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 electromyographic (EMG) changes in humans, we have recorded, during a 3-min dynamic handgrip exercise at a high strength (112 w), the surface EMG and the compound evoked muscle action potential (M-wave) in control conditions, and this after ingestion of a well known cyclooxygenase blocker i.e. acetylsalicylic 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 concentration from blood samples drawn from an antecubital vein and we noted that its production was not affected by ASA (single dose or 3-day treatment). We observed at the end of exercise that no change in M-wave duration and conduction time occurred though the median frequency always fell. However, we noted 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 elicited by exhausting contractions and affect the EMG changes.