Applying a holistic hamstring injury prevention approach in elite football: 12 seasons, single club study.

The aim was to investigate the preventive effect of a complex training program based on holistic hamstring health understanding in elite professional soccer players. This study involved an elite club in Europe and was conducted over 12 seasons. The last 2 seasons were the intervention period, and the others were the control seasons. During the intervention period, players performed a complex program organized into different interventions throughout the week having as a priority the player health. Hamstring injuries, absenteeism, injury rates, and injury burden between the control and intervention seasons were compared using a rate ratio (RR) with 95% CI. Players had a mean exposure of 333.5 ± 18.6 hours per season with no significant differences between the intervention and control seasons. The overall injury rate was 3 times lower during the two intervention seasons than during the previous seasons (P < .01); the match injury rate was 2.7 times lower (P < .01) and the training rate 4.3 times (P < .01). Injury burden was almost 4 times lower during the two intervention seasons than during the previous seasons (P < .01), and recurrences in the control group were 10% vs 0% in the intervention group. Hamstring injuries were reduced ~3 times during the seasons in which elite football players were exposed to multicomponent, complex prevention training with individual approaches based on player needs, management of training load, individualized physiotherapy treatment, and planned staff communication, in comparison to the control seasons without a clearly defined and structured injury prevention intervention.

Training-induced changes in anterior pelvic tilt: potential implications for hamstring strain injuries management.

An association has been reported between dynamic anterior pelvic tilt (APT) and hamstring injuries; however, no research has examined if a training-based preventive intervention could alter APT. Therefore, the aim of the present study was to examine if a specific 6-week multimodal intervention, based on the theoretical influence of neighbouring joints and biomechanical interactions between muscles that are inserted to the pelvis, induced changes in APT, during walking gait, hamstring flexibility and trunk endurance. Thirty-five active healthy males volunteered for this single-blind controlled trial and were split into two groups based on baseline data: a control group (CG, n = 20, continued their normal physical activities), and an intervention group (IG, n = 15, performed the intervention programme for 18 sessions over 6 weeks). A significant (p = 0.001) decrease in the APT kinematics during gait, significant increase in the Active Knee Extension Test (p = 0.001), and a significant increase in trunk endurance performance for flexion (p = 0.001), extension (p = 0.001) and side bridge (p = 0.001) were observed, in IG after the 6-week programme, compared to CG.

Under-exposure to official matches is associated with muscle injury incidence in professional footballers.

External workload from matches is considered one of the most important muscle injury risk factors for football teams. However, there is scarce published evidence to support this belief. This study examined whether a particular profile of external match workload existed prior to a muscle injury. A total of 144 professional football players belonging to 2 teams were monitored over three seasons. For each muscle injury, a profile of external workload variables was determined for 5 to 8 games and expressed as: time playing exposure, total distance (TD) covered and high-speed running (HSR) covered. In addition, acute:chronic workload ratio (ACWR) was calculated. Sixty players (41.6%) reported a total of 86 muscle injuries during the three seasons. Muscle injuries occurred principally in matches (79.1%), the hamstring being the most affected muscle (44.1%). Injured players displayed substantially lower accumulated exposure time (ES = 0.45), TD (ES = 0.45) and HSR (ES = 0.39) in comparison with uninjured players in the last 5 games prior to injury. Compared to the uninjured players, ACWR for exposure (ES = -0.29/0.02) and running load (ES = -0.24/0.00) did not differ between match 5 and 2 prior to the injury, although uninjured players displayed a substantially greater ACWR in all 3 variables (ES = 0.31/0.35) than injured players in match 1 prior to the injury. Lower playing exposure (minutes played) and associated reduced running distances (TD and HSR) were observed in injured football players. Being under-loaded in official games could be a mediator for muscle injury in this cohort of elite football players.

Physical Demands of Ball Possession Games in Relation to the Most Demanding Passages of a Competitive Match.

