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The purpose of this study was to determine whether quadriceps or diaphragmatic fatigue or both occur after high-intensity cycle exercise to exhaustion in healthy elderly persons. Ten relatively sedentary male subjects aged 68.3 +/- 1.4 yr (mean +/- SE) (range: 60 to 75 yr) exercised at 65% to 75% of their predetermined maximal work capacity to the limits of tolerance on two separate days. On one occasion, quadriceps twitch force (Q(tw)) was measured during magnetic stimulation of the femoral nerve. On the other occasion, twitch transdiaphragmatic pressure (Pdi(tw)) was measured during bilateral stimulation of the phrenic nerves. Because potentiated twitches may be more sensitive for detecting fatigue, both unpotentiated and potentiated (obtained 5 s after a 5-s maximum voluntary muscle contraction) twitches were measured before and at 10, 30, and 60 min after exercise. During constant-load exercise, subjects exercised at 75 +/- 7 W for 21.9 +/- 1.8 min during the quadriceps studies, and for 17.7 +/- 1.9 min during the diaphragm studies. Peak V O(2) was 1.58 +/- 0.08 L/min during both studies. Pdi(tw) (unpotentiated and potentiated) was not significantly different from baseline at any time after exercise. Unpotentiated Q(tw) was significantly decreased after exercise, to 64.0 +/- 6.3% of the baseline value at 10 min after exercise (p < 0.0003), and remained significantly decreased at 30 min after exercise. Potentiated Q(tw) was also significantly decreased after exercise, to 63.5 +/- 2.7% of the baseline value at 10 min after exercise (p < 0.0001), and remained significantly decreased at 30 and 60 min after exercise. In conclusion, high-intensity cycle exercise to exhaustion results in significant contractile fatigue of the quadriceps muscle but not of the diaphragm in healthy, relatively sedentary, elderly subjects.

Patients with chronic obstructive pulmonary disease (COPD) are at a mechanical disadvantage and should be predisposed to the development of diaphragmatic fatigue when the ventilatory system is stressed by exercise. The purpose of this study was to determine whether patients with moderately severe COPD develop contractile fatigue of the diaphragm after cycle exercise to the limits of tolerance. Twelve male patients with COPD, age 61.4 +/- 3.0 yr, participated. Their forced expiratory volume in 1 s (FEV(1)) was 1.79 +/- 0.14 L, 49.6 +/- 3.4% of predicted. Patients cycled at 60-70% of their predetermined maximal work capacity until they had to stop because of intolerable symptoms. Twitch transdiaphragmatic pressure (Pdi,tw) was measured during cervical magnetic stimulation before and 10, 30, and 60 min after exercise. A persistent fall in Pdi,tw postexercise of >/= 10% was considered potentially indicative of contractile fatigue of the diaphragm. Patients cycled for 10.2 +/- 2.0 min at a workload of 59.9 +/- 4.3 W. Patients exercised maximally relative to their capacity reaching a peak oxygen consumption (V O(2)) of 108.1 +/- 2.8% of the peak V O(2) obtained during a preliminary maximal incremental exercise test. Pdi,tw was not significantly different from baseline at any time postexercise. Pdi,tw was 19.9 +/- 1.6 cm H(2)O at baseline, 19.6 +/- 2.0 cm H(2)O at 10 min postexercise, 18. 6 +/- 2.0 cm H(2)O at 30 min postexercise, and 19.5 +/- 1.7 cm H(2)O at 60 min postexercise. In the individual patients, two of the patients had a persistent >/= 10% fall in Pdi,tw postexercise, potentially indicative of contractile fatigue of the diaphragm. In conclusion, the majority of patients with moderately severe COPD do not develop contractile fatigue of the diaphragm after high-intensity constant workload cycle exercise to the limits of tolerance.