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·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 ± 0.08 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. © Georg Thieme Verlag KG Stuttgart

Anaerobic capacity, isometric endurance, and Laser sailing performance

Laser sailors have to tolerate fatiguing contractions of the lower-body muscles for prolonged periods. The aims of the present study were (1) to evaluate the difference between top-ranked and club sailors, in their capacity to resist fatigue during sustained isometric and maximal power exercise, and (2) to examine the relationships between the above parameters and performance on a Laser simulator and competitive racing performance according to the national ranking list. Eight Greek nationally ranked Laser sailors were compared with eight club sailors. Each sailor performed: (a) an effort to the limit of tolerance on the Laser simulator, (b) an effort to the limit of tolerance of isometric endurance for the right leg on an isokinetic dynamometer, and (c) a Wingate test of maximal lower-body anaerobic power on a cycle ergometer. In the nationally ranked sailors, isometric endurance time (mean 160 s, s = 50) and endurance time on the Laser simulator (1381 s, s = 1354) were significantly (P > 0.05) longer than in the club sailors (101 s, s = 29 and 565 s, s = 367, respectively), whereas the final minute heart rate (in both groups: 149 beats. min-1, s = 22) and the mean arterial pressure (nationally ranked sailors: 129 mmHg, s = 16; club sailors: 120 mmHg, s = 21) on the Laser simulator were not different between groups. During the Wingate test, the nationally ranked sailors had a significantly lower index of fatigue (42%, s = 5) than the club sailors (49%, s = 6). Isometric endurance time was significantly correlated with the Wingate index of fatigue (r = -0.73; P > 0.001). The nationally ranked sailors' mean and maximal anaerobic powers were significantly correlated with their national ranking positions (r = -0.83 and -0.71, respectively). It is suggested that isometric endurance and anaerobic power are well-developed in Laser class sailors and may influence their sailing performance. Furthermore, compared with club sailors, the nationally ranked sailors are able to sustain the same intensity of lower-limb isometric contractions for much longer with similar cardiovascular responses

Heritability in Neuromuscular Coordination: Implications for Motor Control Strategies

Purpose: The aim of this study was to assess the relative power of genetic and environmental contribution to the variation observed in neuromuscular coordination. Methods: Using the twin model and comparing intrapair differences between monozygotic (MZ) and dizygotic (DZ) twins, we derived heritability estimates (h2). Forty healthy male twins, 10 MZ and 10 DZ pairs, aged 21.5 ± 2.4 and 21 ± 2.1 yr, respectively, performed a series of elbow flexions in one degree of freedom with different velocities attempting to accurately reach a target. Neuromuscular coordination was evaluated for both accuracy and economy of movement and assessed by kinematics and EMG activity. Results: The heritability in movement accuracy as assessed by the displacement from the target at 70% maximal velocity was 0.87. The accuracy at 30% and 50% of maximal velocity showed that the intrapair variation of MZ twins did not differ significantly from that of DZ twins. High heritability indexes of 0.85 and 0.73 were found for neuromuscular coordination as expressed by movement economy, assessed by the relative EMG activity of biceps long head at 70% and 50% of maximal velocity; no genetic dependence was found for low velocities. Conclusions: In this study, heredity accounted for most of the existing differences in neuromuscular coordination in fast movements. This implies that movement strategies, which are organized in the CNS and control fast movements, are also strongly genetically dependent

Insulin sensitivity derived from oral glucose tolerance testing in athletes: Disagreement between available indices

