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 [Formula: see text] Ten young male subjects (22.9 yrs) performed 30 minutes of exercise on a cycle ergometer at an intensity corresponding to 70%peak [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] Key words: excess postexercise oxygen consumption, muscle sounds, acoustic myography

Resting muscle sounds in anesthetized patients

It is known that contracting muscle makes low frequency sound vibrations.Small vibrations of uncertain origin are found over resting muscle. These could be shown to beof muscle origin if they significantly diminish in response to agents expected to decrease muscleactivity. Thiopental, propofol, and neuromuscular-junction blocking muscle relaxants have suchproperties. Twenty-one subjects slated for elective surgery for which they would routinely beanesthetized and paralysed gave informed consent to having a small accelerometer taped upontheir supine biceps (9 subjects), or volar forearm (12 subjects). Recordings were made in fourstages while subjects: (i) lifted a 2-kg weight just off the sponge armrest on whichtheir outstretched arm lay; (ii) relaxed their arm in the awake state prior toanesthesia; (iii) had anesthesia induced with intravenous thiopental (n = 11)or propofol (n = 10); and (iv) were paralysed. Recordings were digitised at172-Hz and 6-s segments fast Fourier transformed (FFT). Total signal power, as determined bythe area under the power spectrum, was significantly different (p < 0.05) in all stages forthe biceps and in all but stages (iii) from (iv) in the forearm. It appearsthat resting muscle generates measurable vibrations.Key words: muscle sounds, accelerometer, anesthesia.

Muscle sounds during voluntary and stimulated contractions of the human adductor pollicis muscle

The relationships between force, electromyography (EMG), and muscle sounds recorded by acoustic myography (AMG) were investigated for both voluntary and stimulated isometric contractions in the adductor pollicis muscle. Voluntary activity was performed at 10, 25, 50, 75, 85, and 100% of maximal voluntary contraction (MVC) force. Stimulated contractions were produced by supramaximal electrical stimulation of the ulnar nerve at the wrist at frequencies of 10, 20, 30, 50, 70, and 100 Hz. Contractions lasted for 4 s each, and were performed in random order with a 3-min rest between each. The voluntary and stimulation studies were performed in random order between subjects. Simultaneous recordings were obtained for force, force oscillation (from the differentiated force signal), and raw and integrated AMG (IAMG) and EMG (IEMG). During voluntary contractions, IAMG increased with force up to MVC (r2 = 0.99, P less than 0.001) in a curvilinear fashion and a similar relationship was seen between force and IEMG (r2 = 0.99, P less than 0.001). Conversely, during stimulated contractions as stimulation frequency increased, IAMG decreased in a fashion mirroring the frequency-force curve. The frequency of the AMG signal matched stimulation frequency and declines in total IAMG were due to reductions in amplitude of the AMG signal. The stimulation frequency-oscillation of force relationship was identical to that seen for stimulation frequency and IAMG. Integrated EMG increased linearly with stimulation frequency (r = 0.99). The stimulation results suggest that muscle sounds reflect oscillation of muscle fibers and that AMG signal characteristics are determined by motor control mechanisms rather than intrinsic contractile processes.