Lower limb fatigue, during walking in patients with COPD

Background: The contribution of quadriceps muscle fatigue to cycling exercise intolerance is well recognized in COPD. Whether muscle fatigue occurs in plantar and dorsi-flexor muscles during walking is still unknown in these patients. Aim: To compare muscle strength and fatigue induced by walking exercise in plantar and dorsi-flexor muscles between COPD patients and healthy subjects. Method: Eleven patients with COPD (FEV1 58±15%pred.) and 11 healthy subjects matched for age and BMI performed a 12-minute walking exercise. The speed and slope of the treadmill were adjusted to achieve a targeted 40 Kcal energy expenditure for each subject. Maximal voluntary contraction (MVC) and twitch force (Tw) measured by magnetic stimulation were obtained for plantar and dorsi-flexor muscles prior to and 15 minutes after exercise. Results: At rest, MVC and Tw tended to be lower in COPD patients compared to healthy subjects for plantar (51.5±12.8 vs 65.6±21.7 kg, p=0.08 and 10.9±3.7 vs 13.2±2.6 kg, p=0.09) and dorsi-flexor (24.8±10.7 vs 32.7±8.4 kg, p=0.06 and 4.2±1.4 vs 6.12±1.3 kg, p<0.05) muscles. In COPD patients both, MVC and Tw were significantly decreased 15 min after exercise for plantar-flexor (-8±10% and -15±21%, p<0.05) and for dorsi-flexor (-6±11% and-31±19%, p<0.05) muscles. There was no difference in healthy subjects post-exercise for either plantar-flexor (1±10% and -4±14%), or dorsi-flexor muscles (1±3% and 4±7%). Conclusion: Muscle weakness and a susceptibility to develop muscle fatigue after walking occur in the plantar and dorsi-flexor muscles in patients with COPD compared to controls. Project supported by the Réseau en santé respiratoire du FRSQ