Mehis Viru

Hormonal responses to whole-body vibration in men

Abstract 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.

Effect of restricted blood flow on exercise-induced hormone changes in healthy men

Abstract To test the influence of the accumulation of metabolites on exercise-induced hormone responses, plasma concentrations of cortisol, growth hormone (GH), insulin, testosterone, thyrotropin (TSH), free thyroxine (fT4) and triiodothyronine (T3) were compared during exercise performed under normal conditions (control) and under conditions of restricted blood flow of exercising leg muscles (ischaemia) in nine healthy young men. Blood supply was reduced by 15%–20% by the application of 50 mmHg external pressure over the exercising leg. During 45-min cycling exercise during ischaemia the increase in GH concentration was twice as large as under normal conditions. Despite the below-threshold exercise intensity for activation of the pituitary-adrenocortical system under normal exercise conditions ischaemic exercise elicited cortisol and T3 responses (concentration increases of 83% and 9.5%, respectively). Ischaemic exercise attenuated the decrease of plasma insulin concentration found under normal conditions. The concentrations of testosterone, TSH and fT4 were not changed significantly during exercise performed in either condition. The results support the suggested essential role of muscle metaboreceptors in the control of hormone responses during muscle activity.

Exercise-induced hormone responses in girls at different stages of sexual maturation.

Abstract The dependence of exercise-induced hormone responses on sexual maturation was tested in a 3-year longitudinal experiment on 34 girls (aged 11–12 years at the beginning). Sexual maturation was evaluated by Tanners five-stage scale. Children cycled for 20-min at 60% maximal oxygen uptake once a year. Cortisol, insulin, growth hormone, β-oestradiol, progesterone and testosterone concentrations in venous blood were determined by radioimmunoassay procedures. Basal concentrations of growth hormone increased and of cortisol decreased when breast stage III was reached. Reaching breast stage IV was associated with an increase in basal concentrations of β-oestradiol, progesterone and testosterone. The exercise induced significant increases in concentrations of cortisol, growth hormone and β-oestradiol and a decrease in insulin concentration. At breast stage III the increase in cortisol concentration was to a lower level [467 (SEM 42) vs 567 (SEM 46)nmol · l−1] and growth hormone concentration to a higher level [29.4 (SEM 0.5) vs 12.8 (SEM 0.4)ng · ml−1], while the fall in insulin concentration was less pronounced [postexercise level 10.6 (SEM 0.9) vs 7.8 (SEM 0.8)mU · l−1] than in stage II. The magnitude of the cortisol response was reduced in the last stage of breast development (+42.1% vs +55.5% at stage II, +66.2% at stage III, and +50.0% at stage IV). The magnitude of β-oestradiol response was the lowest in breast stage IV (+15.8%) and the highest at stage V (+41.1%). The progesterone response became significant at stage IV and testosterone response at stage V. In conclusion, we found that reaching breast stage III was associated with altered responses of cortisol, insulin and growth hormone concentrations while the responses of the sex hormone concentrations became pronounced in the last stages of sexual maturation.

Comparison of the hormonal responses to exhaustive incremental exercise in adolescent and young adult males

OBJECTIVE Evaluate hormonal responses to incremental-stage exercise (EX) test to exhaustion in adolescents. SUBJECTS AND METHODS Adolescents were tested at 16 years of age in Tanner Stage 4 (TS4) and at 17 years of age in Tanner Stage 5 (TS5) (n = 6). Adults were tested at 21 ± 1 y. (X ± SD) (n = 4) and served as controls. Blood samples were taken at rest, at the end of each EX stage. RESULTS Main effects for EX in cortisol (p < 0.01, increasing with each EX stage) and for subject group for testosterone (T) occurred (p < 0.01; TS4 < TS5, adults). Interaction effect of group by EX stage occurred for GH (p < 0.05). GH increased in response to EX in all groups, however, the magnitude of increase was significantly less for TS5 and adults than TS4. CONCLUSIONS Differences in T and GH responses for TS4 than those for TS5 and adults reflect the differing maturation levels of the endocrine system between Tanner Stages. TS5 adolescents are more similar to young adults in hormonal responses to EX than are TS4 adolescents.

Characterization of the cortisol response to incremental exercise in physically active young men.

