1-RM was re-assessed every 4 weeks to adjust training load and ensure progressive overload. After completing the 12 weeks of training, a subsequent training program for the contralateral leg was offered to those participants who only trained one of their lower limbs (ie, study arm i and ii) and whose lower limb muscle power asymmetry was greater than 15%; that is, a level of asymmetry that exceeds the normal physiological range. 25 For a better characterization of training programs, the principal mechanical characteristics (load, time under tension, range of movement, work, velocity, acceleration, force, power as well as the relative loss of velocity, force and power within each exercise set) of LL-PT and HL-PT were tested during the third training session.

| Procedures
Comprehensive and detailed information about procedures has been previously depicted in the respective methods paper. 26 The following outcomes were evaluated at three different time points: week 0 (W0) corresponding to the beginning of CTR, week 8 (W8) corresponding to the end of CTR and the beginning of the intervention period, and week 20 (W20) corresponding to the end of the intervention period. The participants completed two familiarization sessions before W0, and the final evaluation (ie, W20) was conducted at least 72 h after the last exercise session to ensure that participants were fully recovered.
To measure neuromuscular performance (ie, muscle function), the 1-RM and force-velocity (F-V) relationship were measured unilaterally through a progressive load test (including at least 4 loads ranging from 40% of body mass to 1-RM), previously validated, 27 performed on the horizontal leg press device instrumented with a linear position transducer (Linear encoder, Chronojump Bosco System, Spain; 1019 Hz) and a force plate (Type 9286BA, Kistler, Switzerland; 1000 Hz). A linear model was fitted to F-V data collected above 45% of the theoretical maximal isometric force (F 0 ), which together with maximal unloaded velocity (V 0 ) were obtained from the force and velocity intercepts, respectively. 22 Accordingly, both the slope of the F-V relationship (S FV ) and maximal muscle power (P max ) were determined. Moreover, since the validity of V 0 values obtained from linear models has recently been questioned, 28 the velocity exerted at 50% of F 0 (ie, the optimal velocity (V opt ) or the velocity coinciding with P max ) was also calculated. In addition, the velocity and power values at 85% of the individual body weight were calculated (V 0.85BW and P 0.85BW , respectively) as proxies of unilateral physical function. This value (0.85 body weight) was chosen based on previous evidence on unilateral force demands registered in older adults while performing a functional task. 29 Besides, the maximal isometric force (MIF) and the rate of force development (RFD) in the first 50, 100 and 200 ms (RFD50, RFD100 and RFD200, respectively) after the onset of the contraction were evaluated through maximal voluntary isometric contractions (MVIC) of the knee extensors performed on a custom-built rigid chair (Telju Fitness, Spain) instrumented with a strain gauge (Linear Force-SmartLead, Noraxon, USA; 1500 Hz, resolution = 0.07 N). 22 For this purpose, the participants were seated with knee and hip angles of 90º and 120º, respectively (180º full extension). The tested lower leg was connected to the strain gauge through an ankle brace fixed just above the malleoli and a steel cable with minimal compliance. The participants were instructed to extend their knee as fast and strong as possible and hold the contraction for 3 s after the cue "ready, set, go!". Moreover, strong verbal encouragement and visual feedback were given to ensure maximal efforts. Countermovement prior to contraction onset was not allowed and checked by an experienced evaluator through force signal inspection. Participants were also instructed to avoid any movements, involving the trunk or hip. The best three of five valid trials (separated by 60 s) were averaged and considered for analysis. Surface electromyography signals (EMG) of the quadriceps (vastus lateralis, vastus medialis and rectus femoris muscles) and biceps femoris (long head) muscles were acquired during MVICs (DTS EMG sensors & Desktop DTS, Noraxon, USA). The SENIAM recommendations were followed when placing bipolar electrodes. 30 Force and EMG signals were synchronously captured and processed within the same software (Myoresearch 3.10, Noraxon, USA). EMG signals were amplified and filtered with a band-pass filter between 10 and 500 Hz (common mode rejection ratio <100 dB, input impedance <100 MΩ and gain = 500) and then smoothed (100 RMS) and normalized to the muscle-specific maximum value registered during MVICs. Finally, the integrated area under the EMG signal (iEMG) during the first 50, 100, and 200 ms of contraction (QiEMG50, QiEMG100 and QiEMG200, respectively) was determined together with the corresponding biceps femoris co-activation. 22,31 . An automated threshold method was used to detect the onsets of muscle excitation and force production as the instant when each signal exceeded a level corresponding to the mean plus 3 SD of their respective baseline noise. Finally, muscle morphology was evaluated through ultrasound-based measurements over the mid-thigh portion (50% of femur length) of each leg (MyLab 25, Esaote Biomedica, Italy; 50 mm, 10-15 MHz linear-array probe). 22 The cross-sectional area of the rectus femoris and the vastus lateralis (RF CSA and VL CSA ) were determined at the same site, using the extended field of view feature of the scanner to detect changes in muscle size.
Images were analyzed with Fiji, an open-source software for biomedical image analysis. 32 Then, images of the vastus lateralis were acquired in the fascicle plane at an individually determined optimal location (characterized by parallel aponeuroses and consistency of the fascicle orientation) to analyze muscle architecture. An automated software was used to compute the dominant fascicle pennation angle (VL PA ) and length (VL FL ). 33 To maximize accuracy and reliability, minimal pressure and abundant transmission gel were applied during the examination. All images were captured and analyzed by the same experienced operator. Demonstrative ultrasound images from a representative subject are shown in Figure 2. Moreover, the position of the EMG electrodes and ultrasound probe was recorded onto a transparent acetate sheet placed on the surface of the thigh to achieve consistency in measurement sites across testing days. Inter-session (7 days) coefficients of variation for MIF, and RFD at 50, 100, and 200 ms were 4.7, 27.1, 21.0, and 12.4%, respectively. Coefficients of variation for RF CSA , VL CSA, VL PA , and VL FL were 5, 3.8, 6.2 and 10%, respectively.

| Statistical analysis
Data are presented as means ± standard deviation. Normality was assessed by the Shapiro-Wilk's test and data were logtransformed in case of non-normal distribution. The outcomes were registered as the absolute changes noted during the 8-week control period (ie, W8 minus W0) and the 12-week power training period (ie, W20 minus W8). Linear mixedeffect model analyses were conducted to evaluate the main effects of treatment: CTR, LL-PT and HL-PT. Of note, linear mixed-effect models are generally recognized for their ability to handle missing data (eg, legs that only completed the CTR period) and their adequacy to analyze partially correlated data (eg, two legs of the same participant contributing to two different treatment groups). 34 In addition, linear mixed-effect models combine both, within-subject and between-subject comparisons as required by the provided data. For comparison, treatment (LL-PT vs. HL-PT vs. CTR) was included as a fixed factor, participants as a random factor and baseline values and time (ie, duration of the period) as covariates. The models considered the maximum likelihood estimation and the best-fitting covariance structure. The latter was determined using the chi-square likelihood ratio test, being the variance components the most frequently preferred covariance structure. 35 Pairwise Bonferroni-adjusted comparisons were performed to explore significant differences between treatments. Cohen's d effect sizes were calculated and classified as trivial (0.20), small (0.20-0.49), moderate (0.50-0.79), and large (>0.8). 36 Finally, a sensitivity analysis was conducted to assess the possible effect produced by the different study arms on the results derived from the different treatments following the same above-mentioned procedures. All statistical analyses were performed using SPSS Statistics 24 (IBM Corp, Armonk, NY), and the level of significance was set at α = 0.05.

