***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: Background . Previous research has shown that children can increase their muscular strength and muscular endurance as a result of regular participation in a progressive resistance training program . However , the most effective exercise prescription regarding the number of repetitions remains question able . Objective . To compare the effects of a low repetition – heavy load resistance training program and a high repetition – moderate load resistance training program on the development of muscular strength and muscular endurance in children . Design . Prospect i ve , controlled trial . Setting . Community-based youth fitness center . Subjects . Eleven girls and 32 boys between the ages of 5.2 and 11.8 years . Intervention . In twice-weekly sessions of resistance training for 8 weeks , children performed 1 set of 6 to 8 repetitions with a heavy load ( n = 15 ) or 1 set of 13 to 15 repetitions with a moderate load ( n = 16 ) on child-size exercise machines . Children in the control group ( n = 12 ) did not resistance train . One repetition maximum ( RM ) strength and muscular endurance ( repetitions performed posttraining with the pretraining 1-RM load ) were determined on the leg extension and chest press exercises . Results . One RM leg extension strength significantly increased in both exercise groups compared with that in the control subjects . Increases of 31.0 % and 40.9 % , respectively , for the low repetition – heavy load and high repetition – moderate load groups were observed . Leg extension muscular endurance significantly increased in both exercise groups compared with that in the control subjects , although gains result ing from high repetition – moderate load training ( 13.1 ± 6.2 repetitions ) were significantly greater than those result ing from low repetition – heavy load training ( 8.7 ± 2.9 repetitions ) . On the chest press exercise , only the high repetition – moderate load exercise group made gains in 1-RM strength ( 16.3 % ) and muscular endurance ( 5.2 ± 3.6 repetitions ) that were significantly greater than gains in the control subjects . Conclusion . These findings support the concept that muscular strength and muscular endurance can be improved during the childhood years and favor the prescription of higher repetition – moderate load resistance training programs during the initial adaptation period The purpose of the present study was to examine the influence of direct supervision on muscular strength , power , and running speed during 12 weeks of resistance training in young rugby league players . Two matched groups of young ( 16.7 ± 1.1 years [ mean ± SD ] ) , talented rugby league players completed the same periodized resistance-training program in either a supervised ( SUP ) ( N = 21 ) or an unsupervised ( UNSUP ) ( N = 21 ) environment . Measures of 3 repetition maximum ( 3RM ) bench press , 3RM squat , maximal chin-ups , vertical jump , 10– and 20-m sprints , and body mass were completed pretest ( week 0 ) , midtest ( week 6 ) , and posttest ( week 12 ) training program . Results show that 12 weeks of periodized resistance training result ed in an increased body mass , 3RM bench press , 3RM squat , maximum number of chin-ups , vertical jump height , and 10– and 20-m sprint performance in both groups ( p < 0.05 ) . The SUP group completed significantly more training sessions , which were significantly correlated to strength increases for 3RM bench press and squat ( p < 0.05 ) . Furthermore , the SUP group significantly increased 3RM squat strength ( at 6 and 12 weeks ) and 3RM bench press strength ( 12 weeks ) when compared to the UNSUP group ( p < 0.05 ) . Finally , the percent increase in the 3RM bench press , 3RM squat , and chin-upmax was also significantly greater in the SUP group than in the UNSUP group ( p < 0.05 ) . These findings show that the direct supervision of resistance training in young athletes results in greater training adherence and increased strength gains than does unsupervised training BACKGROUND : In developed societies levels of daily physical activity ( PA ) among school-age children are decreasing . This implies risk factors for cardiovascular and metabolic diseases . Specific strategies to improve levels of PA are needed . In prepubertal boys there is evidence that strength training increases spontaneous PA outside of training . METHODS : A total of 102 schoolchildren ( age 10–14 years ) in Switzerl and were r and omly assigned to  physical education classes or to participate twice weekly at a guided strength training program for 19 weeks  . Spontaneous PA energy expenditure ( PAEE ; 3axial accelerometry for 7 days ) , leg and arm strength , and body composition ( dual energy radiograph absorptiometry ) were measured at baseline , after 19 weeks of training intervention , and after 3 months of washout . RESULTS : There were no significant differences between the groups at baseline . In the intervention group , PAEE increased by 10 % from baseline to end of training in boys ( P = .02 ) , but not in girls . Leg and