Phenotype transformation toward hypersensitivity to soreness in post-exercise muscle

Acute muscle soreness and delayed onset muscle soreness (DOMS) are familiar post-exercise muscle discomforts. While DOMS is intensively investigated, the features and associated somatosensory alterations of acute muscle soreness remain less understood. To this end, thirty healthy adults underwent a strenuous wrist extension protocol targeting the left extensor carpi radialis (ECR), with the ipsilateral flexor carpi ulnaris (FCU) and contralateral ECR as control muscles. Mechanical, vibration, and pressure sensitivities were measured before and immediately after exercise. Participants qualitatively described their sensory experiences using descriptors from the McGill Pain Questionnaire. During exertion, participants predominantly identified soreness, rather than pain, as the main sensation in the exercised muscle (Lt ECR). After exercise, the exerted muscles exhibited significantly increased sensitivity to pressure (p < 0.001) and decreased sensitivity to mechanical stimulation (p = 0.039), with no significant changes in controls (Lt FCU and Rt ECR). Before exercise, pressing sensations were reported by 60% of participants during pressure stimulation of the muscle. After exercise, 76.7% of participants newly identified the pressure-induced sensation as soreness, suggesting a phenotypic transformation toward soreness hypersensitivity following exertion. Our findings clarified the phenotypic characteristics of acute muscle soreness and revealed a phenotype transformation toward soreness hypersensitivity in acute muscle soreness.