| Training mechanical characteristics
The mechanical characteristics of LL-PT and HL-PT as assessed during a standard training session are shown in Table 1. Briefly, greater total mechanical work and higher power values were achieved during LL-PT compared to HL-PT. Both training protocols provoked small relative velocity losses (average value for all exercise sets: ⁓5%), but relative power losses were larger in LL-PT than in HL-PT (⁓11% vs. ⁓6%, respectively). These results are comparable to earlier findings by our group obtained in a similar sample. 37

| 1-RM and F-V on the horizontal leg press
The baseline values and changes in leg press 1-RM and F-V relationship characteristics by time and treatment condition are shown in Table 2 Figure 3.
With regard to P max , large to moderate improvements were registered after LL-PT (p ≤ 0.001, ES = 0.79) and HL-PT (p < 0.001, ES = 0.65), while no changes were seen after CTR (p = 0.752, ES = 0.02). Changes in P max were significantly greater in both LL-PT and HL-PT as compared to CTR (F = 26.663, p < 0.001; post hoc: both, p < 0.001).
The velocity (V 0.85BW ) and power (P 0.85BW ) produced at a load corresponding to 85% of body weight increased after both LL-PT and HL-PT (all, p < 0.001, ES = 0.54-0.77), whereas no changes were observed after CTR (both, p ≥ 0.223, ES = 0.06-0.05). Differences between the training conditions and CTR were significant for both V 0.85BM (F = 30.213, p < 0.001, post hoc p < 0.001) and P 0.85BW (F = 29.279, p < 0.001, post hoc p < 0.001) ( Figure 4A,B, respectively). Finally, the sensitivity analysis showed no difference in the effects provoked by each training intensity regardless of the treatment conducted on the contralateral leg (F = 0.015-0.797, p ≥ 0.382).

| Maximal isometric force and rate of force development of knee extensors
The baseline values and changes of parameters obtained from the isometric knee extensor strength tests by time and treatment condition are shown in Table 3 Comparisons of changes in RFD values between treatments failed to reach statistical significance (all F ≤ 2.807, p ≥ 0.064), although a trend toward greater increases in RFD50 in LL-PT compared to CTR was noted (p = 0.075).
Concomitantly, small but significant positive adaptations in QiEMG50 were observed after LL-PT (p = 0.046, ES = 0.36), but not after HL-PT or CTR (all p ≥ 0.512, ES = 0.07-0.04). No changes in QiEMG100 and QiEMG200 were observed (all p ≥ 0.376; ES = 0.00-0.16). Besides, no differences between treatments were found for QiEMG, irrespective of the time intervals in which it was measured (F ≤ 1.139, p ≥ 0.323). Finally, biceps femoris co-activation during the first 200 ms remained unchanged (p ≥ 0.699, ES ≤ 0.29) and no treatment effect was found (F = 0.111, p = 0.894) (data are not shown). Finally, the changes observed after HL-PT and LL-PT were independent of the intervention conducted on the contralateral leg, as revealed the sensitivity analysis (F = 0.001-0.430, p ≥ 0.519).

| Mid-thigh muscle mass and architecture
Trivial to moderate and moderate increments in RF CSA and VL CSA , respectively, were found after LL-PT and HL-PT (all p ≤ 0.035, ES = 0.13-0.35), whereas no changes were observed after CTR (p ≥ 0.343, ES = −0.03 to 0.00) ( Figure 5A,B). The effect of treatment was statistically significant for both RF CSA (F = 12.860, p < 0.001) and VL CSA (F = 26.005, p < 0.001), with post hoc analyses revealing that all changes except RF CSA after LL-PT (p = 0.068) were greater after either training intervention than those seen after CTR (all p < 0.001). Regarding muscle architecture, HL-PT provoked moderate increases in VL PA (p = 0.004, ES = 0.37), whereas no changes were observed after LL-PT (p = 0.908, ES = −0.02) and CTR (p = 0.191, ES = 0.08) ( Figure 5C). An overall trend toward significant differences between treatments (F = 2.676, p = 0.073) was not confirmed by post hoc analyses (all p ≥ 0.131). Neither significant changes (p > 0.199) nor effects of treatment (F = 1.189, p = 0.308) were found for VL FL ( Figure 5D). Finally, the sensitivity analysis showed that the changes observed in VL CSA after HL-PT were higher when the contralateral leg was not trained (F = 5.793; p = 0.025). The remaining effects provoked by each training intervention were independent of the intervention conducted on the contralateral leg (F = 0.012-2.900, p ≥ 0.105).

