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The aim of the present study was to assess the reliability, usefulness, validity, age-related differences and responsiveness of a 25-m side-step cutting maneuver test (V-cut test). Fifty young male basketball players performed the V-cut test on 2 occasions separated by 5-7 days to assess test-retest reliability and determine a priori usefulness. Twenty subjects also completed both the L-Run and 505 test to analyze the possible relationships among these 3 tests. Furthermore, 33 players performed the V-cut test 4 times throughout the season to analyze responsiveness. Finally, 53 players (U-14 to U-20) were assessed in the V-cut test to examine the age-related differences. Reliability scores showed high intraclass correlation coefficient (ICC = 0.90) and low coefficient of variation (CV=1.4%). The responsiveness of the V-cut test was good, as the typical short- (1.5-1.7%), mid- (1.6-3.1%) and long-term (3.3%) changes in V-cut performance were higher than the CV. Low (r=0.64; CL90%: 0.34; 0.82) to moderate (r=0.76; CL90%: 0.53; 0.88) relationships were found between the V-cut test with the 505 and L-Run test, respectively. Age-related differences analysis showed better V-cut test performance as age increased in adolescent basketball players. The V-cut test is reliable to assess change of direction ability (CODA) and it could be used to monitor CODA in adolescent basketball players. [ABSTRACT FROM AUTHOR]

The aims of this study were to determine the effect of different compositions in transition games (TGs) on the load of soccer players and to evaluate their performance in physical tests. Using a GPS system, 18 players were monitored during: 3vs2, 2vs1 and 1vs1. Distance covered (DC), DC 18-20.9 km·h -1 , 21-23.9 km·h -1 ,>24 km·h -1 , peak speed, accelerations (Acc) and decelerations (Dec)>1.0 m·s -2 and>2.5 m·s -2 and rate of perceived exertion (RPE) were recorded. Before and after each TG, countermovement-jump (CMJ), 15- (S 15 ) and 30 m (S 30 ) speed tests were assessed. TG 3vs2 showed greater DC and Dec>1.0 m·s -2 than TG 2vs1 , and DC, DC 18.0-23.9 km·h -1 , Acc>1.0 m·s -2 and Dec>2.5 m·s -2 than TG 1vs1 ( p <0.01). TG 2vs1 achieved higher DC, DC 18.0-23.9 km·h -1 , and Acc>2.5 m·s -2 ( p <0.01) but lower peak speed ( p =0.02) and RPE ( p =0.02) than TG 1vs1 . Post-intervention, TG 1vs1 showed lower CMJ and higher S 15 ( p =0.02), while TG 3vs2 , showed improvements in CMJ ( p <0.01). The three tasks showed large variations for DC>24 km·h -1 , Acc>1.0 m·s -2 , Dec>1.0 m·s -2 and Dec>2.5 m·s -2 . The load of TGs is sensitive to their player composition., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

The aim of this study was to compare the running demands of transition games (TGs) and official matches, analysing their requirements according to the performance of each position. An observational design was used to examine the activity of 20 soccer players during official matches and TGs. GPS technology was used to monitor the total distance covered (DC), distance at speeds between 14-17.9 km•h -1 , 18-21 km•h -1 , and above 21 km•h -1 , peak speed, accelerations and decelerations above 2.5 m•s -2 , and Player Load for both activities. All players were assigned to groups: centre-backs (CBs), fullbacks (FBs), defensive midfielders (DMFs), offensive midfielders (OMFs), wide midfielders (WMFs) and strikers (Ss). TGs showed greater total DC, DC 14-17.9 km•h -1 , DC 18-21 km•h -1 , DC >21 km•h -1 , accelerations and decelerations >2.5 m•s -2 , and Player Load (p < 0.01). CBs, FBs and Ss showed more DC, DC 14-17.9 km•h -1 , DC 18-21 km•h -1 , DC >21 km•h -1 , accelerations and decelerations >2.5 m•s -2 and Player Load in TGs (p < 0.01). In the midfielder positions, transition game players showed greater DC 18-21 km•h -1 , DC >21 km•h -1 , accelerations and decelerations >2.5 m•s -2 than in matches (p < 0.05). DMFs showed higher total DC (p < 0.05) and WMFs greater DC and DC 14-17.9 km•h -1 (p < 0.01) in these drills. During transition games CBs showed greater DC 14-17.9 km•h -1 than FBs, and greater DC than Ss (p < 0.05). FBs performed more decelerations >2.5 m•s -2 than DMFs and OMFs (p < 0.05). TGs produced a homogenized load in soccer players, independent of their position, which exceeded the external load of official matches., Competing Interests: The authors declare no conflict of interest., (Copyright: © Academy of Physical Education in Katowice.)

The aim of this study was to analyze the differences in internal and external load during Soccer-7 and Soccer-11, comparing positional requirements and neuromuscular fatigue in both modalities. Twenty-four young soccer players were monitored in Soccer-7 and Soccer-11 matches using global positioning systems. Total distance covered (TD), distance covered at high speed (HSR), distance covered at very high speed (VHSR), peak speed, accelerations (Acc) and decelerations (Dec) and rate of perceived exertion (RPE) were recorded differentiating between central backs (CB), midfielders (MF), external players (EX) and forwards (FW). Neuromuscular fatigue were assessed using a jump test. During Soccer-11, players showed significantly higher TD, HSR and VHSR, with low Acc and greater RPE compared with Soccer-7. During Soccer-11, all positions recorded significantly greater TD, distance at HSR and at VHSR than Soccer-7. In terms of playing position, CB, MF and FW achieved significantly higher Peak Speed during Soccer-1, but there was no difference for EX. During Soccer-7 all positions performed significantly higher numbers of Acc. Although the Soccer-7 modality is considered an optimal format for the development of young soccer players, there is a significant difference in match running activity for all playing positions with respect to the Soccer-11 format., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

