Accelerometer Cut Points for Physical Activity Assessment of Older Adults with Parkinson’s Disease

OBJECTIVE To define accelerometer cut points for different walking speeds in older adults with mild to moderate Parkinson's disease. METHOD A volunteer sample of 30 older adults (mean age 73; SD 5.4 years) with mild to moderate Parkinson's disease walked at self-defined brisk, normal, and slow speeds for three minutes in a circular indoor hallway, each wearing an accelerometer around the waist. Walking speed was calculated and used as a reference measure. Through ROC analysis, accelerometer cut points for different levels of walking speed in counts per 15 seconds were generated, and a leave-one-out cross-validation was performed followed by a quadratic weighted Cohen's Kappa, to test the level of agreement between true and cut point-predicted walking speeds. RESULTS Optimal cut points for walking speeds ≤ 1.0 m/s were ≤ 328 and ≤ 470 counts/15 sec; for speeds > 1.3 m/s, they were ≥ 730 and ≥ 851 counts/15 sec for the vertical axis and vector magnitude, respectively. Sensitivity and specificity were 61%-100% for the developed cut points. The quadratic weighted Kappa showed substantial agreement: κ = 0.79 (95% CI 0.70-0.89) and κ = 0.69 (95% CI 0.56-0.82) for the vertical axis and the vector magnitude, respectively. CONCLUSIONS This study provides accelerometer cut points based on walking speed for physical-activity measurement in older adults with Parkinson's disease for evaluation of interventions and for investigating links between physical activity and health.