Johan Lahti

Objective To test whether a musculoskeletal multifactorial and individualised hamstring muscle injury (HMI) risk reduction programme could reduce HMI risk in professional football. Methods We conducted a prospective cohort study in Finnish premier football league teams, with the 2019 season used as a control and an intervention conducted in the 2021 season. Screening was conducted to provide individualised programmes and monitor progress. Cox regression with hazard ratio (HR) was used with HMI as outcome and season as explanatory variable, including all players for primary analysis and those who performed the two seasons for secondary analysis. Results 90 players were included in the control and 87 in the intervention seasons; 31 players performed in the 2 seasons. Twenty HMIs were recorded during the control and 16 during the intervention seasons. Cox regression analyses revealed that HMI risk at any given time was not significantly different between control and intervention seasons (for all players: HR 0.77 (95% CI 0.39 to 1.51), p=0.444; for the 31 players: HR 0.32 (95% CI 0.01 to 1.29), p=0.110)). For the 31 players, the HMI burden was significantly reduced in the intervention compared with the control season (RR 0.67 (95% CI 0.53 to 0.85)). Higher compliance with knee strength training, maximal velocity exposure and lower performance reductions in maximal theoretical horizontal force and knee flexor force were associated with lower HMI incidence. Conclusions Although the primary analysis did not reveal any significant effect of the intervention to reduce HMI risk in professional football, the programme was feasible, and additional secondary analyses showed a significant association between the intervention and lower HMI burden, incidence and risk.

The aim of this study was to analyse the influence of fatigue on sprint biomechanics. Fifty-one football players performed twelve maximal 30 m sprints with 20 s recovery between each sprint. Sprint kinetics were computed from running speed data and a high-frequency camera (240 Hz) was used to study kinematic data. A cluster analysis (K-mean clustering) was conducted to classify individual kinematic adaptations. A large decrease in maximal power output and less efficiency in horizontally orienting the ground reaction force were observed in fatigued participants. In addition, individual changes in kinematic components were observed, and, according to the cluster analysis, five clusters were identified. Changes in trunk, knee, and hip angles led to an overall theoretical increase in hamstring strain for some players (Cluster 5, 20/51) but to an overall decrease for some others (Cluster 1, 11/51). This study showed that the repeated sprint ability (RSA) protocol had an impact on both kinetics and kinematics. Moreover, fatigue affected the kinematics in a different way for each player, and these individual changes were associated with either higher or lower hamstring length and thus strain.

The aim of this pilot study was to analyze the potential association of a novel multifactorial hamstring screening protocol with the occurrence of hamstring muscle injuries (HMI) in professional football. 161 professional male football players participated in this study (age: 24.6 ± 5.36 years;...

Clear decreases in horizontal force production capacity during sprint acceleration have been reported after hamstring injuries (HI) in football players. We hypothesized that lower F_H0 is associated with a higher HI occurrence in football players. We aimed to analyze the association between sprint running horizontal force production capacities at low (F_H0) and high (V₀) velocities, and HI occurrence in football. This prospective cohort study included 284 football players over one season. All players performed 30 m field sprints at the beginning and different times during the season. Sprint velocity data were used to compute sprint mechanical properties. Players’ injury data were prospectively collected during the entire season. Cox regression analyses were performed using new HI as the outcome, and horizontal force production capacity (F_H0 and V₀) was used at the start of the season (model 1) and at each measurement time point within the season (model 2) as explanatory variables, adjusted for individual players’ (model 2) age, geographical group of players, height, body mass, and previous HI, with cumulative hours of football practice as the time scale. A total of 47 new HI (20% of all injuries) were observed in 38 out of 284 players (13%). There were no associations between F_H0 and/or V₀ values at the start of the season and new HI occurrence during the season (model 1). During the season, a total of 801 measurements were performed, from one to six per player. Lower measured F_H0 values were significantly associated with a higher risk of sustaining HI within the weeks following sprint measurement (HR = 2.67 (95% CI: 1.51 to 4.73), p < 0.001) (model 2). In conclusion, low horizontal force production capacities at low velocity during early sprint acceleration (F_H0) may be considered as a potential additional factor associated with HI risk in a comprehensive, multifactorial, and individualized approach.

Introduction: Hamstring muscle injuries (HMI) continue to plague professional football. Several scientific publications have encouraged a multifactorial approach; however, no multifactorial HMI risk reduction studies have been conducted in professional football. Furthermore, individualisation of HMI management programmes has only been researched in a rehabilitation setting. Therefore, this study aims to determine if aspecificmultifactorial and individualised programme can reduce HMI occurrence in professional football.Methods and analysis: We conducted a prospective cohort study over two seasons within the Finnish Premier League and compare the amount of HMI sustained during a control season to an intervention season. Injury data and sport exposure were collected during the two seasons (2019–2020), and a multifactorial and individualised HMI risk reduction programme will be implemented during intervention season (2020). After a hamstring screening protocol is completed, individual training will be defined for each player within several categories: lumbo-pelvic control, range of motion, posterior chain strength, sprint mechanical output and an additional non-individualised ‘training for all players’ category. Screening and respective updates to training programmes were conducted three times during the season. The outcome will be to compare if there is a significant effect of the intervention on the HMI occurrence using Cox regression analysis.Ethics and dissemination: Approval for the injury and sport exposure data collection was obtained by the Saint-Etienne University Hospital Ethics Committee (request number: IORG0007394; record number IRBN322016/CHUSTE). Approval for the intervention season was obtained from the Central Finland healthcare District (request and record number: U6/2019).

