Smaller biceps femoris aponeurosis size in legs with a history of hamstring strain injury

Biceps femoris long head (BF LH) aponeurosis size was compared between legs with and without prior hamstring strain injury (HSI) using two approaches: within-group (injured vs. uninjured legs of previous unilateral HSI athletes) and between-group (previously injured legs of HSI athletes vs. legs of No Prior HSI athletes). MRI scans were performed on currently healthy, competitive male athletes with Prior HSI history (n =23;≥1 verified BF LH injury; including a sub-group with unilateral HSI history; most recent HSI 1.6±1.2 years ago) and pair-matched athletes with No Prior HSI history (n =23). Anonymized axial images were manually segmented to quantify BF LH aponeurosis and muscle size. Prior unilateral HSI athletes' BF LH aponeurosis maximum width, aponeurosis area, and aponeurosis:muscle area ratio were 14.0-19.6% smaller in previously injured vs. contralateral uninjured legs (paired t-test, 0.008≤P≤0.044). BF LH aponeurosis maximum width and area were also 9.4-16.5% smaller in previously injured legs (n =28) from Prior HSI athletes vs. legs (n =46) of No Prior HSI athletes (unpaired t-test, 0.001≤P≤0.044). BF LH aponeurosis size was smaller in legs with prior HSI vs. those without prior HSI. These findings suggest BF LH aponeurosis size, especially maximum width, could be a potential cause or consequence of HSI, with prospective evidence needed to support or refute these possibilities.