How does a simulated soccer match affect regional differences in biceps femoris muscle architecture?

Soccer is played by thousands of athletes across the globe and its participation increases the overall risk of injury, in particular, hamstring strain injuries (HSI). Biceps femoris (BF) has been shown to be involved the in 5 out of 6 HSI cases and risk factors including fatigue and short BF fascicle length (FL) have been identified. Furthermore, previous studies suggest that different muscle regions may undergo different strains during dynamic tasks, which could contribute to injury risk. The primary aim of this study was to evaluate the effects of a soccer match on regional differences in the BF muscle architecture. A secondary aim was to assess the reliability of the extended field of view (EFOV) 2D ultrasound imaging to measure muscle architecture parameters. Muscle architecture was assessed, using ultrasound, in 9 amateur soccer players and 5 physically active men, before and after a 45 minutes soccer specific fatigue protocol (SAFT)or 20 mintues of rest, respectively. Significant muscle architecture changes were found after SAFT, however, these were smaller than the minimal detectable change associated with the scanning method. No correlations were found between force reductions and muscle architecture changes. Good reliability was found for FL measurements but poor reliability was found for pennation angle and muscle thickness. Muscle architecture changes after 45 minutes of a football match may not be a mechanism to explain the increased HSI rates. Furthermore, when using EFOV ultrasound, care must be taken when interpreting statistically significant results, since these can be below the minimal detectable change or not reliable for all the parameters.