title: Monitoring Load, Recovery, and Performance in Young Elite Soccer Players EFFECT OF DIRECT SUPERVISION OF A STRENGTH COACH ON MEASURES OF MUSCULAR STRENGTH AND POWER IN YOUNG RUGBY LEAGUE PLAYERS Effects of aerobic training on the exercise-induced decline in short-passing ability in junior soccer players. A 12-month prospective cohort study of injury in international rowers Cardiac output and stroke volume changes with endurance training: the HERITAGE Family Study. Physiological and performance effects of generic versus specific aerobic training in soccer players. Soccer specific aerobic endurance training The New Zealand rugby injury and performance project. VI. A prospective cohort study of risk factors for injury in rugby union football Influence of an intensified competition on fatigue and match performance in junior rugby league players. Reliability of the PEDro scale for rating quality of randomized controlled trials. Can we detect non-functional overreaching in young elite soccer players and middle-long distance runners using field performance tests? Influence of training and match intensity on injuries in rugby league Relationship between training load and injury in professional rugby league players. Changes in perceived stress and recovery in overreached young elite soccer players. Risk Factors for Injury in Subelite Rugby League Players Monitoring Changes in Rugby League Players' Perceived Stress and Recovery during Intensified Training Generic versus small-sided game training in soccer. Improving Repeated Sprint Ability in Young Elite Soccer Players: Repeated Shuttle Sprints Vs. Explosive Strength Training
abstract: Brink , MS , Nederhof , E , Visscher , C , Schmikli , SL , and Lemmink , KAPM . Monitoring load , recovery , and performance in young elite soccer players . J Strength Cond Res 24(3 ) : 597 - 603 , 2010-The purpose of this study was to investigate the relation between training load , recovery , and monthly field test performance in young elite soccer players to develop training guidelines to enhance performance . In a prospect i ve , nonexperimental cohort design , 18 young elite soccer players registered training and match duration for a full competitive season by means of daily training logs . Furthermore , session rating of perceived exertion ( RPE ) and total quality of recovery ( TQR ) scores were recorded . Weekly duration ( TLd ) , load ( duration × session RPE = TLrpe ) , and TQR scores were calculated for 1 and 2 weeks before a monthly submaximal interval shuttle run tests to determine interval endurance capacity . Participants spent on average 394.4 ± 134.9 minutes per week on training and game play with an average session RPE of 14.4 ± 1.2 ( somewhat hard ) and TQR of 14.7 ± 1.3 ( good recovery ) . R and om intercept models showed that every extra hour training or game play result ed in enhanced field test performance ( p < 0.05 ) . Session RPE and TQR scores did not contribute to the prediction of performance . The duration of training and game play in the week before field test performance is most strongly related to interval endurance capacity . Therefore , coaches should focus on training duration to improve interval endurance capacity in elite soccer players . To evaluate the group and individual training response , field tests should be frequently executed and be incorporated in the training program 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 To examine the effects of aerobic interval training on the decline in short-passing ability caused by a short bout of high-intensity intermittent activities . For this r and omized controlled trial , 26 junior soccer players ( mean age , 17.8 + /- 0.6 years ; mean height , 178 + /- 5 cm ; mean body mass , 74.5 + /- 6.9 kg ) were recruited . After baseline measurements , subjects were r and omly allocated to 1 of 2 groups : the control group ( CG ) or the aerobic interval training group ( ITG ) . The ITG completed 4 weeks of high-intensity aerobic training , consisting of 4 bouts of running for 4 min at 90%-95 % of maximal heart rate , with 3 min of active recovery between sets , in addition to normal training .  