Author(s): TAKEMURA, M., KANAMORI, A., MIYAKAWA, S., Institution: リハビリテーション健康科学部学科, Country: JAPAN, Abstract-ID: 766

INTRODUCTION:
It is said that sports injuries are more likely to occur during fatigue. In addition, the function of neuromuscular cooperativeness is important for smooth switching and turning movements that cause sports injuries. The silent period (SP) is a pause in muscular electrical activity observed in a surface electromyography, before a muscular activity is started, leading up to a rapid response movement. The SP contains a pre-motion silent period (PMSP) and a switching silent period (SSP). The SSP is a muscular electrical activity silent period that appears in both the agonist and antagonist muscles, prior to motion when the voluntary movement is performed as quickly as possible. It is defined as the period from the disappearance of muscle discharge in the agonist muscle to the onset of muscle activity in the antagonist muscle. Its appearance mechanism is such that the SP preceding a voluntary movement is thought to involve efferent impulses from the cerebral cortex of the frontal lobe, the cerebellum, and the brain stem repression domain. The period of SSP is also said to be an index that reflects neuromuscular cooperativeness. Therefore, the purpose of this study was to examine chronological changes in neuromuscular cooperativeness before and after muscle fatigue loading using the SP and to examine neuromuscular cooperativeness functions using muscular electrical discharge pauses, or SSP.
METHODS:
The chronological changes in neuromuscular cooperativeness before and after muscle fatigue loading of 15 female university athletes (height, 161.8 ± 9.7 cm; weight, 55.2 ± 7.2 kg; age, 20.4 ± 1.4 years) were examined using the indicators of SSP and pre-motor time (PMT) before muscle fatigue loading and immediately after, 5 minutes after, 10 minutes after, and 15 minutes after muscle fatigue loading. The muscle fatigue loading made use of BIODEX (180deg/s), conducting knee flexion and extension exercises up to a reduction of 50% of maximum muscle strength on one side. This was accompanied by five jump repetitions each on the left and right side before, immediately after, 5 minutes after, 10 minutes after, and 15 minutes after the loading, at which time PMT and SSP were calculated from surface electromyography of the rectus femoris (RF) and the biceps femoris (BF) muscles taken each time.
RESULTS:
The results showed no significant differences between the loading side and the non-loading side, and between measurement times, for the RF PMT. However, SSP of the loading side showed significantly prolonged durations for the period immediately following loading and 5 minutes after (p<0.05) as compared with the period before loading.
CONCLUSION:
These results suggest that fatigue of the knee flexor and extensor muscles immediately decreases neuromuscular coordination during jumping. During muscle fatigue, neuromuscular coordination is impaired and athletes may be more susceptible to injury. The results of this study also show that most of that coordination is restored within 10 minutes.