Serial sarcomere adaptation to eccentric overload training is blunted in ovariectomized rats

Abstract

Eccentric contractions performed to long muscle lengths impose high mechanical stress and strain on the muscle fiber, providing a stimulus for longitudinal growth (i.e., increases in serial sarcomeres number (SSN)). Conventional (CONV) resistance training incorporates eccentric and concentric phases; however, mechanical loading is constrained by the concentric phase. Eccentric overload (ECCOVERLOAD) training has a maximal load throughout the eccentric phase increasing the potential for greater sarcomerogenesis. The purpose was to investigate ECCOVERLOAD and CONV training on mechanical and morphological adaptation in ovary‐intact and OVX rats. Intact and OVX Sprague–Dawley rats performed 4 weeks (×3/week) of ECCOVERLOAD or CONV resistance training. Mechanical measures were tested pre‐ and post‐training. Fascicle length and sarcomere length were measured to obtain SSN. Torque increased (p < 0.001) similarly across groups at the shorter muscle (p = 0.075) and greater at the longer muscle lengths (p = 0.002) in OVX rats. In the soleus, there was a training× hormone status× training group (p = 0.028) interaction, such that intact rats showed the greatest improvement in SSN with ECCOVERLOAD (~13%), which was higher than both CONV intact (~3%) and OVX rats in either training condition (ECCOVERLOAD ~1%, CONV ~5%). Therefore, OVX had a blunted adaptation in longitudinal muscle remodeling in response to ECCOVERLOAD training.