The main aim of this study was to determine the physical demands of different small-sided ball possession games (SSBPGs) according to player field position and compare these demands in relation to the most demanding passages of play (MDP) in competitive matches. Global positioning system data were obtained from 25 football players (20.4 ± 2.1 yrs, 1.78 ± 0.66 m, 69.7 ± 6.1 kg) belonging to the reserve squad of a Spanish La Liga Club. Players were categorized according to positional groups; full back (FB), central defender (CD), midfielder (MF), wide midfielder (WMF) and forwards (FW). The variables analyzed were relativized to metres per minute (m·min-1): total distance covered (TD), TD at high speed (HSR; >19.8 km·h-1), TD at sprint (SPR; >25.2 km·h-1), the number of accelerations (ACC) and decelerations (DEC) at high intensity (> +/-3 m·s-2), the average metabolic power (AMP; W·kg-1) and the high metabolic load distance (HMLD; >25.5 W·kg-1). The MDP were analyzed using a rolling average method, where maximal values were calculated for 3 and 5 minutes to compare with SSBPGs using AMP as a criterion variable. The results were obtained from the SSBPGs relative to the MDP (expressed in %) for each player position. FB showed the greatest magnitude of overload in ACC/DEC according to the MDP in the two smaller SSBPGs formats (201-217%), whereas MF showed lower values (105-140%). The load expressed in relation to the MDP can be different depending on the format of the SSBPGs and the characteristics of playing position. These factors should be considered by the coaches when planning training.

Estimating fat-free mass in elite youth male soccer players: cross-validation of different field methods and development of prediction equation.

This study determined the most effective field method for quantifying fat-free mass (FFM) in elite youth male soccer players compared to dual X-ray absorptiometry (DXA) values and to develop prediction equations for FFM based on anthropometric variables. Forty-one male elite-standard youth soccer players, ages 16.2-18.0 years, undertook FFM assessments including bioelectrical impedance analysis, and different skinfold-based prediction equations. DXA provided a criterion measure of FFM. Correlation coefficients, bias, limits of agreement, and differences were used as validity measures, and regression analyses to develop soccer-specific prediction equations. Slaughter et al (1988), Durnin and Wormersley (1974), and Sarria et al (1998) equations showed the lowest biases, and no significant, standardized, and substantial differences against DXA. The new youth soccer-specific anthropometric equation explained 91% of the DXA-derived FFM variance using three circumferences, eight skinfolds, and one bone breadth. All field methods compared in this study may not be adequate for estimating FFM in elite youth male soccer players, except the equations of Slaughter et al (1988), Durnin and Wormersley (1974), and Sarria et al (1998). We recommend the use of the new soccer-specific equation proposed in this study as a valid alternative to DXA to quantify FFM among elite youth male players.

A Repeated Power Training Enhances Fatigue Resistance While Reducing Intraset Fluctuations.

Oliver, GS, Julio, TF, Moras, G, José Luis, AS, and Alberto, MV. A repeated power training enhances fatigue resistance while reducing intraset fluctuations. J Strength Cond Res 33(10): 2711-2721, 2019-The present study analyzed the effects of adding upper-body repeated power ability (RPA) training to habitual strength training sessions. Twenty young elite male basketball players were randomly allocated into a control group (CON, n = 10) or repeated power group (RPG, n = 10) and evaluated by 1 repetition maximum (1RM), incremental load, and RPA tests in the bench press exercise before and after a 7-week period and a 4-week cessation period. Repeated power group performed 1-3 blocks of 5 sets of 5 repetitions using the load that maximized power output with 30 seconds and 3 minute of passive recovery between sets and blocks, respectively. Between-group analysis showed substantial greater improvements in RPG compared with CON in: best set (APB), last set (APL), mean power over 5 sets (APM), percentage of decrement, fluctuation decrease during APL and RPA index (APLpost/APBpre) during the RPA test (effect size [ES] = 0.64-1.86), and 1RM (ES = 0.48) and average power at 80% of 1RM (ES = 1.11) in the incremental load test. The improvements of APB and APM were almost perfectly correlated. In conclusion, RPA training represents an effective method to mainly improve fatigue resistance together with the novel finding of a better consistency in performance (measured as reduced intraset power fluctuations) at the end of a dynamic repeated effort.

Association of Monocarboxylate Transporter-1 (MCT1) A1470T Polymorphism (rs1049434) with Forward Football Player Status.

