Validity of physical activity measures in individuals after total knee arthroplasty.

OBJECTIVE: To determine the concurrent criterion-related validity of 2 activity monitors in comparison with the criterion method of indirect calorimetry in older adults after total knee arthroplasty (TKA).
DESIGN: Validation study.
SETTING: Subjects completed 9 increasingly demanding daily activities in a research laboratory; each activity was performed for 7 minutes, for a total of 80 minutes, while the activity monitors and criterion method were used concurrently. PARTICIPANTS: Subjects (N=21, 67% women) had a mean age ± SD of 68±7 years and a body mass index of 29±4.
INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Energy expenditure (in kcal/min) measured by accelerometer-based and multisensor-based monitors and by a criterion method. Validity was assessed by the paired t test, intraclass correlation coefficient (ICC), and Bland-Altman plots comparing the measurements from the activity monitors with those of the criterion method.
RESULTS: Measurements from the accelerometer-based monitor were significantly lower than those of the criterion method across all walking and nonwalking activities. The underestimations ranged from 40% to 100%. The accelerometer-based monitor demonstrated small to moderate agreement compared with the criterion method (ICCs from 0 to .38). Measurements from the multisensor-based monitor were significantly lower than those of the criterion method during several nonwalking activities; yet, the differences were minor (2%-19%). Measurements from the multisensor-based monitor during walking activities were not different compared with the criterion method. The multisensor-based monitor demonstrated moderate to excellent agreement with the criterion method (ICCs from .48 to .81).
CONCLUSIONS: The multisensor-based monitor showed better criterion-related validity than the accelerometer-based monitor and should be considered as a tool to measure physical activity in individuals after TKA.