| DISCUSSION
The main findings of this investigation were: (i) LL-PT induced positive changes in early RFD and muscle excitation levels and tended to provoke greater gains in movement velocity than HL-PT; (ii) HL-PT induced greater adaptations in 1-RM and VL PA , and tended to benefit force development against heavy loads more than LL-PT; (iii) both LL-PT and HL-PT led to similar gains in P max , functional power and velocity, and mid-thigh muscle size. To our knowledge, this is the first study to compare heavy-vs. light-load power training in terms of the changes in the F-V relationship in older adults. In our study, the training adaptations were found to be loadspecific, with HL-PT being superior to LL-PT in promoting gains in F 0 (+17.8 vs. +8.6%) and 1-RM (+24.0 vs. +16.5%). In line with our results, De Vos et al. 15 found a dose-response relationship in the 1-RM gains provoked by 12 weeks of heavy-(80% 1-RM), moderate-(50% 1-RM) and light-(20% 1-RM) load power training 1-RM (mean gains: 20%, 16% and 13%, respectively) in well-functioning older adults. By contrast, other studies that looked into the training responses of power training interventions in mobility-limited older adults (ie, SPPB score <9 points) 17 or for shorter durations (ie, 6 weeks) 16 reported that the power gains in the high-force portion of the F-V relationship were similar independently of the load used.
Regarding the low-force/high-velocity region of the F-V spectrum, both load conditions elicited significant improvements in V 0 , but larger effects were noted after LL-PT. This is partly in accordance with a previous study 38 that found superior velocity-related adaptations after 12 weeks of high-speed power training (ie, intensities corresponding to 40% 1-RM, movement execution as fast as possible) than traditional slow-speed resistance training (ie, 80% 1-RM, 2 s during concentric phase) in well-functioning older adults. As compared to this study, our subjects were also requested to perform repetitions as fast as possible when working against heavy resistances. This approach appears to yield better outcomes in HL-PT. 9,10 The fact that the adaptations T A B L E 2 Baseline values and changes in leg press one-repetition maximum and force-velocity relationship characteristics Abbreviations: 1-RM, one-repetition maximum; CI, confidence interval; CTR, control period (note that CTR represents a control period rather than a parallel group); ES, effect size; F 0 , force intercept; HL, heavy-load power-oriented resistance training; LL, light-load power-oriented resistance training; P max , maximum muscle power; S FV , slope of the force-velocity relationship; V 0 , velocity intercept; V opt , optimal velocity or velocity produced at maximum power.
to training load-is also reflected by the changes in S FV , which tended to differ between HL-PT and LL-PT (Table 2). Despite the evident rightward displacement of the F-V relationship after both training conditions, HL-PT led to a steeper trajectory of F-V line (ie, more F 0 -oriented adaptations) whereas it was flattened after LL-PT (ie, more V 0 -oriented adaptations) ( Table 2, Figure 3). The resultant increases in P max , however, did not differ significantly after LL-PT and HL-PT (⁓ +40% and +28%, respectively). It may be concluded that the improvement in P max noted after LL-PT was mostly the result of an improved capacity to produce force at high movement velocities, whereas gains at both the velocityand force-end of the F-V spectrum appear to contribute almost equally to the P max adaptations seen after HL-PT. While velocity-specific adaptations after power training have been previously reported in older adults, 16,38 this is the first study to directly show load-specific changes in the F-V relationship. The differences in training responses notwithstanding, it is important to note that both LL-PT and HL-PT may be beneficial to improve physical function. While direct measurements of functional capacity (eg, through walking or sit-to-stand tests) reflect the performance of both legs and were, therefore, not considered in the present study, movement velocity (V 0.85BW ) and power production (P 0.85BW ) were assessed at loads that are representative of force demands in locomotion (ie, at 85% of body weight). These parameters increased to an extent safely beyond the respective thresholds of clinically meaningful improvements (10% and 7%, respectively). 39 In terms of contraction explosiveness, moderate to small effects, on early RFD (ie, ≤100 ms) were observed only after LL-PT, accompanied by a small, yet significant increase in the level of quadriceps femoris excitation (QiEMG50). This result suggests that increased neural drive contributes to the improvement of rapid force production in LL-PT. 21 While several parameters, such as tendon mechanical properties, muscle fiber type and muscle morphology, 40 may equally influence RFD, the improvement in the neural drive is worth mentioning since older adults typically struggle to activate their quadriceps muscles to the same extent in LL-PT as in HL-PT. 37 Interestingly, despite existing solid evidence about the effectiveness of heavy traditional resistance training and power training to improve RFD in older adults, 41 no improvements were seen after HL-PT, and RFD100 and RFD200 were not affected by either intervention. It is possible that this lack of improvement is due to the different exercises performed for training and testing (leg press vs. knee extension, respectively). 42,43 It is worth noting that performance and muscle excitation adaptations observed were load-specific, although they could have been partly F I G U R E 3 Force-velocity relationships. Data obtained before (dashed lines) and after (solid lines) the control period (CTR, n = 89), light-load (LL-PT, n = 21) and heavy-load (HL-PT, n = 22) power-oriented resistance training are shown in panels A, B and C, respectively. Note that CTR represents a control period rather than a parallel group. The lines represent mean values and the gray areas the corresponding 95% confidence intervals (mean goodness of fit: R 2 = 0.98 ± 0.02) influenced by potential cross-education derived from those participants completing HL-PT and LL-PT (ie, study arm III). This suggests that different training targets could be developed simultaneously between legs, which will be explored in detail in a separate paper (under review).
Regarding muscle morphology adaptations, power training has recently been shown to be as effective in increasing muscle size of older adults as traditional resistance training. 11 However, the intensity at which power training should be performed to maximize muscle hypertrophy has not been thoroughly investigated so far. In our study, both LL-PT and HL-PT induced noticeable muscle hypertrophy (on average +7% and +9%, respectively) in the rectus femoris and vastus lateralis muscles. This degree of muscle growth is comparable to that typically seen after traditional resistance training. Indeed, a systematic review reported that in older adults the average gains in appendicular muscle size ranged between 9-11%, independently F I G U R E 4 Leg press movement velocity and power output. Changes (∆) in movement velocity (A) and power output (B) at forces equivalent to 85% of body weight (0.85 BW) noted after the control period (CTR, n = 89), light-load (LL-PT, n = 21) and heavy-load (HL-PT, n = 22) power-oriented resistance training. Symbols, bars and error bars show individual data, adjusted means and 95% confidence intervals (CI; error bars), respectively, for each treatment. Circles, triangles, and squares correspond to CTR, LL-PT and HL-PT, respectively. Symbols are filled according to the study arm I (gray), II (black) and III (black and gray). Note that CTR represents a control period rather than a parallel group. The results of statistical tests of between-group differences in treatment effects are indicated on the top of each panel. Withingroup comparisons (time effects) with effect sizes and 95% confidence intervals of changes are shown separately for each treatment of whether training interventions were performed with heavy or light loads. 19 The fact that, in our study, the hypertrophic response was similar in both loading conditions is interesting, since the total amount of mechanical work performed-which is considered to be a major determinant of resistance training-induced hypertrophy in older adults 19 -was significantly larger in LL-PT (Table 1). One possible explanation for this observation is that stretchshortening cycles may facilitate the execution of repetitions more in LL-PT as compared to HL-PT, 44 which would limit the anabolic response to exercise. 45,46 In terms of changes in muscle architecture, VL PA was significantly increased only after HL-PT (+7.5%), which agrees with the larger changes in force production (ie, F 0 and 1-RM) observed after this intervention. 47,48 VL FL , by contrast, was not significantly affected by either form of power training. In contrast, a previous study involving light-load plyometric exercise (using a trampoline training device) in older adults has shown meaningful increases in VL FL and VL PA (+8 and +7%, respectively). 13 The discrepancies between studies may derive from differences in the training device used and some methodological limitations in determining this measure in our study (with large portions of fascicle length lying outside the available field-of-view) potentially introducing bias. 49 While it is possible that LL-PT (which resembles plyometric exercise to a certain extent) would benefit the effectiveness of the stretch-shortening cycle, it remains to be explored whether LL-PT or HL-PT would have greater adaptive potential in this regard. Some limitations should be considered when interpreting the present findings. The experimental F-V data were fitted using linear models. These may be less sensitive in detecting adaptations induced at the low-force/high-velocity portion of the F-V than hyperbolic models. 50 Moreover, physical performance was not directly assessed since typically measured outcomes such as gait speed or sit-to-stand performance are affected by both legs; however, we determined the changes in unilateral power and movement velocity at a relative intensity (ie, 85% of body weight) that is representative of the force demands encountered in locomotion and other tasks of daily living. Thus, these measures may serve as proxies of the functional adaptations provoked by the power training programs. The MIF and RFD measurements were intentionally performed using a custom-built chair for knee extension rather than the leg press used for training, as the knee extension device was more rigid and, thus, better suited for the evaluation of explosive strength. 40 At the same time, we acknowledge that, ideally, training and testing should be performed on the same devices. Ultrasound scans were obtained in two of the four heads of the quadriceps femoris muscle and at a single level of femoral length only. This was due to time constraints in data acquisition and poor reliability of measurements obtained off-center. Considering the possibility of regional hypertrophy 51 and the demonstrated intra-and intermuscular variability of quadriceps architecture, 52 our results reflecting the changes in muscle size and architecture should be interpreted with caution. Finally, the influence of possible cross-education in those subjects training both legs at different intensities (ie, subjects in study arm III) cannot be completely discarded, although the sensitivity analyses revealed the consistency of the results for each of the different treatments (ie, training intensities) regardless of the study arm.
In conclusion, power training provokes significant improvements in muscle strength, power and size in older adults independently of the load used. Importantly, power training across of wide range of loads appears to improve the power output when working against resistances that are typical for the force demands encountered in locomotion and further activities of daily living. Nevertheless, the adaptations of central characteristics of the force-velocity profiles differed between loads, suggesting that HL-PT may preferentially stimulate force-related muscle power adaptations whereas LL-PT might be more suitable for developing the velocity component of muscle power, according to the larger effect size observed.