The aim of this study was to investigate the association between the MCT1 (monocarboxylate transporter 1) A1470T polymorphism and positional roles in a large cohort of professional football players from five different countries. We compared genotype distributions of the MCT1 A1470T polymorphism between football players (n=694) and non-athlete controls (n=781) from Italy, Poland, Lithuania, Ukraine and Malta, and we analyzed the MCT1 genotype distributions with respect to the players' positions in the field (e. g. forwards, midfielders, defenders and goalkeepers). Genomic DNA was extracted from either buccal epithelium or peripheral blood using a standard protocol. In the pooled cohort of Italian, Polish, Lithuanian and Ukrainian football players, forwards (n=148) were more likely than controls (n=781) to possess the A allele (χ2=7.067, p=0.029, FDR q value 0.116), with a greater likelihood of having the AA genotype compared with the TT genotype (OR=1.97; C.I.=1.07-3.64; p=0.021, FDR q value 0.086). The MCT1 AA genotype was significantly more frequent in forwards then in controls. Further studies are needed to confirm these findings in other professional football player cohorts.

Validation of Field Methods to Assess Body Fat Percentage in Elite Youth Soccer Players.

This study determined the most effective field method for quantifying body fat percentage in male elite youth soccer players and developed prediction equations based on anthropometric variables. Forty-four male elite-standard youth soccer players aged 16.3-18.0 years underwent body fat percentage assessments, including bioelectrical impedance analysis and the calculation of various skinfold-based prediction equations. Dual X-ray absorptiometry provided a criterion measure of body fat percentage. Correlation coefficients, bias, limits of agreement, and differences were used as validity measures, and regression analyses were used to develop soccer-specific prediction equations. The equations from Sarria et al. (1998) and Durnin & Rahaman (1967) reached very large correlations and the lowest biases, and they reached neither the practically worthwhile difference nor the substantial difference between methods. The new youth soccer-specific skinfold equation included a combination of triceps and supraspinale skinfolds. None of the practical methods compared in this study are adequate for estimating body fat percentage in male elite youth soccer players, except for the equations from Sarria et al. (1998) and Durnin & Rahaman (1967). The new youth soccer-specific equation calculated in this investigation is the only field method specifically developed and validated in elite male players, and it shows potentially good predictive power.

The influence of successive matches on match-running performance during an under-23 international soccer tournament: The necessity of individual analysis.

This study investigated the effects of successive matches on match-running in elite under-23 soccer players during an international tournament. Match-running data was collected using a semi-automated multi-camera tracking system during an international under-23 tournament from all participating outfield players. Players who played 100% of all group stage matches were included (3 matches separated by 72 h, n = 44). Differences in match-running performance between matches were identified using a generalised linear mixed model. There were no clear effects for total, walking, jogging, running, high-speed running and sprinting distance between matches 1 and 3 (effect size (ES); -0.32 to 0.05). Positional analysis found that sprint distance was largely maintained from matches 1 to 3 across all positions. Attackers had a moderate decrease in total, jogging and running distance between matches 1 and 3 (ES; -0.72 to -0.66). Classifying players as increasers or decreasers in match-running revealed that match-running changes are susceptible to individual differences. Sprint performance appears to be maintained over successive matches regardless of playing position. However, reductions in other match-running categories vary between positions. Changes in match-running over successive matches affect individuals differently; thus, players should be monitored on an individual basis.

Impact of Fitness Characteristics on Tennis Performance in Elite Junior Tennis Players.

