Atko 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.

Monitoring strength training: neuromuscular and hormonal profile

PURPOSE This study investigated changes induced by a single heavy resistance training session on neuromuscular and endocrine systems in trained athletes, using the same exercises for training and testing. METHODS Five different groups volunteered: track and field male sprinters (MS, N = 6), track and field female sprinters (FS, N = 6), body builders (BB, N = 6), and weight lifters performing low-repetition exercise (WLL, N = 4) and high-repetition exercise (WLH, N = 4). In training, the work performed during half and full squat exercise was monitored for mechanical power output as well as EMG analysis on leg extensor muscles of the subjects belonging to the MS, FS, and BB groups. Just before and immediately after the training session, venous blood samples were obtained for RIA determination of testosterone (T), cortisol (C), lutropin (LH), human prolactin (PRL), and follitropin (FSH) in FS and MS. In the other three groups (BB, WLH, and WLL), the hormonal profile was limited to T and human growth hormone (hGH) only. RESULTS After training the power developed in full squat demonstrated a statistically significant decrease (P < 0.01) in MS and no changes in FS. The EMG activity remained constant during the training session. Consequently, the EMG/Power ratio increased in both MS and FS, although only in MS a statistical significance was noted (P < 0.05). In MS immediately after the session the levels of C, T, and LH were significantly lower (P < 0.05). No changes were found in FS. In both groups and in BB significant negative correlation was found between changes in T level and EMG/Power ratio in half squat performance. CONCLUSIONS It is likely that adequate T level may compensate the effect of fatigue in FT fibers by ensuring a better neuromuscular efficiency.

Research Methodology: Endocrinologic Measurements in Exercise Science and Sports Medicine

OBJECTIVE To provide background information on methodologic factors that influence and add variance to endocrine outcome measurements. Our intent is to aid and improve the quality of exercise science and sports medicine research endeavors of investigators inexperienced in endocrinology. BACKGROUND Numerous methodologic factors influence human endocrine (hormonal) measurements and, consequently, can dramatically compromise the accuracy and validity of exercise and sports medicine research. These factors can be categorized into those that are biologic and those that are procedural-analytic in nature. RECOMMENDATIONS Researchers should design their studies to monitor, control, and adjust for the biologic and procedural-analytic factors discussed within this paper. By doing so, they will find less variance in their hormonal outcomes and thereby will increase the validity of their physiologic data. These actions can assist the researcher in the interpretation and understanding of endocrine data and, in turn, make their research more scientifically sound.

Steroid and pituitary hormone responses to rowing: relative significance of exercise intensity and duration and performance level

SummaryTo analyse the relative significance of exercise intensity and duration as well as of performance capacity, hormone changes were recorded in 16 male rowers in two experiments separated by a year. The test exercises consisted of 7-min (at the supramaximal intensity) and 40-min rowing (at the level of the anaerobic threshold) on a rowing apparatus. In addition, somatotropin and cortisol responses were estimated in rowing for 8 × 2000 m in 14 rowers of national class. All three tests caused significant increases in somatotropin and cortisol concentrations in the blood. Follitropin concentrations were elevated in the 7-min exercise test in the second experiment and in the 40-min exercise test in both experiments. Lutropin and progesterone concentrations increased during the more prolonged exercise in the first experiment. No common change was found in testosterone concentrations. Cortisol and somatotropin responses to the 40-min rowing test at anaerobic threshold were more pronounced than to the 7-min exercise test at supramaximal intensity. When the rowers achieved a national class level of performance (the second experiment) the hormone responses to 7-min supramaximal exercise were increased. During the 8 × 2000-m rowing test cortisol but not somatotropin concentration increased to an extremely high level in the rowers of national class. It is concluded that in strenuous exercise cortisol and somatotropin responses were triggered by the exercise intensity threshold. The exact magnitude of the response would seem to have depended on additional stimuli caused by exercise duration and on possibility of mobilizing hormone reserves.

Motor performance status in 10 to 17‐year‐old Estonian girls

The improvement of motor abilities is associated with the periodical acceleration of changes in adolescents of both sexes. The present cross‐sectional study is aimed at establishing smooth curves of motor performance status in 10 to 17‐year‐old girls. Motor performance was tested in 902 girls with the aid of 30 m dash, standing long jump, vertical jump, pushing a stuffed ball (2 kg), standing quintuplet jump, isometric strength of back extensor muscles, trunk forward flexion and 1‐min ergocycling at the highest possible rate. Statistically significant differences of all studied motor abilities between the age groups of 10–12 were indicated. In height and body mass the most pronounced differences (on average 6.5 cm and 7.7 kg, respectively) appeared between the age groups of 12 and 13. At the age of 13 the group results were statistically higher than those at 12 in pushing a stuffed ball, vertical jump, quintuplet jump, strength of back extensors muscle, 30 m dash and ergocycling test, but not in standing long jump and trunk forward flexion. At the age of 14 the performance was not higher than at 13, except in the vertical jump and quintuplet jump. From 14 to 16 years of age differences reappeared in the results of vertical jump, quintuplet jump, pushing a stuffed ball, 1‐min cycling and trunk forward flexion but not in the 30 m dash and standing long jump. The lack of significant differences between the age groups of 16 and 17 indicated the final stabilization of tested motor abilities. The obtained results suggest the existence of several periods in motor performance status in 10 to 17‐year‐old Estonian girls: 1) The biggest differences in the mean results of the tests on motor abilities occurred between ages 10–11, 11–12 and 12–13, which coincide with the biggest differences in height and weight at the same age. 2) The differences in the mean results of most tests on motor abilities stabilized between the age groups of 13 and 14. The mean results of 14‐year‐old girls were lower in some tests compared to the results of 13‐year‐olds. 3) The positive differences in the mean results remained between the age groups of 14–15 and 15–16 (excluding the sprint velocity and standing long jump). 4) The final stabilization of motor abilities occurred at the age of 16 to 17.

