Gender differences in mechanical properties of the Achilles tendon: Longitudinal response to repetitive loading exercise
Gender differences have been observed in the mechanical properties of the Achilles tendon, which may help to explain the increased risk of injury in males. However, the response and recovery of tendon mechanics to repetitive loading exercise, as well as gender dependent responses, are not well understood. Our purpose was to compare Achilles tendon mechanical properties between males and females prior to, immediately after, and 60-minutes following a repetitive loading exercise. Seventeen female (age: 24.0 ± 3.9yrs; height: 167.4 ± 6.9cm; mass: 64.9 ± 8.5kg) and 18 male (age: 23.9 ± 2.4yrs; height: 179.2 ± 5.09cm; mass: 78.4 ± 8.7kg) recreationally active individuals volunteered. Utilizing isokinetic dynamometry and diagnostic ultrasound, baseline levels of Achilles tendon force, elongation, stiffness, stress, strain and Young’s modulus were assessed prior to 100 successive calf raises using a Smith machine at 20% of participant body mass. Outcomes were reassessed immediately, and 60-minutes post-exercise. Females exhibited less Achilles tendon force, stiffness, stress and modulus compared to males, regardless of time point. Both genders responded to repetitive loading exercise similarly, with immediate decreases in mechanical properties of the Achilles tendon from baseline to immediately post-exercise. Tendon properties were observed to be equal to baseline values at 60-min post-exercise. Baseline differences in tendon properties may help to explain the disparity in injury risk, as both genders responded to and recovered from exercise similarly. Future research should aim to include additional time points (both leading up to and following 60-minutes), and assess tendon responses to more sport specific activities, while also including patients diagnosed with Achilles tendon injuries.