The impact of fitness characteristics on tennis performance in adolescent players is not clearly understood. Therefore, the aim of the present study was to test whether physical characteristics are related to players' competitive level (i.e., national youth ranking). A secondary aim was to compare adolescent tennis players by performance level (i.e., regional selected players and the national team). A total of 902 male and female junior players (aged, 11-16 years) in Germany were evaluated using a physical testing battery: grip strength; countermovement jump; 10 and 20-m sprint; tennis-specific sprint; overhead, forehand, and backhand medicine ball throws (MBT); serve velocity and tennis-specific endurance test (hit and turn tennis test). Results showed that serve velocity (r = -0.43 to 0.64 for female subjects [♀]; r = -0.33 to 0.49 for male subjects [♂]) and upper-body power (e.g., MBT r = -0.26 to -0.49 ♀; r = -0.20 to -0.49 ♂) were the most correlated predictors of tennis performance (i.e., national youth ranking) in both female and male tennis players. Moreover, national selected players showed better performance levels than their regional counterparts, mainly in the most predictive physical characteristics (i.e., serve velocity: effect size [ES], 0.78-1.04 ♀; ES 0.92-1.02 ♂, MBT: ES, 0.66-0.88 ♀; ES, 0.67-1.04 ♂) and specific endurance (ES, 0.05-0.95 ♀; ES, 0.31-0.73 ♂). The present findings underline the importance of certain physical attributes, especially serve velocity and strength- and power-related variables (upper body), and suggest the need to include these parameters in the area of training, physical testing, and talent identification of young tennis players.

The Relative Age Effect and Physical Fitness Characteristics in German Male Tennis Players.

The aims of the study were to test: 1) whether the relative age effect (RAE) was prevalent in young (U12-U18) German male tennis players; 2) the potential influence of age and/or skill level on RAE and 3) whether maturity, anthropometric and fitness measures vary according to birth date distribution in elite youth tennis players. For the present study the following male populations were analysed: Overall German population (n = 3.216.811), all players affiliated to the German Tennis Federation (DTB) (n = 120.851), players with DTB official ranking (n = 7165), regional (n = 381) and national (n = 57) squads (11-17 years old), as well as the top 50 German senior players were analyzed. RAEs were more prevalent at higher competitive levels with more players born in the first quarter of the year compared with the reference population for ranked (29.6%), regional (38.1%) and national (42.1%) players. No systematic differences were found in any of the maturity, anthropometric and fitness characteristics of the regional squad players born across different quarters. RAEs are present in the DTB competitive system and it was more pronounced at higher competitive levels. Compared with early born, late born players who were selected into elite squads did not differ in maturation, anthropometric and fitness characteristics. Key pointsRAEsexist in the selection of youth tennis players in Germany, a greater percentage of players analyzed was born in the 1st quarter compared to all licensed tennis players in the country, and more pronounced with an increased competition level in youth players.Players born later in the selection year and still selected in elite squads were likely to be similar across a range of physical fitness attributes compared with those born earlier in the year.The selection process should be reevaluated and changed to reduce the impact of RAEs on tennis players.

Negative Associations between Perceived Training Load, Volume and Changes in Physical Fitness in Professional Soccer Players.

The purpose of this study was to examine the usefulness of the rating of perceived exertion training load for monitoring changes in several aerobic fitness and neuromuscular performance variables during 9 weeks of soccer training in young professional players. Nineteen male soccer players (20.2 ± 1.9 years) belonging to the same reserve team of a Spanish La Liga Club participated in this study. Countermovement jump (CMJ), CMJ arm swing, single leg CMJ, a sprint running test (i.e., 5 m and 15 m times) and an aerobic fitness running test were performed at the start of the pre-season (Test 1) and 9 weeks later (Test 2). During 9 weeks, after each training session and match, players reported their rating of perceived exertion (RPE) separately for respiratory (RPEres) and leg musculature (RPEmus) effort. The training load (TL) was calculated by multiplying the RPE value by the duration in minutes of each training session or match. Accumulated RPEmus, and associated TL, as well as accumulated training volume were negatively correlated with the changes in most physical fitness attributes after 9 weeks of training (r = -0.51 to -0.64). Present results suggest that a high perception of leg muscular effort associated with training sessions and matches, as well as an excessive accumulation of training volume (time), can impair the improvement in several physical fitness variables believed to be relevant for on-field soccer performance. Therefore, the independent assessment of leg muscular effort to quantify TL can be an interesting additional monitoring measure in soccer training. Key pointsThe purpose of this study was to examine the usefulness of the perceived exertion-derived TL for monitoring changes in several aerobic fitness and neuromuscular parameters during 9 weeks of soccer training in young professional players.A high perception of leg muscular effort associated with training and matches, as well as an excessive accumulation of training volume (time), can impair several physical fitness factors believed to be relevant for on-field soccer performance.The independent assessment of muscular effort to quantify TL can be an interesting additional monitoring measure in soccer training.