The effect of a single-circuit weight-training session on the blood biochemistry of untrained university students

SummaryThe metabolic and hormonal responses to an intensive single-circuit weight-training session were studied in 15 untrained male students. The training programme consisted of ten exercises, employing all the large groups of muscles. Students performed three circuits using a work-to-rest ratio of 30 s:30 s at 70% of one-repetition maximum. The whole programme lasted 30 min. Blood samples were obtained from the anticubital vein 30 min before exercise, immediately after exercise finished and after 1-h, 6-h, and 24-h periods of recovery.The training session produced significant increases in the plasma adrenocorticotropic hormone, cortisol, aldosterone, testosterone, progesterone and somatotropin concentrations. The plasma level of insulin and C-peptide remained unchanged. The strength exercises caused elevated ratios of cortisol:testosterone and cortisol:insulin, indicating a prevalence of stimulation of catabolic processes as well as of mobilization of energy reserves but during the recovery period the reverse of this was observed. Immediately after exercise the mean lactate concentration was 7.19 mmol · 1−1, SD 0.56, the glucose concentration increased significantly during exercise and decreased rapidly during recovery. The high density lipoprotein-cholesterol increased in 1-h period of recovery compared with the initial level. The concentration of total cholesterol, low density lipoprotein-cholesterol and triglyceride, did not change. Packed cell volume did not change during exercise or recovery.

Mobilisation of Structural Proteins During Exercise

SummaryIn general, the mobilisation of structural proteins is necessary for enzyme synthesis and for renewing cellular structures with amino acids and precursors of nucleone acids. However, during exercise the adaptive synthesis of proteins occurs only in the liver to some extent. In muscle tissue most protein synthesis is suppressed, although the synthesis of certain proteins in muscle remains unchanged or even increases. The general suppression of protein synthesis in muscle leaves much of the free amino acid pool unused. The break- down of tissue proteins may also increase in various tissues, but there is no convincing evidence for proteolysis of contractile proteins in active muscle.As a result of these processes, an increased pool of available free amino acids is created. The main use of free amino acids is connected with the energy requirement of muscular activity, through the oxidation of branched-chain amino acids and the use of alanine in gluconeogenesis. In active muscles the output of alanine is increased. It is based on usage of pyruvate, which is produced in increased amounts due to intensified glycogenosis and glycolysis, and of amino groups, which are liberated in oxidation of branched-chain amino acids. In the liver, alanine is consumed. The carbon skeleton of alanine is required for gluconeogenesis and the liberated amino groups are used in ureagenesis. The branched- chain amino acids are transported from the liver to active muscle for their oxidation. The increases in the free amino acid pool, in the rate of the glucose-alanine cycle, and in the use of amino acids in the liver are stimulated by an increased level of glucocorticoids and a decreased level of insulin during exercise.During recovery after exercise the use of amino acids for adaptive protein synthesis is intensified. This coincides with a persistently high rate of protein breakdown, constituting an increased rate of protein turnover. During recovery, the production of 3-methylhistidine by previously active muscles increases. It results in an increase in urinary output of 3- methylhistidine after exercise. Immediately after exercise the level of free 3-methylhistidine is elevated in the intestine for only a short time and the fact that it does not contribute significantly to the delayed increase in the excretion of 3-methylhistidine excretion after exercise must be considered as a sign of increased turnover of contractile proteins, helping to restore a good contractile function. Thus, the mobilisation of structural proteins gives an additional energy for contracting muscles during exercise and creates conditions for recovery and development of active cellular structures after exercise.

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.

Postexercise recovery period: carbohydrate and protein metabolism

The essence of the postexercise recovery period is normalization of function and homeostatic equilibrium, and replenishment of energy resources and accomplishment of the reconstructive function. The repletion of energy stores is actualized in a certain sequence and followed by a transitory supercompensation. The main substrate for repletion of the muscle glycogen store is blood glucose derived from hepatic glucose output as well as from consumption of carbohydrates during the postexercise period. The repletion of liver glycogen is realized less repidly. It depends to a certain extent on hepatic gluconeogenesis but mainly on supply with exogenous carbohydrates. The constructive function is founded on elevated protein turnover and adaptive protein synthesis. Whereas during and shortly after endurance exercise intensive protein breakdown was found in less active fast‐twitch glycolytic fibers, during the later course of the recovery period the protein degradation rate increased together with intensification of protein synthesis rate in more active fast‐twitch glycolytic oxidative and slow‐twitch oxidative fibers.

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.