Maximum oxygen uptake , Yo-Yo Intermittent Recovery Test level 1 ( YYIRT ) , and short-passing ability ( measured using the Loughborough Soccer Passing Test ( LSPT ) ) were measured before and after a 5 min high-intensity simulation ( HIS ) , reproducing the most intense phase of a match . The ITG ( n = 11 ) , but not the CG ( n = 10 ) , showed a significant 12 % and 4 % increase in YYIRT and maximal oxygen consumption after training , respectively , and reduced the worsening in LSPT penalty time after the HIS ( p < 0.05 ) . The relative exercise intensity during HIS decreased in the ITG only ( p < 0.01 ) . Our results demonstrated that junior soccer players may benefit from aerobic training to attenuate the decline in short-passing ability caused by a short bout of intermittent activities completed at the same pretraining workload Objective In this study , the injury incidence and association with type and volume of training in international rowers were described . Design A prospect i ve cohort design was used over a 12-month period . Patients 20 international rowers who were competing as part of the Irish Amateur Rowing Union squad system . Methods The rowers were interviewed monthly , and data were collected regarding their training and competition exposure as well as their injury experience . Results A mean injury rate of 3.67 per 1000 exposure hours was reported with a total of 44 injuries reported in a 12-month period . The mean number of injuries sustained per athlete was 2.2 ( 1.24 ) over the 12-month period . The area where the greatest number of injuries were reported was the lumbar spine ( 31.82 % of total injuries , 95 % CI 20 to 50 ) ( fig 2 ) followed by the knee ( 15.91 % of total injuries , 95 % CI 10 to 30 ) and the cervical spine ( 11.36 % of total injuries , 95 % CI 5 to 24 ) . Half of the injuries ( 22 injuries , 50 % of total reported injuries ) were to the spine ( χ2 = 30.8 , df = 9 , p = 0.0003 ) . Ergometer training load was the most significantly associated with injury risk ( r = 0.68 , p = 0.01 ) . Conclusion International rowers are at higher risk of injury than most non-contact sports and some contact sports . The high risk of lumbar spine injury and the significant association of high volume of ergometer training merit further research to reduce time and competition lost to injury PURPOSE The purpose of this study was to determine the magnitude of changes in cardiac output ( Qc ) , stroke volume ( SV ) , and arterial-mixed venous oxygen difference ( a-vO2 diff ) during submaximal exercise following a 20-wk endurance training program , with the primary focus on identifying differences in response by race , sex , and age . METHODS The participants in this study ( N = 631 ) were healthy and previously sedentary men ( N = 277 ) and women ( N = 354 ) of varying age ( 17 - 65 yr ) and race ( blacks , N = 217 ; whites , N = 414 ) who had completed the HERITAGE Family Study protocol . After baseline measurements , participants trained on cycle ergometers 3 d x wk(-1 ) for a total of 60 exercise sessions starting at the HR associated with 55 % of maximal oxygen uptake ( VO2max ) for 30 min/session and building to the HR associated with 75 % of VO2max for 50 min/session , which was maintained during the last 6 wk . HR , Qc ( CO2 rebreathing ) , and SV ( Qc/HR ) were determined in duplicate at 50 W and at 60 % of VO2max on two different days both before and after training . RESULTS After training , there were significant decreases in HR and Qc , and significant increases in SV and a-vO2 diff at 50 W ( except for no change in a-vO2 diff in black men ) . The changes in HR differed by sex and age , and the changes in SV , Qc , and a-vO2 diff differed by race . Qc decreased by 0.6 L x min(-1 ) at 50 W for the total sample , consistent with the decrease in VO2 at this power output . At 60 % of VO2max HR decreased , and SV , Q , and a-VO2 diff increased . There were small differences in response by sex ( HR and SV ) , race ( HR ) , and age ( HR and Qc ) . CONCLUSION It is concluded that the cardiovascular systems of men and women , blacks and whites , and younger and older subjects are not limited in their ability to adapt to endurance training The aim of this study was to compare the effects of specific ( small-sided games ) vs. generic ( running ) aerobic interval training on physical fitness and objective measures of match performance in soccer . Forty junior players were r and omly assigned to either generic ( n=20 ) or specific ( n=20 ) interval training consisting of 4 bouts of 4 min at 90 - 95 % of maximum heart rate with 3 min active rest periods , completed twice a week . The following outcomes were measured at baseline ( Pre ) , after 4 weeks of pre-season training ( Mid ) , and after a further 8 weeks of