Changes in repeated-sprint performance in relation to change in locomotor profile in highly-trained young soccer players.

The aim of this study was to examine the effects of changes in maximal aerobic (MAS) and sprinting (MSS) speeds and the anaerobic reserve (ASR) on repeated-sprint performance. Two hundred and seventy highly-trained soccer players (14.5 ± 1.6 year) completed three times per season (over 5 years) a maximal incremental running test to approach MAS, a 40-m sprint with 10-m splits to assess MSS and a repeated-sprint test (10 × 30-m sprints), where best (RSb) and mean (RSm) sprint times, and percentage of speed decrement (%Dec) were calculated. ASR was calculated as MSS-MAS. While ∆RSb were related to ∆MSS and ∆body mass (r(2) = 0.42, 90%CL[0.34;0.49] for the overall multiple regression, n = 334), ∆RSm was also correlated with ∆MAS and ∆sum of 7 skinfolds (r(2) = 0.43 [0.35;0.50], n = 334). There was a small and positive association between ∆%Dec and ∆MAS (r(2) = 0.02 [-0.07;0.11], n = 334). Substantial ∆MSS and ∆MAS had a predictive value of 70 and 55% for ∆RSm, respectively. Finally, ∆ASR per se was not predictive of ∆RSm (Cohen's = +0.8 to -0.3 with increased ASR), but the greater magnitude of ∆RSm improvement was observed when MSS, MAS and ASR increased together (0.8 vs. +0.4 with ASR increased vs. not, additionally to MSS and MAS). Low-cost field tests aimed at assessing maximal sprinting and aerobic speeds can be used to monitor ∆RS performance.

Effects of age, maturity and body dimensions on match running performance in highly trained under-15 soccer players.

The aim of the present study was to compare, in 36 highly trained under-15 soccer players, the respective effects of age, maturity and body dimensions on match running performance. Maximal sprinting (MSS) and aerobic speeds were estimated. Match running performance was analysed with GPS (GPSport, 1 Hz) during 19 international friendly games (n = 115 player-files). Total distance and distance covered >16 km h(-1) (D > 16 km h(-1)) were collected. Players advanced in age and/or maturation, or having larger body dimensions presented greater locomotor (Cohen's d for MSS: 0.5-1.0, likely to almost certain) and match running performances (D > 16 km h(-1): 0.2-0.5, possibly to likely) than their younger, less mature and/or smaller teammates. These age-, maturation- and body size-related differences were of larger magnitude for field test measures versus match running performance. Compared with age and body size (unclear to likely), maturation (likely to almost certainly for all match variables) had the greatest impact on match running performance. The magnitude of the relationships between age, maturation and body dimensions and match running performance were position-dependent. Within a single age-group in the present player sample, maturation had a substantial impact on match running performance, especially in attacking players. Coaches may need to consider players' maturity status when assessing their on-field playing performance.

Mechanical determinants of acceleration and maximal sprinting speed in highly trained young soccer players.

Abstract The aim of the present study was to examine, in highly trained young soccer players, the mechanical horizontal determinants of acceleration (Acc) and maximal sprinting speed (MSS). Eighty-six players (14.1 ± 2.4 year) performed a 40-m sprint to assess Acc and MSS. Speed was measured with a 100-Hz radar, and theoretical maximal velocity (V0), horizontal force (F0) and horizontal power (Pmax) were calculated. Within each age group, players were classified as high Acc/fast MSS (>2% faster than group mean), medium (between -2% and +2%), and low/slow (>2% slower). Acc and MSS were very largely correlated (-0.79; 90% confidence limit [-0.85; -0.71]). The determinants (multiple regression r2 = 0.84 [0.78; 0.89]) of Acc were V0 (partial r: 0.80 [0.72; 0.86]) and F0 (0.57 [0.44; 0.68]); those of MSS (r2 = 0.96 [0.94; 0.97]) were V0 (0.96 [0.94; 0.97]) and Pmax (0.73 [0.63; -0.80]). High/Med have likely greater F0 (Cohen's d: +0.8 [0.0; 1.5]), V0 (+0.6 [-0.1; 1.3]) and Pmax (+0.9 [0.2; 1.7]) than Low/Med. High/Fast have an almost certainly faster V0 (+2.1 [1.5; 2.7]) and a likely greater Pmax (+0.6 [-0.1; 1.3]) than High/Med, with no clear differences in F0 (-0.0 [-0.7; 0.6]). Speed may be a generic quality, but the mechanical horizontal determinants of Acc and MSS differ. While maximal speed training may improve both Acc and MSS, improving horizontal force production capability may be efficient to enhance sprinting performance over short distances.

