The aim of this study was to evaluate the acute responses of blood hormone concentrations and neuromuscular performance following whole-body vibration (WBV) treatment. Fourteen male subjects [mean (SD) age 25 (4.6) years] were exposed to vertical sinusoidal WBV, 10 times for 60 s, with 60 s rest between the vibration sets (a rest period lasting 6 min was allowed after 5 vibration sets). Neuromuscular performance tests consisting of counter-movement jumps and maximal dynamic leg presses on a slide machine, performed with an extra load of 160% of the subjects body mass, and with both legs were administered before and immediately after the WBV treatment. The average velocity, acceleration, average force, and power were calculated and the root mean square electromyogram (EMGrms) were recorded from the vastus lateralis and rectus femoris muscles simultaneously during the leg-press measurement. Blood samples were also collected, and plasma concentrations of testosterone (T), growth hormone (GH) and cortisol (C) were measured. The results showed a significant increase in the plasma concentration of T and GH, whereas C levels decreased. An increase in the mechanical power output of the leg extensor muscles was observed together with a reduction in EMGrms activity. Neuromuscular efficiency improved, as indicated by the decrease in the ratio between EMGrms and power. Jumping performance, which was measured using the counter-movement jump test, was also enhanced. Thus, it can be argued that the biological mechanism produced by vibration is similar to the effect produced by explosive power training (jumping and bouncing). The enhancement of explosive power could have been induced by an increase in the synchronisation activity of the motor units, and/or improved co-ordination of the synergistic muscles and increased inhibition of the antagonists. These results suggest that WBV treatment leads to acute responses of hormonal profile and neuromuscular performance. It is therefore likely that the effect of WBV treatment elicited a biological adaptation that is connected to a neural potentiation effect, similar to those reported to occur following resistance and explosive power training. In conclusion, it is suggested that WBV influences proprioceptive feedback mechanisms and specific neural components, leading to an improvement of neuromuscular performance. Moreover, since the hormonal responses, characterised by an increase in T and GH concentration and a decrease in C concentration, and the increase in neuromuscular effectiveness were simultaneous but independent, it is speculated that the two phenomena might have common underlying mechanisms.

This study examined the influence of exercise intensity upon the cortisol response of the hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined exercise at intensities of 40, 60, and 80% maximal oxygen uptake (VO2max) in an attempt to determine the intensity necessary to provoke an increase in circulating cortisol. Twelve active moderately trained men performed 30 min of exercise at intensities of 40, 60, and 80% of their VO2max, as well as a 30-min resting-control session involving no exercise on separate days. Confounding factors such as time of day--circadian rhythms, prior diet--activity patterns, psychological stress, and levels of exercise training were controlled. Cortisol and ACTH were assessed in blood collected immediately before (pre-) and after (post-) each experimental session. Statistical analysis involved repeated measures analysis of variance and Tukey post-hoc testing. The percent change in cortisol from pre- to post-sampling at each session was: resting-control, 40, 60, and 80% sessions (mean+/-SD) =-6.6+/-3.5%, +5.7+/-11.0%, +39.9+/-11.8%, and +83.1+/-18.5%, respectively. The 60% and 80% intensity magnitude of change was significantly greater than in the other sessions, as well as from one to another. The ACTH responses mirrored those of cortisol, but only the 80% exercise provoked a significant (p<0.05) increase pre- to post-exercise. The calculated changes in plasma volume for the resting-control, 40%, 60%, and 80% sessions were: +2.2+/-3.0%, -9.9+/-5.0%, -15.6+/-3.5%, and -17.2+/-3.3%, respectively. Collectively, the cortisol findings support the view that moderate to high intensity exercise provokes increases in circulating cortisol levels. These increases seem due to a combination of hemoconcentration and HPA axis stimulus (ACTH). In contrast, low intensity exercise (40%) does not result in significant increases in cortisol levels, but, once corrections for plasma volume reduction occurred and circadian factors were examined, low intensity exercise actually resulted in a reduction in circulating cortisol levels.

The aim of this study was to investigate the effects of whole-body vibrations (WBV) on the mechanical behaviour of human skeletal muscle. For this purpose, six female volleyball players at national level were recruited voluntarily. They were tested with maximal dynamic leg press exercise on a slide machine with extra loads of 70, 90, 110 and 130 kg. After the testing, one leg was randomly assigned to the control treatment (C) and the other to the experimental treatment (E) consisting of vibrations. The subjects were then retested at the end of the treatment using the leg press. Results showed remarkable and statistically significant enhancement of the experimental treatment in average velocity (AV), average force (AF) and average power (AP) (P < 0.05-0.005). Consequently, the velocity-force and power-force relationship shifted to the right after the treatment. In conclusion, it was affirmed that the enhancement could be caused by neural factors, as athletes were well accustomed to the leg press exercise and the learning effect was minimized.

No abstract

Classical studies of H. Selye [27] on the general adaptation syndrome evidenced involvement of the adrenal cortex in adaptation processes. Accordingly, cortisol has been nominated as the adaptation hormone. However, during the past 15 ± 20 years several researchers in exercise physiology and sports medicine have had the opinion that the decreased ratio of testosterone/cortisol indicates a predominance of catabolism that is undesirable for adaptation and improvement of performance in athletes. In their opinion, an increased cortisol concentration is ªguiltyº of association with maladaptation.In 1986 Adlercreutz and coworkers [1] focused attention to the ratio testosterone/cortisol. They proposed using the ratio between free testosterone and cortisol as an indication of overstrain if the ratio decreases more than 30 % or if the ratio is less than 0.35´10 ±3 . This way, an extreme situation in the balance of anabolic and catabolic stimuli may be detected. However, the proposed quantitative measure was later forgotten and any decrease in the ratio was considered as a bad indication including an association with overtraining. Attention has not paid to the fact that Adlercreutz et al.[1] considered free but not total testosterone concentration in the blood. Moreover, Adlercreutzs team focused on the overreaching rather than overtraining. Actually, in a number of studies the decreased ratio was associated with improved performance of athletes [17,32]. In high-level rowers, the cortisol response to all-out exercise increased in conjunction with improved performance during a training year [28].The purpose of the present editorial is to comment the actual significance of cortisol in exercise and to correct several misunderstandings in evaluation of cortisol responses in athletes. Cortisol FunctionThis hormone has a wide spectrum of tasks in metabolic control (Fig. 1). Indeed, activation of catabolic processes and anti-anabolic action are included. However, these are essential tools for adaptation in the stress situation. The adaptive significance of catabolic changes consists, first of all, in creation of an increased pool of free amino acids. Therefore, branched chain amino acids can be used as additional substrate of oxidation. Moreover, free amino acids are available as ªbuilding blocksº for protein synthesis. Synthesis of several ultimately needed proteins is necessary during stress situation (including exercise), but it will be the dominating process during the late recovery period. Among metabolic inductors are those, which are produced in protein degradation (see Mader [20]). Catabolic processes continue also during the recovery period [35] ensuring the destruction of physiologically exhausted elements of protein structures in order to make possible their substitution by newly synthesized proteins.Protein synthesis is controlled at three levels: pre-translation level (induction), translation level, and post-translation level [2]. The post-translation control consists of adjusting the number of protein molecules to t...