Respiratory responses to sustained isometric muscle contractions in man: the effect of muscle mass.

Abstract

SUMMARY1. Respiratory responses to sustained isometric contractions of a small mass of muscle (the finger flexors) during handgripping, and of a larger mass of muscle (the quadriceps) during extension of the leg at the knee, have been studied in man.2. For both masses of muscle the increases of ventilation and of oxygen consumption were greater for contractions at 40 % maximum voluntary contraction (MVC) than for contractions at 20 % MVC.3. The increase of ventilation was not related to the mass of muscle involved. 4. At 20% MVC oxygen consumption during contraction of the quadriceps was greater than that during handgripping. At 40 % MVC the oxygen consumptions were similar. The oxygen debts following both handgrip and knee extensor contractions at 20 % MVC were negligible. Following 40 % MVC contractions of the quadriceps a significant oxygen debt was recorded but no debt was apparent following 40 % MVC contractions of the finger flexors.5. The increases of ventilation during isometric exercise were generally inappro-

Toward the optimal waveform for electrical stimulation of human muscle

“…The mean RQ rose slightly (11%) from baseline during the involuntary isometric contractions, demonstrating the increase in carbon dioxide production during the stimulations with the Russian, sine, and square waveforms. Following cessation of the Russian and square waveform stimulations, the RQ returned to baseline values by the end of the 5-min recovery period, whereas following the stimulations with sine waveform, the mean RQ decreased to 20% less than the original baseline resting value, signifying an increase in _ V V O 2 throughout the recovery period, possibly to reduce the negligible oxygen debt suggested by Imms and Mehta (1989).…”

Cerebral Blood Flow Velocity during and after Sustained Isometric Skeletal Muscle Contractions in Man

“…It would seem important to investigate cerebral blood flow in subjects who hyperventilate during isometric exercise and to continue monitoring during recovery since at the end of the contraction blood pressure falls quickly back to control levels while the reduced PACO~ recovers more slowly [7]. These studies are of practical importance because a reduction of cerebral blood flow may lead to postural instability and possibly to falling if the subjects were standing during exercise.…”

“…In contrast, during isometric contractions sustained towards exhaustion, there may be quite marked hyperventilation in some subjects with profound falls in PACO~ [6-81. Since this type of exercise also causes marked elevations of blood pressure [6,7,91, it may have conflicting influences on cerebral blood flow.…”

Human Exercise

“…In some subjects ventilation is eucapnic, whereas others hyperventilate and lower arterial Pco.. Although the oxygen debt is negligible following handgrip exercise, ventilation is raised during recovery despite end-tidal PCO, (PET,co2) being reduced (Imms & Mehta, 1989). The failure of the reduced PET,CO, to suppress ventilation suggests that one or more of the drives to ventilation which operate during exercise may persist into recovery.…”

“…This is due in part to the temporal and spatial variation of MPF and CF, which might be caused by rotation of motor unit activity. (Duncan et al 1981;Imms & Mehta, 1989). In some subjects ventilation is eucapnic, whereas others hyperventilate and lower arterial Pco..…”