Transient effect of aerobic exercise training on insulin sensitivity

• Exercise training elicited a consistent increase in VO 2peak . • Conversely insulin sensitivity rose after initial training but returned to baseline. • Benefits of insulin sensitivity from exercise are transient with continued training. Aerobic exercise training has well established effects on increasing insulin sensitivity. However, the extent to which exercise in the absence of weight loss and/or negative energy balance results in sustained elevation in insulin sensitivity is unclear. This study aimed to assess the effects of long-term aerobic exercise training on insulin sensitivity in healthy premenopausal women while controlling for energy balance. Female participants ages 20–40 (Mean BMI=27.0) trained three times per week throughout the study on a cycle ergometer under supervision of an exercise physiologist. Participants completed a pre-training evaluation and three post-training evaluations at times ranging from 8 to 20 weeks post-baseline, including insulin sensitivity and peak VO 2 testing. Before each evaluation, participants stayed overnight in a room calorimeter for 23 h and food intake was adjusted to maintain energy balance. A cycle ergometer graded exercise test was completed after warm-up to determine peak oxygen uptake (VO 2peak ). Hyperinsulinemic-euglycemic clamp measures were conducted to determine insulin sensitivity. Adjusted and unadjusted models were performed for log insulin sensitivity and peak VO 2 using linear model for repeated measures. Data from 31 participants with complete data were analyzed. The models determined that mean VO 2peak ( F = 5.56 (3,89) p = 0.0015) and mean insulin sensitivity ( F = 3.92 (3,65) p = 0.0123) differed among timepoints. Exercise training elicited an increase in VO 2peak from pre-training (25.5 ± 1.15) to all three post-training evaluations (26.7 ± 1.15 vs. 27.4 ± 1.07 vs. 27.2 ± 1.17, respectively). In contrast, insulin sensitivity increased from pre-training to first post-training evaluation, but then returned to levels not different from baseline at the subsequent two evaluations. Improvement in insulin sensitivity resulting from exercise training appears to be transient and returns to baseline with continued training.