This study examined the cortisol response to incremental exercise; specifically to see if there was an increase in blood cortisol levels at low intensity exercise (i.e., < 60% VO2 intensity threshold) and determine whether a linear relationship existed between the blood cortisol responses and exercise of increasing workloads (i.e., intensity). Healthy, physically active young men (n = 11) completed exercise tests involving progressive workload stages (3 min) to determine peak oxygen uptake responses (VO2). Blood specimens were collected at rest and at the end of each stage and analyzed for cortisol. Results showed cortisol was significantly increased from resting levels at the end of the first exercise stage (80 W; 41.9 +/- 5.4% peak VO2) and remained significantly elevated from rest until the exercise ended. Interestingly, however, the cortisol concentrations observed at 80 W through 200 W did not significantly differ from one another. Thereafter, during the final two stages of exercise the cortisol concentrations increased further (p < 0.01). The subjects exceeded their individual lactate thresholds over these last two stages of exercise. Regression modeling to characterize the cortisol response resulted in significant regression coefficients (r = 0.415 [linear] and r = 0.655 [3rd order polynominal], respectively; p < 0.05). Comparative testing (Hotelling test) between the two regression coefficents revealed the polynominal model (sigmoidal curve) was the significantly stronger of the two (p = 0.05). In conclusion, the present findings refute the concept that low intensity exercise will not provoke a significant change in blood cortisol levels and suggest the response to incremental exercise involving increasing exercise workloads (i.e., intensities) are not entirely linear in nature. Specifically, a sigmoid curve more highly accurately characterizes the cortisol response to such exercise.

Evaluation of Endocrine Activities and Hormonal Metabolic Control in Training and Overtraining

An essential task of hormones in metabolic control is to interference into cellular autoregulation and to ensure an extensive mobilization of resources of the body. Otherwise the actualization of potential capacities of the body is impossible. Accordingly, the exercise performance depends on influence of hormones on metabolic processes. Therefore, the magnitudes of hormonal responses in exercises, including competition performance, as well as their interrelations, allow us to understand the actual mobilization of various metabolic resources. However, in monitoring of training the significance of hormonal studies is not limited only by this approach. The determination of hormones can provide information on the adaptation to certain levels of exercise intensity and duration, as well as on disorders of adaptation, including exhaustion of the organism’s adaptivity and overtraining phenomena. Hormonal responses can be used for assessment of the trainable effect of exercise session and for control of the recovery period. In order to get actually information and to avoid misunderstandings and wrong depiction, several cautions and limitations must be taken into the consideration.

Cortisol and Testosterone in Exercise at the Onset of Puberty in Boys

Previous studies have failed to demonstrate that aerobic exercises increase the adrenocortical activity in prepubescent boys. The purpose of the present study was to check this fact using a longitudinal approach. Two cohorts of boys participated in a one-year follow-up. The first cohort consisted of 14 boys at sexual maturation stage 1 (age 10 to 11 years) and the second cohort of 5 boys at stage 2 (age 12 years) at the onset of the observation. Boys performed 20-min aerobic exercise on a cycle ergometer at the beginning and end of the year of observation. Before and 5 min after the exercise, blood cortisol and testosterone were determined by radioimmunoassays. Before the onset of puberty (stage 1) cortisol increase during exercise was found in only 25% of boys. Exercise induced significant increase of cortisol level after achieving sexual maturation stage 2. Testosterone response was insignificant at the first three stages of sexual maturation.

Sports Physiology and Endocrinology (Endurance vs. Resistance Exercise)

Sporting performances have continued to improve ever since records have been kept. This continued ability of athletes to improve and perform at higher levels is a function of enhanced exercise training adaptation, technological developments in equipment, and improved health–medical care. The exercise training adaptations are seen as paramount in this process and represent a more clear understanding by exercise scientist of the physiology of adaptation and the exercise stimulus to bring about those adaptations. Physiologically, one system critical in the adaptation process (“plasticity”) is the endocrine system and the hormones associated with it. Hormones serve as chemical messengers to initiate and regulate key aspects of anabolism and catabolism in cells. In the context of skeletal muscle cells, this involves enhancing contractile elements as well as energy substrate mobilization–utilization capacity, all potentially leading to improved sporting performance. With this in mind, the intent of this specific chapter is to review the responses and adjustments/adaptations of the endocrine system as affected by exercise training. Specifically, the discussion is focused on this topic as it pertains to athletes who participate in sporting activities that involve training which predominantly emphasizes endurance (e.g., distance runners) versus resistance (e.g., weight lifters) training activities.