training during the regular season ( Post ) : maximum oxygen uptake , lactate threshold ( Tlac ) , running economy at Tlac , a soccer-specific endurance test ( Ekblom 's circuit ) , and indices of physical performance during soccer matches ( total distance and time spent st and ing , walking , and at low- and high-intensity running speed ) . Training load , as quantified by heart rate and rating of perceived exertion , was recorded during all training sessions and was similar between groups . There were significant improvements in aerobic fitness and match performance in both groups of soccer players , especially in response to the first 4 weeks of pre-season training . However , no significant differences between specific and generic aerobic interval training were found in any of the measured variables including soccer specific tests . The results of this study showed that both small-sided games and running are equally effective modes of aerobic interval training in junior soccer players Background : In professional soccer , a significant amount of training time is used to improve players ' aerobic capacity . However , it is not known whether soccer specific training fulfils the criterion of effective endurance training to improve maximal oxygen uptake , namely an exercise intensity of 90–95 % of maximal heart rate in periods of three to eight minutes . Objective : To determine whether ball dribbling and small group play are appropriate activities for interval training , and whether heart rate in soccer specific training is a valid measure of actual work intensity . Methods : Six well trained first division soccer players took part in the study . To test whether soccer specific training was effective interval training , players ran in a specially design ed dribbling track , as well as participating in small group play ( five a side ) . Laboratory tests were carried out to establish the relation between heart rate and oxygen uptake while running on a treadmill . Corresponding measurements were made on the soccer field using a portable system for measuring oxygen uptake . Results : Exercise intensity during small group play was 91.3 % of maximal heart rate or 84.5 % of maximal oxygen uptake . Corresponding values using a dribbling track were 93.5 % and 91.7 % . No higher heart rate was observed during soccer training . Conclusions : Soccer specific exercise using ball dribbling or small group play may be performed as aerobic interval training . Heart rate monitoring during soccer specific exercise is a valid indicator of actual exercise intensity Objectives —Although the nature of rugby injury has been well documented , little is known about key risk factors . A prospect i ve cohort study was undertaken to examine the association between potential risk factors and injury risk , measured both as an injury incidence rate and as a proportion of the playing season missed . The latter measure incorporates a measure of injury severity . Methods —A cohort of 258 male players ( mean ( SD ) age 20.6 ( 3.7 ) years ) were followed through a full competitive season . At a preseason assessment , basic characteristics , health and lifestyle patterns , playing experience , injury experience , training patterns , and anthropometric characteristics were recorded , and then a battery of fitness tests were carried out . Results —A multiple regression model identified grade and previous injury experience as risk factors for in season injury , measured as an injury incidence rate . A second model identified previous injury experience , hours of strenuous physical activity a week , playing position , cigarette smoking status , body mass index , years of rugby participation , stress , aerobic and anaerobic performance , and number of push ups as risk factors for in season injury , measured as proportion of season missed . Conclusions —The findings emphasise the importance of previous injury as a predictor of injury incidence and of missing play . They also show the importance of considering both the incidence rate and severity of injury when identifying risk factors for injury in sport OBJECTIVES The aim of this study was to assess the physiological responses to an intensified  rugby league competition  and explore the relationships between fatigue and match performance . DESIGN Prospect i ve cohort study . METHODS Fifteen junior rugby league players ( n=8 forwards , 7 backs ; mean±SE , age 16.6±0.2 years ; body mass 81.6±3.0 kg ; and height 