Contractile fatigue of the quadriceps muscle predicts improvement in exercise performance after pulmonary rehabilitation.

Rationale: We hypothesized that among patients with chronic obstructive pulmonary disease, those who develop quadriceps contractile fatigue (QCF) after exhaustive submaximal cycle exercise would have a greater response to exercise training than those who do not develop QCF (NQCF).

Methods: Patients (N = 132) had measurement of QCF at baseline. Six-minute walk distance (6 MWD), maximal incremental cycle exercise testing, and quality of life measured by the Chronic Respiratory Questionnaire were obtained before and after pulmonary rehabilitation (PR).

Results: Eighty of the 132 patients (60.6%) developed QCF following constant workload exhaustive cycle exercise. Patients who developed QCF had a significantly greater improvement in 6 MWD following PR (45.3 ± 45.2 m) than those who did not (27.5 ± 45.7 m; P= .032). When baseline differences between patients who developed QCF and NQCF were accounted for, the difference in 6 MWD remained significant. Patients who developed QCF were not more likely to identify leg fatigue as the factor limiting exercise (56.2% of QCF group stated that leg fatigue was the limiting factor compared with 47.9% in the NQCF group; P= .46). When baseline differences were accounted for, the symptom causing exercise termination was not a predictor of the response to PR.

Conclusion: Patients who were capable of developing QCF had a significantly greater improvement in 6 MWD after PR compared to NQCF. Symptoms causing exercise termination could not be used to predict the development of contractile fatigue or the response to PR.