Nine male pairs of monozygotic twins aged 11-14 years, height 147 (7.6) cm and body mass 39.7 (9.6) kg, participated in this study. Twin zygocity was tested using morphological, dermatoglyphic and hematologic methods, and Tanner's five stages were used for the evaluation of biological maturation. One twin from each pair undertook training for 6 months, three times a week, with running at 85-120% of the lactate anaerobic threshold (LT). Anthropometrics, determination of maximum O(2) uptake (.VO(2max)), LT and maximal blood lactate concentration ([La](max)) was carried out before, during and after training. No significant difference existed between the trained twins and their untrained brothers before training. After training, the trained twins increased their .VO(2max), (per kg body mass) by 10.6% and their LT by 18.2% (P<0.01), reaching values that differed significantly from those of their untrained brothers [57.5 (3.6) ml.kg(-1).min(-1) vs 55.4 (3.3) ml.kg(-1).min(-1) and 13.4 (1.1) km.h(-1) vs 12.7 (1.1) km.h(-1), respectively]. In addition, in the trained twins relative body fat was reduced (P<0.05) from 17.8 to 16.2% and their somatotype altered significantly (decrease of endomorphy and mesomorphy and increase of ectomorphy), while in the untrained twins there was no change in these parameters. Both groups of twins significantly increased their absolute .VO(2max) after the 6 months of training, the trained by 14,9% [from 2.08 (0.43) to 2.37 (0.45) l.min(-1)] and the untrained by 10.5% [from 2.10 (0.41) to 2.32 (0.47) l.min(-1)], but no difference was registered between them. A comparison of the intrapair changes in .VO(2max) of prepubertal and pubertal twins showed an influence of training in the prepubertal (19.3% vs 5.2%) but not in the pubertal twins (12.7% vs 13.1%). Using analysis of variance, the relative importance of training, heredity and their interaction was evaluated to be 20%, 70% and 10%, respectively, for the change in body fat, 35%, 45% and 20%, respectively, for the change in relative .VO(2max) and 25-30%, 50-60% and 15-20%, respectively, for the change in LT. In conclusion, training during pubertal growth can favour aerobic power (depending on body composition) as well as aerobic capacity, but it has no effect on absolute .VO(2max). Genetic control seems to have a strong effect on the extent of adaptations, and the genotype-training interaction explains a small, but prominent part of them.

The aim of this study was to assess the effect of physical exertion (treadmill) on mental performance (matching a comparison design). Nine pairs of monozygotic twins (boys aged 11 to 14 yr.) were randomly divided into two groups, one trained and one untrained, while eight boys of the same age served as a control group. The trained group underwent a specifically designed program lasting six months. The trained and untrained groups performed on the treadmill for 20 min. at a running speed intensity above their individual anaerobic thresholds. Mental performance was evaluated by analysing mean number of correct answers, time taken to reach correct answers (decision time), and wrong answers. A 3 x 2 (group x pre/posttest) analysis of variance with repeated measures on the last factor yielded no significant differences; however, significant pre- versus posttest differences on correct answers and decision times occurred among the exercised groups.

To investigate the effect of physical exertion on simple reaction time and continuous attention of sport participants, an experiment was conducted with 46 male university students and 12 male cyclists. The subjects were assigned to three experimental and two control groups. The subjects of the experimental groups were asked to perform, following a 5-min, period of warming up, a high intensity exercise protocol for 5 min., on a mechanically braked cycle ergometer (Group A) or a moderate intensity exercise protocol for 30 min, on the same cycle ergometer (Groups B and C). Shortly before and immediately after the physical exercise subjects of all groups were asked to perform a test of simple reaction time and continuous attention. The subjects of the control groups were asked to perform at rest both tests of the simple reaction time and the continuous attention twice, with a 10-min. and a 35-min. interval between the first and second attempts, respectively. The results did not support the notion that exercise of moderate or high intensity influences significantly the cognitive performance of aerobically trained or untrained subjects. The results are discussed in the light of the current research findings concerning exertion and human psychomotor performance.