Determinants, reliability, and usefulness of a bench press repeated power ability test in young basketball players.

The aim of the present study was to analyze the main determinants of an upper-body repeated power ability (RPA) test and to examine its reliability and usefulness. Forty-five highly trained, male, young basketball players performed the RPA test (5 sets of 5 repetitions with 30 seconds of passive recovery within sets) on 2 sessions separated by 5-7 days. Power output was registered using a linear encoder attached to the barbell. Results showed no significant differences (p > 0.05) between each set in both sessions and trivial (<0.2) effect sizes in all the analyzed variables. For every set, intraclass correlation coefficient was very high (0.96-0.98) and coefficient of variation was low (3.3%-4.3%). Because the typical error of measurement values were lower or similar than the smallest worthwhile change (SWC0.2 = 0.2 × between-subject SD), the usefulness of most variables was rated as "good" or "OK" considering that small changes would be detected by this test. The percentage of power decrement could only be used to detect large effects (>1.2 × between-subject SD). An almost perfect correlation (r = 0.99; 90% confidence interval, 0.98-0.99) was found between the average power in set 1 (APbest) and the average power over 5 sets (APmean). In conclusion, the main determinant of RPA test is APbest, and because of the high reliability scores obtained, this protocol may be used to assess upper-body RPA in relatively experienced young athletes.

Reduced Match Exposure in the Previous 2 Matches Accounts for Hamstring Muscle Injury Incidence in Professional Football Players.

BACKGROUND: Hamstring strain injuries are one of the most prevalent injuries in football (soccer). We examined the influence of accumulated match-play exposure on the occurrence of hamstring strain injury in professional football from 2 teams (Spanish 1st Division, LaLiga) over 3 seasons, and determined specific cut-off points as indicators of injury risk. HYPOTHESIS: Overloaded players would be more likely to sustain a hamstring injury. STUDY DESIGN: Prospective, controlled, observational study. LEVEL OF EVIDENCE: Level 2b. METHODS: Playing time, total running distance, and high-speed running (>24 km/h) distance during official matches of players that sustained a hamstring injury were compared with uninjured, paired controls. Cumulative playing time and running performance of 4 matches before the injury was computed. Relative risk (RR) of injury occurrence was estimated by generalized estimating equations. Diagnostic accuracy was determined by receiver operating characteristics and the area under the curve. RESULTS: Thirty-seven hamstring strain injuries occurred, representing 23 ± 18 absence days per injury. Thirty-seven controls (uninjured players) were used as comparators. Low match-play exposures during 1 and 2 matches before injury were likely to explain injury occurrence (RR: 14-53%; P < 0.01). Metrics from the match before the hamstring muscle strain demonstrated the best accuracy to predict injury occurrence: high-speed running distance ≤328 m (sensitivity, 64%; specificity, 84%), playing time ≤64 min (sensitivity, 36%; specificity, 97%), and running distance ≤5.8 km (sensitivity, 39%; specificity, 97%). CONCLUSION: Relatively reduced competitive exposure in the previous 2 matches was associated with higher hamstring injury risk in professional football players. CLINICAL RELEVANCE: Screening simple metrics such as the accumulated match exposure during official matches and considering specific cut-off points for some running variables may be good indicators of injury risk and may assist in better individual injury management in professional soccer players.

Supramaximal intermittent running performance in relation to age and locomotor profile in highly-trained young soccer players.

