***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The aim of this study was to compare sprint performance over 10 and 20 m when participants ran while towing resistances , weighing between 0 and 30 % of body mass . The sample of 33 participants consisted of male rugby and soccer players ( age 21.1 ± 1.8 years , body mass 83.6 ± 13.1 kg , height 1.82 ± 0.1 m ; mean ± s ) . Each participant performed two sets of seven sprints over 20 m using a Latin rectangular design . The times were recorded at 10 and 20 m using electronic speed gates . The sprints of 13 players were  video-recorded  to allow calculation of stride length and frequency . For both sprints , a quadratic relationship was observed between sprint time and resistance as sprint time increased from 2.94 s to 3.80 s from 0 to 30 % resistance . This relationship was statistically significant but considered not to be meaningful for performance because , over the range of resistances used in this study , the quadratic model was never more than 1 % ( in terms of sprint time ) from the linear model . As resistance increased , the stride length shortened , with mean values of 1.63 ± 0.13 m at 0 % body mass and 1.33 ± 0.13 m at 30 % of body mass . There was no significant change in stride frequency with increasing resistance . The results show that in general there is an increase in sprint time with an increase in resistance . No particular resistance in the range tested ( 0 – 30 % ) can be recommended for practice The purpose of this study was to compare changes in velocity-specific adaptations in moderately resistance-trained athletes who trained with either low or high resistances . The study used tests of sport-specific skills across an intermediate-to high-velocity spectrum . Thirty NCAA Division I baseball players were r and omly assigned to either a low-resistance ( 40–60 % 1 repetition maximum [ 1RM ] ) training group or a high-resistance ( 70–90 % 1RM ) training group . Both of the training groups intended to maximally accelerate each repetition during the concentric phase ( IMCA ) . The 10 weeks of training consisted of 4 training sessions a week using basic core exercises .  Peak force , velocity and power were evaluated during set angle and depth jumps as well as weighted jumps using 30 and 50 % 1RM .  Squat 1RMs  were also tested . Although no interactions for any of the jump tests were found , trends supported the hypothesis of velocity-specific training . Percentage gains suggest that the combined use of heavier training loads ( 70–90 % 1RM ) and IMCA tend to increase peak force in the lower-body leg and hip extensors . Trends also show that the combined use of lighter training loads ( 40–60 % 1RM ) and IMCA tend to increase peak power and peak velocity in the lower-body leg and hip extensors . The high-resistance group improved squats more than the low-resistance group ( p < 0.05 ; + 22.7 vs. + 16.1 kg ) . The results of this study support the use of a combination of heavier training loads and IMCA to increase 1RM strength in the lower bodies of resistance-trained athletes OBJECTIVES To investigate the physical dem and s of professional rugby league match-play using microtechnology , and to compare these dem and s with typical training activities used to prepare players for competition . DESIGN Prospect i ve cohort study . METHODS Thirty elite rugby league players participated in this study . Seven hundred and eighty-six . training data sets and 104 data sets from National Rugby League matches were collected over one playing season . Movement was recorded using a commercially available microtechnology unit ( minimaxX , Catapult Innovations ) , which provided information on speeds , distances , accelerations , physical collisions and repeated high-intensity efforts . RESULTS Mean distances covered during match-play by the hit-up forwards , wide-running forwards , adjustables , and outside backs were 3,569 m , 5,561 m , 6,411 m , and 6,819 m , respectively . Hit-up forwards and wide-running forwards were engaged in a greater number of moderate and heavy collisions than the adjustables and outside backs , and more repeated high-intensity effort bouts per minute of play ( 1 bout every 4.8 - 6.3 min ) . The physical dem and s of traditional conditioning , repeated high-intensity effort exercise , and skill training activities were all lower than the physical dem and s of competition . CONCLUSIONS These results demonstrate that absolute distances covered during professional rugby league matches are greater for outside backs , while the collision and repeated high-intensity effort dem and s are higher for hit-up forwards and wide-running forwards . The specific physical dem and s of competitive play , especially those dem and s associated with collisions and repeated