The reliability, validity, and stability of a measure of physical activity in the elderly

Objective measurement of functional upper-extremity movement using accelerometer recordings transformed with a threshold filter

BACKGROUND AND PURPOSE

The consensus is that the most important outcome for rehabilitation is functional activity in the life situation. Constraint-Induced Movement Therapy, a new treatment that transfers in-clinic gains to the life situation, demands objective measurement of real-world movement. However, direct, objective, and accurate measures of arm use in the real world are not available. Previous attempts to use accelerometry to measure extremity movement have failed because of unacceptable variability. This problem has been addressed here by use of a threshold filter.

METHODS

Nine stroke patients and 1 healthy individual wearing accelerometers were videotaped while they carried out their usual activities at home or in the clinic; the duration of their arm, torso, and ambulatory movements was judged by 2 observation teams. In addition, 11 college students performed 5 standardized activities of daily living for varying durations in the laboratory. The accelerometer data were transformed; the raw value recorded for a given epoch was set to a constant if it exceeded a low threshold.

RESULTS

The threshold-filtered recordings measured the duration of movement accurately and with very little variability. Correlations between the threshold-filtered recordings and the observer ratings of the duration of arm, torso, and ambulatory movements were 0.93, 0.93 and 0.99, respectively; the corresponding correlations for the raw values were -0.17, 0.34, and 0.85.

CONCLUSIONS

These results present initial evidence for the validity of threshold-filtered accelerometer recordings for objectively measuring the amount of real-world upper-extremity movement as an index of treatment outcome for rehabilitation patients.

Detecting bouts of physical activity in a field setting

The purposes of this study were to assess the TRITRAC and CSA for: (a) interaccelerometer agreement; (b) agreement in detecting patterns of moderate-intensity physical activity; and (c) agreement in detecting walking patterns recorded in a diary. Thirty-one women wore both the TRITRAC and CSA accelerometers for three consecutive days. Interaccelerometer agreement (measured with generalizability coefficients) ranged from .88 to .99. In total, 71.3% of the accelerometers' patterns agreed in length, with CSA patterns being on average significantly longer. Interaccelerometer agreement in detecting patterns of brisk walking, as recorded in a diary, was comparable (69.4%). Interaccelerometer discrepancies may be related in part to the threshold employed by each instrument for classifying moderate intensity patterns.