The aim of the study was to examine supramaximal intermittent running performance in highly-trained young soccer players, with regard to age and locomotor profile. Twenty-seven Under 14, 19 U16 and 16 U18 highly-trained soccer players performed an incremental intermittent running test (30-15 Intermittent Fitness Test) to assess supramaximal intermittent running performance (VIFT), an incremental running test to estimate maximal aerobic speed (VVam-Eval) and a 40-m sprint to estimate maximal sprinting speed (MSS). U16 and U18 presented very likely greater VIFT (19.2 ± 0.9, 19.7 ± 1.0 vs. 17.4 ± 0.9 km · h(-1)) and VVam-Eval (16.2 ± 0.9, 16.7 ± 1.0 vs. 14.6 ± 0.9 km · h(-1)) than U14, while there was no clear difference between U16 and U18. MSS (25.1 ± 1.6, 29.3 ± 1.6 and 31.0 ± 1.1 km · h(-1) for U14, U16 and U18) was very likely different between all groups. When data were pooled together, VIFT was very largely correlated with VVam-Eval and MSS (overall r =0.89, partial r = 0.74 and 0.29, respectively). Within-age group correlations showed that the older the players, the greater the magnitude of the correlations between VIFT and VVam-Eval (r = 0.67, 0.73 and 0.87). In conclusion, the major predictors of VIFT were, in order of importance, VVam-Eval and MSS; however, the older the players, the greater the correlations with VVam-Eval.

Reliability and stability of anthropometric and performance measures in highly-trained young soccer players: effect of age and maturation.

The purpose of this study was to assess both short-term reliability and long-term stability of anthropometric and physical performance measures in highly-trained young soccer players in relation to age and maturation. Data were collected on 80 players from an academy (U13-U18, pre- (n = 14), circum- (n = 32) and post- (n = 34) estimated peak height velocity, PHV). For the reliability analysis, anthropometric and performance tests were repeated twice within a month. For the stability analysis, these tests were repeated 12 times over a 4-year period in 10 players. Absolute reliability was assessed with the typical error of measurement, expressed as a coefficient of variation (CV). Relative reliability and long-term stability were assessed using the intraclass correlation coefficient (ICC). There was no clear age or maturation effect on either the CVs or ICCs: e.g., Post-PHV vs. Pre-PHV: effect size = -0.37 (90% confidence limits (CL):-1.6;0.9), with chances of greater/similar/lower values of 20/20/60%. For the long-term stability analysis, ICCs varied from 0.66 (0.50;0.80) to 0.96 (0.93;0.98) for 10-m sprint time and body mass, respectively. The short-term reliability of anthropometry and physical performance measures is unlikely to be affected by age or maturation. However, some of these measures are unstable throughout adolescence, which questions their usefulness in a talent identification perspective.

Running demands and heart rate response in rugby sevens referees.

The purpose of this study was to examine for the first time the match running demands and heart rate (HR) responses associated with elite rugby sevens referees. Twelve referees were analyzed over 38 games, using Global Positioning System. Referees covered an average distance of 1665.2 ± 203.5 m per game (15.1 ± 0.5 minutes). Over this distance, 22.3% (371.8 ± 48.9 m) was spent standing and walking, 25.9% (431.2 ± 92.6 m) jogging, 12.4% (206.5 ± 53.2 m) cruising, 23.8% (395.6 ± 94.3 m) striding, 8% (133.3 ± 61.6 m) high-intensity running, and 7.6% (126.7 ± 87.3 m) sprinting. The average maximal distance of sprints, the number of sprints, and the mean sprint distance over the game were 31.3 ± 13.4 m, 5.76 ± 3.6 sprints, and 19.9 ± 7.8 m, respectively. The referee's work-to-rest ratio was 3.5:1. There were no statistical differences between the first and second half in any of the running variables analyzed. The average HR in the second half (160 ± 9 b·min(-1); 86 ± 5% maximal heart rate (HRmax) of the estimated) was higher (p < 0.05) than the HR recorded in the first half (154 ± 11 b·min(-1); 83 ± 6% of the estimated HRmax). This study also suggests that the physical demands of referring in rugby sevens are quite different from those encountered in other rugby codes, and the training regimes need to meet the increased overall running demands and high-intensity running activity.