| PERSPECTIVES
Power training is considered a cornerstone in resistance training programs for older adults given its greater potential to improve functional performance in comparison to traditional resistance training. 53 Although it is known that a wide range of intensities may be used to develop muscle power and functional performance in older adults, 18 the influence of training with different loads on the F-V relationship is still poorly understood in this population. The results of our study demonstrate that in power training in older adults both light and heavy loads may be used to induce improvements in muscle function and muscle hypertrophy. However, HL-PT is more appropriate to develop high-force capabilities, while LL-PT appears to be superior in promoting gains in movement velocity and, thus, the performance in explosive tasks. Therefore, HL-PT should be prescribed to older people with force deficits, whereas LL-PT should be recommended to older people presenting with performance deficits at for panels A, B, C and D, respectively. Symbols, bars and error bars show individual data, adjusted means and 95% confidence intervals (CI; error bars), respectively, for each treatment. Circles, triangles, and squares correspond to CTR, LL-PT and HL-PT, respectively. Symbols are filled according to the study arm I (gray), II (black) and III (black and gray). Note that CTR represents a control period rather than a parallel group. The results of statistical tests of between-group differences in treatment effects are indicated on the top of each panel. Within-group comparisons (time effects) with effect sizes and 95% confidence intervals of changes are shown separately for each treatment. Note that the post hoc comparison of rectus femoris cross-sectional area between CTR and LL failed to reach statistical significance ( a , p = 0.068) the high-velocity, low-force end of the F-V spectrum. 20 Such individualized prescription may maximize the benefits of power training and help counteract the agerelated decline in functional ability.


Use of fitness to improve students' physical qualities

. The rhythm and tempo of music has a beneficial impact on a person's desire to perform in unison movements. They can calm or excite the human nervous system and have a beneficial effect on the overall physical condition of the person. Regular fitness classes help to improve the mental and physical performance of students. Types and forms of fitness aerobics allow you to use an individual approach when choosing tools and methods in physical education lessons. In our opinion, the motor mode during fitness classes should correlate with the psychological and emotional state of the participants, as well as with their overall level of physical development. As a result of regular fitness classes in physical education classes, students improve the functioning of the musculoskeletal system and improve the development of skeletal muscles. The introduction of teaching in higher educational institutions of the training course "Valeology" in our opinion will allow students to gain important knowledge they need throughout their lives.

Introduction
Physical culture and sports are inextricably linked to a person's ability to acquire new skills necessary in their professional activities. In our opinion , efforts to preserve the state of personal health of students and the health of people around them should play an important role in the process of physical and moral education of students, as well as in the formation of a common culture of comprehensive personal development.
According to [1], an important problem that modern society requires from higher education is the training of specialists who, in addition to high professional skills, still have the required level of health, to maximize the disclosure of their creative and professional potentials.
According to [2], improving the quality of students ' training in higher education should provide not only for the availability of physical education classes in the curriculum, but also for providing students with comprehensive knowledge about the influence of external factors on the state of human health.
The use of physical training classes for students, according to [3], should provide for the choice of the correct motor mode, which would correlate with the emotional and psychological state of the student and the overall level of his physical development.
According to [4,5], the dosed level of sports loads and their diverse nature make it possible to increase the level of physiological human reserves, as well as to avoid excessive overstrain of the human body during muscle work.
According to [6,7], an important indicator of the level of physical condition of a person is the state of the cardiovascular and respiratory systems of a person, as well as the level of overall physical performance of the entire human body.
Although the study of the problem of the influence of fitness on the human body has been studied for quite a long time, the question of the use of fitness in physical education classes has not yet been fully investigated . As part of this research work, we developed and put into practice a curriculum based on student fitness classes.

Methods
During the implementation of this study, we studied the impact of fitness classes on the process of improving the overall physical qualities of students. The classes took place during the training sessions on physical education with students of the Law Faculty of the Dnipro Polytechnic during the 2018/2019 academic year.
At the beginning of the study, we tested the level of general physical fitness of the trainees according to the following parameters: 1. Speed testing. It provided for students to run on the spot for 10 seconds and run at a distance of 60 meters for girls and run on the spot for 20 seconds and run at a distance of 100 meters for boys. In this test, we used pedometers to measure the number of steps taken by students per unit of time.
2. Measurement of the force of arms. In the process of measuring the strength of the hands, spring-loaded wrist dynamometers and exercises in the 24-kilogram kettlebell press, push-ups on the uneven bars and pull-ups on the crossbar were used for boys and girls. Hand strength dynamometry was performed for both hands for both boys and girls. In girls, the performance of the strength test involved measuring the number of exercises performed to bend the arms from the prone position for 2 minutes.
3. Measurement of coordination and dexterity. In order to test coordination and dexterity, special exercises were used, including movements with the right and left hand, exercises with a skipping rope and a ball for girls, as well as a shuttle run of 6x10 meters for boys.
4. Testing of mobility and flexibility in the joints. The measurement of joint mobility and flexibility was carried out by measuring the amplitude of their body movement in the subjects. In this test, the exercise was used to bend forward without bending the legs. The degree of flexibility in the vertebral column was measured by the distance from the floor to the fingertips at the maximum tilt of the subject. To determine the degree of mobility of the subjects of the knee compositions, squat exercises with hands behind the head were used. On the basis of this exercise was carried out to measure the degree of mobility at the knee. The final result was evaluated in points. The level of mobility in the students ' ankle joints was determined by the following method: the student was sitting on the floor, the feet of his feet were oriented perpendicular to the floor surface. Mobility was measured by the ability of the subject to stretch the toes of the feet, from the initial position to the maximum possible extension of the foot, the result of the measurements was evaluated according to the point system. 5. Endurance testing. As an exercise for testing endurance, the 5000-meter run for boys and 2500-meter run for girls was used.
6. Measurement of bounce. Jumping ability was measured on the basis of the subjects ' jumps from the spot.
The authors give the indicators of physical qualities tests in Table 1:

Results
In order to improve the students of the study group we tested, we used a technique that included performing various physical exercises during the background sound of musical accompaniment. This, in turn, not only had a positive effect on the emotional and psychological state of the students, but also allowed them to use a personal approach to each student individually, taking into account the level of their physical fitness. In our opinion, the composition of health-improving fitness classes should include the following types of loads: stretching, strength and aural load. Taking this into account, the classes that we conducted with students during physical education lessons were divided into three parts: 1. Warm-up. The goal of the workout was to increase heart rate and breathing speed up metabolism, warming the body, increasing the level of elasticity of muscles, tendons and ligaments students. The preparatory part began with the process of repeating and learning the basic movements and movements that are used in dance aerobics, such as "Marsh", " Step-Ter", "Step-Touch", "Cross", "V-Step", as well as knee lifts "Knee lift" and back flops "Leg Curl". Students were allowed to work with their hands as if they were walking or to fix them on their belts. The duration of the warm-up part was approximately 8-12 minutes.
2. The main part of the lesson. The main part of the training session was aimed at improving students ' coordination skills and learning new ligaments.
During the main part of the training, a constant aerobic load in the non-stop mode was used. This involved learning a series of small, repetitive combinations of movements, which consisted of a set of basic movements, which were supplemented by hand movements in the form of jerks and swings. During the main part of the lesson, we used an individual approach to each student, students with a lower level of physical fitness performed hand movements at a convenient pace for them. In order to increase the level of aerobic exercise, students were replaced with some basic movements such as "Cha-Cha-Cha", "cross", "mambo", and step movements were combined with jumps with jumps "Jumping", leg swings "Kick", as well as running on the spot "Jog". More physically prepared students, in order to improve their physical form, had the opportunity to further increase the level of load by using dumbbells weighing from 1 to 2.5 kg.
In the final part of the lesson, students performed stretching exercises for various muscle groups.
At the same time, the teacher conditionally divided the students into three subgroups according to their level of physical fitness: 1) Students with good physical fitness and coordination abilities had the opportunity to perform a bunch of exercises completely, and if desired, use additional weights.
2) Students with a weak level of physical fitness, but a good level of coordination abilities performed movements with a reduced amplitude of hand movement or without the use of rebounds. They could independently set the level of their load.
3) Students with poor coordination and a weak level of physical fitness performed only elementary movements with their legs and arms, trying to match their movements to the musical rhythm.
3. The final stage of the lesson. At the final stage of our classes, we conducted exercises for stretching, or "stretching". This took place within 6-8 minutes. This part of the lesson also provided for an individual approach to each student, depending on the level of his physical development. The task of stretching was to relieve the load on the muscles by stretching Due to the fact that the mobility of the joints and the elasticity of the ligaments are individual in each person, the stretching exercises were performed in such a way that when bending, students did not experience excessive load in the spine, as well as in the ankle and knee joints. If the student felt pain and discomfort during the tilt in front, then he could perform this exercise in a light version. He could just round his back and bend his knees a little. The correct performance of stretching exercises helped to improve the elasticity of the ligaments, muscles and tendons of the students, in addition to the normal state of the heart rate of the students.
If a person experienced discomfort or pain when leaning forward, then a light version of this exercise was recommended -slightly bend the knees and round the back. With the correct performance of this stretching exercise, the elasticity of the muscles, ligaments and tendons was increased, and the heart rate returned to normal.
A specific feature of music is that moods, experiences, and ideas are expressed through a harmonious combination of rhythmic sounds and tones. Using them, a person has the opportunity to convey their mood, as well as their feelings and emotions. Music affects not only the human attention, but also has a beneficial effect on the intellectual and creative abilities of a person. Music can help a person relax or give additional strength. According to [8,9], classical music has a great energy potential, and is able to have a beneficial effect on the human body.
We hold the view that the rhythm and tempo of music have a stimulating effect on the desire to perform motor movements in unison. They can excite or calm the human nervous system, and therefore affect the overall physical condition of the student.
Fitness classes on a regular basis, in our opinion, contribute to improving the level of physical and mental performance. The effectiveness of fitness classes is largely dependent on the selected musical accompaniment.
According to [10], music encourages a person to have certain emotions and feelings that correlate with various forms of physical activity. Popular music compositions increase the level of human mood, increase concentration, and also give a charge of cheerfulness and energy.
We adhere to the point of view that for each type of wellness fitness, it is necessary to select the appropriate tempo and musical style. For example, for aerobics classes, a rhythmic musical accompaniment that can set the necessary tempo will be most effective. For training in gyms, in our opinion, the best option is rock music.
Since the musical tempo can have a great impact on the physical and mental state of a person, in our opinion, for physical exertion of a large level of intensity, the music tempo is about 105-135 beats per minute, and for pilates classes from 60 to 100 beats per minute. At the same time, we believe that when choosing a musical tempo, first of all, the state of physical fitness of the students should be taken into account.
At the end of the academic year, we once again tested the physical condition of the students, the results of which are presented in Table 2.
Therefore, based on the results of the study, we come to the conclusion that fitness classes during physical education classes contribute to the improvement of students ' physical qualities.

Discussion
In modern times, the concept of "fitness" has firmly entered the lives of many people who want to be in good physical shape. This can be achieved through regular and persistent training and an appropriate level of physical activity. The process of managing and organizing training work requires a well-thought-out preparation of training sessions for the teacher.
Due to the differences in the individual physiological characteristics of students and their level of physical fitness, different students learn different movements in fitness. In this regard, we believe that an individual approach to training based on the level of physical fitness of students will be optimal.
A musical composition that sounds during a fitness class can increase the mood of those involved, reduce the feeling of fatigue, liberates and promotes the performance of clear and rhythmic movements. Pleasant music helps students quickly recover their strength after physical or mental work.
At the same time, too long classes with increased intensity of physical activity can have a negative impact on the human body.

Conclusions
Based on our research, we came to the conclusion that the forms and types of fitness aerobics make it possible to apply an individual approach when choosing methods and means of physical education. The methodology developed by us in this work allows us to develop the optimal training option for students in accordance with their level of physical fitness.
With regular exercise fitness among students is the development of skeletal muscle, improving the functioning of the musculoskeletal system. As a result of regular exercise, students ' resistance to stressful situations increases, as well as the degree of adaptability to physical exertion.
In our opinion, an important contribution to the acquisition of the necessary knowledge about health can be made by the introduction of mandatory teaching of the valeology course in higher educational institutions. Problems that valeology studies late or early all people face throughout their lives. Therefore, the study of obtaining knowledge by students that contributes to the preservation and promotion of health should be a state, and not just a personal task.


The Use of Social Media for the Development of Digital Literacy of Students: From Adequate Use to Cognition Tools

—The study focuses on the possibility of turning social media into an effective tool to improve digital literacy and facilitate cognition. In view of this, a one-month experiment involving 268 eighth graders from two Moscow schools was conducted; the participants were divided into a control and an experimental group. The students were encouraged to independently search and develop social network skills to solve educational issues and improve cognition. Objective performance tests were conducted based on the curriculum results. According to the academic performance, the mean grade on a 12-point scale in the experimental group increased from 7.77 to 8.76 points, while in the control group the change remained within the statistical error (7.64 and 7.76, respectively). A strong correlation between the grades obtained in different groups (0.8 when comparing the final results in two groups) was found. The study can be put into practice within the framework of the widespread introduction of social media in school curricula as a tool to access information, develop digital literacy and the ability to use digital cognition tools being supervised and supported by a skillful teacher.

