Muscle mass and insulin sensitivity in postmenopausal women after 6-month exercise training

ABSTRACT

Objective The common belief that high muscle mass improves insulin sensitivity is controversial and even recent studies have established that larger muscle mass is associated with insulin resistance in sedentary postmenopausal women. Physical activity induces a beneficial effect in muscle size and its metabolic properties. Hence, larger muscle mass induced by exercise training should ameliorate insulin sensitivity and the negative relationship between larger muscle mass and insulin sensitivity should disappear. This study examined the induced changes in muscle mass and insulin sensitivity in postmenopausal women after 6-month exercise training along with their possible correlations.

Methods Forty-eight sedentary, overweight-to-obese postmenopausal women followed a 6-month mixed exercise training (three sessions/week; endurance and resistance). Lean body mass (LBM) and fat mass (FM) were measured by DXA, then the muscle mass index (MMI) was calculated (MMI = LBM (kg)/height (m²)). Fasting glucose and insulin measurements were obtained and insulin resistance (IR) was estimated by the HOMA-IR formula.

Results Baseline MMI was correlated with IR (r = 0.219, p = 0.015). After intervention, significant differences were observed in body weight, FM%, MMI, and glycemia, and changes in MMI were significantly correlated with changes in IR (r = 0.345, p = 0.016). Also linear regression showed that the increase in MMI explained 28% of the deterioration in insulin sensitivity (p = 0.001).

Conclusions After 6 months of mixed training, changes in muscle mass remained correlated with changes in insulin resistance, overweight-to-obese women with large muscle gains being more insulin-resistant. This supports that muscle quality and functionality, and the loss of fat mass, should be targeted rather than muscle mass gains in postmenopausal women, especially in a context of no energy restriction.

Key words:

• MUSCLE MASS
• INSULIN SENSITIVITY
• MIXED EXERCISE TRAINING
• MENOPAUSE

ACKNOWLEDGEMENTS

We thank all the subjects who volunteered for the studies; without them these data would not be available. We also thank all the research team members of our laboratory at CDRV, our exercise physiologists and the research coordinator Karine Perreault, for their valuable work for this project; a special thanks to Martine Fisch, our research nurse.

Conflict of interest The authors report no conflict of interest. The authors alone are responsible for the content and writing of this paper.

Source of funding This work was funded by the Canadian Institutes of Health Research (CIHR) and the Canadian Diabetes Association. Razieh Barsalani retains a postdoctoral training award from the FRQS (Fonds de recherche du Québec-Santé). Isabelle J. Dionne holds a Canada Research Chair on Exercise Recommendations for a Healthy Aging.