Associations of the Stair Climb Power Test With Muscle Strength and Functional Performance in People With Chronic Obstructive Pulmonary Disease: A Cross-Sectional Study

Abstract

The Stair Climb Power Test (SCPT) is a functional test associated with leg muscle power in older people. The purposes of this study were to compare the results of the SCPT in people with chronic obstructive pulmonary disease (COPD) and people who were healthy and to explore associations of the SCPT with muscle strength (force-generating capacity) and functional performance. The study was a cross-sectional investigation. Twenty-one people with COPD and a predicted mean (SD) percentage of forced expiratory volume in 1 second of 47.2 (12.9) and 21 people who were healthy and matched for age, sex, and body mass were tested with the SCPT. Knee extensor and flexor muscle torque was assessed with an isokinetic dynamometer. Functional performance was assessed with the Timed "Up & Go" Test (TUG) and the Six-Minute Walk Test (6MWT). People with COPD showed lower values on the SCPT (28%) and all torque measures (∼ 32%), except for eccentric knee flexor muscle torque. In people with COPD, performance on the TUG and 6MWT was lower by 23% and 28%, respectively. In people with COPD, the SCPT was moderately associated with knee extensor muscle isometric and eccentric torque (r ≥.46) and strongly associated (r=.68) with the 6MWT. In people who were healthy, the association of the SCPT with knee extensor muscle torque tended to be stronger (r ≥.66); however, no significant relationship between the SCPT and measures of functional performance was found. The observational design of the study and the use of a relatively small convenience sample limit the generalizability of the findings. The SCPT is a simple and safe test associated with measures of functional performance in people with COPD. People with COPD show deficits on the SCPT. However, the SCPT is only moderately associated with muscle torque and thus cannot be used as a simple surrogate for muscle strength in people with COPD.