CHANGES IN SOMATOSENSORY INPUT FOLLOWING LOCAL MUSCLE FATIGUE / 体力科学

We studied whether exercise fatigue affects somatosensorv input using somatosensory evoked potential (SEP) . Sixteen subjects performed intermittent grip strength exercises with muscle fatigue while ignoring electrical stimulation given to an elbow. We induced SEP in the exercise task (during contraction) in every stage (first stage, middle stage and final stage) . In addition, we induced SEP in the exercise task during relaxation in the first stage and final stage. As a result, the early component amplitude of SEP decreased with the progress of exercise (manifestation of muscle fatigue) during contraction and relaxation. Our findings suggested that somatosensory input decreased with the manifestation of muscle fatigue. Somatosensory input is necessary for control of voluntary movement. Therefore, we speculate that these factors play a role in decreased performance of athletes competing in long-duration events.

FATIGABILITY OF MOTOR UNITS IN FIRST DORSAL INTEROSSEUS MUSCLE EVALUATED USING COLLISION METHOD / 体力科学

We evaluated motor unit (MU) fatigue in the first dorsal interosseous muscle (FDI) using the collision principle. Eight healthy men exerted 70% (short-duration fatigue task: SDF task) and 30% (long-duration fatigue task: LDF task) maximum voluntary contraction of isometric abductions in the left FDI until exhausted. Before and after voluntary contractions, the ulnar nerve was stimulated at the wrist and elbow with supramaximal intensity, and a pair of M-waves was obtained. Fatiguerelated changes were studied in mean power frequency (MPF), averaged rectified value (ARV) calculated from surface EMG, and motor nerve conduction velocity (MCV) and distribution of motor nerve conduction velocity (DMCV) calculated from M-waves. The MPF of voluntary EMG decreased, whereas ARV increased significantly during SDF and LDF tasks, indicating fatigue had developed in the FDI. Endurance was significantly shorter in the SDF task than in the LDF task (p<0.01), whereas differences between tasks were not seen in MPF and ARV changes. Tasks did not affect MCV, but lower components in DMCV increased for both tasks. Increased lower components were larger in the LDF task than in the SDF task. The shift in DMCV indicated that fatigued MUs stopped activity and enduring MUs, which had lower axon conduction velocity, were activated selectively. These results suggest that the collision principle is applicable in evaluating motor unit fatigability.

The mechanism of the latent reacyion time in the elderly men. Differance by the task completions / 体力科学

The mechanism of the latent reaction time in task completion in elderly men was investigated by comparing the reaction time (RT), EMG-RT and motor time (MT) in young and elderly men. The motor performance was recorded as task completion through as a WS-RS, simple reaction or a choice reaction for each movement using a handgrip and switch.<BR>In this study, we found that the RT and EMG-RT of elderly men in all movements of WS-RS and choice reaction tasks were significantly longer than those of young men, especially in the choice reaction tasks were striking. Moreover, the MT of elderly men in all tasks was significantly longer than those of young men.<BR>These findings suggest that the latent RT and EMG-RT in a choice reaction task may be due to relayed information processing through as the discrimination and cognition functions in the brain, and that it may be also influenced by the mechanism of the latent reaction time of task completion in elderly men.

P300 EVOKED BY SOMATOSENSORY STIMULUS AND S-R COMPATIBILITY / 体力科学

The purpose of this study was to examine how S-R compatibility affected P 300, the stimulusevaluation process and response process. The P 300 component is thought to reflect information processing of stimuli. Previous studies used visual stimuli. In this study, we measured S-R compatibility effects on EMG-RT and P 300 using electrical somatosensory stimuli. Subjects performed the oddball task (Task 1) and the four-choice stimuli response task (Task 2) . They were presented electrical stimuli through ring electrodes on the index and little fingers of both hands and instructed to respond quickly to stimuli. S-R compatibility was decided by position of the stimuli. EMG-RT and P 300 latency for compatible and incompatible conditions were analyzed.<BR>For ERP analysis, data of subjects who reacted faster to compatibility ware used. Neither P 300 latency nor amplitude differed significantly between compatibility and incompatibility in Tasks 1 and 2, but for Task 2, latency tended to be prolonged by incompatibility. Therefore, it is thought that S-R compatibility mainly has an effect on response processing. However, judging from the tendency of P 300 latency to be prolonged by incompatibility for Task 2, it was considered that there is the possibility that S-R compatibility influenced P 300 latency, even if using a somatosensory stimulus.

EVENT-RELATED POTENTIALS (ERPs) AND LONG-TERM PHYSICAL EXERCISE / 体力科学

Electrophysiologic effects of physical exercise were investigated by comparing a training group and non-training group. ERPs were recorded by oddball paradigm using auditory stimuli as well as count and reaction tasks. EMG-RT was recorded during the reaction task. No reliable exercise effects on N100 amplitudes or latencies were observed. Concerning P300 amplitudes, no significant difference between the training group and non-training group was seen although P300 latencies of the training group were significantly shorter than those of the non-training group in the count task. Moreover, EMG-RT of the training group was significantly shorter than that of the non-training group.<BR>These findings suggest that the long-term physical exercise improved the efficiency of informa-tion processing and superior cognitive function in the brain.