Introduction
Over the past 10 years, social media or social networks have become a crucial part of the information landscape and the most important part of social reality. Initially, social media used to be a communication tool; today they have become a medium of political influence, the basis for the business processes of many companies, and an important modern education tool [1], [2]. Studies on the use of social media by school and university students were mainly focused on studying the consequences of their active involvement in this service. In most cases, the researchers pointed to the development of a number of behavioral and psychological disorders associated with the excessive use of social networks. There is a unanimous opinion that active involvement in social media has a negative impact on academic performance at any age [3] - [6]. It is also indicated that the most typical disorders associated with the use of social media are impaired attention, inability to concentrate arbitrarily for a long time, weakening willpower, addiction, anxiety and constant desire to check messages [7].
The correlation between social media as a communication tool and the behavior of adolescents has been carefully studied. It was revealed that in this age group the two most powerful motivations are the desire to gain recognition and the desire to belong to a particular group [8] - [10]. Social networks naturally facilitate the formation of groups and are intended for this. However, marketing techniques and modern product promotion strategies based on the characteristics of the user psychology leads to greater addiction. Thus, adolescents often want to correspond to an unrealistic ideal, which is found on a social network and there may be depression caused by the inability to match it [4]. Social networks are often a cause of social exclusion in adulthood [11].
On the other hand, researchers, in particular in medicine and psychology, note the beneficial effects of social media on some social groups. They help older people improve memory, increase social motivation, develop communication and cognitive abilities [12], [13]. There is a great number of studies that examine the way social media can be used in education [14] - [16]. This is especially relevant as students are already using social media to search for and exchange information in their area of interest.
Nevertheless, the researchers note that social networks have already penetrated into our daily life and they will continue to play a decisive role due to a number of important services that they provide: ease and speed of communication, access to information at any time. It is believed that the key function of social media is the selection of information from the enormous amount of available data based on the natural differentiation of group interests. For example, within the group of people interested in biology each participant finds and shares the content that is most interesting to them. Social media can be effective cognitive tools due to the "group filtering" tool [14], [17], [18]. Modern social media make it possible to effectively use office applications, in particular cloud storage and data access services, to build distributed computing and communication systems, as well as to quickly exchange information. These services are important cognition and development tools, and the tools of creative activity and the creation of new products in the information economy [19], [1]. Therefore, in order to bring up an adequate and skilled citizen of the new era, it is necessary to constantly improve digital literacy and master the tools provided by the modern digital environment [20], [21]. This can be promoted by the use of social media in schooling and higher education.
The present study considers the possibility of using social networks as a basis for increasing digital literacy and teaching students to use them as a tool to improve selfdevelopment and self-education. In this aspect, social media have not been sufficiently and practically studied.

Methods and Materials
The study took place at First Moscow State Medical University. It involved 268 8th graders from two Moscow schools. The study period was 30 days long (1 month). The students were invited to participate in the study through the announcement made at their schools. Participation was completely voluntary and it was agreed with the parents, teachers, and the school administration. To ensure the ethics of the study, the results did not affect the final assessment of the participants. The short study period is due to the need to save time and energy of the participants to successfully complete their current school curriculum. Thus, participation in the study was not expected to adversely affect academic performance and well-being. The study course used in the experiment was a continuation of the adopted school curriculum. Therefore, the experiment did not require any extra efforts to address the issues related to the study organization. The participants were not aware of the participation of their fellow students and teachers. Communication was carried out through specially created anonymous accounts on social networks. Thus, we did not have access to the personal data of each study participant.
There were two groups: an experimental group consisting of 132 participants and a control one involving136 participants. The number of male and female participants in both groups was equal; however, this is insignificant for the purpose of the study. To complement the course, we used multimedia educational materials posted on the Internet, in particular on Facebook, YouTube, Twitter, and Instagram. Most of the communication with the teacher also took place on these social media platforms. The teachers and students were instructed in the use of certain social media features to increase the effectiveness of learning and facilitate the search for educational materials. Thus, while studying the academic subject, the students also had an integrated digital literacy course. In case of questions or difficulties associated with the education-related use of social networks, the students could contact support accounts which provided them with a quick response or professional help in less than half an hour. The study was not focused on collaborative learning, but collaboration was encouraged; it arose spontaneously as discussions and student requests to each other.
The control group and the experimental group had access to the same educational materials and available opportunities. However, the experimental group was guided by the teacher and the participants had to do the exercises and use the proposed digital materials to complete the course. The control group could use these opportunities on their own.
Before the beginning of the experiment, the participants were surveyed about the social media they use. Based on previous studies [22], [23], 4 key uses of social networks by schoolchildren were identified: entertaining, cognitive, communicative (for communication) and informative (obtaining socially useful information). The study was conducted by analyzing the history of browsing and accessing social networks from personal electronic devices of participants. The data was transmitted anonymously and encrypted so that the source of the data could not be determined. Thus, the study is based on objective information rather than subjectively expressed opinions. There was a similar study that took place a day later after the end of the research cycle.
The participants used a specific tag to access the educational resources; the tag was used to count the number of references to various sources. The analysis of this information reflected the development of the cognitive skills of the participants. Based on the available studies on cognitive processes in social networks [24], the key factors that transform social networks into cognitive tools are the independent use of the possibilities of finding educational materials and going beyond the course. The search and independent use of social networks for identifying, processing and utilizing information directly demonstrate an increase in the digital literacy of participants.
An objective study of the academic performance of students was conducted based on the experiment results. In order to make the assessment as realistic as possible, the study was based on a 12-point scale that is traditionally used in school education. The mean grade and the assessment variance (average deviation) were calculated in each group; the correlation between the grades of each group obtained before and after the experimental course, as well as between the final grades of both groups, was examined. The analysis of the correlation allowed the researchers to evaluate the change in personal assessments of each participant in the correlation groups.
The hypothesis of this study is that there should be a strong correlation between the grades within the group and between the experimental and control groups if the use of social media in the learning process and the increase in digital literacy really affect the quality of education.
The hypothesis of our study is that the accentuated use of social networks in education under the supervision of teachers and based on appropriate pedagogical methods (encouragement, comparison of achievements with other students, support and respect from peers) should contribute communicative activities on social media platforms, improve academic performance and change preferences by making learners use social media as a cognitive tool. The latter should be evidenced by the change in the percentage ratio of the number of requests for network resources intended for entertainment and resources for communication, knowledge improvement, and information search.
The study has certain limitations, in particular, it does not consider the gender analysis of personal characteristics of the participants and the dependence of their success in using social media on the socio-economic status of the family, as well as the level of education in the family. According to the number of studies, these are the key factors predicting success in learning and using social media. There is also a need for further research on digital literacy of both high school students and teachers. In the present study, the problem was addressed through coaching and expert support. In our opinion, all these research aspects should be carefully studied in the future.

