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

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 (ECC_OVERLOAD) training has a maximal load throughout the eccentric phase increasing the potential for greater sarcomerogenesis. The purpose was to investigate ECC_OVERLOAD 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 ECC_OVERLOAD 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 ECC_OVERLOAD (~13%), which was higher than both CONV intact (~3%) and OVX rats in either training condition (ECC_OVERLOAD ~1%, CONV ~5%). Therefore, OVX had a blunted adaptation in longitudinal muscle remodeling in response to ECC_OVERLOAD training.