TIME COURSE OF THE RESPONSE OF ??VO2MAX TO ENDURANCE TRAINING IS GENOTYPE DEPENDENT 719

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.