The aims of the present study were to determine whether available "fasting" and oral glucose tolerance test-derived insulin sensitivity indices could effectively discriminate between individuals with higher than normal insulin sensitivity, and whether they would all provide similar information in clinical practice. Sprint runners (n = 8), endurance runners (n = 8) and sedentary controls (n = 7) received a 75-g oral glucose tolerance test. All participants were healthy lean males, aged 21-29 years. Besides glucose and insulin responses, a total of nine such indices were computed. Fasting as well as post-load glucose concentrations were similar in the three groups, while basal plasma insulin and the insulinaemic response to glucose were both higher in untrained individuals (at P < 0.05 and P < 0.02, respectively). There were no differences between endurance and sprint runners. The results for insulin sensitivity, however, were quite variable: three indices showed that both groups of athletes were more insulin-sensitive than controls; three indicated that this was the case for endurance runners only; one indicated that this was the case for sprint runners only; and two showed that sprint runners were more insulin-sensitive than either sedentary individuals or endurance runners (all differences were significant at P < 0.05). Controlling for total body weight or lean mass did not effectively resolve this disagreement. Apparently, the various insulin sensitivity indices examined provided different quantitative and qualitative information, despite insulin action being greater in both groups of athletes relative to controls, as reflected by their similar glucose tolerance with lower insulin concentrations. We suggest, therefore, that the use and interpretation of such indices among physically active individuals be made with caution. © 2005 Taylor & Francis

Prediction of over(V, ̇) O2 max from a new field test based on portable indirect calorimetry

We assessed the validity and reliability of the new 15 m square shuttle run test (SST) for predicting laboratory treadmill test (TT) maximal oxygen uptake (over(V, ̇) O2 max) compared to the 20 m multistage shuttle run test (MST) in 45 adult males. Thirty participants performed a TT and a SST once to develop a over(V, ̇) O2 max prediction model. The remaining 15 participants performed the TT and MST once and the SST twice for cross-validation purposes. Throughout testing over(V, ̇) O2 max was determined via portable indirect calorimetry while blood lactate concentration was assessed at the fifth recovery minute. Comparisons of TT over(V, ̇) O2 max (51.3 ± 3.1 ml kg-1 min-1) with SST measured (51.2 ± 3.2 ml kg-1 min-1) and predicted (50.9 ± 3.3 ml kg-1 min-1) over(V, ̇) O2 max showed no differences while TT blood lactate was higher compared to SST (10.3 ± 1.7 mmol vs. 9.7 ± 1.7 mmol, respectively). In contrast, MST measured (53.4 ± 3.5 ml kg-1 min-1) and predicted (57.0 ± 4.5 ml kg-1 min-1) over(V, ̇) O2 max and blood lactate (11.2 ± 2.0 mmol) were significantly higher compared to TT. No test-retest differences were detected for SST measured and predicted over(V, ̇) O2 max and blood lactate. It is concluded that the SST is a highly valid and reliable predictive test for over(V, ̇) O2 max. © 2009 Sports Medicine Australia

Altered hemodynamic regulation and reflex control during exercise and recovery in obese boys

The aims of the present study were to assess in obese and lean boys 1) the hemodynamic responses and baroreflex sensitivity (BRS) to isometric handgrip exercise (HG) and recovery and 2) the muscle metaboreflex-induced blood pressure response and the variables that determine this response. Twenty-seven boys (14 obese and 13 lean boys, body mass index: 29.2 ± 0.9 vs. 18.9 ± 0.3kg/m 2, respectively) participated. The testing protocol involved 3 min of baseline, 3 min of HG (30% maximum voluntary contraction), 3 min of circulatory occlusion, and 3 min of recovery. The same protocol was repeated without occlusion. At baseline, no differences were detected between groups in beat-to-beat arterial pressure (AP), heart rate (HR), and BRS; however, obese boys had higher stroke volume and lower total peripheral resistance than lean boys (P < 0.05). During HG, lean boys exhibited higher HR and lower BRS compared with their obese counterparts. In lean boys, BRS decreased during HG compared with baseline, whereas in obese boys, it was not significantly modified. In lean boys, TPR was elevated during HG and declined after exercise, whereas in obese boys, TPR did not significantly decrease after exercise cessation. In the postexercise period, BRS in lean boys returned to baseline, whereas an overshoot was observed in obese boys. Postexercise BRS was correlated with body mass index (R = 0.56, P < 0.05). Although the metaboreflex-induced increase in AP was similar between obese and lean children, it was achieved via different mechanisms: in lean children, total peripheral resistance was the main contributor to AP maintenance during the metaboreflex, whereas in obese children, stroke volume significantly contributed to AP maintenance during the metaboreflex. In conclusion, obese normotensive children demonstrated altered cardiovascular hemodynamics and reflex control during exercise and recovery. Copyright © 2010 the American Physiological Society