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Clinical Investigations: COPD |

Quantitating Physical Activity in COPD Using a Triaxial Accelerometer*

Bonnie G. Steele, PhD, RN; Lyn Holt, MS; Basia Belza, PhD, RN; Scott Ferris, MS; S. Lakshminaryan, MD; David M. Buchner, MD, MPH
Author and Funding Information

*From the Department of Biobehavioral Nursing and Health, University of Washington School of Nursing (Drs. Steele and Belza), Rehabilitation Care Services (Mr. Ferris), and University of Washington School of Medicine (Dr. Lakshminaryan), Veterans Affairs Puget Sound Health Care System, Seattle Division, Seattle, WA; Good Samaritan Medical Center (Ms. Holt), Puyallup, WA; and the Physical Activity and Health Branch (Dr. Buchner), Division of Nutrition and Physical Activity, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA.

Correspondence to: Bonnie G. Steele, PhD, RN, Respiratory Clinical Nurse Specialist, Medical Specialties and Primary Care Service (111-B), Veterans Affairs Puget Sound Health Care System, 1660 Columbian Way South, Seattle, WA 98108; e-mail: Bonnie.Steele@med.va.gov



Chest. 2000;117(5):1359-1367. doi:10.1378/chest.117.5.1359
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Study objective: To determine the reliability, validity, and stability of a triaxial accelerometer for walking and daily activity measurement in a COPD sample.

Design: 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.

Measurements 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.

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