Resting mechanomyography after aerobic exercise

A number of mechanisms have been proposed for the elevation in oxygen consumption following exercise. Biochemical processes that return muscle to its preexercise state do not account for all the oxygen consumed after exercise. It is possible that mechanical activity in resting muscle, which produces low frequency vibrations (i.e., muscle sounds: mechano-myographic [MMG] activity), could contribute to the excess postexercise oxygen consumption. Therefore the purpose of this study was to determine whether the resting MMG amplitude changes after exercise, and whether the change is related to the elevation in oxygen consumption (VO2). Ten young male subjects (22.9 yrs) performed 30 minutes of exercise on a cycle ergometer at an intensity corresponding to 70% peak VO2. Oxygen consumption was measured by indirect calorimetry, and MMG by an accelerometer placed over the mid-quadriceps before exercise and for 5.5 hours after exercise. MMG activity, expressed as mean absolute acceleration, was significantly elevated for the 5.5 hours of measurement after exercise (p < 0.05). MMG and VO2 decayed exponentially after exercise with time constants of 7.2 minutes and 7.4 minutes, respectively. We conclude that muscle is mechanically active following exercise and that this may contribute to an elevated VO2.