We tested the hypothesis that the degree of adaptation to highly focused sprint training at opposite ends of the sprint Force-Velocity (FV) spectrum would be associated with initial sprint FV profile in rugby athletes. Training-induced changes in sprint FV profiles were computed before and after an eight-week in-season resisted or assisted sprint training protocol, including a three-week taper. Professional male rugby players (age: 18.9 ± 1.0 years; body height: 1.9 ± 0.0 m; body mass: 88.3 ± 10.0 kg) were divided into two groups based on their initial sprint FV profiles: 1) Heavy sled training (RESISTED, N = 9, velocity loss 70–80%), and 2) assisted acceleration training (ASSISTED, N = 12, velocity increase 5–10%). A total of 16 athletes were able to finish all required measurements and sessions. According to the hypothesis, a significant correlation was found between initial sprint FV profile and relative change in sprint FV profile (RESISTED: r = −0.95, p < 0.01, ASSISTED: r = −0.79, p < 0.01). This study showed that initial FV properties influence the degree of mechanical response when training at different ends of the FV spectrum. Practitioners should consider utilizing the sprint FV profile to improve the individual effectiveness of resisted and assisted sprint training programs in high-level rugby athletes.

Sprint performance is an essential skill to target within soccer. However, time-consuming intervention models could be easily rejected by coaches. Therefore, alternative and efficient field training options are warranted. One such method could be heavy resisted sprint training. However, it is unknown whether such overload will be efficient in assisting increases in sprint performance in a professional setting, and whether violating kinematic specificity via heavy loading will lead to changes in unloaded sprinting kinematics. Thus, we investigated whether heavy resisted training affects sprint performance and sagittal plane kinematics. Training-induced changes in sprint FV-profiles were computed before and after the 9-week, 2 sessions x week protocol. Out of the two recruited teams (N = 32, age: 24.1 ± 5.0 years: height: 180 ± 10 cm; body-mass: 76.7 ± 7.7 kg), one was used as a control group continuing training as normal (CON, N = 13), while the experimental team was divided into two subgroups based on their initial sprint performance: 1) Heavy sled training with the 60% velocity drop (N = 10) and 2) 50% velocity drop load (N = 9). Both experimental groups improved significantly all 0-30-m split times (p < 0.05, d = -0.62 – -1.25), with post-hoc showing HS50% improving significantly compared to CON in 0-10-m split (d = 1.03) and Pmax (d = 1.16). No differences in sprinting kinematics were observed. With appropriate coaching, heavy sled training could be a pragmatic option to assist improvements in sprint performance without adverse changes in sprinting kinematics in professional soccer players.

The primary means for disseminating sport and exercise science research is currently through journal articles. However, not all studies, especially those with null findings, make it to formal publication. This publication bias towards positive findings may contribute to questionable research practices. Preregistration is a solution to prevent the publication of distorted evidence resulting from this system. This process asks authors to register their hypotheses and methods before data collection on a publicly available repository or by submitting a Registered Report. In the Registered Reports format, authors submit a Stage 1 manuscript to a participating journal that includes an introduction, methods, and any pilot data indicating the exploratory or confirmatory nature of the study. After a Stage 1 peer review, the manuscript can then be offered in-principle acceptance, rejected, or sent back for revisions to improve the quality of the study. If accepted, the project is guaranteed publication, assuming the authors follow the data collection and analysis protocol. After data collection, authors re-submit a Stage 2 manuscript that includes the results and discussion, and the study is evaluated on clarity and conformity with the planned analysis. In its final form, Registered Reports appear almost identical to a typical publication, but give readers confidence that the hypotheses and main analyses are less susceptible to bias from questionable research practices. From this perspective, we argue that inclusion of Registered Reports by researchers and journals will improve the transparency, replicability, and trust in sport and exercise science research.

Different stance widths are commonly utilized when completing the barbell back squat during athletic general preparedness training. Width manipulation is thought to influence sagittal plane stimuli to the hip and knee extensors, the primary extensor musculature in the squat. However, how width manipulation affects frontal plane stimuli is less understood. Knowledge of hip and knee net joint moments (NJM) could improve exercise selection when aiming to improve sport‐specific performance and prevent injuries. Fourteen adult amateur rugby athletes were recruited for this study. After a familiarization period, participants performed wide‐ (WIDE, 1.5× greater trochanter width) and narrow‐stance (NARROW, 1× greater trochanter width) barbell back squats to femur parallel depth, using relative loads of 70% and 85% of one‐repetition maximum. Sagittal and frontal plane hip and knee kinetics and kinematics were compared between widths. A Bonferroni‐corrected alpha of 0.01 was employed as the threshold for statistical significance. Knee flexion angle was statistically greater in NARROW than WIDE (P < 0.0001,d = 2.56‐2.86); no statistical differences were observed for hip flexion angle between conditions (P = 0.049‐0.109,d = 0.33‐0.38). Hip‐to‐knee extension NJM ratios and knee adduction NJMs were statistically greater in WIDE than NARROW (P < 0.007,d = 0.51‐1.41). At femur parallel, stance width manipulation in the barbell back squat may provide substantial differences in biomechanical stimulus in both the sagittal plane and the frontal plane. In certain contexts, these differences may have clinically relevant longitudinal implications, from both a performance and a injury prevention standpoint, which are discussed.