Achilles tendon ruptures are common injuries. Sex differences are present in mechanical properties of uninjured Achilles tendon, but it remains unknown if these differences extend to tendon healing. We hypothesized that ovariectomized females (OVX) and males would exhibit inferior post-injury tendon properties compared to females. Male, female, and OVX Sprague-Dawley rats (n = 32/group) underwent acclimation and treadmill training prior to blunt transection of the Achilles tendon mid-substance. Injured hindlimbs were immobilized for 1 week, followed by gradual return to activity and assessment of active and passive hindlimb function. Animals were euthanized at 3 or 6 weeks post-injury to assess tendon structure, mechanics, and composition. Passive ankle stiffness and range of motion were superior in females at 3 weeks; however, by 6 weeks, passive and active function were similar in males and females but remained inferior in OVX. At 6 weeks, female tendons had greater normalized secant modulus, viscoelastic behavior, and laxity compared to males. Normalized secant modulus, cross-sectional area and tendon glycosaminoglycan composition were inferior in OVX compared to females at 6 weeks. Total fatigue cycles until tendon failure were similar among groups. Post-injury muscle fiber size was better preserved in females compared to males, and females had greater collagen-III at the tendon injury site compared to males at 6 weeks. Despite male and female Achilles tendons withstanding similar durations of fatigue loading, early passive hindlimb function and tendon mechanical properties, including secant modulus, suggest superior healing in females. Ovarian hormone loss was associated with inferior Achilles tendon healing.
- Achilles tendon
- Tendon healing
- Sex differences
- Copyright © 2016, Journal of Applied Physiology