arm strength were increased owing to training intervention in both boys and girls . All other variables were unchanged . Baseline PAEE was significantly negatively correlated with changes of PAEE . CONCLUSIONS : Targeted strength training significantly increases daily spontaneous PA behavior in boys . The less active children showed the greatest increase in spontaneous PAEE . Girls showed a similar increase in strength , but not in spontaneous PAEE . This may be explained by their earlier pubertal development . Strength training may be a promising strategy in schools to counteract decreasing levels of PA The aim of this study was to determine the effectiveness of two different resistance training programs on lower limb explosive and reactive strength in young female athletes . Fifty seven rhythmic gymnasts were r and omly assigned to unspecific resistance training with dumbbells ( 12 repetition maximum squats )  ( n = 19 ; age = 12.0 + /- 1.8 years ) or to specific resistance training with weighted belts ( 6 % of body mass ; n = 18 ; age = 11.9 + /- 1.0 years ) . Squat jump test , counter movement jump test , hopping test , flexibility of the hip , and anthropometric measures were assessed before and after six weeks training . The main result was that both unspecific resistance training and specific resistance training protocol s positively affected the jumping performance , with an increase of the lower limb explosive strength of 6 - 7 % , with no side effects . Counter movement jump flight time increased significantly ( p < 0.01 ) while hopping test ground contact time significantly decreased ( p < 0.01 ) . No significant differences were detected among groups for flexibility , body mass , calf and thigh circumferences . Therefore , six weeks of resistance training that integrates different elements of rhythmic gymnastics training enhance jumping ability in young female athletes Abstract Ramírez-Campillo , R , Gallardo , F , Henriquez-Olguín , C , Meylan , CMP , Martínez , C , Álvarez , C , Caniuqueo , A , Cadore , EL , and Izquierdo , M. Effect of vertical , horizontal , and combined plyometric training on explosive , balance , and endurance performance of young soccer players . J Strength Cond Res 29(7 ) : 1784–1795 , 2015—The aim of this study was to compare the effects of 6 weeks of vertical , horizontal , or combined vertical and horizontal plyometric training on muscle explosive , endurance , and balance performance .  Forty young soccer players aged between 10 and 14 years were r and omly divided into control ( CG ; n = 10 ) , vertical plyometric group ( VG ; n = 10 ) , horizontal plyometric group ( HG ; n = 10 ) , and combined vertical and horizontal plyometric group ( VHG ; n = 10 ) . Players performance in the vertical and horizontal countermovement jump with arms , 5 multiple bounds test ( MB5 ) , 20-cm drop jump reactive strength index ( RSI20 ) , maximal kicking velocity ( MKV ) , sprint , change of direction speed ( CODS ) , Yo-Yo intermittent recovery level 1 test ( Yo-Yo IR1 ) , and balance was measured . No significant or meaningful changes in the CG , apart from small change in the Yo-Yo IR1 , were observed while all training programs result ed in meaningful changes in explosive , endurance , and balance performance . However , only VHG showed a statistically significant ( p ⩽ 0.05 ) increase in all performance test and most meaningful training effect difference with the CG across tests . Although no significant differences in performance changes were observed between experimental groups , the VHG program was more effective compared with VG ( i.e. , jumps , MKV , sprint , CODS , and balance performance ) and HG ( i.e. , sprint , CODS , and balance performance ) to small effect . The study demonstrated that vertical , horizontal , and combined vertical and horizontal jumps induced meaningful improvement in explosive actions , balance , and intermittent endurance capacity . However , combining vertical and horizontal drills seems more advantageous to induce greater performance improvements The purpose of this study was to investigate whether 6 weeks of static hamstring stretching effects range of motion ( ROM ) , sprint , and vertical jump performances in athletes . Twenty-one healthy division III women 's track and field athletes participated in the study . Subjects were tested for bilateral knee ROM ; 55-m sprint time ; and vertical jump height before , at 3 weeks , and after the 6-week flexibility program . Subjects were r and omly assigned to treatment and control groups and warmed up with a 10-minute jog on a track before a hamstring stretching protocol . The stretching protocol consisted of four repetitions held for 45 seconds , 4 days per week . Four variables ( left and right leg ROM , 55-m sprint time , vertical jump ) were analyzed using a repeated- measures analysis of variance design . No significant differences ( P ≤ 0.05 ) were found with any of the four variables between the stretching and control groups . Six weeks of a static hamstring stretching protocol did not improve knee ROM or sprint and vertical jump performances in women track and field athletes . The use of static stretching should be restricted to post practice or competition because of the detrimental effects reported throughout the literature . Based on the current investigation , it does not seem that chronic static stretching  has a positive or negative impact on athletic performance . Thus , the efficacy of utilizing this practice is question able and requires further investigation The aim of this study was to investigate whether variation in estrogen levels during the menstrual cycle influences susceptibility to exercise-induced muscle damage after stretch-shortening cycle exercise .  