Asymmetry of paraspinal EMG-time characteristics in idiopathic scoliosis.

The purpose of this study was to investigate the activation pattern of the paraspinal muscles in scoliotic and normal subjects. Force-time and electromyography (EMG)-time curves of paraspinal muscles were recorded during maximal isometric trunk extensions in 15 girls with adolescent idiopathic scoliosis (AIS) and in 14 healthy girls with structurally normal spines. The isometric force-time curves as well as the maximal integrated electromyography (IEMG) activities that were recorded from both sides of the thoracic and lumbar spine did not show any significant differences between the two subject groups. However, in the subjects with AIS, the IEMG activities recorded at the onset and during the early (submaximal) phases of muscle contraction were significantly higher in the left lumbar muscles compared with the right side. The observed intensity-specific EMG asymmetry in the present scoliotic subjects may be attributed to the imbalanced neural input associated with AIS that may also have pathogenetic importance in the etiology of idiopathic scoliosis.

Hormonal adaptations and modelled responses in elite weightlifters during 6 weeks of training.

The concentrations of serum testosterone, sex-hormone-binding-globulin (SHBG) and luteinizing hormone (LH) were examined throughout 1-year of training in six elite weightlifters. A systems model, providing an estimation of fatigue and fitness, was applied to records of training volume and performance levels in clean and jerk. The analysis focused on a 6-week training period during which blood samples were taken at 2-week intervals. A 4-week period of intensive training (period I) could be distinguished from the following 2-week period of reduced training (period II). During period I, decreases in serum testosterone (P less than 0.05) and increases in serum LH concentrations (P less than 0.01) were observed; a significant correlation (r = 0.90, P less than 0.05) was also observed between the changes in serum LH concentration and in estimated fitness. The magnitude of LH response was not related to the change in serum androgens. On the other hand, the change in testosterone:SHBG ratio during period II was significantly correlated (r = 0.97, P less than 0.01) to the LH variations during period I. These finding suggested that the LH response indicated that the decrease in testosterone concentration was not primarily due to a dysfunction of the hypothalamic-pituitary system control, and that the fatigue/fitness status of an athlete could have influenced the LH response to the decreased testosterone concentration. The negative effect of training on hormonal balance could have been amplified by its influence on the hypothalamic-pituitary axis. A decrease in physiological stress would thus have been necessary for the completion of the effect of LH release on androgenic activity.

Neuromuscular adaptations during short-term "normal" and reduced training periods in strength athletes.

Neuromuscular adaptations during a 2-week "normal" strength training period followed by a 1-week reduced training period were investigated in ten strength athletes. No systematic changes were observed in the maximal voluntary neural activation (averaged integrated EMG) of leg extensor muscles, in the cross-sectional area (CSA) of the QF muscle or in maximal voluntary isometric force production characteristics of the leg extensor muscles in the whole subject sample over the entire strength training period of 3 weeks. However, significant increases were observed both in the maximal neural activation (p less than 0.05) and maximal force (from 4547 +/- 613 to 4923 +/- 901 N; p less than 0.05) of the muscles at the very end of the 1-week reduced training period in group A which consisted of five best strength athletes within the whole subject group. In group B consisting of five other athletes at a lower level no systematic changes were observed during the reduced training period. The present findings suggest that neuromuscular adaptations in strength athletes are very limited in magnitude at least during short term strength training. Maximal strength performance in highly trained strength athletes may be brought to the peak level not necessarily during "normal" strength training but more likely after some period of time with a reduced volume of training. The present observations support the concept of the periodization of training in highly trained strength athletes and indicate the important role of the nervous system in leading to the peak in their maximal strength.

Physiological performance capacity in different prepubescent athletic groups.

Endurance, strength and speed capacity were investigated among prepubescent male weight lifters (EL), endurance runners (ER) and sprint runners (SR). The subjects were selected by their coaches and all of them were classified as promising and successful junior athletes in the age groups of 10-13 years. Twelve boys belonged to athletic group (AG) and their performance capacity was compared to normally active control (C) boys (n = 9). Biological age was significantly (p less than 0.05) greater in AG (11.3 +/- 0.9 years) than in C (10.2 +/- 1.4 years) but in chronological age there was no difference between the groups. Maximal oxygen uptake was significantly (p less than 0.05) higher in AG (62.3 +/- 3.1 ml.kg-1.min-1) than in C (55.4 +/- 7.7 ml.kg-1.min-1). The endurance runners had the highest value (66.5 +/- 2.9 ml.kg-1.min-1). In anaerobic characteristics there were no significant differences. The rise of centre of gravity (0.26 +/- 0.03 m) of AG in a test for the best drop jump was clearly (p less than 0.05) higher than that (0.22 +/- 0.03 m) of C. The weight lifters and sprint runners were the best in the test for force production. AG had significantly (p less than 0.01) shorter choice reaction time (261 +/- 39 ms) than C (344 +/- 81 ms). Testosterone correlated with jump performances (p less than 0.05), biological age (p less than 0.01) and chronological age (p less than 0.001). Growth hormone correlated significantly only with biological age (p less than 0.05) and testosterone (p less than 0.001). In conclusion, endurance capacity (aerobic) and strength capacity were greater in the athletic group than in the control group and it was suggested that training background and more advanced biological maturation of the athletes affected especially their strength capacity. The parameters used in this investigation can be utilized for talent selection in sport.