178.9±1.8 cm ) competed in five 40min games  over 5 days ( two games each on days 1 and 2 , one game on day 4 , and no games on days 3 and 5 ) . Over the competition , players performed a countermovement jump to assess neuromuscular fatigue , provided a fingertip blood sample to measure blood creatine kinase , and completed a question naire to monitor perceived wellbeing ; ratings of perceived effort were recorded following each game . Global positioning system and video analysis of each game were used to assess match performance . RESULTS Over the first 3 days , there were progressive and large increases in neuromuscular fatigue which peaked 12h after game 4 ( forwards ES=4.45 , p=0.014 ; backs ES=3.62 , p=0.029 ) , and muscle damage which peaked 1h post game 4 ( forwards ES=4.45 , p=0.004 ; backs ES=3.94 p=0.012 ) , as well as reductions in perceived wellbeing . These measures gradually recovered over the final 2 days of the competition . Compared to the backs , the forwards experienced greater increases in creatine kinase following game 2 ( ES=1.30 ) and game 4 ( ES=1.24 ) and reductions in perceived wellbeing ( ES=0.25 - 0.46 ) . Match intensity , high-speed running , and repeated-high intensity effort bouts decreased in games 4 and 5 of the competition . Small to large associations were observed between the changes in fatigue , muscle damage and match performance , with significant correlations between creatine kinase and repeated high-intensity effort bout number ( r=-0.70 , p=0.031 ) and frequency ( r=0.74 , p=0.002 ) and low-speed activity ( r=-0.56 , p=0.029 ) . CONCLUSIONS Fatigue and muscle damage accumulate over an intensified competition , which is likely to contribute to reductions in high-intensity activities and work rates during competition BACKGROUND AND PURPOSE Assessment of the quality of r and omized controlled trials ( RCTs ) is common practice in systematic review s. However , the reliability of data obtained with most quality assessment scales has not been established . This report describes 2 studies design ed to investigate the reliability of data obtained with the Physiotherapy Evidence Data base ( PEDro ) scale developed to rate the quality of RCTs evaluating physical therapist interventions . METHOD In the first study , 11 raters independently rated 25 RCTs r and omly selected from the PEDro data base . In the second study , 2 raters rated 120 RCTs r and omly selected from the PEDro data base , and disagreements were resolved by a third rater ; this generated a set of individual rater and consensus ratings . The process was repeated by independent raters to create a second set of individual and consensus ratings . Reliability of ratings of PEDro scale items was calculated using multirater kappas , and reliability of the total ( summed ) score was calculated using intraclass correlation coefficients ( ICC [ 1,1 ] ) . RESULTS The kappa value for each of the 11 items ranged from.36 to.80 for individual assessors and from.50 to.79 for consensus ratings generated by groups of 2 or 3 raters . The ICC for the total score was.56 ( 95 % confidence interval=.47-.65 ) for ratings by individuals , and the ICC for consensus ratings was.68 ( 95 % confidence interval=.57-.76 ) . DISCUSSION AND CONCLUSION The reliability of ratings of PEDro scale items varied from " fair " to " substantial , " and the reliability of the total PEDro score was " fair " to " good . Objective To study whether field performance tests can make a valid distinction between non-functionally overreaching ( NFO ) athletes and control athletes . Design Monthly field performance tests were used to determine a performance decrement ( PD ) throughout a season . Athletes with a minimum of 1 month PD were compared with control athletes without a PD on mood characteristics and resting levels of stress hormones . Setting Sporting field and sports medical laboratory . Participants 129 young elite athletes , 77 soccer players and 52 middle-long distance runners were followed prospect ively during the 2006–2007 season . Fifteen of them were invited to the laboratory . Eight athletes showed a performance decrease lasting longer than 1 month , and seven athletes without a performance decrease acted as their controls . Main outcome measures Performance changes over time were measured using field tests .  