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The relationship between insulin resistance (HOMA-IR), percent body fat, and aerobic fitness (VO2max per unit fat free mass; mL/kgFFM/min) was examined in 1,710 children. Percent body fat was estimated from sum of skinfolds, and VO2max was estimated from submaximal cycle ergometer tests. Overnight fasting blood samples were obtained. VO2max (mL/kgFFM/min) and percent body fat were correlated with HOMA-IR (r=-0.076, p < .002; r=.420, p < .001, respectively); as was VO2max in units of mL/kg/min (r=-0.264, p < .001). When VO2max in mL/kg/min was used, a progressive increase in HOMA-IR was found with decreasing fitness (p < .05). However, when mL/kgFFM/min was used, HOMA-IR scores remained similar between moderate-fit and low-fit group. The stronger association between aerobic fitness (mL/kg/min) and HOMA-IR is partially due to the significant association of fat mass to HOMA-IR. Therefore, our recommendation is to express aerobic fitness in units of mL/kgFFM/min to eliminate the confounding factor of adiposity and better understand the influence of muscle on insulin resistance.
Ahn and McMurray are with the Dept. of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, NC. Harrell is with the Dept. of Nursing, University of North Carolina at Chapel Hill, Chapel Hill, NC.