A systems model of training responses and its relationship to hormonal responses in elite weight-lifters.

A systems model, providing an estimation of fatigue and fitness levels was applied to a 1-year training period of six elite weight-lifters. The model parameters were individually determined by fitting the predicted performance (calculated as the difference between fitness and fatigue) to the actual one. The purpose of this study was to validate the systems model by comparing the estimated levels of fatigue and fitness with biological parameters external to the model calculation. The predicted and the actual performances were significantly correlated in each subject. The calculated fitness and fatigue levels were related to serum testosterone concentration, testosterone: cortisol and testosterone: sex hormone binding globulin ratios. The best results were obtained by the comparison between fitness and testosterone levels, which varied in parallel in each subject. In two subjects this correlation was significant (r = 0.91, P less than 0.05, and r = 0.92, P less than 0.01). The fitness changes calculated in each subject between the 15th and the 51st weeks of training were significantly correlated with the changes in serum testosterone concentration measured in the same period (r = 0.99, P less than 0.001). For the whole group testosterone and fitness variations were also significantly intercorrelated (r = 0.73, P less than 0.001). Correlations, less homogeneous and less significant, were calculated also for other hormones and ratios. These results suggest that (1) the relationships between training and performance can be described by the systems model, (2) the estimated index of fitness has a physiological meaning. The fatigue index remains to be clarified.

Daily changes in neural activation, force-time and relaxation-time characteristics in athletes during very intense training for one week.

Daily changes in neural activation, force-time and relaxation characteristics of the leg extensor muscles were examined in 8 elite strength athletes during a very intense strength training period with two daily sessions for one week. The maximal neural activation (integrated EMG) of the muscles and their maximal isometric extension force remained statistically unaltered during the entire experimental period. Average integrated EMG of the muscles during the rapid relaxation phase of the isometric contraction and the relaxation-time curve remained statistically unaltered as well. However, considerable decreases (p less than 0.05-0.001) occurred both in the neural activation and in the force production in the early phases of the rapid isometric contraction during the course of the one-week period. After one full day of rest only slight and statistically nonsignificant changes took place in the mean values of the neuromuscular performance variables examined. The present findings indicate that the high overall daily volume of heavy resistance strength training stimuli may have a considerable role in leading to temporary worsening specifically in the rapid neural activation and correspondingly in rapid force production of the neuromuscular performance capacity even during a very short training period. In athletic training the volume of these types of training stimuli should therefore be carefully considered and matched with the specific purpose of the training season and with the specific requirements of various athletic activities.

Specificity of endurance, sprint and strength training on physical performance capacity in young athletes.

Three prebubescent athlete groups of endurance runners (E; n = 4), sprinters (S; n = 4) and weightlifters (WL; n = 4) and one control group (C; n = 6) as well as one junior but postpubescent weightlifter group (JWL; n = 6) volunteered as subjects in order to investigate specific effects of endurance, sprint and strength training on physical performance capacity during a 1 year follow-up period. The prepubescent E-group had higher (p less than 0.05) VO2 max (66.5 +/- 2.9 ml x kg1 x min-1) already at the beginning of the study than the other three groups. The prepubescent WL-group demonstrated greater (p less than 0.05) maximal muscular strength than the E-group and the WL-group increased its strength greatly by 21.4% (p less than 0.05) during the follow-up. No significant differences were observed in physical performance capacity between the prepubescent WL- and S-groups. Both groups demonstrated a slightly (ns.) better force-time curve recorded from the leg extensor muscles than the E-group and significant (p less than 0.05) increases occurred in these two groups in dynamic explosive performance during the follow-up. The postpubescent JWL-group demonstrated much greater (p less than 0.001) muscular mass and maximal strength than the prepubescent groups. No significant changes occurred in explosive types of performances in these athletes but significant (p less than 0.05) increase took place in the maximal neural activation and strength of the leg extensor muscles during the 1 year.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum hormone concentrations during prolonged training in elite endurance-trained and strength-trained athletes.