high-intensity efforts , were not well matched by those observed in traditional conditioning , repeated high-intensity effort exercise , and skills training activities . Further research is required to investigate whether modifications need to be made to these training activities to better prepare players for the dem and s of National Rugby League competition UNLABELLED Fast acceleration is an important performance factor in h and ball . In addition to traditional sprint training ( TST ) , resisted-sprint training ( RST ) is a method often used to improve acceleration . However , studies on RST show conflicting results , and underlying mechanisms have not been studied . PURPOSE To compare the effects of RST , by sled towing , against TST on sprint performance and muscle architecture . METHODS Participants ( n=18 ) were assigned to either RST or TST and completed 2 training sessions of RST or TST per week ( 10 wk ) , in addition to their normal team training .  Sprint tests ( 10 and 30 m ) and measurements of muscle architecture were performed pre- and posttraining . RESULTS Beneficial effects were found in the 30-m-sprint test for both groups ( mean ; ±90 % CL : TST=-0.31 ; ±0.19 s , RST=-0.16 ; ±0.13 s ) , with unclear differences between the groups . Only TST had a beneficial effect on 10-m time ( -0.04 ; ±0.04 s ) , with a likely difference between the 2 groups ( 85 % , ES=0.60 ) . Both groups had a decrease in pennation angle ( -6.0 ; ±3.3 % for TST and -2.8 ; ±2.0 % for RST ) , which had a nearly perfect correlation with percentage change in 10-m-sprint performance ( r=.92 ) . A small increase in fascicle length ( 5.3 ; ±3.9 % and 4.0 ; ±2.1 % for TST and RST , respectively ) was found , with unclear differences between groups . DISCUSSION TST appears to be more effective than RST in enhancing 10-m-sprint time . Both groups showed similar effects in 30-m-sprint time . A similar , yet small , effect of sprint training on muscle architecture was observed in both groups The purpose of this study was to compare the effects of combined strength and plyometric training with strength training alone on power-related measurements in professional soccer players . Subjects in the intervention team were r and omly divided into 2 groups . Group ST ( n = 6 ) performed heavy strength training twice a week for 7 weeks in addition to 6 to 8 soccer sessions a week . Group ST+P ( n = 8) performed a plyometric training program in addition to the same training as the ST group . The control group ( n = 7 ) performed 6 to 8 soccer sessions a week . Pretests and posttests were 1 repetition maximum ( 1RM ) half squat , countermovement jump ( CMJ ) , squat jump ( SJ ) , 4-bounce test ( 4BT ) , peak power in half squat with 20 kg , 35 kg , and 50 kg ( PP20 , PP35 , and PP50 , respectively ) , sprint acceleration , peak sprint velocity , and total time on 40-m sprint . There were no significant differences between the ST+P group and ST group . Thus , the groups were pooled into 1 intervention group . The intervention group significantly improved in all measurements except CMJ , while the control group showed significant improvements only in PP20 . There was a significant difference in relative improvement between the intervention group and control group in 1RM half squat , 4BT , and SJ . However , a significant difference between groups was not observed in PP20 , PP35 , sprint acceleration , peak sprinting velocity , and total time on 40-m sprint . The results suggest that there are no significant performance-enhancing effects of combining strength and plyometric training in professional soccer players concurrently performing 6 to 8 soccer sessions a week compared to strength training alone . However , heavy strength training leads to significant gains in strength and power-related measurements in professional soccer players UNLABELLED A " negative interaction " between step length and step rate refers to an increase in one factor result ing in a decrease in the other . PURPOSE S There were three main purpose s : a ) to investigate the relative influence of the determinants of step length and step rate , b ) to determine the sources of negative interaction between step length and step rate , and c ) to investigate the effects of manipulation of this interaction . METHODS Thirty-six athletes performed maximal-effort sprints .  