Feature of event-related potentials in developing children / 体力科学

We examined here, changes in event-related potentials (ERPs) in eighteen children from 7 to 12 years and twelve adults. In addition to ERPs, we examined changes of EMG-RT. Subjects performed an auditory target discrimination task, in which 1000 Hz tones (target) and 2000 Hz tones (standard) were randomly presented with probabilities of 0.2 and 0.8.<BR>We found P300 as most consistent component of ERPs since childhood. P300 latency and EMG-RT in children was significantly prolonged than in adults (p<0.01) . P300 amplitude in children was significantly larger than in adults (p<0.05) . We concluded that both stimulus evaluation time and response selection time in children are more prolonged than that in adults, although ERPs is confirmed in children.

Influence of precontraction of an agonist muscle on CNV and H reflex during the fixed foreperiod of a motor action. Different amount of the precontraction / 体力科学

This study was carried out to investigate the influence of pre-movement tonic contraction on the Contingent Negative Variation (CNV) and Flexor Carpi Radialis (FCR) H reflex between the warning (WS) and response signal (RS) (foreperiod : FP) . Two levels of contraction were designed and the accompanying FCR Electromyography (EMG) was directly returned to the subject to sustain constant contraction. The subjects were 10 normal volunteers. Either small or middle (7.9±5.6% or 16.0±6.3% of the standard FCR EMG) contraction was sustained and the isometric wrist flexion movement was performed as quickly as possible following the RS.<BR>EMG Reaction time (RT) in the small contracting condition was shorter than that in the resting condition (nothing performed during the foreperiod) in almost all subjects, but in the middle contracting condition EMG RT was not similar. The CNV amplitude for the late period of the FP, which was considered to be related to the motor preparation, was larger in the middle contracting condition than in the resting condition, although the small contracting condition was similar to the resting condition. The H reflex amplitude for the late period of the FP tended to be smaller than the control level in the small and middle contracting conditions, but it was not significant. However, in over half of the subjects, whose CNV amplitude for the late period of the FP increased linearly depending on the conditions, the H reflex amplitude was smaller than the control level in both contracting conditions, but it was not linear. These results indicate that the modulation of the EMG RT was not directly associated with the CNV or H reflex amplitudes for the late period of the FP, and a functional difference in the set for the RS between the spinal and the upper level of the central nervous system was present.

Effects of 24-hours sleep deprivation on central information processing. Examination using event-related potentials (P300) / 体力科学

The purpose of this study was to investigate the effect of the sleep deprivation for central information processing. Therefore we examined the changes in the amplitude and the latency of P300 event-related potentials (ERPs) before and after sleep deprivation in eight subjects. In addition to P300, we examined the power spectral changes of the EEG and the R-R intervals at rest before ERP measurements. The subjects performed an auditory target discrimination task and were instructed to keep mental count of each target stimulus. Then 2000 Hz tones (target) and 1000 Hz tones (nontarget) were randomly presented with probabilities of 0.2 and 0.8.<BR>P300 latency at Fz, Cz, C3 and C4 was significantly prolonged after sleep deprivation (p<0.05) . P300 amplitude at Cz after sleep deprivation was significantly smaller than before sleep deprivation (p<0.05) . Alpha 1 power (8-10 Hz) at Cz on EEG was significantly decreased after sleep deprivation, but no other bands changed on EEG. The R-R interval was also significantly extended after sleep deprivation. We concluded that both central information processing and the autonomic nervous system may be influenced by sleep deprivation.

The change of event-related potentials with choice task / 体力科学

Event-related potentials (ERPs) were recorded from 9 normal subjects engaged in a somatosensory target discrimination task. Subjects were instructed (1) to keep a mental count of each target or (2) to rotate a grip in the direction of abduction after each target stimulus using the right hand. Target stimuli were electrical pulses delivered randomly through ring electrodes to the left second digit with probabilities of 0.2, and nontarget stimuli were delivered to the left fifth digit with probabilities of 0.8.<BR>P 100 was prominent in somatosensory tasks, and had a widespread distribution on the scalp without having any relation to kinds of tasks, therefore, P 100 reflects the sensation of somatosensory stimulation. N 140 was largest at Fz in both counting and movement tasks, so our result supported the hypothesis that N 140 is generated in the frontal lobes regions. Moreover, N 140 latency was shorter during movement than during counting. These results indicate that N 140 is related to carrying out movement. P 300 was largest at Cz during counting, and largest at Pz and C4' during movement. These results also indicate that P 300 may have multiple intracerebral generators since P300 origin differs based on the kind of tasks or stimuli. In addition, the appearance of P300 after nontarget stimuli indicates that P 300 reflects a non-selective postdecision closure of cognitive activity. In conclusion, each component of ERPs may have a specific origin and specific characteristics.

Effect of alcohol intake on microvascular and EEG responses to cold water stimulation. .DELTA.DPG and EEG power spectral analysis / 体力科学

In this study, we examined changes in the amplitude of differential digital photoplethysmogram (ΔDPG) and the power spectral changes of EEG at rest during cold water immersion of the contralateral fingers (2°C), and after alcohol intake (0.3 g/kg) in 8 male subjects. This experiment showed that the ΔDPG amplitude decreased at rest and finger blood pressure was increased during the cold water stimulation, but there was no signifincant change in heart rate and EEG power spectrum. On chronological measurements for 30 minutes after alcohol intake, ΔDPG amplitude decreased slightly and finger blood pressure increased. Heart rate also tended to increase, and the alpha 1 power (8.0-9.8 Hz) on EEG gradually increased. The ODPG and finger blood pressure responses to cold water stimulation every 10 minutes was decreased after alcohol intake, whereas heart rate was not affected. However, a decrease in the alphal power after stimulation was revealed. From these results, it may be concluded that during 5-10 s of cold water stimulation, increased skin sympathetic nerve activity was one of the factors that raises blood pressure.