Exercise-induced inflammatory reaction affects electromyographic changes in skeletal muscle during dynamic contractions in humans

In order to assess the role of exercise-induced inflammatory reactions on e lectromyographic (EMG) changes in humans, we have recorded, during a 3-min dynamic handgrip exercise at a high strength (112 w), the surface EMG and t he compound evoked muscle action potential (M-wave) in control conditions, and this after ingestion of a well known cyclooxygenase blocker i.e. acetyl salicylic acid (ASA), either as a single dose treatment (10 mg/kg) and as a 3-day treatment (30 mg/kg per day). The power spectrum density function of EMG allowed us to compute both the median frequency (MF) and the energies in a low- and a high-frequency band. We estimated the lactic acid concentra tion from blood samples drawn from an antecubital vein and we noted that it s production was not affected by ASA (single dose or 3-day treatment). We o bserved at the end of exercise that no change in M-wave duration and conduc tion time occurred thou gh the median frequency always fell. However, we no ted that the slope of the MF vs. time regression line was halved after the 3-day ASA treatment which may indicate that inflammatory reactions are elic ited by exhausting contractions and affect the EMG changes. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.