To ensure both optimal health and performances, monitoring physiological and psychological states is of main importance for athletes. It is well known that monitoring heart rate variability and using validated questionnaires is useful for monitoring both the health and training status of athletes of different sports. Motorsports such as rally require high levels of physical and mental preparation thus information about psychophysiological status of rally athletes is fundamental. The aim of this study was to assess the autonomic regulation, stress, recovery conditions of one driver and one co-driver competing at the Italian National Rally Championship during their competition period. Heart rate variability parameters, acute recovery and stress states were assessed the day before, during the two days of race and the day following the races. Results showed that driver and co-driver had a sharp decrease of mean RR intervals, root mean square of successive differences between normal heartbeats, and standard deviation of the N-N interval during race days, while the stress index showed the inverse trend, and this behaviour was clearly visible in the Poincaré plots and power spectrum density graphs. The acute recovery and stress states questionnaire showed significant differences in recovery and stress scoring for the driver but not for the co-driver, although the trends were similar. This study describes the psychophysiological demands of a rally competition period suggesting that a daily evaluation of heart rate variability, recovery, stress states is useful for monitoring health status in rally athletes and could be implemented to make decision about training and recovery strategies., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

The aims of this study were to compare the influence of transition game (TG) size on the external and internal loads of young professional soccer players and to describe the high-speed profile of these drills in response to pitch dimensions. Eighteen young professional soccer players (age: 16.1 ± 0.3 years; height: 178.3 ± 5.4 cm; weight: 70.1 ± 6.2 kg) performed a 3vs2 TG on pitches measuring 40 × 30 m (TG 30 ), 40 × 50 m (TG 50 ) and 40 × 70 m (TG 70 ) m. Distance covered (DC); accelerations-decelerations above 1.0 m · s -2 and 2.5 m · s -2 ; rate of perceived exertion (RPE); maximal heart rate and time above 90%; DC at 18.0 to 21.0 km · h -1 (DC 18-20.9 km · h -1 ); DC at 21.0 to 23.9 km · h -1 (DC 21-23.9 km · h -1 ); DC above 24.0 km · h -1 (DC > 24 km · h -1 ); and peak speed and sprint profile (duration, distance and maximal speed) were measured. TG 30 achieved lower DC, DC above 18 km · h -1 , peak speed, sprint distance and RPE than TG 50 and TG 70 (p < 0.01 and p < 0.05) and lower sprint duration and maximal speed sprint than TG 70 (p < 0.01). TG 30 and TG 50 achieved higher Acc > 1.0 and > 2.5 m · s -2 respectively than TG 70 (p < 0.05). TG 70 showed greater DC above 21 km · h -1 , peak speed, sprint distance and maximal speed sprint than TG 50 (p < 0.01). Soccer coaches should use larger TGs to overload variables related to high speed and sprint demands during training and smaller TG formats to stimulate the accelerations of the soccer players., Competing Interests: The authors declare no conflict of interest., (Copyright © Biology of Sport 2023.)

This study examined the training load on professional soccer players during transition games performed with different bout durations and their effects on speed and jump tests. Fourteen young soccer players played a transition game of different bout durations: 15 (TG 15 ), 30 (TG 30 ), and 60 (TG 60 ) seconds. Total distance covered (DC), accelerations and decelerations above 1.0 and 2.5 m·s -2 , rate of perceived exertion (RPE), maximal heart rate (HR max ) and above 90% (HR >90 ), distance covered between 18.0-20.9 km·h -1 (DC 18.0-20.9 km·h -1 ), 21.0-23.9 km·h -1 (DC 21.0-23.9 km·h -1 ), above 24.0 km·h -1 (DC>24.0 km·h -1 ), peak speed, sprint profile, sprint, and countermovement jump tests were recorded. TG 15 obtained greater DC, DC>21.0 km·h -1 , Player load, Acc>2.5 m·s -2 than TG 30 and TG 60 ( p <0.01) and Acc<2.5 m·s -2 , Dec>2.5 m·s -2 than TG 60 ( p <0.01). TG 30 showed more HR >90 and RPE ( p <0.01) than TG 15, and DC, DC>18.0 km·h -1 , Player load, Acc>2.5 m·s -2 , Dec>2.5 m·s -2 , HR >90 and RPE than TG 60 ( p <0.01 and<0.05). Transition games showed lower sprint and jump results after the intervention ( p <0.01). Bout duration has been configured as an important constraint that influences the transition games and the performance of soccer players., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

The aim of this study was to evaluate the effects of different time periods on the internal and external loads of soccer players during small-sided games (SSGs). Seventeen young soccer players performed a SSG of 5 vs. 5 + 5 with 2 floaters, where two teams had possession of the ball, and one had to recover it. With established periods of 30 s (SSG 30 ), 1 min (SSG 1 ) or 2 min (SSG 2 ), teams participated in a defensive role for these periods of time. Total distance covered, moderate speed running distance, high speed running distance, sprint running distance, accelerations, decelerations and Player Load were monitored using global positioning systems devices. The maximal heart rate and modified training impulse were monitored using heart rate monitors. The rating of perceived exertion (RPE) was also measured. Data showed a small increase between SSG 30 and SSG 1 in Player Load (ES = -0.35; p < 0.01), and a small increase in high speed running (ES = -0.41; p < 0.05) and sprinting (ES = -0.47; p < 0.01) between SSG 30 and SSG 2 . Also, SSG 1 showed a small increase in sprinting (ES = -0.57; p < 0.01) and accelerations (ES = -0.37; p < 0.05) with respect to SSG 2 . In addition, SSG 2 showed a small increase in the RPE with respect to SSG 30 (ES = 0.46; p < 0.05). The results indicate that shorter defensive periods in SSGs increased high speed running, while longer defensive periods promoted greater perceived exertion. Manipulation of the duration of defensive periods in SSGs is a variable that should be considered in soccer training., Competing Interests: The authors have no potential conflicts of interest that are directly relevant to the content of this study., (Copyright: © Academy of Physical Education in Katowice.)

