Do athletes with hamstring strain injury have shorter muscle fascicles in the injured limb?

INTRODUCTION

Previous studies have suggested that a reduced length of the biceps femoris long head (BF) fascicles may increase the risk of hamstring strain injury (HSI). However, it remains unclear whether the BF fascicles of the injured limb are shorter than those of the contralateral limb in athletes with an acute HSI.

OBJECTIVE

To investigate the between-limb asymmetry of BF fascicle length in amateur athletes with an acute HSI.

METHODS

Male amateur athletes were evaluated using ultrasound scans within five days following an HSI. The BF fascicle length was estimated using a validated equation.

RESULTS

Eighteen injured athletes participated in this study. There was no significant difference (p = 0.27) in the length of BF fascicles between the injured limb (9.53 ± 2.55 cm; 95%CI 8.26 to 10.80 cm) and the uninjured limb (10.54 ± 2.87 cm; 95%CI 9.11 to 11.97 cm). Individual analysis revealed high heterogeneity, with between-limb asymmetries (percentage difference of the injured limb compared to the uninjured limb) ranging from -42% to 25%. Nine out of the 18 athletes had a fascicle length that was more than 10% shorter in the injured limb compared to the uninjured limb, five athletes had a difference of less than 10%, and four athletes had a fascicle length that was more than 10% longer in the injured limb compared to the uninjured limb.

CONCLUSION

The architecture characteristics of injured and uninjured muscles is not consistent among athletes with HSI. Therefore, rehabilitation programs focused on fascicle lengthening should be evaluated on a case-by-case basis.