Results
An objective study of the academic performance of the participants (Table 1) showed a strong correlation between the mean grades in both groups before and after the experiment (0.81 and 0.97 in the experimental and the control groups, respectively). Thus, it should be assumed that the increase in the mean grade of the experimental group (from 7.77 to 8.76 out of 12 points) is relevant and correlates with the teaching method being discussed. There is also a strong correlation between the performance of the control and experimental groups (0.8). Therefore, teacher supervision and the subsequent check of student tasks, as well as student encouragement greatly affect academic performance in the social media learning environment. In the control group, there were no changes in the academic performance of students (the mean grade increased from 7.63 to 7.76 after the experiment; the change is within the statistical error and may be discarded).  Figure 1 shows the distribution of the number of social media logins made by the study participants for educational purposes. The students were asked to use a special tag when they used the network specifically for the purpose of solving educational problems. The margin of error limits are also indicated in Figure 1. The graph shows that all data is relevant and the comparable values are beyond the mutual margin of error.
Obviously, it can be concluded that the experimental group uses social media much more actively compared to the control group, where the indicators are 2.5-3 times lower. The activity of the control group is due to the fact that the participants could also receive the same services as the experimental group participants, but only at their own request and as an extracurricular activity. Regular declines in social media activity were observed on Saturday and Sunday when school classes were not conducted. It should be noted that at the weekend the activity of the experimental group also decreased, but it still remained noticeable.  Table 2 shows the total number of references to educational materials throughout the study period in both groups and their distribution by characteristics. In the experimental group, the largest number of social media logins was made in order to access and process educational materials, as well as to complete the tasks set by the teachers (a total of 9,452 references to various resources). The figure is also due to the fact that some of these tasks were related to the development of digital literacy skills, and not only the work with educational materials. The total number of social media logins in the control group is only 15.16% of the number of the experimental group. The use of independently found sources and extracurricular materials is of critical importance for the research purposes. In the control group, these indicators are 8.51% and 9.52% of the number of social media logins made by the experimental group, respectively. Thus, in the experimental group, the increase in digital literacy and the possibilities of using social media as cognitive tools exceeded the control group indicator by more than 10 times.
At the same time, in the control group, social media were mainly accessed for educational purposes to contact teachers and other students. Based on the experience of the MOOC and other sources [25], most students studying without external control tend to skip exercises and have insufficient motivation to complete the course.  Figure 2 shows the use of social media for educational purposes according to the characteristics described above. The graph clearly confirms that social networks are not commonly used as cognitive tools; however, special training programs greatly contribute to the process. According to Figure 3, it can be concluded that the control group scarcely uses social media as cognitive tools; thus, this indicator remains within the statistical error. At the same time, most logins (55.31%) were made for communicative purposes as evidenced by many other studies on the use of social networks as a tool means or basis for education. iJET -Vol. 16, No. 02, 2021 The results of the objective study of the purposes of students in using social media before and after the experiment are presented in Figure 4 and Figure 5. The data is expressed as a percentage of the number of references to a particular resource for a specific purpose. In this case, the time of using a particular resource is not considered; however, it can be a very important and relevant indicator that is not in the scope of the present study and requires further research.
A close correlation between the results in the control and experimental groups is observed before the experiment. The largest number of references to resources is associated with entertainment (71.16% in the control group and 70.23% in the experimental group). The use of social media for communication is also noticeable (22.76% and 21.22%, respectively). The data generally agrees with similar data described in other studies [26], [25]. After the one-month course, there were completely different results. At the same time, the use of social media for entertainment decreased in the control group (up to 65.55%) while there was a very interesting phenomenon in the experimental group: the use of social media for entertainment, cognition, and communication was 30.11%, 36.15% and 31.01%, respectively.
It should be recognized that the result is largely determined by the active influence of the curriculum and the regular daily experience of using social media to complete the school curriculum. Based on the findings of our study, we cannot conclude whether these results will be stable and fixed in the behavior of the experimental group participants for long. This is a limitation of our research, and the aspects of fixing changes in the use of cognitive tools in social media require further careful study. It is obvious that the use of social media for obtaining information has not changed much, which may be due to the participants belonging to a certain social and age group. Adolescents of this age are usually little involved in social life, political choice, social and economic activities, and housekeeping; therefore, they do not need this kind of information. This aspect of the research also requires further study.

Discussion
The studies on the use of social media in education are mainly focused on either their negative effects on academic performance and well-being of students [8], [18], [27], or the use of social networks in integrated e-learning and mobile learning processes [17], [28]. In the latter case, social media are used as a "vehicle" to ensure the exchange of educational information. Over the last five years, there have been a number of studies considering the features of using social media and the ways they can be used for pedagogical purposes. Most studies rely on constructivism, which allows investigating the construction of the reality model as it occurs in the exchange of information in the network [25].
In particular, it has been found that there are some gender differences in the use of social networks. On average, women spend more time on social networks, create more independent content, and share it more often [14], [29], [25]. This feature can be observed in the early school years if children at this age already have access to communication technologies [30]. Three key factors in the use of social networks have been identified: the consumption of content (including content determination, search and selection), content sharing and content creation. At the same time, researchers believe that content sharing is the most positive factor in influencing adolescent users. The actions of the vast majority of users are reduced to this activity [31], [32]. There are dramatically different strategies of the content use at school, in the classroom, and outside of the classroom curriculum. The consumption of content outside of the classroom is characterized by a decrease in social activity, a decrease in creativity (content creation processes); however, it is generally more intensive. Most of this activity relates to the consumption of entertainment content. It has been noted that when social media are used in the learning process, most users aged 6-16 prefer to distinguish their own social life in the network and the learning processes. A lot of students have difficulties associated with the need to keep teachers "close" or identify, select, and like educational information that does not match their socialized personality, which they promote on social media [4], [10].
It has been revealed that there are different groups of social network behavior predictors that determine involvement in social media inside and outside the classroom. Moreover, in the school context, there are more of them and the creative component of user activity is much higher. The research has also revealed two most important contextual factors that dramatically affect user behavior in social media: the level of education and socio-economic status of the family. The latter factor is still relevant from the perspective of the availability of personal electronic devices that provide children and adolescents with the access to social media. At the same time, it has been found that users coming from low socio-economic households were proner to blog and generate their own content compared to those from wealthier families who tend to consume or share the content.
The studies on the digital literacy phenomenon are also closely related to the integration of social media into the life of society. Researchers acknowledge the fact that today there is no clear or universally accepted definition of digital literacy. A number of researchers define it as the ability to use electronic devices, programs, the Internet and various communication protocols between them. This definition is close to "computer literacy", which is the term used for a long time in Russia. According to other scientists, it is the use of information mechanisms, primarily blogs, information exchange and search, communication with other participants in social networks, etc. [2], [20].
It is very important to understand the essence of motivation in order to use social media in education. The study of the adequacy of self-esteem of young schoolchildren provided interesting findings. Self-esteem implies a high level of self-awareness; it has been concluded that the creation of special conditions, including the lack of competition between participants, the development of simple articulation tasks and the absence of the need to make up complex sentences allow children to perform an adequate and accurate assessment of their knowledge and skills [33]. A number of studies also confirm that the use of social media, in particular blogging and micro-blogging, improve writing skills, lengthen the sentences used, and enlarge the vocabulary of users [19], [12]. In addition, there is an improvement in the cognitive processes of those who actively use social media under teacher supervision or in the context of their conscious goals [27]. The present study relies on this data. The fact most users who do not have external motivation and are not supervised by the teacher use social media as a means of entertainment or communication has been confirmed.

