Impact of Aerobic Exercise Training on Age-Related Changes in Insulin Sensitivity and Muscle Oxidative Capacity

TLDR

Insulin resistance rises and muscle oxidative capacity falls with age, yet physical activity may counteract these changes. The study investigated whether a 16‑week aerobic exercise program versus control activity improves insulin sensitivity and muscle mitochondrial function in adults aged 21–87. Participants (65 exercise, 37 control) completed the program for 16 weeks, with outcomes assessed by intravenous glucose tolerance tests and measurements of mitochondrial enzyme activity, mRNA, and protein markers. Exercise increased VO₂peak, mitochondrial enzyme activity, GLUT4 expression, and reduced abdominal fat and triglycerides, but only younger participants showed improved insulin sensitivity while older adults had similar mitochondrial responses without insulin sensitivity gains.

Abstract

Insulin resistance increases and muscle oxidative capacity decreases during aging, but lifestyle changes—especially physical activity—may reverse these trends. Here we report the effect of a 16-week aerobic exercise program (n = 65) or control activity (n = 37) performed by men and women aged 21–87 years on insulin sensitivity and muscle mitochondria. Insulin sensitivity, measured by intravenous glucose tolerance test, decreased with age (r = −0.32) and was related to abdominal fat content (r = −0.65). Exercise increased peak oxygen uptake (Vo2peak; 10%), activity of muscle mitochondrial enzymes (citrate synthase and cytochrome c oxidase, 45–76%) and mRNA levels of mitochondrial genes (COX4, ND4, both 66%) and genes involved in mitochondrial biogenesis (PGC-1α, 55%; NRF-1, 15%; TFAM, 85%). Exercise also increased muscle GLUT4 mRNA and protein (30–52%) and reduced abdominal fat (5%) and plasma triglycerides (25%). None of these changes were affected by age. In contrast, insulin sensitivity improved in younger people but not in middle-aged or older groups. Thus, the muscle mitochondrial response to 4 months of aerobic exercise training was similar in all age-groups, although the older people did not have an improvement in insulin sensitivity.