A study of 1 year was performed on nine elite endurance-trained athletes (swimmers) and on eight elite strength-trained athletes (weightlifters) in order to examine the effects of training on the endocrine responses and on physical performance capacity. The measurements for the determination of serum hormone concentrations were performed at about 4-month intervals during the course of the year. The primary findings demonstrated that during the first and most intensive training period of the year in preparing for the primary competitions similar but statistically insignificant changes were observed in the concentrations of serum testosterone, free testosterone and cortisol in both the endurance-trained and strength-trained groups. After that period the changes in hormonal response over the year were infrequent and minor. A significant (p less than 0.01) decrease occurred in the strength-trained group in serum-free testosterone during the second period, which was characterized by the highest overall amount of training. Over the entire year the concentrations of serum hormones remained statistically unaltered in both groups. Slight but statistically insignificant increases of 1.2% +/- 0.8% and 2.1% +/- 5.1% were observed in the competitive performances over the year in the endurance-trained and strength-trained groups, respectively. The present findings in the two groups of elite athletes, who differed greatly with regard to the type of physiological loading, demonstrated that the overall hormonal responses both during the most intensive and during prolonged training periods were rather similar and the infrequent small changes remained well within the normal physiological range.(ABSTRACT TRUNCATED AT 250 WORDS)

Daily hormonal and neuromuscular responses to intensive strength training in 1 week.

Daily adaptive responses in the neuromuscular and endocrine systems to a 1-week very intensive strength training period with two training sessions per day were investigated in eight elite weight lifters. The morning and the afternoon sessions resulted in acute decreases (P less than 0.05-0.01) in maximal isometric strength and in the maximal neural activation (iEMG) of the leg extensor muscles, but the basic levels remained unaltered during the entire training period. Significant (P less than 0.05-0.01) acute increases in serum total and free testosterone levels were found during the afternoon sessions. During the 1-week training period, serum total and free testosterone concentrations decreased gradually (P less than 0.05-0.001) as observed in the basic morning values before the sessions, but after 1 day of rest serum total and free testosterone reached (P less than 0.01 and 0.05) the pretraining level. The sessions resulted also in acute changes (P less than 0.05-0.01) in serum cortisol and somatotropin concentrations, but the basic morning levels did not change during the training period. The present findings suggest that during a short period of intense strength training the changes especially in serum testosterone concentrations indicate the magnitude of physiologic stress of training. The acute changes in serum hormone concentrations during a period of a few days do not, however, necessarily directly imply the changes in performance capacity. A longer period of follow-up lasting a few weeks is probably needed if an individual trainability status of a strength athlete is to be evaluated on the basis of the hormone determinations.

Neuromuscular and hormonal adaptations in athletes to strength training in two years.

Neuromuscular and hormonal adaptations to prolonged strength training were investigated in nine elite weight lifters. The average increases occurred over the 2-yr follow-up period in the maximal neural activation (integrated electromyogram, IEMG; 4.2%, P = NS), maximal isometric leg-extension force (4.9%, P = NS), averaged concentric power index (4.1%, P = NS), total weight-lifting result (2.8%, P less than 0.05), and total mean fiber area (5.9%, P = NS) of the vastus lateralis muscle, respectively. The training period resulted in increases in the concentrations of serum testosterone from 19.8 +/- 5.3 to 25.1 +/- 5.2 nmol/l (P less than 0.05), luteinizing hormone (LH) from 8.6 +/- 0.8 to 9.1 +/- 0.8 U/l (P less than 0.05), follicle-stimulating hormone (FSH) from 4.2 +/- 2.0 to 5.3 +/- 2.3 U/l (P less than 0.01), and testosterone-to-serum sex hormone-binding globulin (SHBG) ratio (P less than 0.05). The annual mean value of the second follow-up year for the serum testosterone-to-SHBG ratio correlated significantly (r = 0.84, P less than 0.01) with the individual changes during the 2nd yr in the averaged concentric power. The present results suggest that prolonged intensive strength training in elite athletes may influence the pituitary and possibly hypothalamic levels, leading to increased serum levels of testosterone. This may create more optimal conditions to utilize more intensive training leading to increased strength development.

Neuromuscular and hormonal responses in elite athletes to two successive strength training sessions in one day.

Acute neuromuscular and endocrine adaptations to weight-lifting were investigated during two successive high intensity training sessions in the same day. Both the morning (I) (from 9.00 to 11.00 hours) and the afternoon (II) (from 15.00 hours to 17.00 hours) training sessions resulted in decreases in maximal isometric strength (p less than 0.01 and less than 0.05), shifts (worsening) in the force-time curve in the absolute scale (p less than 0.05 and ns.) and in decreases in the maximal integrated EMG (p less than 0.01 and less than 0.05) of the selected leg extensor muscles. Increases in serum total (p less than 0.05) and free testosterone (p less than 0.01) and in cortisol (p less than 0.01) concentrations were found during training session II. These were followed by decreases (p less than 0.001 and p less than 0.01 and ns.) in the levels of these hormones one hour after the termination of the session. The responses during the morning training session were different with regard to the decreases in serum total testosterone (p less than 0.05), free testosterone (ns.) and cortisol (p less than 0.05). Only slight changes were observed in the levels of luteinizing hormone and sex hormone-binding globulin during the training sessions. Increases (p less than 0.01) took place in somatotropin during both training sessions. The present findings suggest that high intensity strengthening exercises may result in acute adaptive responses in both the neuromuscular and endocrine systems. The diurnal variations may, however, partly mask the exercise-induced acute endocrinological adaptations in the morning.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between training volume, physical performance capacity, and serum hormone concentrations during prolonged training in elite weight lifters.

