ABSTRACT

　Exercise-Associated Muscle Cramps （EAMC） are sudden, involuntary muscle contractions that often occur during or after physical activity. Despite their commonality, the exact physiological mechanisms underlying EAMC remain elusive and are the subject of ongoing research. Two primary hypotheses have been proposed to explain their origin: the central nervous system origin hypothesis and the peripheral nervous system origin hypothesis. The central nervous system origin hypothesis suggests that muscle cramps may be triggered by abnormal neural activity originating from the brain or spinal cord. This theory posits that disruptions in motor neuron firing patterns, possibly due to fatigue or electrolyte imbalances, could lead to the involuntary contractions observed in EAMC. On the other hand, the peripheral nervous system origin hypothesis proposes that cramps arise from abnormalities in the nerves directly controlling the affected muscles, possibly due to compression, injury, or metabolic changes within the muscle fibers themselves. The aim of this study is to elucidate changes associated with EAMC. Matrix sEMG was used to monitor the muscle activity patterns in the lateral gastrocnemius muscle during repetitive plantar flexion exercises of the dominant foot. As the results, during the onset of muscle cramp precursors, the muscle activity patterns changed that the sEMG signals exhibited increased amplitude and had a high-frequency band at the localized site. Concurrently, the new innervation zones observed. These findings provide support for the central nervous system hypothesis by suggesting that muscle cramps occur due to a disruption of the size principle in conventional muscle contractions, leading to irregular firing of motor neurons.

DECENTE SPORTS SCIENCE Vol.46/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE