The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis an...

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Creatine and Creatinine Metabolism

Resistance exercise has been shown to elicit a significant acute hormonal response. It appears that this acute response is more critical to tissue growth and remodelling than chronic changes in resting hormonal concentrations, as many studies have not shown a significant change during resistance training despite increases in muscle strength and hypertrophy. Anabolic hormones such as testosterone and the superfamily of growth hormones (GH) have been shown to be elevated during 15-30 minutes of post-resistance exercise providing an adequate stimulus is present. Protocols high in volume, moderate to high in intensity, using short rest intervals and stressing a large muscle mass, tend to produce the greatest acute hormonal elevations (e.g. testosterone, GH and the catabolic hormone cortisol) compared with low-volume, high-intensity protocols using long rest intervals. Other anabolic hormones such as insulin and insulin-like growth factor-1 (IGF-1) are critical to skeletal muscle growth. Insulin is regulated by blood glucose and amino acid levels. However, circulating IGF-1 elevations have been reported following resistance exercise presumably in response to GH-stimulated hepatic secretion. Recent evidence indicates that muscle isoforms of IGF-1 may play a substantial role in tissue remodelling via up-regulation by mechanical signalling (i.e. increased gene expression resulting from stretch and tension to the muscle cytoskeleton leading to greater protein synthesis rates). Acute elevations in catecholamines are critical to optimal force production and energy liberation during resistance exercise. More recent research has shown the importance of acute hormonal elevations and mechanical stimuli for subsequent up- and down-regulation of cytoplasmic steroid receptors needed to mediate the hormonal effects. Other factors such as nutrition, overtraining, detraining and circadian patterns of hormone secretion are critical to examining the hormonal responses and adaptations to resistance training.

Hormonal Responses and Adaptations to Resistance Exercise and Training

BackgroundThe injury risk in football is high, but little is known about causes of injury.PurposeTo identify risk factors for football injuries using a multivariate model.Study DesignProspective cohort study.MethodsParticipants were 306 male football players from the two highest divisions in Iceland. Before the 1999 football season started, the following factors were examined: height, weight, body composition, flexibility, leg extension power, jump height, peak O2 uptake, joint stability, and history of previous injury. Injuries and player exposure were recorded throughout the competitive season.ResultsOlder players were at higher risk of injury in general (odds ratio [OR] = 1.1 per year, P = 0.05). For hamstring strains, the significant risk factors were age (OR = 1.4 [1 year], P < 0.001) and previous hamstring strains (OR = 11.6, P < 0.001). For groin strains, the predictor risk factors were previous groin strains (OR = 7.3, P = 0.001) and decreased range of motion in hip abduction (OR = 0.9 [1°], P = 0...

Risk factors for injuries in football.

CARDINALE, M., and C. BOSCO. The use of vibration as an exercise intervention. Exerc. Sport Sci. Rev., Vol. 31, No. 1, pp. 3–7, 2003. The use of vibration as a means for enhancing athletic performance is a recent issue in exercise physiology. Current evidence suggests that vibration is effective in

The Use of Vibration as an Exercise Intervention

The reliability of power in tests of physical performance affects the precision of assessment of athletes, patients, clients and study participants. In this meta-analytic review we identify the most reliable measures of power and the factors affecting reliability. Our measures of reliability were the typical (standard) error of measurement expressed as a coefficient of variation (CV) and the percent change in the mean between trials. We meta-analysed these measures for power or work from 101 studies of healthy adults. Measures and tests with the smallest CV in exercise of a given duration include field tests of sprint running (∼0.9%), peak power in an incremental test on a treadmill or cycle ergometer (∼0.9%), equivalent mean power in a constant-power test lasting 1 minute to 3 hours on a treadmill or cycle ergometer (0.9 to 2.0%), lactate-threshold power (∼1.5%), and jump height or distance (∼2.0%). The CV for mean power on isokinetic ergometers was relatively large (>4%). CV were larger for nonathletes versus athletes (1.3 ×), female versus male nonathletes (1.4 ×), shorter (∼1-second) and longer (∼1-hour) versus 1-minute tests (≤1.6 ×), and respiratory- versus ergometer-based measures of power (1.4 to 1.6 ×). There was no clear-cut effect of time between trials. The importance of a practice trial was evident in studies with >2 trials: the CV between the first 2 trials was 1.3 times the CV between subsequent trials; performance also improved by 1.2% between the first 2 trials but by only 0.2% between subsequent trials. These findings should help exercise practitioners and researchers select or design good measures and protocols for tests of physical performance.

