Muscle hyperalgesia in postexercise muscle soreness assessed by single and repetitive ultrasound stimuli

This study hypothesized the presence of muscle hyperalgesia and central hyper-excitability in postexercise muscle soreness (PEMS). PEMS was induced by standardized eccentric exercise of the first dorsal interosseous (FDI) muscle of the right hand using a newly designed hand exerciser. The left-hand FDI served as a control. Concentric maximum voluntary contraction, pressure pain threshold (PPT), pain threshold to a single ultrasonic stimulus (US1), and pain summation threshold to a 2 Hz train of five ultrasonic stimuli (US5) were used to assess the FDI. Measurements were performed at intervals up to 48 hours after exercise. The PPT in the test hand was minimum after 24 hours. US1 was not significantly different in the test and control hands at any time before or after the exercise, whereas US5 was significantly lower than control after 24 hours (P = .03). Facilitation of the temporal summation pain threshold, calculated as a ratio between US1 and US5, was maximum at 24 hours compared with the control hand (P = .005). This indicates that temporal summation was facilitated as a component of the muscle hyperalgesia and the ultrasonic stimuli can be used as a noninvasive method to determine central mechanisms of muscle hyperalgeisa.