Profile of Mood States and resting levels of adrenocorticotrophic hormone ( ACTH ) and cortisol in blood were measured in the laboratory . Results PD athletes showed several symptoms typical of the non-functional state of overreaching ( OR ) . The PD group scored higher on depression and anger than controls . They also showed a specific pattern of correlations between negative mood subscales ( tension , fatigue and depression ) , which was absent in controls . ACTH levels at rest were similar , but lower cortisol levels in PD athletes pointed at a blunted cortisol response . Cortisol levels were decoupled from ACTH levels only in PD athletes . Conclusions Implementing performance-related criteria in field tests can help coaches and sports physicians to distinguish NFO athletes from athletes with balanced workload and recovery The aim of this study was to examine the influence of perceived intensity , duration and load of matches and training on the incidence of injury in rugby league players . The incidence of injury was prospect ively studied in 79 semi-professional rugby league players during the 2001 season . All injuries sustained during matches and training sessions were recorded . Training sessions were conducted from December to September , with matches played from February to September . The intensity of individual training sessions and matches was estimated using a modified rating of perceived exertion scale . Training load was calculated by multiplying the training intensity by the duration of the training session . The match load was calculated by multiplying the match intensity by the time each player participated in the match . Training load increased from December ( 278.3 [ 95 % confidence interval , CI 262.2 to 294.5 ] units ) to February ( 385.5 [ 95 % CI 362.4 to 408.5 ] units ) , followed by a decline until September ( 98.4 [ 95 % CI 76.5 to 120.4 ] units ) . Match load increased from February ( 204.0 [ 95 % CI 186.2 to 221.8 ] units ) to September ( 356.8 [ 95 % CI 302.5 to 411.1 ] units ) . More training injuries were sustained in the first half of the season ( first vs second : 69.2 % vs 30.8 % , P < 0.001 ) , whereas match injuries occurred more frequently in the latter stages of the season ( 53.6 % vs 46.4 % , P < 0.001 ) . A significant relationship ( P < 0.05 ) was observed between changes in training injury incidence and changes in training intensity ( r = 0.83 ) , training duration ( r = 0.79 ) and training load ( r = 0.86 ) . In addition , changes in the incidence of match injuries were significantly correlated ( P < 0.05 ) with changes in match intensity ( r = 0.74 ) , match duration ( r = 0.86 ) and match load ( r = 0.86 ) . These findings suggest that as the intensity , duration and load of rugby league training sessions and matches is increased , the incidence of injury is also increased OBJECTIVES To investigate the relationship between training load and injury in professional rugby league players ; DESIGN Prospect i ve cohort study ; METHODS Seventy-nine professional rugby league players ( mean±SD age , 23.3±3.8 years ) participated in this four-year study . A periodized field , strength , and power training program was implemented , with training loads progressively increased in the general preparatory phase of the season and reduced during the competitive phase of the season . Training loads and injuries were recorded for each training session . RESULTS Training load was significantly related ( P<0.05 ) to overall injury ( r=0.82 ) , non-contact field injury ( r=0.82 ) , and contact field injury ( r=0.80 ) rates . Significant relationships were also observed between the field training load and overall field injury ( r=0.68 ) , non-contact field injury ( r=0.65 ) , and contact field injury ( r=0.63 ) rates . Strength and power training loads were significantly related to the incidence of strength and power injuries ( r=0.63 ) . There was no significant relationship between field training loads and the incidence of strength and power injuries . However , strength and power training loads were significantly ( P<0.01 ) associated with the incidence of contact ( r=0.75 ) and non-contact ( r=0.82 ) field training injuries . CONCLUSIONS These findings suggest that the harder rugby league players train , the more injuries they will sustain , and that high strength and power training loads may contribute indirectly to field injuries . Monitoring of training loads and careful scheduling of field and gymnasium sessions to avoid residual fatigue is warranted to minimize the effect of training-related injuries on professional rugby league players The aim of this study was to prospect ively monitor sport-specific performance and assess the stress-recovery balance in overreached ( OR ) soccer players and controls . During two competitive seasons , 94 players participated in the study . The  stress-recovery balance ( RESTQ-Sport ) and sport-specific performance ( Interval Shuttle Run Test )  were assessed monthly . Seven players with performance decrement of at least a month were classified as OR .  