The purpose of this study was to compare the fascicle length, angle pennation and mechanical properties of the biceps femoris long head (BFlh) in dominant and non-dominant limbs in previously injured and uninjured professional football players. Fifteen professional football players were recruited to participate in this study. Seven players had suffered a BFlh injury during the previous season. Myotonometry mechanical properties were measured in the proximal, common tendon and distal BFlh using MyotonPRO, and angle pennation and fascicle length were also measured. We observed significantly higher distal BFlh frequency, stiffness, decrement, relaxation and creep than in the common tendon and proximal BFlh. The previously injured players showed significantly higher frequency and stiffness, and lower relaxation and creep in the dominant BFlh than did uninjured players. There were no significant differences between the fascicle length and angle pennation in previously injured and uninjured BFlh. Myotonometric measurement provides a quick and inexpensive way to check the properties of the BFlh in professional football players. Professional football players with previous BFlh injury showed higher intrinsic tension and a poorer capacity to deform than did players with no injury to the BFlh., Competing Interests: The authors declared no conflict of interest., (Copyright © Biology of Sport 2023.)

Objective: The aim of the present study was to compare the fascicle length, pennation angle, muscle thickness and stiffness of the biceps femoris long head, and eccentric hamstring strength between injured dominant limbs, injured non-dominant limbs, uninjured dominant limbs and uninjured non-dominant legs in previously injured players, and between dominant and non-dominant legs in uninjured elite soccer players., Materials and Methods: Twenty elite soccer players participated in this study. Ultrasound imaging and MyotonPRO were used to determine the morphological and mechanical properties of the biceps femoris long head. Isokinetic and Nordic hamstring exercises were used to assess eccentric hamstring strength., Results: Previously injured players showed substantially lower fascicle length and muscle thickness, and significantly higher biceps femoris long head stiffness than uninjured players, without differences between limbs., Conclusion: The morphological and mechanical properties of elite soccer players with hamstring injury history were different from those in uninjured players. The lack of differences between limbs showed that these values are characteristics of individual players that must be considered in the design of programs to prevent BFlh injury.

Background: Muscle strain injuries (MSIs) in the hamstrings are among the most prevalent injuries in elite soccer. We aimed to examine the relation between biomechanical maladaptation in eccentric strength and neuromuscular factors separated by their time and frequency domains., Methods: 20 elite soccer players with a previous history of unilateral MSI in the M. biceps femoris (BF) long head and 20 without MSI participated. Knee flexion torques, rate of torque development (RTD) and electromyographic signals (EMG) of the BF, the M. semitendinosus (SMT) and knee extensors were obtained during unilateral maximal eccentric knee flexions performed at slow (30°/s) and fast (120°/s) angular speeds. Root mean squares and mean power frequency (MF) was calculated., Results: In the group with a history of MSI, reduced maximal eccentric flexion torque (slow eccentrics -8±11, p<0.05; fast eccentrics -18±13 N*m, p<0.05) and RTD (-33±28 N*m/s, p<0.05; -95±47 N*m/s, p<0.05) concomitantly occurred with diminished agonistic myoelectrical activities (-4±5% of MVC, p<0.05; -10±7% of MVC, p<0.05) and MFs (-24±13 Hz, p<0.05; -24±18 Hz, p<0.05) in the BF. Simultaneously, antagonistic myoelectric activity was elevated (+4±3% of MVC, p<0.05; +3±3% of MVC, p<0.05) in MSI affected legs as compared to unaffected legs for both eccentric contractions. Deficits in myoelectrical activity (r2 = 0.715, p<0.05; r2 = 0.601, p<0.05) and MF (r2 = 0.484, p<0.05; r2 = 0.622, p<0.05) correlated with deficits in maximal torque in the affected leg in the MSI group. Analysis of SMT demonstrated no significant differences., Conclusion: Positive relationships between neuromuscular deficits and the reduced eccentric strength profile underpin neuronal inhibition after MSI. This persistent involvement of dysfunctional synergist and antagonist neural hamstring function in strength weakness is of clinical relevance in sports medicine for prevention and rehabilitation., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2022 Ritzmann et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Present soccer demands are increasing in terms of running requirements and the number of matches until youth soccer players experience several periods of fixture congestion during the season. Currently, congested periods have not been extensively studied in this population. For this reason, this study aimed to compare the running demands of professional youth soccer players in congested periods according to their specific playing positions. Twenty youth players were grouped according to their position: Central Defenders (CD), Fullbacks (FB), Midfielders (MF), Wide Midfielders (WM) and Strikers (ST). A GPS system was used to monitor the players during the first (M1), second (M2) and third (M3) matches played during a congested period, measuring their total distance covered (TDC), DC 18.0−20.9 km·h−1, DC 21.0−23.9 km·h−1, DC > 24.0 km·h−1, number of high accelerations (>2.5 m·s−2), number of high decelerations (<2.5 m·s−2) and peak speed (km·h−1). M1, M2 and M3 showed the same TDC, DC 18.0−20.9 km·h−1, DC 21.0−23.9 km·h−1, DC > 24.0 km·h−1, number of high accelerations, and peak speed (p > 0.05). The statistical analysis showed significant differences between M1, M2 and M3 in the decelerations recorded between M1 and M3 (p < 0.05). Likewise, each position showed specific behaviours during the congested period, with all showing at least one difference in DC 18.0−20.9 km·h−1, 21.0−23.9 km·h−1 or >24.0 km·h−1 between M1, M2 and M3 (p < 0.05). In conclusion, coaches should pay attention to the fatigue produced by the number of high decelerations. Secondly, an individualized training protocol should be considered according to the running requirements of each position when youth professional soccer players are involved in a congested period.

The aims of this study were to compare the load of three tasks designed to train features of soccer: a transition game, a small-sided game with a change of playing area, and a large-sided game. Twenty young elite players performed these tasks. Variables measured were total distance covered (DC), distance covered at 14.0-17.9 km·h -1 (DC 14.0-17.9 km·h -1 ), distance covered at 18.0-21 km·h -1 (DC 18-21 km·h -1 ), distance covered > 21 km·h -1 (DC>21 km·h -1 ), peak speed, accelerations and decelerations > 1.0 and > 2.5 m·s -2 , player load, and rate of perceived exertion. Transition games produced greater DC 18-21 km·h -1 , DC>21 km·h -1 , peak speed and Acc>2.5 m·s -2 than the other drills (p<0.01) and higher DC 14-17.9 km·h -1 (p<0.01), Dec>1 m·s -2 (p<0.05) and Dec>2.5 m·s -2 (p<0.01) than the large-sided game. Both sided games produced more DC (p<0.01), Acc>1 m·s -2 (p<0.01) and player load (p<0.01 and p<0.05, respectively) than the transition game. During the small-sided game, significantly higher DC 14-17.9 km·h -1 , DC 18-21 km·h -1 and DC>21 km·h -1 were recorded in comparison with the large-sided game (p<0.01). The studied parameters showed lower variation in the transition game. Coaches could use transition games to train high speed running in counter-attack contexts., Competing Interests: The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript., (Thieme. All rights reserved.)

