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Nine pairs of monozygotic twins of both sexes were submitted to a 20 week endurance training program, five times per week, 40 min per session, at an average of 80% of maximal heart rate reserve. Testing and training were performed on cycle ergometers. ˙VO2max was measured before (T1) and after (T4) the training program, as well as at the 7th (T2) and 14th (T3) week. Training significantly (p<0.01) increased ˙VO2max (Mean± SD; T1:2.6 ± 0.7; T2: 2.8 ± 0.7; T3: 2.8 ± 0.8 and T4: 3.0 ± 0.7 L·min-1). The time course of˙VO2max response to training is shown in thetable. Average increases in ˙VO2max reached 0.13, 0.31 0.42 after 7, 14 and 20 weeks of training, respectively. However, these changes were not randomly distributed among pairs, as about 2 to 6 times(F ratio) more variance was found between pairs than within pairs in the˙VO2max response to training. The intraclass correlations quantifying the intrapair resemblance in the response to training reached 0.31(p=.20) for the changes observed after 7 and 14 weeks of training and 0.71(p=.008) after 20 weeks. These results indicate that the response of˙VO2max to endurance training is genotype dependent and that this genotype-training interaction effect increases with the duration of training.
Purpose Fitness decline, high body mass index (BMI), and insulin resistance (IR) are associated with worsening cardiometabolic risk factors prospectively; modification of the fitness change effect by BMI and IR remains unknown. Methods Participants from the Coronary Artery Risk Development in Young Adults study without diabetes at year 0 (Y0) (n = 2048, 43.4% men; mean age, 25 yr) had fitness quantified by treadmill at Y0 and Y20. Y0 BMI was normal (nBMI <25 kg·m−2) or high (hBMI ≥25 kg·m−2). Y0 IR status was insulin sensitive (IS) (homeostatic model assessment IR <1.84 (75th percentile)) or insulin resistant (IR) (homeostatic model assessment IR ≥1.84). Four groups were established: nBMI/IS, hBMI/IS, nBMI/IR, and hBMI/IR. Y0 fitness was low (<33rd percentile for sex) or average high (≥33rd percentile for sex). Fitness change (treadmill time: Y20–Y0) was maintained (increase or decline ≤20th percentile for sex) or decreased (decline >20th percentile for sex). The outcomes were incident diabetes and percentage change over 25 yr in weight, waist girth, blood pressure, and lipid profile. Analysis was by multiple linear regression and proportional hazards regression with adjustment for individual characteristics. Results Maintained fitness after 20 yr was associated with greater increase in HDL cholesterol and less increase in weight, waist girth, blood pressure, and triglycerides than decreased fitness, similarly for the groups defined by BMI and IR. Maintained fitness reduced the rate of incident diabetes in IS but not IR participants. Conclusions Maintained fitness after 20 yr was associated with more favorable middle-age cardiometabolic risk factors than decreased fitness; this benefit might be blunted by baseline IR.