Reliability of Power in Physical Performance Tests

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.

Hormonal responses to whole-body vibration in men.

Summary 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<0AE05‐0AE005). 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.

/pdf/adaptive-responses-of-human-skeletal-muscle-to-vibration-ay6293tzqq.pdf

Adaptive responses of human skeletal muscle to vibration exposure

The aim of this study was to evaluate the in- fluence of vibration on the mechanical properties of arm flexors. A group of 12 international level boxers, all members of the Italian national team, voluntarily par- ticipated in the experiment: all were engaged in regular boxing training. At the beginning of the study they were tested whilst performing forearm flexion with an extra load equal to 5% of the subjects' body mass. Following this, one arm was given the experimental treatment (E; mechanical vibration) and the other was the control (no treatment). The E treatment consisted of five repetitions lasting 1-min each of mechanical vibration applied during arm flexion in isometric conditions with 1 min rest between them. Further tests were performed 5 min immediately after the treatment on both limbs. The results showed statistically significant enhancement of the average power in the arm treated with vibrations. The root mean square electromyogram (EMGrms) had not changed following the treatment but, when divided by mechanical power, (P) as an index of neural eA- ciency, it showed statistically significant increases. It was concluded that mechanical vibrations enhanced muscle P and decreased the related EMG/P relationship in elite athletes. Moreover, the analysis of EMGrms re- corded before the treatment and during the treatment itself showed an enormous increase in neural activity during vibration up to more than twice the baseline values. This would indicate that this type of treatment is able to stimulate the neuromuscular system more than other treatments used to improve neuromuscular properties.

/pdf/influence-of-vibration-on-mechanical-power-and-4hqs9eways.pdf

Influence of vibration on mechanical power and electromyogram activity in human arm flexor muscles.

The validation of a new dynamometer for evaluation of dynamic muscle work is presented. The device was based on a precise measurement of load displacements of any machine using gravitational loads as external resistance. It allowed, through a sensor consisting of an infrared photo interrupter, the calculation of velocity, force and power during concentric, eccentric and stretch-shortening cycle activity. To validate the dynamometer 33 male and female track and field athletes (12 throwers and 21 jumpers) participated in the study. The throwers (4 women and 8 men) were asked to perform half-squat exercises on a slide machine with a load of 100% of the subject's body mass. The day-to-day reproducibility of half-squat exercises gave a correlation coefficient ofr = 0.88, 0.97 and 0.95 for average push-off force (AF), average push-off velocity (AV), and average push-off power (AP) respectively. Comparison of half-squat measurements was performed against jumping and running test evaluation by the jumpers (7 women and 14 men). The interrelationships among the different variables studied demonstrated a strong correlation between AF, AV and AP and sprinting and jumping parameters (r = 0.53−0.97;P < 0.05−0.001). Using values of AF, AV and AP developed in half-squat exercises executed with different loads, ranging from 35% to 210% of the subject's body mass, it was also possible to establish the force-velocity and power-velocity relationships for both male and female jumpers. In any individual case, the maximal error due to the measurement system was calculated to be less than 0.3%, 0.9% and 1.2% for AF, AV, and AP respectively. Given the accuracy of the ergometer, the high reliability found between 2 days of measurements, and the specificity of the results it is suggested that the dynamic dynamometer would be suitable for evaluation of athletes performing specific skills. In addition, because single and multiple joint movements involving appropriate muscle groups can be easily performed, physiological characteristics could be evaluated for both athletic and rehabilitation purposes. Therefore, because of its simplicity of use and application, and its low cost the dynamometer would be suitable for both laboratory and field conditions.

C. Bosco

Papers

The Use of Vibration as an Exercise Intervention

Hormonal responses to whole-body vibration in men.

Adaptive responses of human skeletal muscle to vibration exposure

Influence of vibration on mechanical power and electromyogram activity in human arm flexor muscles.

A dynamometer for evaluation of dynamic muscle work