A follow-up study of 1 year was performed on 11 male elite weight lifters. Several parameters including training volume, weight lifting performance, and serum hormone concentrations were measured during seven test occasions. In addition, the same measurements were repeated three times during a 6-week period preceding the primary competition, which took place about 5 months after beginning of the follow-up. The primary findings were observed during the 6-week period from which the first 2 weeks of stressful training was associated with significant decreases (P less than 0.01-0.001) in serum testosterone concentration, in testosterone/cortisol and in testosterone/SHBG ratios, and with a significant (P less than 0.001) increase in serum LH concentration. The individual changes during the stressful training in serum testosterone/SHBG ratio were related (r = .63; P less than 0.05) to the individual changes in the weight lifting result in the clean and jerk lift. During the following "normal" 2-week and reduced 2-week training periods, the concentration of serum testosterone remained unaltered, but serum cortisol and serum LH decreased significantly (P less than 0.05-0.01). During these periods, the serum testosterone/SHBG ratio increased (P less than 0.01). The individual changes during this preparatory 4-week training before the primary competition in serum testosterone/SHBG ratio and the individual changes in the weight lifting result in the clean and jerk lift correlated significantly with each other (r = .68; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

EMG, muscle fibre and force production characteristics during a 1 year training period in elite weight-lifters.

The effects of a 1 year training period on 13 elite weight-lifters were investigated by periodical tests of electromyographic, muscle fibre and force production characteristics. A statistically non-significant increase of 3.5% in maximal isometric strength of the leg extensors, from 4841 +/- 1104 to 5010 +/- 1012 N, occurred over the year. Individual changes in the high force portions of the force-velocity curve correlated (p less than 0.05-0.01) with changes in weight-lifting performance. Training months 5-8 were characterized by the lowest average training intensity (77.1 +/- 2.0%), and this resulted in a significant (p less than 0.05) decrease in maximal neural activation (IEMG) of the muscles, while the last four month period, with only a slightly higher average training intensity (79.1 +/- 3.0%), led to a significant (p less than 0.01) increase in maximum IEMG. Individual increases in training intensity between these two training periods correlated with individual increases both in muscular strength (p less than 0.05) and in the weight lifted in the clean & jerk (p less than 0.05). A non-significant increase of 3.9% in total mean muscle fibre area occurred over the year. The present findings demonstrate the limited potential for strength development in elite strength athletes, and suggest that the magnitudes and time courses of neural and hypertrophic adaptations in the neuromuscular system during their training may differ from those reported for previously untrained subjects. The findings additionally indicate the importance of training intensity for modifying training responses in elite strength athletes.

Electromyographic and force production characteristics of leg extensor muscles of elite weight lifters during isometric, concentric, and various stretch-shortening cycle exercises.

Electromyographic and force production characteristics of leg extensor muscles of elite weight lifters (n = 14) were examined during isometric, concentric, and various stretch-shortening cycle exercises. The data showed that utilization of stored elastic energy of leg extensor muscles was observable in countermovement jumping (CMJ) conditions performed at various loads. These greater (P less than 0.01-0.001) vertical jumping heights obtained in CMJ conditions in comparison to the respective squat jumps (SJ) took place at all loads examined from 0 up to 180 kg with no differences in the average IEMG activity between the concentric phases of the performances. In various dropping jumps (from 20 to 100 cm), the average jumping heights were not, however, greater than in the squat jump. The jumping heights both in SJ and CMJ correlated negatively (r = -0.56 and -0.58; P less than 0.05) with the time of isometric force production. Maximal isometric force correlated (r = 0.61; P less than 0.01) with the thigh girth but not (r = 0.22; NS) with the mean muscle fiber area of the vastus lateralis muscle. The jumping heights in SJ and CMJ performed with higher (100-140 kg) loads correlated more significantly (r = 0.76-0.79; P less than 0.01-0.001) than that of maximal isometric force (r = 0.47-0.67; P less than 0.05-0.01) with the results in the Olympic weight lifting. The present findings indicate the important role of effective recoil of the elastic energy in the muscle during the stretch-shortening cycle.(ABSTRACT TRUNCATED AT 250 WORDS)