Yudai Takarada

Evaluation of muscle damage after a rugby match with special reference to tackle plays

Objective: To investigate blood indices of muscle damage after a competitive rugby match. Methods: Fifteen elite amateur rugby players volunteered to participate (mean (SE) age 26.6 (0.7) years, height 179.8 (1.0) cm, weight 87.4 (2.2) kg, and Vo2max 58.5 (1.2) ml/kg/min). The study was conducted after two competitive matches during the 1999–2000 season. Plasma concentrations of lactate, potassium (K+), sodium (Na+), and myoglobin, and the activity of creatine kinase were measured before and after the matches. In addition, the number of tackles by and on each subject and the average duration of the work and rest periods were analysed using video recordings of the matches. Results: Myoglobin concentration and creatine kinase activity showed appreciable transient increases after the match. Peak values for myoglobin concentration (980 (166) μg/l) and creatine kinase activity (1081 (159) U/l) were observed 45 minutes and 24 hours after the match respectively. Positive and significant correlations were observed between the number of tackles and both peak myoglobin concentration (r = 0.85, p<0.01; n = 14) and peak creatine kinase activity (r = 0.92, p<0.01; n = 14). Plasma lactate and K+ concentrations also showed appreciable increases after the match, whereas plasma Na+ concentration showed a gradual decrease. The mean duration of the work and rest periods were 21.5 (2.2) and 24.3 (3.1) seconds respectively. Conclusions: The rugby matches resulted in serious structural damage to the muscles, the extent of which was highly dependent on the number of tackles.

Applications of vascular occlusion diminish disuse atrophy of knee extensor muscles.

PURPOSE We have previously shown that the combination of low-intensity resistive exercise and moderate vascular occlusion induces in humans a marked increase in growth hormone secretion and muscular hypertrophy. The present study investigated the effects of vascular occlusion on the size of thigh muscles in patients who underwent an operation for the reconstruction of the anterior cruciate ligament to see whether it attenuates the disuse muscular atrophy without any exercise combined. METHODS Two sessions of occlusive stimulus, each consisting of five repetitions of vascular occlusion (mean maximal pressure, 238 mm Hg) for 5 min and the release of occlusion for 3 min, were applied daily to the proximal end of the thigh from 3rd to 14th days after the operation. Changes in the cross-sectional area (CSA) of thigh muscles were analyzed with magnetic resonance images taken on the 3rd and 14th day after the operation. RESULTS Without occlusive stimulus (control), the CSAs of knee extensors and flexors decreased by 20.7 +/- 2.2% and 11.3 +/- 2.6% (mean +/- SEM, N = 8), whereas with the occlusive stimulus, they decreased by 9.4 +/- 1.6% and 9.2 +/- 2.6% (N = 8), respectively. The relative decrease in CSA of knee extensors was significantly (P < 0.05) larger in the control group than in the experimental group. CONCLUSION The results indicate that the occlusive stimulus effectively diminishes the postoperation disuse atrophy of knee extensors.

Effects of low-intensity resistance exercise with short interset rest period on muscular function in middle-aged women.

We investigated the effect of low-intensity resistance exercise training on muscular size and strength where the interset rest period was shortened so as to reduce the metabolite clearance. Female subjects (aged 45.4 ± 9.5 years, n = 10) performed bilateral knee extension exercises in a seated position on an isotonic leg extension machine. The exercise sessions consisted of 3 sets of exercise at a mean intensity of ∼50% 1RM with an interset rest period of 30 seconds and was performed twice a week for a period of 12 weeks. The strength and the cross-sectional area (CSA) of the knee extensors and flexors were examined with an isokinetic dynamometer and magnetic resonance imaging (MRI), respectively. The CSAs of the knee extensors and flexors increased by 7.1 ± 1.6% (p < 0.01, Wilcoxon signed rank test) and 2.5 ± 1.4% (not significant), respectively. Isometric and isokinetic strengths increased significantly (p < 0.01) at all velocities examined, whereas no significant change was observed in those of knee flexors. These results indicate that a low-intensity resistance exercise with a short interset rest period is substantially effective in inducing muscular hypertrophy and concomitant increase in strength.

Maximal Voluntary Force Strengthened by the Enhancement of Motor System State through Barely Visible Priming Words with Reward

The topic of unconscious influences on behaviour has long been explored as a means of understanding human performance and the neurobiological correlates of intention, motivation, and action. However, what is relatively unknown is whether subconsciously delivered priming stimuli, with or without rewards, can affect individuals’ maximum level of force produced with their best effort. We demonstrated using transcranial magnetic stimulation that barely visible priming of an action concept, when combined with a reward in the form of a consciously visible positive stimulus, could alter the state of the motor system. In accordance with this neurophysiological alteration, the prime-plus-reward stimuli significantly increased the hand-grip force level of maximum voluntary contraction with little conscious awareness. This is the first objective evidence that the barely conscious presence of a behavioral goal can influence the state of the motor system and arouse latent ability for human force exertion.

