Effect of 6-minute walk test on neuromuscular properties of patients with chronic obstructive pulmonary disease.

Objective: The objective of this study was to evaluate the neuromechanical properties of the knee extensor muscles before and after the 6-minute walk test (6MWT) in chronic obstructive pulmonary disease (COPD) patients and control subjects.

Materials And Methods: COPD patients from the Department of Pulmonology of the Hospital de Clinicas de Porto Alegre and age- and sex-matched control volunteers without COPD were included in this study. Body composition and lower limb strength assessed by maximal voluntary isometric contraction (MVIC) of the knee extensors) were assessed before and after the 6MWT. The total reaction time (TRT), premotor time (PMT) and motor time (MT) were assessed using surface electromyography of the rectus femoris and vastus lateralis knee extensor muscles.

Results: Eighteen patients COPD patients (10 men, FEV 36 ± 12% of predicted) and 8 control subjects (5 men, FEV 82 ± 7% of predicted) were included. COPD patients had lower muscle strength before (21.77 ± 7.86 kg) and after the 6MWT (11.16 ± 4.70 kg) compared with control subjects (33.50 ± 14.01 kg before; 29.25 ± 16.66 kg after). After the 6MWT, COPD patients showed a significant reduction in the MVIC and a significant increase in the TRT and PMT, which did not occur in control subjects. The reaction time parameters were higher in COPD patients after the 6MWT compared with control subjects. The TRT (r = -0.535, P < 0.005) and PMT (r = -0.549, P < 0.005) were inversely correlated with the MVIC after the 6MWT.

Conclusions: Neuromuscular changes associated with upper motor neuron activation contribute to MVIC impairment in COPD patients after performing a functional test.