The presence of inter-limb asymmetries can influence strength performance and represent an injury risk factor for team sport athletes. The present study aimed to investigate the effects of changes in resistance loads using different assessment modalities on the magnitude and the direction of inter-limb asymmetry within the same leg. Fifteen young elite soccer players from the same professional academy performed rear-foot-elevated-split-squat-test at different loading conditions (body mass with no overload, 25% of body mass, 50% of body mass 50%), isokinetic knee flexor (concentric 30°·s-1, concentric 60°·s-1, eccentric 90°·s-1) and extensor (concentric 60°·s-1, eccentric 60°·s-1). The outcomes from the agreement analyses suggested moderate level agreement between body mass vs body mass 25% (Kappa = 0.46), with no agreement or fair agreement for the other between-assessment comparison. Our results demonstrated that the magnitude and direction of within-limb strength imbalances were inconsistent when compared within the same assessment under different resistance load conditions., Competing Interests: The authors have declared that no competing interests exist.

Several studies have confirmed the efficacy of strength training to maximize soccer player performance during competition. The aim of this meta-analysis was to determine the effects of different strength training protocols on short-sprint and vertical jump performance of professional soccer players from the first division of their countries. The following inclusion criteria were employed for the analysis: (a) randomized studies; (b) high validity and reliability instruments; (c) studies published in a high-quality peer-reviewed journal; (d) studies involving professional soccer players from the first division; (e) studies with descriptions of strength training programs; and (f) studies where countermovement jump and 10-m sprint time were measured pre and post training. Overall, the different strength-oriented training schemes produced similar performance improvements, which seem not to depend on the training strategy. Strength training appears to have a lower effect when applied during in-season than when applied in pre-season periods in first division soccer players. In this meta-analysis it is not possible to confirm that strength training in isolation is capable of improving the short-sprint and jump performance of elite soccer players. The congested fixture schedule and, thus, the limited time to perform complementary (non-specific) training sessions, may contribute to these reduced effects., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

The purpose of this study was to analyze the influence of tactical behavior on physical performance of the three best Spanish soccer teams. Team 1 employed a 1-4-4-2 formation with compact defence and direct attacks, Team 2 employed an indirect style of play with a 1-4-3-3 formation and Team 3 used a 1-4-3-3 formation with elaborate attacks and strong counter-attacks. 816 individual situations of 54 professional soccer players categorized as fullbacks (FB), central defenders (CD), central midfielders (MF), wide midfielders (WM), and strikers (S) were included in the analysis. Their performance was examined with a player-tracking system. The analyzed variables included total distance covered, distance covered above 14, 21 and 24 km·h -1 , as well as distance covered in possession of the ball and without possession of the ball. Team 2 covered a substantially lower distance >14 km·h -1 than Team 1 and substantially lower distances >14, >21, and >25km·h -1 than Team 3. No differences in running activity were found between Teams 1 and 3. However, there were substantial differences between the specific positions of the three teams. CD in Team 1 covered the lowest distance by a substantial margin in almost all variables analysed, whereas MF travelled substantially greater distances than did other positions. WM in Team 1 covered the greatest distance >18 and >21km·h - 1 , while S in Team 2 had the lowest distance covered in almost all the variables, and FB in Team 3 showed the lowest total distance covered and distance covered >14km·h -1 . WM in Team 2 had the greatest distance covered in possession, while S in Team 3 had the greatest distance covered out of possession. The results indicate that different team formations and associated tactical demands have a significant influence on running performance., (© 2022 Jose Asian-Clemente, Luis Suarez-Arrones, Bernardo Requena, Alfredo Santalla, published by Sciendo.)

Background: The purpose of the present study was to analyze the internal and external loads on regular and floater players during standardized small-sided games (SSGs) with different numbers of players (teams of 3, 5, or 7 players)., Methods: Fifteen male semi-professional football players played different SSGs maintaining the same relative area per player. Total distance (TD), distance covered at different speeds (DC), the number of accelerations and decelerations, maximal (HRmax) and mean (HRmean) heart rate and rate of perceived exertion (RPE) were registered., Results: Regular players showed greater internal and external loads in SSGs with 3 and 5 players without floaters than with floaters (ES 0.60-to-1.27). Likewise, with floaters, regular players in the SSGs with 3 performed more accelerations (ES 1.40 and 1.17) and with 7 achieved higher TD, DC>14 km·h -1 , HRmax and HRmean (ES 0.66-to-2.79) than any other. During SSGs with 7 players the floaters showed a higher TD and decelerations than in other SSGs (ES 0.47-to-1.70), and a higher DC (0-6.9 km·h -1 ,14-17.9 km·h -1 ) and RPE than in SSGs with 3 players (ES 0.59-to-0.89). During SSGs with 5, the floaters showed a higher TD, HRmax, HRmean and RPE than in SSGs with 3 (ES 0.86-to-1.45). In all SSGs, regular players showed higher TD, DC (14-17.9 km·h -1 ), accelerations, decelerations and HRmean than floaters (ES 1.24-to-6.23)., Conclusions: Coaches must carefully design SSGs because the number of players and the presence or absence of floaters can affect the external-internal load expressed.