Stress and recovery measures were assessed between groups ( OR vs healthy players ) and at different times within the OR group . An unfavorable total recovery score appeared 2 months before diagnosis when compared with the reference values of the healthy group established at the start of the season ( P=0.009 ) and also over the two seasons ( P=0.028 ) . The scales Emotional Stress ( P=0.044 ) , Physical Recovery ( P=0.009 ) , General Well-being ( P=0.001 ) and Sleep Quality ( P=0.045 ) were sensitive to OR compared with the average of the healthy group over the two seasons . Finally , Fatigue and Being in Shape demonstrated the largest changes in stress and recovery within the OR players ( effect size=1.14 and 1.50 ) . The longitudinal monitoring of performance and changes in stress and recovery may be useful for the detection of OR in its earliest stage . The information obtained from these tests can be used to optimize individual training and recovery programs Background Although player fatigue and playing intensity have been suggested to contribute to injuries in rugby league players , no study has confirmed if the level of physical fitness is a risk factor for injury in rugby league players . The aim of this study was to identify risk factors for injury in subelite rugby league players . Hypothesis Low physical fitness levels are risk factors for injury in subelite rugby league players . Study Design Cohort study ; Level of evidence , 2 . Methods One hundred fifty-three players from a subelite rugby league club underwent preseason measurements of muscular power ( vertical jump ) , speed ( 10- and 40-m sprint ) , and maximal aerobic power ( multistage fitness test ) over 4 competitive seasons . All injuries sustained by players were prospect ively recorded over the 4 competitive seasons . Results The risk of injury was greater in players with low 10- and 40-m speed . Players with a low maximal aerobic power had a greater risk of sustaining a contact injury . In addition , players who completed less than 18 weeks of training before sustaining their initial injuries were at greater risk of sustaining a subsequent injury . Conclusions Subelite rugby league players with low speed and maximal aerobic power are at an increased risk of injury . In addition , players who complete less than 18 weeks of training before sustaining an initial injury are at greater risk of sustaining a subsequent injury . These findings highlight the importance of speed and endurance training to reduce the incidence of injury in subelite rugby league players This study assessed whether the Recovery-Stress Question naire for Athletes ( RESTQ-Sport ) could be used to monitor changes in perceived stress and recovery during intensified training of rugby league players . 20 semiprofessional rugby league players were divided into two equal groups r and omly assigned to complete 6 wk . of Normal Training or Intensified Training , each followed with a 7-day taper . Multistage Fitness Test performance and RESTQ – Sport measures were taken at the beginning , at 2-wk . intervals , and at the end of the training period . Endurance significantly decreased with Intensified Training and returned to baseline levels following the taper , while remaining unchanged in the Normal Training group . The RESTQ – Sport scores with training were positively related to stress subscale scores ( Fatigue , Disturbed Breaks , and General Stress ) and recovery subscale measures ( Success , Physical Recovery , Being in Shape , Self-efficacy , Social Relaxation , General Well-being , and Sleep Quality ) decreasing in the Intensified Training group and then normalising following the taper ( Stress subscales : Fatigue and General Stress , and Recovery subscales : Physical Recovery and General Well-being ) . The RESTQ – Sport is a practical psychometric tool for monitoring responses to training in team-sport athletes The aim of this study was to compare 7 weeks of soccer-specific small-sided game ( SSG ) and mixed generic fitness training , on selected physiological , perceptual and performance variables .  