Effect of long-term strength training on glucose metabolism. Implications for individual impact of high lean mass and high fat mass on relationship between BMI and insulin sensitivity

The aim of this study was to examine the independent effect of high lean mass on glucose metabolism, as well as its consequences on the classic relationship between BMI and insulin sensitivity (SI) in 3 groups: 1) 8 strength-trained males with BMI >27 kg/m² (athletes); 2) 10 sedentary males with BMI >27 kg/m² (obese); and 3) 12 sedentary males with BMI 22-25 kg/m² (control). Body composition was measured with impedance analysis. Iv glucose tolerance test was performed at 09:00 h after overnight fast. Estimation of insulin sensitivity and glucose effectiveness by Minimal Model Approach. Plasma glucose and insulin determination by glucose-oxidase and RIA respectively. BMI and lean mass (LM) were greater in athletes than in controls, but there were no differences in fat mass (FM), basal glucose (Gb), basal insulin (Ib), glucose tolerance (Kg), SI, glucose effectiveness (Sg), acute insulin response to glucose (AIRG) and leptin. Obese showed greater FM, leptin, Ib and AIRG than athletes, while SI was lower; BMI, LM, Gb, Kg and Sg were similar. BMI, FM, LM, Ib, AIRG and leptin were lower in controls than in obese, while SI index was greater; Gb, Sg and Kg were similar. We found that: 1) Resistance exercise does not modify glucose effectiveness, but can improve insulin sensitivity through FM reduction (LM augmentation alone has no effect on glucose metabolism); and 2) High BMI causes insulin resistance only if it depends on adipose tissue hypertrophy.