The aim was to determine if players with a prior hamstring strain injury (HSI) exhibit bilateral deficits in knee flexor eccentric strength and hamstring muscle volume and differences in sprinting performance compared with players without a history of HSIs. Forty-six male professional soccer players participated in this study. Eccentric knee flexor strength, hamstring muscle volume (MRI), and a 20-m running sprint test (5- and 10-m split time) were assessed at the start of the preseason. Eccentric knee strength of the previously injured limbs of injured players was greater (ES: 1.18-1.36) than the uninjured limbs in uninjured players. Previously injured limbs showed possibly larger biceps femoris short heads (BFSh) and likely semitendinosus (ST) muscle volumes than the contralateral uninjured limbs among the injured players (ES: 0.36) and the limbs of the uninjured players (ES: 0.56), respectively. Players who had experienced a previous HSI were possibly slower in the 5-m (small ES: 0.46), while unclear differences were found in both the 10-m and 20-m times. Players with a prior HSI displayed greater eccentric knee flexor strength, possibly relatively hypertrophied ST and BFSh muscles, and possibly reduced 5-m sprinting performances than previously uninjured players. This can have implication for the design of secondary hamstring muscle injury prevention strategies.

We outline a case of success in the rehabilitation of a Romanian first-division soccer player who sustained an anterior cruciate ligament (ACL) rupture with a meniscal tear during competition in the 2012-2013 season. The ligament was reconstructed with an autologous hamstrings graft and partial meniscectomy was performed. The player returned to same-level competition in 7 months and has remained at that level, free of knee injury, to the present (6 years later). Based on postoperative phase 1 as proposed by the Royal Dutch Society for Physical Therapy, we proposed a clinical progression of exercises with video demonstrations to address body functions and structures and the level of activities and participation. All phase 1 objectives were achieved, and all criteria needed to advance to phase 2 of the ACL rehabilitation process were attained., (© by the National Athletic Trainers' Association, Inc.)

Purpose : The aim of this study was to examine the short and long-term effects of a simple strength training program on muscle injury prevention in soccer players. Methods : Twenty-seven U-19 elite male soccer players participated in the study. The investigation was conducted over two consecutive and similar seasons (e.g., the same staff, players, weekly training schedule), the first being the control and the second the experimental season. The strength program was carried out 2 times per week, for 10 weeks, during part of the preseason and in-season. Injury incidence and absence days were compared between both seasons, according to the injury rate ratio (IRR), with 95% CI and the Z test. Results : A lower number of total and hamstring injuries were recorded during the experimental (9 and 2, respectively) compared to the control (15 and 7, respectively) period. During the 10 weeks intervention period, the injury rate ratio (IRR) was lower in the experimental season than in the control season (IRR = 8.12; 95% CI: 1.00-66.03; effect size (ES) = 3.30, large). In addition, there was a decline in absence days per injury and in the number of absence days/1000 h (IRR = 2.44; 95% CI: 1.90-3.14; ES = 1.12) during the experimental season. Conclusion : The results of this study suggest that this simple strength-training program could reduce the muscle injury incidence during its application period in young soccer players.

The aim was to compare the running activity in official matches with that achieved in two small-sided games, designed with the same relative area per player but with different constraints and field dimensions, aiming to stimulate high-speed and very-high-speed running. Seventeen young professional players played one 5 vs . 5+5 with 2 floaters, varying in terms of whether there was a change of playing area (SSG CA ) or not change (SSG NC ). Running activity was monitored using GPS and the following variables were recorded: total distance covered; high-speed distance (18-21 km·h -1 ); very high-speed distance (>21 km·h -1 ); peak speed; accelerations and decelerations between 2-3 m·s -2 and above 3 m·s -2 . SSG CA achieved statistically higher total distance, high-speed, peak speed and number of accelerations and decelerations than SSG NC (large to small magnitude). Both drills showed statistically greater high speed, number of accelerations and decelerations than official matches (large to small magnitude). Moreover, SSG CA exhibited statistically more total distance and distance at higher speed than official matches (moderate and small magnitude, respectively). In contrast, official matches showed statistically higher peak speeds than both training tasks and more very high speed than SSG NC (large and moderate magnitude, respectively). Coaches could use SSG CA to promote greater running activity in soccer players., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

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., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The primary aim of the present study was to analyze mechanical responses during inertial knee- and hip-dominant hamstring strengthening exercises (flywheel leg-curl and hip-extension in conic-pulley), and the secondary aim was to measure and compare regional muscle use using functional magnetic resonance imaging. Mean power, peak power, mean velocity, peak velocity and time in the concentric (CON) and eccentric (ECC) phases were measured. The transverse relaxation time (T2) shift from pre- to post-exercise were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. Peak and mean power in flywheel leg-curl were higher during the CON than the ECC phase (p<0.01). ECC peak power was higher than CON phase (p<0.01) in conic-pulley hip-extension exercise, while mean power was higher during the CON than ECC phase (p<0.01). Flywheel leg-curl showed a higher T2 values in ST and BFs and BFl (p<0.05), while the conic-pulley hip-extension had a higher T2 values in the proximal region of the ST and BFl (p<0.05). In conclusion, ECC overload was only observed in peak power during the conic-pulley hip-extension exercise. Flywheel leg-curl involved a greater overall use of the 4 muscle bellies, more specifically in the ST and BFs, with a selective augmented activity (compared with the conic-pulley) in the 3 regions of the BFs, while conic-pulley hip-extension exercise selectively targeted the proximal and medial regions of the BFl. Physiotherapists and strength and conditioning coaches should consider this when optimizing the training and recovery process for hamstring muscles, especially after injury., Competing Interests: The authors have declared that no competing interests exist.

Coaches at the professional level are often concerned about negative side effects from testing and intensive resistance training periods, and they are not willing to base their training prescriptions on data obtained from semiprofessional or amateur football players. Consequently, the purpose of this study was to analyze the reliability and effectiveness of two adductor injury active prevention programs using the adductor/abductor ratio and deficit between legs, on the basis of adduction-abduction power output during the exercises proposed, in professional football players. Forty-eight professional football players undertook complementary strength training for the adductor and abductor muscles in their dominant and non-dominant legs, once or twice a week throughout the playing season. The volume of the session was determined by the adductor/abductor ratio and the deficit between legs in the last session training measured. The number and severity of muscle injuries per 1000 h of exposure were recorded. Both prevention programs showed a very low rate of adductor injury (0.27 and 0.07 injuries/1000 h) with mild-to-moderate severity, maintaining a balance in percentage asymmetry between dominant and non-dominant legs for adductor (10.37%) and in the adductor/abductor ratio (0.92) in top professional football players throughout the season. The strength conditioning program proposed can help to prevent adductor muscle injuries in top professional football players.

