Author(s): HAVERS, T., SCHÖNFELDER, M., WACKERHAGE, H., GEISLER, S., Institution: IST UNIVERSITY OF APPLIED SCIENCES, Country: GERMANY, Abstract-ID: 2521

INTRODUCTION:
Studies in humans (Heymsfield et al., 2021) and animal models (Izumiya et al., 2008) show that muscle hypertrophy is often associated with a reduction in fat mass and improvement of glucose homeostasis. However, this has not been systematically investigated. Thus, the aim of this project was to systematically review the literature on the effects of global muscle hypertrophy on fat mass and glucose variables (i.e., HbA1c or blood glucose) in humans and animals.
METHODS:
PubMed, SportDiscus and Scopus were searched in August 2023 for articles in which global muscle hypertrophy was induced in humans (i.e. resistance training, pharmacological intervention or both) or animals (mice, rats, pigs; resistance training, pharmacological intervention, genetic modification) and fat mass and/or glucose homeostasis (i.e. HbA1c or blood glucose) was reported. We considered lean body mass (LBM), fat-free mass (FFM) or skeletal muscle mass (SMM) measured by dual-energy X-ray absorptiometry (DXA) or bioelectrical impedance analysis (BIA) as muscle size variables. We calculated the percentage change from pre- to post-intervention for the respective outcome. In animal studies, muscle mass and fat mass post-intervention (DXA or dissection) were normalised to the animals body weight and the percentage difference between the treatment and animal control condition was calculated. In addition, blood glucose data were obtained. The percentage change/ difference in muscle mass was plotted against the percentage change/difference in fat mass or HbA1c/blood glucose.
RESULTS:
A total of 114 studies (93 human, 21 animal) met the inclusion criteria. Overall, across all human interventions, muscle mass increased by 2.6% (DXA) and 3.2% (BIA), HbA1c decreased by 4.1%, and fasting glucose decreased by 5.8%. When each outcome was related to its percentage change of muscle mass, HbA1c decreased by 4.1%, fasting glucose by 5.8% and fat mass by 4.00%, while muscle mass increased by 1.9%, 3.3% and 2.7% respectively. Similarly, animal models with more muscle mass relative to body weight had better blood glucose (-16.2%) and reduced fat mass relative to body weight (-25.1%) compared to their controls.
CONCLUSION:
This systematic literature analysis suggests that skeletal muscle hypertrophy results in fat loss and improved glucose homeostasis variables such as HbA1c.

References
1) Heymsfield et al., JAMA Netw Open, 2021
2) Izumiya et al., Cell Metab, 2008