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Abdominal muscle fatigue after maximal ventilation in humans

1996; American Physiological Society; Volume: 81; Issue: 4 Linguagem: Inglês

10.1152/jappl.1996.81.4.1477

8750-7587

D Kyroussis, Gary Mills, Michael I. Polkey, Carl‐Hugo Hamnegård, Νikolaos Koulouris, Malcolm Green, John Moxham,

Musculoskeletal pain and rehabilitation

Kyroussis, Dimitris, Gary H. Mills, Michael I. Polkey, Carl-Hugo Hamnegard, Nicholaos Koulouris, Malcolm Green, and John Moxham. Abdominal muscle fatigue after maximal ventilation in humans. J. Appl. Physiol. 81(4): 1477–1483, 1996.—Abdominal muscles are the principal muscles of active expiration. To investigate the possibility of abdominal muscle low-frequency fatigue after maximal ventilation in humans, we stimulated the nerve roots supplying the abdominal muscles. We used a magnetic stimulator (Magstim 200) powering a 90-mm circular coil and studied six normal subjects. To assess the optimum level of stimulation and posture, we stimulated at each intervertebral level between T 7 and L 1 in the prone, supine, and seated positions. At T 10 , we used increasing power outputs to assess the pressure-power relationship. Care was taken to avoid muscle potentiation. Twitch gastric pressure (Pga) was recorded with a balloon-tipped catheter. Mean (±SD) baseline twitch Pga measured with the subjects in the prone position at T 10 was 23.5 ± 5.4 cmH 2 O. Within-occasion mean twitch Pga coefficient of variation was 4.6 ± 1.1%. Twitch Pga was measured with the subjects in the prone position with stimulation over T 10 before and after 2 min of maximal isocapnic ventilation (MIV). Twenty minutes after MIV, mean twitch Pga fell by 17 ± 9.1% ( P = 0.03) and remained low 90 min after MIV. We conclude that after maximal ventilation in humans there is a reduction of twitch Pga and, therefore, of low-frequency fatigue in abdominal muscles.