Quadriceps fatigue after cycle exercise in patients with COPD compared with healthy control subjects

Study objectives: Quadriceps fatigue can occur in patients with COPD after exhaustive cycle exercise. The purpose of this study was to determine whether the degree of fatigue elicited by cycle exercise was greater in patients with COPD compared with matched control subjects. Subjects: Nine male patients with COPD with a mean (± SE) age of 66 ± 3 years and mean FEV₁ values of 1.31 ± 0.15 L and 36 ± 5% predicted were compared to nine healthy male subjects with a mean age of 66 ± 2 years. Methods: Patients with COPD exercised at 60% of peak work capacity until exhaustion. Healthy elderly subjects exercised at a workload that was chosen to produce a similar absolute oxygen uptake (V̇o₂) during constant-load exercise as that obtained by the patients with COPD. Quadriceps fatigue was detected by measuring twitch force (unpotentiated twitch force [TwQu] and potentiated twitch force [TwQp]) before and after cycle exercise. Results: Patients with COPD exercised for a mean duration of 8.4 ± 1.8 min. V̇o₂ during exercise was 50 ± 6% of predicted. The healthy elderly control subjects exercised for 10 min, generating a V̇o₂ of 48 ± 1% predicted. TwQu fell significantly postexercise in the patients with COPD but not in the matched control subjects. TwQp fell significantly postexercise in both groups, but the fall in TwQp postexercise was significantly greater in the patients with COPD. Conclusion: For the same absolute V̇o₂ and duration of cycle exercise, the amount of fatigue elicited was significantly greater in the patients with COPD compared to age-matched healthy control subjects.