Heritability of the rate of torque development.

AIM: The aim of this study was to estimate the genetic and environmental contribution to the variation observed in the rate of torque development (RTD), which is considered an important determinant of sport performance. METHODS: Nine monozygotic (MZ) and seven dizygotic (DZ) twin pairs, of both sexes aged 19-26 years, performed three isometric maximal voluntary contractions with the knee at 70 degrees and 40 degrees of flexion (0 degrees=terminal extension) on a Contrex Isokinetic dynamometer. The RTD was extracted from the force time curves and calculated in two different ways, giving rise to two indices, the maximal rate of torque development (MRTD), and the torque at the first 100 msec (F100msec). Heritability estimates (h2) were derived on the basis of intrapair variances between MZ and DZ twin pairs. RESULTS: A significant genetic influence (P<0.05) was found for both RTD indices (h2=0.99, and 0.93 for MRTD, and F100msec respectively) at only 40 degrees of knee flexion, an angle associated with intensive neural activation. CONCLUSION: The maximal rate of torque development of knee extensor muscles during the initial phase of their contraction and at enhanced neural activation, is under strong genetic influence.

Genetic variation of maximal velocity and EMG activity.

There is a scarcity of studies on genetic variation of essential components of neuromuscular performance, such as maximal velocity and EMG activity during maximal effort. Using the twin model and comparing intrapair differences between monozygotic (MZ) and dizygotic (DZ) twins, we derived for these neuromuscular components heritability estimates (h2), signifying the phenotypic variance due to genetic differences. A group of forty healthy male twins, 10 MZ and 10 DZ pairs, aged 21.5 +/- 2.4 and 21.0 +/- 2.1 yr, respectively, performed dynamic elbow flexion to assess maximal velocity, and maximal isometric contraction to assess EMG activity of the biceps brachii muscle. Intrapair differences for maximal velocity in MZ and DZ twins were 0.22+/- 0.04 and 0.55 +/- 0.17 m x s(-1), and intrapair correlations were 0.95 and 0.54, respectively; h2 for maximal velocity was 0.84. Likewise, intrapair differences for EMG activity during maximal isometric contraction were 0.061 +/- 0.03 in MZ and 0.176 mV in DZ; the respective intrapair correlations were 0.93 and 0.46, and h2 was 0.85. In conclusion, maximal velocity of the upper limb, using a simple movement of a single joint and EMG activity during maximal isometric contraction, seems to be highly heritable characteristics in humans.

Genes and olympic performance: a co-twin study.

An Olympic gold medalist in a 20 km competitive walking race and his identical twin brother, also an Olympic athlete in the same event but with inferior performance, were tested in order to obtain some further insight into the relative importance of genetic factors in modulating athletic excellence. Both twins had undergone the same strenuous, long-term training for 19 years since the age of 15 under the guidance of the same coach. An assessment of their bio-behavioural profiles at 40 years of age, i. e. 7 years after they ceased training, revealed that intrapair differences were negligible in physiological attributes but divergent in personality traits measured. Respective values for the Olympic winner and his identical counterpart were as follows: Body mass index 23.2 and 22.7, cardiac mass index 85.4 and 84.4 g x m2, squatjumping 25.3 and 27.3 cm, VO2 at running speed 9 km x h(-1) 33.1 and 33.6 ml x kg(-1) x min(-1), VO2 max 57.1 and 58.6 ml x kg(-1) x min(-1) (72.5ml x kg(-1) x min(-1) for the Olympic winner at age 22 yrs), reaction to anger 97 and 9 and anger expression 2 and 76 in percentile of the State-Trait Anger Expression Inventory. Findings suggest that although genetic constitution and years of physical training are prerequisites for making an Olympic athlete, success may be largely influenced by personality traits.

Influence of physical exertion on mental performance with reference to training.

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.

Growth and physical training with reference to heredity.

Identical male twins (four sets aged 10 yr, four sets aged 13 yr, and four sets aged 16 yr) were divided so that one twin underwent strenuos endurance training for 10 wk, while his brother served as a control without training. Intrapair comparisons of the training-period changes in aerobic, anaerobic, and cardiorespiratory responses to maximum work on a bicycle ergometer disclosed that 1) 10-yr-old trained twins improved more than untrained twins did in VO2max,2) 16-yr-old trained twins increased their VO2max, O2 pulse, blood lactate, ventilation, and respiratory rate and decreased their maximal heart rates more than their untrained counterparts did, and 3) the trained and the untrained 13-yr-old twins changed commensurately. Further, interage comparisons of the intrapair differences showed that both the 10- and 16-yr olds improved their VO2max more than did the 13-yr olds. In view of this evidence, the old hypothesis that more may be gained by introducing extra exercise at the time when the rate of growth is greatest is not tenable.

The maximum aerobic power of the Temiars.

A settlement of Temiars, an aboriginal tribe residing in the north-eastern jungles of the Malay Peninsula, was selected for a study of their cardiorespiratory fitness. A step-test was used to elicit the Vo2max, V E max and HR max in a group of 19 boys aged 12 to 18 years and 6 men aged 19 - 40 years. The mean VO2max of the boys was found to be 45.9 +/- 6.9 ml-kg-1-min-1 compared with 45.6 +/- 5.4 ml-kg-1-min-1 for the men. The mean V E max, HR max and blood lactate levels were found to be 65.5 +/- 11.31/min and 69.2 +/- 23.71/min; 194 +/- 8 beats/min and 186 +/- 10 beats/min; and 79.8 +/- 13.4 mg% and 97.7 +/- 33.4 mg% respectively. These results are comparable to those obtained in urban populations as well as those found in other primitive communities. Telemetric monitoring of the routine daily physical activity of the men revealed that these jungle dwellers rarely tax their oxygen transport systems in their daily living and their cardiorespiratory functions were similar to communities who do not specifically train for physical fitness.

Genetic basis of individual differences in tissue composition.

A total of 19 pairs of twin adolescent boys, 14 MZ and 5 DZ, were used to determine the relative contribution of the genotype to the individual differences observed in surface density of muscle, subcutaneous fat, and bone. The cross-sectional areas of these tissue components were calculated from photographs of the upper arm, taken by means of an ultrasonic apparatus. The respective mean percentage intrapair difference in MZ and DZ twins was 6.9 and 9.8 for total area, 6.6 and 7.8 for muscle, 13.9 and 32.0 for fat, and 6.7 and 31.3 for bone tissue. Interindividual variations in bone only could be ascribed to genetic differences.