Video and ground reaction force data  were collected at the 16-m mark . Sprint velocity , step length , step rate , and their underlying determinants were calculated . Analyses included correlations , multiple linear regressions , paired t-tests , and a simple simulation based on alterations in flight determining parameters . RESULTS A wide range of step length and step rate combinations was evident , even for subgroups of athletes with similar sprint velocities . This was partly due to a negative interaction that existed between step length and step rate ; that is , those athletes who used a longer step length tended to have a lower step rate and vice versa . Vertical velocity of takeoff was the most prominent source of the negative interaction . CONCLUSIONS Leg length , height of takeoff , and vertical velocity of takeoff are all possible sources of a negative interaction between step length and step rate . The very high step lengths and step rates achieved by elite sprinters may be possible only by a technique that involves a high horizontal and low vertical velocity of takeoff . However , a greater vertical velocity of takeoff might be of advantage when an athlete is fatigued and struggling to maintain a high step rate The purpose of this investigation was to examine the effect of an 8-week training program with heavy- vs. light-load jump squats on various physical performance measures and electromyography ( EMG ) .  Twenty-six athletic men with varying levels of resistance training experience performed sessions of jump squats with either 30 % ( JS30 , n = 9 ) or 80 % ( JS80 , n = 10 ) of their one repetition maximum in the squat ( 1RM ) or served as a control ( C , n = 7 ) . An agility test , 20-m sprint , and jump squats with 30 % ( 30J ) , 55 % ( 55J ) , and 80 % ( 80J ) of their 1RM were performed before and after training . Peak force , peak velocity ( PV ) , peak power ( PP ) , jump height , and average EMG ( concentric phase ) were calculated for the jumps . There were significant increases in PP and PV in the 30J , 55J , and 80J for the JS30 group ( p < 0.05 ) . The JS30 group also significantly increased in the 1RM with a trend towards improved 20-m sprint times . In contrast , the JS80 group significantly increased both PF and PP in the 55J and 80J and significantly increased in the 1RM but ran significantly slower in the 20-m sprint . In the 30J the JS30 group 's percentage increase in EMG activity was significantly different from the C group . In the 80J the JS80 group 's percentage increase in EMG activity was significantly different from the C group . This investigation indicates that training with light-load jump squats results in increased movement velocity capabilities and that velocity-specific changes in muscle activity may play a key role in this adaptation The literature contains some hypotheses regarding the most favorable ground reaction force ( GRF ) for sprint running and how it might be achieved . This study tested the relevance of these hypotheses to the acceleration phase of a sprint , using  GRF impulse as the GRF variable of interest . Thirty-six athletes performed maximal-effort sprints from which video and GRF data were collected at the 16-m mark . Associations between GRF impulse  ( expressed relative to body mass ) and various kinematic measures were explored with simple and multiple linear regressions and paired t-tests . The regression results showed that relative propulsive impulse accounted for 57 % of variance in sprint velocity . Relative braking impulse accounted for only 7 % of variance in sprint velocity . In addition , the faster athletes tended to produce only moderate magnitudes of relative vertical impulse . Paired t-tests revealed that lower magnitudes of relative braking impulse were associated with a smaller touchdown distance ( p < 0.01 ) and a more active touchdown ( p < 0.001 ) . Also , greater magnitudes of relative propulsive impulse were associated with a high mean hip extension velocity of the stance limb ( p < 0.05 ) . In conclusion , it is likely that high magnitudes of propulsion are required to achieve high acceleration . Although there was a weak trend for faster athletes to produce lower magnitudes of braking , the possibility of braking having some advantages could not be ruled out . Further research is required to see if braking , propulsive , and vertical impulses can be modified with specific training . This will also provide insight into how a change in one GRF component might affect the others PURPOSE The aim of this study was to compare the effects of 2 strength and conditioning programs involving either purely vertically oriented or combining vertically and horizontally oriented exercises on soccer-relevant performance variables ( ie , acceleration , jumping ability , peak power , and endurance ) . METHODS Twenty-two professional male soccer players were r and omly assigned to 2 training groups : vertical strength ( VS , n = 11 ) and vertical and horizontal strength ( VHS , n = 11 ) . 
    Output:
    
Conclusions RSS training is a novel training method with potential for the improvement of sprint performance , but its performance benefits over URS training remain to be conclusively demonstrated .