Investigating Sex Differences in Resistance Training-Induced Skeletal Muscle Adaptations in Middle-Aged Adults

Abstract

Introduction: Resistance training improves muscle strength and induces myofiber hypertrophy in young males and females with blunted responses occurring in older adults. These adaptations are partially due to the function of muscle stem cells (MuSCs) and fibro-adipogenic progenitors (FAPs). It remains unknown whether middle-aged males and females respond similarly to resistance training with protein supplementation, specifically at the cellular level. Purpose: The purpose of this study is to investigate the potential sex-specific responses of middle-aged males and females to whole-body resistance training. Methods: Middle-aged adults (N=28), 40-64 years, participated in a 10-week progressive, whole-body resistance training intervention coupled with protein supplementation. Muscle biopsies were collected from the vastus lateralis and stained for fibre morphology, MuSCs, and FAPs. Results: Both sexes increased type II fibre cross-sectional area with training. Myonuclear content, myonuclear domain size, and MuSC content were not altered with training in either sex. Both males and females altered FAP content with training. Interestingly, the change in MuSCs and both FAPs were correlated in males but not females (both P<0.05). It was concluded that there were no sex-specific responses to resistance training in middle-aged males and females; however, MuSCs and FAPs appear to be correlated in males but not females.