Defining the Relationship Between Average Daily Energy Expenditure and Field-Based Walking Tests and Aerobic Reserve in COPD

BACKGROUND: The aims of this study were to determine which tests of exercise capacity relate to average daily energy expenditure (DEE) and to quantify aerobic reserve during daily life in people with COPD. METHODS: A cross-sectional study was undertaken in 26 people with COPD (16 men; FEV(1), 50% ± 16%). Six-min walk distance (6MWD) and incremental shuttle walk distance (ISWD) measures were collected, and peak oxygen uptake (VO(2) peak) was measured during a symptom-limited ramp cycle ergometry test. The SenseWear Armband was worn during the waking hours for 4.4 ± 1.1 days to measure DEE. The intensity at which activities of daily living were undertaken was expressed as a percentage of VO(2) peak. RESULTS: DEE was associated with 6MWD (r = 0.40, P = .046) and ISWD (r = 0.52, P = .007) but not VO(2) peak (mL/kg per min) (r = 0.07, P = .74). Stronger associations were observed between DEE and the body weight-walking distance product for the 6MWD (r = 0.73, P < .001) and ISWD (r = 0.75, P < .001). The average intensity of daily activity was equivalent to 58% ± 11% of VO(2) peak, leaving an average aerobic reserve of 42%. CONCLUSIONS: Both 6MWD and ISWD, but not VO(2) peak, were related to DEE. Because activities of daily living were performed at a high percentage of VO(2) peak, it may be more realistic to optimize habitual DEE in COPD by increasing the frequency or duration rather than the intensity of physical activity.