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 (m(2))). 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.
