Rationale: The health burden of type 2 diabetes (T2DM) is broad and includes having a lower level of aerobic fitness, a predictor of morbidity and mortality. Yet detailed data about determinants of aerobic fitness in diabetics are lacking.
Objective: We examined associations of glycemic control, systemic inflammation, body composition, muscle strength, and habitual physical activity with aerobic fitness in persons with T2DM who were not routine exercisers.
Methodology: Eighty-four subjects (M = 57; F = 27) aged 57.7 +/- 5.7 years were examined at baseline as part of an exercise training study. They were taking their usual medications but were not insulin requiring. Measures were peak oxygen uptake (peak Vo2) assessed on a treadmill; HbA1c; C-reactive protein (CRP); percent body fat by dual-energy x-ray absorptiometry; abdominal fat by magnetic resonance imaging; muscle strength by 1-RM as the total weight lifted during 7 exercises; and habitual physical activity by the Stanford 7-day recall survey. The associations of peak Vo2 with other measures were determined by multivariate regression analysis with gender and age added to the model.
Results: Mean peak Vo2 was 21.7 +/- 5.0 mL kg-1 min-1; HbA1c was 6.8 +/- 1.4%; CRP was 2.8 +/- 2.9 1.0 mg/L; body fat was 35.2 +/- 6.7%; abdominal fat was 567.3 +/- 150.2 cm2; strength was 935.7 +/- 254.2 lb; and total daily energy expenditure was 33.9 +/- 3.0 kcal/kg. In the final model, a lower peak Vo2 was associated with increased body fat, which explained 49% of the variance (P = .001) whereas increased HbA1c explained an additional 4% (P = .02) and decreased total strength explained an additional 4% (P = .01) of the variance in peak Vo2. Older age explained an additional 3% of the variance in peak Vo2 with borderline significance (P = .07). Gender, inflammation, abdominal obesity, and habitual physical activity did not enter the model.
Conclusions: The primary determinant of a lower aerobic fitness was having more total body fat, with a further modest reduction with less tight glycemic control and decreased muscle strength. This finding was independent of gender, age, habitual physical activity, inflammation, and fat distribution. These results emphasize the adverse effects of increased body fat on a key parameter of cardiovascular health and identify an important target for intervention in persons with diabetes.