Hypnotic suggestion alters the state of the motor cortex

Hypnosis often leads people to obey a suggestion of movement and to lose perceived voluntariness. This inexplicable phenomenon suggests that the state of the motor system may be altered by hypnosis; however, objective evidence for this is still lacking. Thus, we used transcranial magnetic stimulation of the primary motor cortex (M1) to investigate how hypnosis, and a concurrent suggestion that increased motivation for a force exertion task, influenced the state of the motor system. As a result, corticospinal excitability was enhanced, producing increased force exertion, only when the task-motivating suggestion was provided during hypnotic induction, showing that the hypnotic suggestion actually altered the state of M1 and the resultant behavior.

Pupil dilations induced by barely conscious reward goal-priming

&NA; The topic of unconscious influences on behavior has long been explored as a way of understanding human performance and the neurobiological correlates of intention, motivation and action. Previous research using transcranial magnetic stimulation has demonstrated that barely visible priming of an action concept, when combined with reward in the form of a consciously perceived positive stimulus, can alter the state of the motor system and enhance the maximal voluntary force level. One possible explanation is that positive stimulus‐induced reward signals are processed by the dopaminergic system in the basal ganglia, motivating individuals to increase the effort they invest in particular behaviors, or to recruit the resources necessary for maintaining those behaviors. If so, given that the dopaminergic system has functionally and anatomically close connections with the noradrenergic system, we hypothesize that the state of the noradrenergic system may be enhanced by the same process. In accord with this hypothesis, we observed that barely visible goal priming with reward caused pupil dilation, suggesting that activity in the noradrenergic system increased. Importantly, this enhancement was accompanied by an unconscious increase in handgrip force. This is the first objective evidence that the pupil‐linked neuromodulatory system is related to implicit learning of the link between physical exertion and reward, probably in the noradrenergic system, resulting in more forceful voluntary motor action in the absence of conscious awareness. HighlightsBarely conscious reward goal‐priming (SR) enhances the motor system state.We investigated influence of SR on noradrenergic system by pupil dilation during SR.SR can induce pupil dilation, leading to more forceful voluntary motor action.The enhancing effect may be related to enhancement of the dopaminergic system state.Pupil dilation is related to implicit learning between physical exertion and reward.

Effect of transient vascular occlusion of the upper arm on motor evoked potentials during force exertion

We previously observed that transient vascular occlusion in volunteers increased the estimation of force exertion with no change in peripheral nerves or muscles. We hypothesized that the primary factor responsible for the overestimation of force exertion during occlusion was the centrally generated motor command, as hypothesized by McCloskey et al. (1974) and McCloskey (1978, 1981). In the present study, we tested the hypothesis that transient vascular occlusion increases the excitability of the primary motor cortex (M1) during force exertion. Healthy human volunteers lay on a bed and squeezed a dynamometer in their right hand. Repetitive gripping forces were exerted at 20%, 40%, or 60% of maximum force, with or without transient (20s) vascular occlusion of the proximal portion of the right upper arm. During the task, single-pulse transcranial magnetic stimulation was applied to the contralateral M1 to induce motor evoked potentials (MEPs) in the flexor carpi ulnaris (FCU) muscle. The MEP amplitudes were enhanced with occlusion under all conditions, with the exception of 60% contraction. In contrast, no significant difference was observed between the MEP amplitudes obtained from the occluded or non-occluded, relaxed FCU muscle. These results suggest that transient vascular occlusion increases the excitability of M1 only during force exertion.

Motivational goal-priming with or without awareness produces faster and stronger force exertion

Previous research has demonstrated that barely visible (subliminal) goal-priming with motivational reward can alter the state of the motor system and enhance motor output. Research shows that these affective-motivational effects result from associations between goal representations and positive affect without conscious awareness. Here, we tested whether motivational priming can increase motor output even if the priming is fully visible (supraliminal), and whether the priming effect occurs through increased cortical excitability. Groups of participants were primed with either barely visible or fully visible words related to effort and control sequences of random letters that were each followed by fully visible positively reinforcing words. The priming effect was measured behaviourally by handgrip force and reaction time to the grip cue after the priming was complete. Physiologically, the effects were measured by pupil dilation and motor-evoked potentials (MEPs) in response to transcranial magnetic stimulation during the priming task. Analysis showed that for both the supraliminal and subliminal conditions, reaction time decreased and total force, MEP magnitude, and pupil dilation increased. None of the priming-induced changes in behaviour or physiology differed significantly between the supraliminal and the subliminal groups, indicating that implicit motivation towards motor goals might not require conscious perception of the goals.

The impact of aerobic exercise training with vascular occlusion in patients with chronic heart failure: Aerobic exercise training with vascular occlusion in CHF

This study aimed to evaluate the impact of aerobic exercise training with vascular occlusion in patients with chronic heart failure.