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 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) approaches. 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) were MRI scanned. Anonymised 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 was 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.