Relationship between aerobic fitness and adipose tissue insulin resistance

Aerobic fitness is associated with greater skeletal muscle insulin sensitivity with regard to glucose uptake. Whether fitness is associated with an improvement in the insulin regulation of adipose tissue lipolysis is unknown. We collated adipose insulin sensitivity, body composition, and fitness data from six of our previously published and two of our unpublished protocols. Adipose tissue insulin resistance index of palmitate (ADIPO-IR_palmitate) data were available for 340 volunteers, and the insulin concentration resulting in a 50% suppression of palmitate rate of appearance (FFA_palmitate IC₅₀) measured using the insulin clamp technique was available for 108 volunteers. Pearson's correlation and multiple linear regression analysis were performed to assess the relationship between the independent variables of aerobic fitness [peak oxygen consumption (V̇o_2peak), mL kg·FFM^-1·min^-1], age, sex, body mass index (BMI), visceral adipose tissue (VAT), body fat, percent body fat, and the dependent variables ADIPO-IR_palmitate and FFA_palmitate IC₅₀. Factors that were univariately correlated (<i>P</i> < 0.001) with ADIPO-IR_palmitate and FFA_palmitate IC₅₀ were BMI, percent body fat, body fat, and VAT. Fitness correlated negatively with ADIPO-IR_palmitate and FFA_palmitate IC₅₀. Stepwise regression analysis showed that fitness independently predicted ADIPO-IR_palmitate and FFA_palmitate IC₅₀ after adjusting for the other significant factors. These findings suggest that aerobic fitness may promote metabolic health through positive effects on adipose tissue. Clinical Trial Registration: NCT00254371; the other protocols were not considered clinical trials at the time they were conducted.<b>NEW & NOTEWORTHY</b> Greater degrees of aerobic fitness are associated with greater insulin-mediated muscle glucose uptake. Insulin regulates adipose tissue lipolysis, whether aerobic fitness affects insulin's ability to regulate lipolysis is unknown. We found that greater fitness is associated with improved adipose tissue insulin responsiveness independent of age, sex, BMI, visceral adipose tissue, body fat (kg), percent body fat, and adipocyte size. This suggests that exercise, if it improves fitness, may improve both adipose tissue and muscle function.