Conclusion
The research hypothesis that the use of social media as part of a school curriculum under the supervision of teachers and based on the use of appropriate pedagogical methods to encourage independent information search increases communicative activities on social networks, improves academic performance and changes the preferences of the experimental group participants by making them use social media as a cognitive tool has been fully confirmed. In the experimental group, the use of social media for entertainment, cognition and communication is balanced (30.11%, 36.15% and 31.01%, respectively). We can consider it as an indicator of achieving a certain level of digital literacy and self-control when using social media. The academic performance in the experimental group has increased (from 7.77 to 8.76 points on a 12-point scale), while in the control group, which did not actively use social media, the mean grade has not changed. The experimental group also showed the ability to independently use social networks as a means of cognition for the search and use of extracurricular materials. At the same time, in the experimental group, this indicator was 10 times higher than that of the control one. The present research should be expanded through a more careful study of the socio-economic and gender aspects of the use of social networks. The research findings can be used to study and integrate social media into traditional classrooms. Social media can help students increase digital literacy and master the skills of the 21st century, including the use of social media as one of the tools of cognition.


Research on Design Method of Children’s Teaching Assisted Toys Based on STEAM Education

During winter and summer vacations, parents are busy with work and have less time to accompany their children. Parents pay more and more attention to children’s independent learning. Therefore, it is particularly important to cultivate children’s self-learning ability. As an indispensable prop in the process of children’s growth, teaching toys play a positive role in children’s forming good habits and building up self-confidence. This article is based on STEAM education concept, through the analysis of the characteristics of existing auxiliary teaching toys, starting from the psychological and behavioral characteristics of children and parents, analyze their demand for auxiliary teaching toys, summarizes the design principle of auxiliary teaching toys, puts forward the design method of the auxiliary teaching toys, provide a reference for toy designers and children’s education.

the purchase of toys, but also gradually began to pay attention to the impact of toys on children's psychology and behavior; Secondly, the playability, interest and education of toys also become the main issues of concern to parents. Based on the analysis of the status quo of STEAM teaching assisted toys and the needs of children and parents for toys, this paper proposes the design method for STEAM teaching assisted toys, hoping to provide a reference direction for the development of children's teaching AIDS and teaching Assisted toys STEAM education.

STEAM Education
STEAM education is a comprehensive education that integrates science, technology, engineering, art and mathematics (Liu, 2020). STEAM is an educational concept that integrates Science, Technology, Engineering, Arts and Mathematics into an interdisciplinary integrated education model. STEAM on cross-border education concept, focusing on practice, compared with the traditional teaching concept, STEAM education pays more attention to cultivate compound talents, their ability to think independently, from the perspective of hands-on practice and thinking training, the ascending children found the problem, problem-solving ability, will exert positive effects on children's creative ability.
Steam teaching assisted toys are adapted from this educational philosophy by incorporating a variety of learning systems into traditional toys. STEAM education emphasizes the educational mode of "learning by doing" and "doing while learning", so that children can experience the joy of hands-on creation. Designers can combine the ideas of STEAM education in the design process to make toys more playable and intelligent while meeting the basic requirements (Qin et al., 2020). So as to cultivate children's comprehensive literacy, promote the development of children's cognitive ability, motor ability, emotional ability and other skills.

Current Status of STEAM Educational Toys
Social competition is gradually increasing, and parents feel great pressure in education. Influenced by the epidemic, more families choose to let their children study at home during winter and summer vacations. As parents are busy with work, they have no time to accompany their children, which increases the demand for teaching-assisted toys. Steam toys can transform difficult knowledge into fun games, thus responding to the diversified development of education, and are deeply loved by children.
In terms of the STEAM teaching Assisted toys market, it can be roughly divided into two categories. One is programming toys based on LEGO, which can be freely splintered through many modules and combined with programming to cultivate children's practical ability and logic ability; the other type is the robot human represented by DFrobot, which is a kind of educational toy with the function of learning and accompanying, and parents can communicate with their children through the robot. Different from traditional toys and teaching

Design Principles for STEAM Educational Toys
Good toys can help children develop good study habits, interpersonal communication, concentration and so on. The educational purpose of STEAM teaching Assisted toys is to enable children to play while contributing to the development of children's intelligence and ability. Therefore, STEAM teaching Assisted toys should be designed to meet the needs of children while focusing on the bottom line of parents.

Development and Cognition
According

Purchase and Use
In the process of the growth and development of children, parents accompany is indispensable, parents as a buyer, they will not allow to ignore, parents hope children can acquire knowledge in the play, the growth of the ability, through the dominant way to see the children change (Song & Jiang, 2020). Therefore, in meeting the demand of children's toys at the same time, can let parents to participate in some common finish operation, Will greatly enhance the interaction between children and their parents; Secondly, parents pay more and more attention to the function and significance of toys in the process of choosing toys, hoping that toys can promote children's physical movement, language, cognition and social development (Yang et al., 2014). Parents hope that children can gain positive guidance and improve their abilities through play.

Thematic Design
The traditional course teaching method is mainly based on textbooks and theo-

Interactive Design
Good toys should help children develop healthy interpersonal relationships and interact with others happily. Therefore, the design of "gamified" toys that can reflect "playmate participation" and "life situation" is an inevitable trend in today's toy design (Yu, 2016). Therefore, it is particularly important to pay attention to the communication and interaction between parents and children, toys and children and children. Interactive toys can be used as a link to pass information to children and parents, play and learn together with children, and enhance children's emotional experience.

Structural Exploration
Existing teaching toys, such as disk splicing toys, Lego toys are made by the combination of modular assembly in the form of structure between the parts can affect the stability in the process of assembling, interoperability, supportive structure not only play toys, also affecting the exterior of the toys form, function of conversion and product design. When children study the structure of the toy, they can understand the characteristics of the toy, the way of assembly and the diversified play, so as to promote children's observation ability, memory ability and thinking ability.
The Spiel Welle scientific exploration drilling machine (  Handy Block programming blocks (Figure 4), through the materialization of the intelligent building blocks, more than 50 programming instructions will be built, through linkage control robot, and the surrounding things to each other, and give different information feedback, in the process of playing stimulate a

Art and Aesthetics
Children's art toys, more from the children's feelings of life, the integration of painting, calligraphy, music and other forms, through art to improve the cultiva- Such as children's 3D printing pen, children can draw anything they imagine unrestrained, not only can exercise their imagination, but also can cultivate children's expression ability, hands-on ability and the ability to summarize things, so that they can understand and recognize more knowledge in the process of creation.

Conclusion
Based on STEAM education concept, children's teaching toys integrate diversified subject knowledge, new technology and art, and cultivate children's practical ability, exploration ability and the ability to analyze and solve problems. Let children be able to think comprehensively, learn in play, through this imperceptible way, make learning interesting, cultivate children's ability to take the initiative to learn, so as to deepen the understanding of knowledge. By analyzing the design principles of STEAM teaching assisted toy, this paper proposes a design method for children's educational toys based on STEAM education, which vigorously promotes the development of STEAM education and provides reference directions for toy designers and children's education.