This study aimed to determine whether spikes in acute:chronic workload ratio (ACWR) are associated with injury incidence, and to examine the differences in external load due to greater or lesser exposure to matches and the long-term effects of the load during a chronic seasonal period. Fifteen professional soccer players belonging to the squad of a European Champions League club were enrolled in this study. External training and match load were assessed from all athletes using a global positioning system (GPS). We calculated the uncoupled ACWR for 10 consecutive competitive microcycles. Injuries were identified and determined by the days of absence. The differences in external load were determined using a linear mixed-model approach. In addition to the null hypothesis testing, the effect size was calculated. Thirteen athletes who did not suffer an injury exceeded several times the critical threshold of an ACWR > 1.5. This is equivalent to 1 player exceeding the critical threshold for ACWR in total distance (TD), 2 players for ACWR at distance covered above moderate speed (MSD), 2 players for ACWR at distance covered above high speed (HSD), 2 players for ACWR at distance covered above very high speed (VHSD), and 2 players for ACWR in DC at sprint per week. One athlete experienced a non-contact muscle strain injury and another a contact -injury manifested as a concussion; both athletes document an ACWR <1.5 within the 4 weeks prior to the injury event. Players with lesser participation in official games covered lower TD (-19.6%, very-large ES), MSD (-24.8%, very-large ES), HSD (-25.1%, moderate ES), VHSD (-25.5%, moderate ES), and DC at sprint (-30.6%, moderate ES) over the course of the 10-weeks period in comparison with the players with greater participation in official games. The present study demonstrated that spikes in the ACWR were not related to a subsequent injury occurrence in professional soccer players. Differences in participation in official games caused significant imbalances in the chronic external loads between players in a squad, which should be minimized in training sessions in order to prevent substantial changes in workload for those who usually do not play., (Copyright © 2020 Suarez-Arrones, De Alba, Röll, Torreno, Strütt, Freyler and Ritzmann.)

The purpose of the study was to examine the differences in bilateral deficit (BLD) at different loadings during the half-squat jump (SJ) and horizontal countermovement jump (HCMJ) to determine if there is a relationship with linear sprint or change of direction (COD). The second goal was to check if fast players were more powerful in SJ and HCMJ than slow players in bilateral performance (BP). Twenty-seven male youth soccer players participated in the study. Players were divided in two groups, faster and slower, according to their sprint performance (10 and 40 m). BLD average power with body weight (BW) and 25%BW were significantly higher than 50%BW ( p < 0.01). BLD during HCMJ was significantly higher than BLD during SJ with BW, 25%BW and 50%BW ( p < 0.01). There were no statistical relationships between BLD and sprint or COD performance ( p > 0.05). Fast players showed significantly higher SJ power with all the different loads and HCMJ than slow players ( p < 0.01), and fast players lost more time executing COD-90° than slow players ( p < 0.01). There were no statistical differences between fast and slow players in BLD. BLD seems to be dependent on motor task, contraction type and load and could not be a proper measure to estimate sprint and COD performance. Faster players are confirmed to be more powerful players than slow players, and decrements in COD could be a key benchmark to identify deficit between linear and COD performance., Competing Interests: The authors declare no conflict of interest.

The aim of the study was to investigate the relationships between countermovement jump (CMJ) height and inertial power in squat and sprint variables with change of direction (COD) performance. Fifty young healthy active males participated in the study. To determine these relationships, we carried out a 10-m linear sprint test (T 10 m), vertical jump tests (CMJ and CMJ Abalakov), an assessment of power relative to bodyweight in a flywheel squat (P bw ), and 10-m COD sprints with two different turn types (COD-90° and COD-180°). T10 m showed statistically large and moderate correlations with T10 m COD-180° (r = 0.55) and T10-m COD-90° (r = 0.41), respectively. Moderate to large correlations between jumping height, linear sprinting, and sprints with COD were found (r = -0.43 to r = -0.59), and there were unclear correlations between jumping height and the loss of speed caused by executing COD (DEC-COD). P bw showed a large correlation with CMJ Abalakov and CMJ jump height (r = 0.65 and r = 0.57, respectively), and a moderate and large correlation with T 10 m, T 10 m COD-180°, and T10 m COD-90° (r = -0.33, r = -0.38, and r = -0.54, respectively). Despite the existence of substantial correlations between variables, straight linear sprinting, jumping performance, CODs and squat power were, for the most part, separate motor qualities (R 2 from 14% to 34%), suggesting that all of them should be specifically assessed and trained.

Based on the high financial and logistical costs associated with the assessment of body composition with dual-energy X-ray absorptiometry (DXA), this study determined which field method has the best correlation with DXA data, and developed an equation to estimate fat-free mass (FFM) using the field anthropometric data in international soccer players. A total of 17 international soccer players participated in this study. DXA values provided a criterion measure of FFM. Correlation coefficients, biases, limits of agreement, and differences were used as validity measures, and regression analyses were used to develop the prediction equation. All field methods used to obtain FFM data showed positive correlations (r from 0.90-0.96) with DXA. Only the equation developed by Deurenberg et al. [6] showed no differences from DXA with a low bias. The main strength of this study was providing a valid and accurate equation to estimate FFM specifically in international soccer players., Competing Interests: Authors declare that they have no conflict of interest., (© Georg Thieme Verlag KG Stuttgart · New York.)

The aim of the study was to examine the effects of a detraining period (DTP) (i.e., off-season) with an individually prescribed training program, and a retraining period (RTP) (i.e., pre-season) combining soccer and flywheel-based strength training on fat-free mass (FFM) and fat-mass (FM) in 10 elite professional male soccer players. The present study used a controlled repeated-measures research design to investigate the changes in FFM and FM using dual-energy X-ray absorptiometry. Whole body %FM increased (effect size (ES) = 0.87 ± 0.46) and FFM reduced after DTP (ES = -0.30 ± 0.19), returning to values comparable to the end of the previous season after RTP. At regional levels, arms, legs, and trunk %FM increased (ES = from 0.42 to 1.29) while trunk-FFM was reduced (ES = -0.40 ± 0.26) after DTP, returning to the values observed at the end of the previous season after RTP. Legs-FFM did not change after DTP, with a substantial increase after RTP in comparison with pre-season values (ES = 0.34 ± 0.29 and 0.53 ± 0.36 for the right and left leg, respectively). Despite the small sample size of the present study, the findings indicate that elite soccer players can be allowed 2 weeks of rest during a five-week DTP, since the changes in %FM and FFM were relatively small, and FM and FFM returned to the optimal initial values for competition after the proposed RTP during the pre-season., Competing Interests: Luis Suarez-Arrones and Nacho Torreno are employees of FC Basel, Rafael Maldonado is an employee of FC Girondins de Bourdeaux. The authors declare there are no competing interests.

