Decline in insulin action with age in endurance-trained humans

We tested the hypothesis that regular endurance exercise prevents the age-related decline in insulin action typically observed in healthy, sedentary adults. An index of whole body insulin sensitivity (ISI), obtained from minimal model analysis of insulin and glucose concentrations during a frequently sampled intravenous glucose tolerance test, was determined in 126 healthy adults: 25 young [27 ± 1 (SE) yr; 13 men/12 women] and 43 older (59 ± 1 yr; 20/13) sedentary and 25 young (29 ± 1 yr; 12/13) and 33 older (60 ± 1 yr; 20/13) endurance trained. ISI values were lower in the older vs. young adults in both sedentary (−53%; 3.9 ± 0.3 vs. 7.0 ± 0.7 ×10−4 · min−1 · μU−1 · ml−1; P < 0.01) and endurance-trained (−36%; 7.9 ± 0.6 vs. 12.4 ± 1.0 ×10−4min−1 · μU−1 · ml−1; P < 0.01) groups, but the value was 72–102% higher in the trained subjects at either age ( P < 0.01). In subgroup analysis of sedentary and endurance-trained adults with similar body fat levels ( n = 62), the age-related reduction in ISI persisted only in the endurance-trained subjects (12.9 ± 1.9 vs. 8.7 ± 1.2 ×10−4 · min−1 · μU−1 · ml−1; P < 0.01). The results of the present study suggest that habitual endurance exercise does not prevent the age-associated decline insulin action. Moreover, the age-related reduction in ISI in endurance-trained adults appears to be independent of adiposity.