Physically active women ( n = 18 ; age = 20.2 ± 1.7 yr ) participated in this research . The subjects performed one session of 100 maximal drop jumps on day 1 or 2 of the follicular phase and another identical session on day 1 or 2 of the ovulatory phase ; the order of the sessions was r and omized . Quadriceps femoris muscle peak torque evoked by electrical stimulation and maximal voluntary contraction , muscle pain , and CK activity were measured before and at various times up to 72 h after exercise . It was found that the high estrogen level during the ovulatory phase might be related to an earlier return to baseline muscle strength after strenuous stretch-shortening cycle exercise in that phase compared with the follicular phase . The estrogen effect appears to be highly specific to the damaged site because the differences in most EIMD markers ( CK , soreness , and low-frequency fatigue ) between the two menstrual cycle phases were small Abstract Escamilla , RF , Ionno , M , deMahy , MS , Fleisig , GS , Wilk , KE , Yamashiro , K , Mikla , T , Paulos , L , and And rews , JR . Comparison of three baseball-specific 6-week training programs on throwing velocity in high school baseball players . J Strength Cond Res 26(7 ) : 1767–1781 , 2012 . Throwing velocity is an important baseball performance variable for baseball pitchers , because greater throwing velocity results in less time for hitters to make a decision to swing . Throwing velocity is also an important baseball performance variable for position players , because greater throwing velocity results in decreased time for a runner to advance to the next base . This study compared the effects of 3 baseball-specific 6-week training programs on maximum throwing velocity .  Sixty-eight high school baseball players 14–17 years of age were r and omly and equally divided into 3 training groups and a nontraining control group . The 3 training groups were the Throwers Ten ( TT ) , Keiser Pneumatic ( KP ) , and Plyometric ( PLY ) . Each training group trained 3 d·wk−1 for 6 weeks , which comprised approximately 5–10 minutes for warm-up , 45 minutes of resistance training , and 5–10 for cool-down . Throwing velocity was assessed before ( pretest ) and just after ( posttest ) the 6-week training program for all the subjects . A 2-factor repeated measures analysis of variance with post hoc paired t-tests was used to assess throwing velocity differences ( p < 0.05 ) . Compared with pretest throwing velocity values , posttest throwing velocity values were significantly greater in the TT group ( 1.7 % increase ) , the KP group ( 1.2 % increase ) , and the PLY group ( 2.0 % increase ) but not significantly different in the control group . These results demonstrate that all 3 training programs were effective in increasing throwing velocity in high school baseball players , but the results of this study did not demonstrate that 1 resistance training program was more effective than another resistance training program in increasing throwing velocity Abstract Radnor , JM , Lloyd , RS , and Oliver , JL . Individual response to different forms of resistance training in school-aged boys . J Strength Cond Res 31(3 ) : 787–797 , 2017—The aim of this study was to examine individual responses to different forms of resistance training on measures of jumping and sprinting performance in school-aged boys . Eighty boys were categorized into 2 maturity groups ( pre- or post – peak height velocity [ PHV ] ) and r and omly assigned to a plyometric training , resistance training , combined training , or control group . Intervention 
    Output:
    
Therefore , we aim ed at examining comparative intervention studies that assessed the effects of age , sex , maturation , and resistance or plyometric training descriptors ( e.g. , training intensity , volume etc . )
Sex has no major impact on resistance training related outcomes ( e.g. , maximal strength , 10 repetition maximum ) .
In terms of plyometric training , around-PHV boys appear to respond with larger performance improvements ( e.g. , jump height , jump distance ) compared with girls .
Different types of resistance training ( e.g. , body weight , free weights ) are effective in improving measures of muscle strength ( e.g. , maximum voluntary contraction ) in untrained children and adolescents .
Effects of plyometric training in untrained youth primarily follow the principle of training specificity .