The present prospective cohort study investigated changes in body composition (BC) in young male football players ( n = 18, 16.1 ± 0.8 years; 181.0 ± 0.1 cm; 71.3 ± 4.9 kg) after combined football and strength training (ST) during a whole in-season period (26 weeks). BC was measured at whole-body absolute and regional levels by dual-energy X-ray absorptiometry in eighteen players at the beginning and at the end of the competitive period. The ST was organized into three different session types: ST in the gym, specific ST on the field, and individual ST (weak points). The results of the present study indicated that fat-free mass (FFM) was substantially higher following the competitive period (5.1% ± 1.2%), while percentage of fat showed no changes during the competitive period. At the regional level, arms' and legs' FFM increased at the end of the season, and bone mineral content (BMC) and density (BMD) increased in arms, legs, pelvis, thoracic spine, and lumbar spine. In conclusion, within the limitation of the potential positive impact of growth and/or maturation, present results seem to indicate that an ST program that supplements football-related training sessions could be an effective option to increase FFM, BMC, and BMD at both whole-body and regional level across the competitive season in young male professional football players., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

The aim of the present study was to evaluate the consequence of implementing a Nordic Hamstring exercise (NHE) protocol during the first 15 to 17 weeks of the season to assess the effect on sprinting and NHE strength (NHEs) in professional football players. The study examined 50 healthy male professional football players (age 18.8±0.8yr; height 176.8±6.9cm; weight 71.3±5.7kg) belonging to 3 of the reserve squads of three Spanish La-Liga clubs divided in 2 intervention teams [Nordic-Group1 (NG-1) and Nordic-Group2 (NG-2, extensive experience in NHE)] and 1 team as a control-group (CG). NHEs and linear sprint (T5, T10, T20-m) were evaluated at the beginning of the season and at the end of an intervention period of conditioning and football training, supplemented with a NHE protocol (24 sessions for NG-1 and 22 sessions for NG-2) or without using the NHE at all (CG). Sprint times were substantially improved in all groups (ES from -2.24±0.75 to -0.60±0.37). NHEs was enhanced absolute and relative to body-mass only in NG-1 after the training period (ES from 0.84±0.32 to 0.74±0.26), while in the NG-2 there were only improvements in average NHEs relative to body-mass (ES = 0.39±0.36). The improvements in T20-m were substantially greater in NG-2 vs. NG-1, and there were no differences in sprint performance changes between NG-1 and CG. Changes in sprinting performance and NHEs were unrelated. NHEs was largely correlated with the body-mass of the players. Results indicate that the improvements in sprint are not dependent on the NHEs changes, with no relationships between NHEs and sprint performance, and between sprint changes and changes in NHEs., Competing Interests: A commercial company employed MG, GR (FC Barcelona) and CFN (Cordoba Club de Fútbol). This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

The aim of this study was to describe the changes in body composition, strength and sprint performance in response to an entire competitive season of football training supplemented with 2 inertial eccentric-overload training sessions a week in young male professional soccer players. Whole body and regional composition (assessed using dual-energy X-ray absorptiometry), power output in half-squat and 40-m sprinting performance were evaluated in fourteen players. The eccentric-overload training consisted of training sessions a week of 1-2 sets of 10 exercises of upper-body and core (Day 1) and lower-body (Day 2), during the entire competitive season (27 weeks). Whole body fat mass decreased (-6.3 ± 3.6%, ES = -0.99 ± 0.54) substantially while lean mass increased (2.5 ± 0.8%, ES = 0.25 ± 0.09), with some regional differences. There was a substantial increase in half-squat power output (from 3% to 14%, ES from 0.45 to 1.73) and sprint performance (from 1.1% to 1.8%, ES from -0.33 to -0.44), however performance changes were not correlated with changes in body composition. A combined soccer and eccentric-overload training program was able to promote positive changes in body composition and physical factors relevant to both on-field performance and injury prevention in elite soccer players., Competing Interests: A commercial company employed AB, RM and NT: ACF Fiorentina. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

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., Competing Interests: The authors declare no conflict of interest., (© Georg Thieme Verlag KG Stuttgart · New York.)

The purpose of this study was to analyse the raw lifting speed collected during four different resistance training exercises to assess the optimal sampling frequency. Eight physically active participants performed sets of Squat Jumps, Countermovement Jumps, Squats and Bench Presses at a maximal lifting speed. A linear encoder was used to measure the instantaneous speed at a 200 Hz sampling rate. Subsequently, the power spectrum of the signal was computed by evaluating its Discrete Fourier Transform. The sampling frequency needed to reconstruct the signals with an error of less than 0.1% was f 99.9  = 11.615 ± 2.680 Hz for the exercise exhibiting the largest bandwidth, with the absolute highest individual value being 17.467 Hz. There was no difference between sets in any of the exercises. Using the closest integer sampling frequency value (25 Hz) yielded a reconstruction of the signal up to 99.975 ± 0.025% of its total in the worst case. In conclusion, a sampling rate of 25 Hz or above is more than adequate to record raw speed data and compute power during resistance training exercises, even under the most extreme circumstances during explosive exercises. Higher sampling frequencies provide no increase in the recording precision and may instead have adverse effects on the overall data quality.

