Background Hamstring Strain Injuries (HSIs) represent 12% of all injuries in soccer players, and their incidence has increased in recent years. Between 53%-84% of HSIs involve the Biceps femoris muscle (BF). Recent studies have shown that soccer players with shorter BF fascicle length (FL) suffer more HSIs and exhibit regional differences in FL and pennation angle (PA) along BF. It is unclear whether there is any regional difference in the degree of change of these parameters after a soccer match.

Objective Describe changes in BF muscle architecture after a simulated soccer match.

Design Controlled laboratory study. Pre and Post single session.

Setting Laboratory. Amateur Level.

Participants Soccer players without acute injuries/illness and no previous lower limb injuries. Data collection is still ongoing. To date, 4 players have been measured and analysed.

Assessment Randomized measurements of muscle architecture parameters at different submaximal contraction intensities, before and after a 45 min. soccer-specific fatigue protocol. Total time 3 hours.

Main Outcome Measures Biceps femoris absolute and relative changes in PA and FL in 3 different regions of the muscle. Results from this ongoing study imply that relative changes in FL were region-dependent, whereby FL shortening after the protocol was greater in the proximal regions at higher contraction intensities (−2.0% vs 12.3% vs 19.5%), but greater in the distal regions at lower contraction intensities (−8.0% vs 6.7% vs 12.4%).

Conclusions After a soccer-specific fatigue protocol, FL and PA of the BF muscle varied regionally and with contraction intensity. Greater FL shortening at proximal regions after a soccer match, especially at higher contraction levels, may be linked to the higher incidence of HSI in these areas, and might help to explain the injury mechanism.