Electrical activity and soreness in muscles after exercise.

Electrical activity and soreness in the quadriceps muscles were examined during a 48-h period after eccentric (EC) and concentric contraction (CC) to study the amplitude and frequency characteristics of the electrical signal after exercise and to study the relationship between the electrical signal and muscle soreness. The exercise protocol included a step test performed for 15 min using a 46-cm step in which one quadriceps contracted eccentrically and one contracted concentrically. Electrical activity was quantified by computing both root mean square electromyograph (rmsEMG) and mean power frequency of the myoelectrical signal during low-level contractions of the muscles. Recordings of muscle activity were made before exercise, immediately after exercise, 1, 12, 24 and 48 h after exercise in 12 volunteer subjects (mean age 28.5 yr). Recordings were made with the subject seated, holding the leg being tested slightly off the ground. Subjects were given a subjective pain rating scale. The before exercise values for rmsEMG (EC = 13.3 microV; CC = 13 microV) and mean power frequency (EC = 55.3 Hz; CC = 54.4 Hz) were within the range that would be expected for surface electrodes. The mean rating of soreness for the eccentrically exercised muscles ranged from slightly uncomfortable at 12 h after exercise to sore during the period 24-48 h after exercise. Subjects reported the concentrically exercised muscles as normal to slightly uncomfortable during the whole recording period. Analysis of variance revealed a significant (P less than 0.05) difference between EC and CC rmsEMG value at 1 h after exercise (EC = 17.2 +/- 7.6; CC = 12.3 +/- 5.5) and at 12 h after exercise (EC = 15.0 +/- 5.0; CC = 12.3 +/- 4.2). The results suggest that an increase in the electrical activity of muscles is needed to produce the same pre-exercise contraction after performing eccentric exercise.(ABSTRACT TRUNCATED AT 250 WORDS)