BackgroundMuscle injuries are one of the main daily problems in sports medicine, football in particular. However, we do not have reliable means to predict the outcome, i.e. return to play (RTP) from severe injury. The aim of the present study was to evaluate the capability of the MLG-R classification system to grade hamstring muscle injuries by severity, offer a prognosis for the RTP, and identify injuries with higher risk of reinjury. And to assess the consistency of our proposed system by investigating its intra-and inter-observer reliability. MethodsAll male professional football players from FC Barcelona (FCB)-senior A and B and the two U-19 teams-with injuries occurred between February 2010 and February 2020 were reviewed. Only players with clinical presentation of hamstring muscle injury, with complete clinic information and magnetic resonance images (MRI), were included. Three different statistical and machine learning approaches (linear regression, random forest, and XGBoost) were used to assess the importance of each factor of the MLG-R classification system in determining the RTP as well as to offer a prediction of the expected RTP. We used the Cohen's kappa and the intraclass correlation coefficient (ICC) to assess the intra-and interobserver reliability. ResultsBetween 2010 and 2020, 76 hamstring injuries corresponding to 42 different players were identified, of which 50 (65.8%) were Grade 3 r , 54 (71.1%) affected the biceps femoris long head (BFlh), and 33 of the 76 (43.4%) were located at the proximal myotendinous junction (MTJ). The mean RTP for Grade 2, 3, and 3 r injuries were 14.3, 12.4, and 37 days, respectively. Injuries affecting the proximal MTJ had a mean RTP of 31.7 days while those affecting the distal part of the MTJ had a mean RTP of 23.9 days. The analysis of the grade 3r BFlh injuries located at the FT showed a median RTP time of 56 days while the injuries located at the central tendon had a shorter RTP of 24 days (p=0.038). The statistical analysis showed an excellent predictive power of the MLG-R classification system with a mean absolute error of 9.8 days and an R-squared of 0.48. The most important factors to determine the RTP were if the injury was at the free tendon (FT) of the BFlh or if it was a Grade 3 r injury. For all the items of the MLG-R classification the intra-and inter-observer reliability was excellent (k > 0.93) except for fibers blurring (κ = 0.68). ConclusionThe main determinant for long RTP after hamstring injury is the injury affecting the connective tissue structures of the hamstring.We developed a reliable hamstring muscle injury classification system based on MRI that showed excellent results in terms of reliability, prognosis capability and objectivity. It is easy to use in clinical 2 daily practice, and can be further adapted to future knowledge. The adoption of this system by the medical community would allow to uniform diagnosis leading to better injury management.

Professional athletes undertake a variety of training programs to enhance their physical performance, technical-tactical skills, while protecting their health and well-being. Regular exercise induces widespread changes in the whole body in an extremely complex network of signaling, and evidence indicates that phenotypical sex differences influence the physiological adaptations to player load of professional athletes. Despite that there remains an underrepresentation of women in clinical studies in sports, including football. The objectives of this study were twofold: to study the association between the external load (EPTS) and urinary metabolites as a surrogate of the adaptation to training, and to assess the effect of sex on the physiological adaptations to player load in professional football players. Targeted metabolic analysis of aminoacids, and tryptophan and phenylalanine metabolites detected progressive changes in the urinary metabolome associated with the external training load in men and women’s football teams. Overrepresentation analysis and multivariate analysis of metabolic data showed significant differences of the effect of training on the metabolic profiles in the men and women teams analyzed. Collectively, our results demonstrate that the development of metabolic models of adaptation in professional football players can benefit from the separate analysis of women and men teams, providing more accurate insights into how adaptation to the external load is related to changes in the metabolic phenotypes. Furthermore, results support the use of metabolomics to understand changes in specific metabolic pathways provoked by the training process.

Objective. To compare the kinematic demands on international women field hockey players during official competition matches. Materials and methods. Sixteen women players (age: 24.7 ± 2.8; weight: 57.9 ± 5.9 kg; height: 165.2 ± 4.9 cm) belonging to the Spanish national team were monitored during 5 matches of the European Championship using global positioning systems (GPS). The analyses were carried out according to the players' positions (defenders, midfielders and forwards), the quarters in the game (Q1, Q2, Q3, Q4), and the number of minutes played. The data analysed included distances, accelerations and decelerations in different intensity ranges. Results. The defenders showed less high-intensity activity (speeds, accelerations and decelerations) than midfielders and forwards (9.4 ± 2.4%; ES: 0.78 with the midfielders and 33.1 ± 7.2%; ES: 2.1, with the defenders). The analysis by quarters showed that in Q4 activity was the highest for all positions. In terms of the number of minutes played, the cluster analysis grouped the players into 3 groups according to the number of minutes played (<32, 32-45 and >45 minutes). The athletes who played <32 covered the greatest distance at a sprint (>21 km/h) and high-intensity distance (>15 km/h) per minute of play compared to the group who played >45 minutes. Conclusions. The results of this study show that the physical demands on élite women hockey players depend on their position on the field, and that there is more activity in the last quarter and less relative high-intensity kinematic activity among the players who play more minutes during the match.

Background Because MRI has shown great accuracy in assessing acute muscle injuries, identification of risk factors for reinjury before return to play (RTP) in professional athletes during the healing process could be very relevant. We assessed the value of MRI findings prior to RTP as predictors of reinjury. Methods Retrospective observational study of 59 professional athletes, mean age 26 years, with first-time acute muscle injury and successful rehabilitation ready to RTP. They underwent MRI within 6 days of the injury and within 7 days prior to RTP. The primary outcome was reinjury. Risk of reinjury was assessed using radiological signs in control MRI scans before RTP. The risk was classified as low, medium or high when none, one or two radiological signs were observed, respectively. Results Reinjury occurred in 9 participants, with a rate of 15.2%. None of the baseline MRI-related variables was significantly associated with reinjury. In the control MRI scan performed within 7 days prior to RTP, three independent findings were significantly associated with reinjury. These included transversal and/or mixed connective tissue gap (p = 0.002), intermuscular oedema (p = 0.015) and callus gap (p = 0.046). In the predictive model of the risk of reinjury, the presence of two of these radiological signs, together with interstitial feathery oedema, was associated with a high risk of recurrence (OR 29.58, 95% CI 3.86–226.64; p = 0.001). Conclusions In professional athletes with acute muscle injuries of the lower limbs successfully rehabilitated, some radiological signs on MRI performed shortly before RTP were associated with a high risk of reinjury.