Study objective: To determine the reliability,
validity, and stability of a triaxial accelerometer for walking and
daily activity measurement in a COPD sample.
Cross-sectional, correlational, descriptive design.
Setting: Outpatient pulmonary rehabilitation program in a
university-affiliated Veterans Affairs medical center.
Participants: Forty-seven outpatients (44 men and 3 women)
with stable COPD (FEV1, 37% predicted; SD, 16%) prior to
entry into a pulmonary rehabilitation program.
and results: Test-retest reliability of a triaxial movement
sensor (Tritrac R3D Research Ergometer; Professional Products; Madison,
WI) was evaluated in 35 of the 47 subjects during three standardized
6-min walks (intraclass correlation coefficient [rICC] = 0.84).
Pearson correlations evaluated accelerometer concurrent validity as a
measure of walking (in vector magnitude units), compared to walking
distance in all 47 subjects during three sequential 6-min walks (0.84,
0.85, and 0.95, respectively; p < 0.001). The validity of the
accelerometer as a measure of daily activity over 3 full days at home
was evaluated in all subjects using Pearson correlations with other
indicators of functional capacity. The accelerometer correlated with
exercise capacity (maximal 6-min walk, r = 0.74;
p < 0.001); level of obstructive disease (FEV1 percent
predicted, r = 0.62; p < 0.001); dyspnea (Functional
Status and Dyspnea Questionnaire, dyspnea over the past 30 days,
r = − 0.29; p < 0.05); and activity self-efficacy
(Activity Self-Efficacy Questionnaire, r = 0.43;
p < 0.01); but not with self-report of daily activity (Modified
Activity Recall Questionnaire, r = 0.14; not
significant). Stability of the accelerometer to measure 3 full days of
activity at home was determined by an rICC of 0.69.
Conclusions: This study provides preliminary data
suggesting that a triaxial movement sensor is a reliable, valid, and
stable measure of walking and daily physical activity in COPD patients.
It has the potential to provide more precise measurement of everyday
physical functioning in this population than self-report measures
currently in use, and measures an important dimension of functional
status not previously well-described.