Resting mechanomyography before and after resistance exercise

A number of mechanisms have been proposed to explain the elevation in oxygen consumption following exercise. Biochemical processes that return muscle to its pre-exercise state do not account for all of the extra oxygen consumed after exercise (excess post-exercise oxygen consumption, EPOC). Muscle at rest after aerobic exercise produces mechanomyographic (MMG) activity of increased amplitude, compared to the pre-exercise state, which declines exponentially with the same time constant as EPOC. The purpose of this study was to determine how the resting MMG is affected by resistance exercise, and whether any change is related to oxygen consumption (VO(2)). Ten young male subjects (22.9 years) performed 30 min of resistance exercise consisting of one set of 10 repetitions at 50% 1-repetition maximum (1-RM) followed by five sets of eight repetitions at 75% of 1-RM for leg press and leg (knee) extension, with 1 min rest between sets. Oxygen consumption was measured by indirect calorimetry, MMG by an accelerometer placed over the rectus femoris, and surface electromyogram (EMG) with electrodes placed distal to the accelerometer. Recordings were made before exercise and for 5.5 h after exercise. MMG activity, expressed as mean absolute acceleration, was significantly elevated after exercise (P = 0.0006), as was EMG activity expressed as root-mean-square voltage (P = 0.03). MMG and VO(2) demonstrated exponential decay after exercise with similar time constants of 7.5 +/- 2.2 and 7.2 +/- 1.0 min, respectively. We conclude that resting muscle is more mechanically active following resistance exercise and that this may contribute to an elevated VO(2).