Purpose: To compare the effects of unilateral and bilateral resistance training on single-leg power output, between-limbs imbalance (BLI), bilateral deficit (BLD), change of direction (COD), and linear sprinting and jumping performance in young elite basketball players., Methods: Twenty-two young (U-16-U-19) male basketball players were randomly assigned either to an exclusive unilateral (UNI) (n = 11) or a bilateral (BIL) (n = 11) resistance-training group during a 6-wk period. Both groups training consisted of 3 unilateral or bilateral 90° back-squat sets. A postdetermined number of repetitions was set until power output dropped to <10% of maximum power (MP) output. In addition, both groups performed 2 sets of 5 unilateral or bilateral drop jumps and 2 sets of 5 unilateral or bilateral countermovement jumps (CMJ). Pre- and posttraining, performance was assessed by an incremental bilateral and unilateral squat-load test, a multiple-COD test (V-cut test), a 15-m-sprint test (7.5 + 7.5 m) with one 180° COD performed with both right (180° RCOD) and left (180° LCOD) legs, a 25-m-sprint test (5- and 15-m split time), and a CMJ test., Results: Within-group analyses showed substantial improvements in 180° RCOD, bilateral and unilateral MP, 25-m-sprint test, and CMJ in both groups. Between-groups analyses showed substantially better results in 180° LCOD, MP with right and left legs, BLI, and BLD in UNI than in BIL., Conclusions: Both training programs substantially improved most of the physical-fitness tests, but only UNI reduced between-limbs asymmetry and achieved greater enhancements in actions that mostly required applying force unilaterally in basketball players.

The aim of this study was to investigate the changes in the relationships between repeated sprint ability (RSA) and anthropometric measures as well as fitness qualities in soccer players. Twenty-one professional soccer players performed several anthropometric and physical tests including countermovement vertical jumps (CMJs), a straight-line 30 m sprint (T30), an RSA test (6 x 20 + 20 m with 20 s recovery), a progressive isoinertial loading test in a full squat, a Yo-Yo Intermittent Recovery Test Level-1 (YYIRT-1) and a 20 m shuttle run test (20mSRT). The mean (RSAmean), the fastest (RSAbest), each single sprint time, and the percentage in a sprint decrease (%Dec) in the RSA test were calculated. RSAbest correlated significantly with RSAmean (r = .82) and with all single sprints (p < 0.05), showing a downward trend as the number of sprints performed increased. No significant relationship was observed between the %Dec and RSA performance. CMJs and the T30 also showed a correlation with RSA performance, whereas lower limb strength did not show any relationship with RSA performance. RSAmean showed significant (p < 0.05) relationships with body mass (r = .44), adiposity (r = .59) and the YYIRT-1 (r = -.62), increasing as the number of repeated sprints increased. The 20mSRT showed minimal relationships with RSA performance. In conclusion, maximal sprint capacity seems to be relevant for the RSA performance, mainly in the first sprints. However, high intermittent endurance capacity and low adiposity might help enhance the RSA performance when increasing the number of repeated sprints.

Purpose: To analyze the match running profile, distance traveled over successive 15 min of match play, heart rates (HRs), and index of performance efficiency (eff index ) of professional soccer players with a global positioning system (GPS) and HR in official competition., Methods: Twenty-six professional players were investigated during full matches in competitive club-level matches (N = 223). Time-motion data and HR were collected using GPS and HR technology., Results: The relative total distance was 113 ± 11 m/min, with substantial differences between halves. For all playing positions, a substantial decrease in total distance and distance covered at >13.0 km/h was observed in the second half in comparison with the first. The decrease during the second half in distance covered at >13.0 km/h was substantially higher than in total distance. The average HR recorded was 86.0% maximal HR, and the relationship between external and internal load (eff index ) was 1.3, with substantial differences between halves in all playing positions, except strikers for eff index . Wide midfielders reflected substantially the lowest mean HR and highest eff index , whereas center backs showed substantially the lowest eff index of all playing positions., Conclusions: The current study confirmed the decrement in a player's performance toward the end of a match in all playing positions. Wide midfielders displayed the highest and fittest levels of physical and physiological demands, respectively, whereas center backs had the lowest and least-fit levels of physical and physiological demands, respectively. The position-specific relationship between external and internal load confirms that players with more overall running performance during the full match were the best in eff index .

The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel leg-curl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T2) shift from pre- to post-MRI were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T2 values increased substantially after flywheel leg-curl in all regions of the BFl (from 9±8 to 16±8%), BFs (41±6-71±11%), and ST (60±1-69±7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13±8-16±5%) and ST (15±7-17±5%). T2 values after the Russian belt deadlift substantially increased in all regions of the BFl (6±4-7±5%), ST (8±3-11±2%), SM (6±4-10±4%), and proximal and distal regions of BFs (6±6-8±5%). T2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFl (11±5-7±5%) and ST (7±3-12±4%). The relevance of such MRI-based inter- and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies., Competing Interests: GR was employed by a commercial company: FC Barcelona. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Purpose: To examine the effects of a low-volume repeated-power-ability (RPA) training program on repeated-sprint and change-of- direction (COD) ability and functional jumping performance., Methods: Twenty-two male elite young basketball players (age 16.2 ± 1.2 y, height 190.0 ± 10.0 cm, body mass 82.9 ± 10.1 kg) were randomly assigned either to an RPA-training group (n = 11) or a control group (n = 11). RPA training consisted of leg-press exercise, twice a week for 6 wk, of 1 or 2 blocks of 5 sets × 5 repetitions with 20 s of passive recovery between sets and 3 min between blocks with the load that maximized power output. Before and after training, performance was assessed by a repeated-sprint-ability (RSA) test, a repeated-COD-ability test, a hop for distance, and a drop jump followed by tests of a double unilateral hop with the right and left legs., Results: Within-group and between-groups differences showed substantial improvements in slowest (RSAs) and mean time (RSAm) on RSA; best, slowest and mean time on repeated-COD ability; and unilateral right and left hop in the RPA group in comparison with control. While best time on RSA showed no improvement in any group, there was a large relationship (r = .68, 90% CI .43;.84) between the relative decrement in RSAm and RSAs, suggesting better sprint maintenance with RPA training. The relative improvements in best and mean repeated-COD ability were very largely correlated (r = .89, 90% CI .77;.94)., Conclusions: Six weeks of lowvolume (4-14 min/wk) RPA training improved several physical-fitness tests in basketball players.