Twenty-five elite youth players were r and omly allocated to either a SSG ( coach selected ) or generic training group ( GTG ) , in a r and omised , parallel matched-group design . In addition to normal training , each group completed two fitness training sessions per week of equal duration . Players completed a V O ( 2 max ) treadmill test , Multistage Fitness Test ( MSFT ) , Yo-Yo Intermittent Recovery Test Level 1 ( YYIRTL1 ) , 12x20 m test of repeated-sprint ability ( RSA ) and 20-m sprint test pre and post training . Training heart rate , perceived training intensity and perceptual fatigue measures were recorded throughout the training period . There were no differences in training heart rate or perceptual well-being measures . However , the GTG did perceive their training to be more intense than SSG . There were no changes in either group for V O ( 2 max ) , MSFT , RSA or sprint performance . However , there were improvements in YYIRTL1 performance for both groups over time , but not between groups . The results show that both types of training are equally effective at improving pre-season YYIRTL1 performance , despite GTG being perceived to be more intense Buchheit , M , Mendez-Villanueva , A , Delhomel , G , Brughelli , M , and Ahmaidi , S. Improving repeated sprint ability in young elite soccer players :  repeated shuttle sprints vs. explosive strength training . J Strength Cond Res 24(10 ) : 2715 - 2722 , 2010-To compare the effects of explosive strength ( ExpS ) vs. repeated shuttle sprint ( RS ) training on repeated sprint ability ( RSA ) in young elite soccer players , 15 elite male adolescents ( 14.5 ± 0.5 years ) performed , in addition to their soccer training program , RS ( n = 7 ) or ExpS ( n = 8) training once a week for a total of 10 weeks . RS training consisted of 2 - 3 sets of 5 - 6 × 15- to 20-m repeated shuttle sprints interspersed with 14 seconds of passive or 23 seconds of active recovery ( ≈2 m·s−1 ) ; ExpS training consisted of 4 - 6 series of 4 - 6 exercises ( e.g. , maximal unilateral countermovement jumps ( CMJs ) , calf and squat plyometric jumps , and short sprints ) . Before and after training , performance was assessed by 10 and 30 m ( 10 and 30 m ) sprint times , best ( RSAbest ) and mean ( RSAmean ) times on a repeated shuttle sprint ability test , a CMJ , and a hopping ( Hop ) test . After training , except for 10 m ( p = 0.22 ) , all performances were significantly improved in both groups ( all p 's < 0.05 ) . Relative changes in 30 m ( −2.1 ± 2.0 % ) were similar for both groups ( p = 0.45 ) . RS training induced greater improvement in RSAbest ( −2.90 ± 2.1 vs. −0.08 ± 3.3 % , p = 0.04 ) and tended to enhance RSAmean more ( −2.61 ± 2.8 vs. −0.75 ± 2.5 % , p = 0.10 , effect size [ ES ] = 0.70 ) than ExpS. In contrast , ExpS tended to induce greater improvements in CMJ ( 14.8 ± 7.7 vs. 6.8 ± 3.7 % , p = 0.02 ) and Hop height ( 27.5 ± 19.2 vs. 13.5 ± 13.2 % , p = 0.08 , ES = 0.9 ) compared with RS . Improvements in the repeated shuttle sprint test were only observed after RS training , whereas CMJ height was only increased after ExpS. Because RS and ExpS were equally efficient at enhancing maximal sprinting speed , RS training-induced improvements in RSA were likely more related to progresses in the ability to change direction
target: Of the few studies examining negative consequences associated with workloads , increases in training load led to increases in injury rates , while longer training duration was associated with a greater incidence of illness .
  Conclusion The combined capacity for adolescent males to grow , train and improve physical performance highlights and underscores an exciting responsiveness to training in the football environment .
  However , the capacity to train has some established barriers for adolescents experiencing high workloads , which could also result in negative consequences .
background: Background The expectation that training enhances performance is well explored in professional sport .
  However , the additional challenges of physical and cognitive maturation may require careful consideration when determining workloads to enhance performance in adolescents .
  Objective The objective of this study was to determine the state of knowledge on the relationship between workloads , physical performance , injury and /or illness in adolescent male football players .