Validity of accelerometry for measurement of activity in people with brain injury.
OBJECTIVE
To evaluate the validity of a uniaxial accelerometer (MTI Actigraph) for measuring physical activity in people with acquired brain injury (ABI) using portable indirect calorimetry (Cosmed K4b(2)) as a criterion measure.


METHODS
Fourteen people with ABI and related gait pattern impairment (age 32 +/- 8 yr) wore an MTI Actigraph that measured activity (counts.min(-1)) and a Cosmed K4b(2) that measured oxygen consumption (mL.kg(-1).min(-1)) during four activities: quiet sitting (QS) and comfortable paced (CP), brisk paced (BP), and fast paced (FP) walking. MET levels were predicted from Actigraph counts using a published equation and compared with Cosmed measures. Predicted METs for each of the 56 activity bouts (14 participants x 4 bouts) were classified (light, moderate, vigorous, or very vigorous intensity) and compared with Cosmed-based classifications.


RESULTS
Repeated-measures ANOVA indicated that walking condition intensities were significantly different (P < 0.05) and the Actigraph detected the differences. Overall correlation between measured and predicted METs was positive, moderate, and significant (r = 0.74). Mean predicted METs were not significantly different from measured for CP and BP, but for FP walking, predicted METs were significantly less than measured (P < 0.05). The Actigraph correctly classified intensity for 76.8% of all activity bouts and 91.5% of light- and moderate-intensity bouts.


CONCLUSIONS
Actigraph counts provide a valid index of activity across the intensities investigated in this study. For light to moderate activity, Actigraph-based estimates of METs are acceptable for group-level analysis and are a valid means of classifying activity intensity. The Actigraph significantly underestimated higher intensity activity, although, in practice, this limitation will have minimal impact on activity measurement of most community-dwelling people with ABI.
Tweedy
Sean M
SM
School of Human Movement Studies, University of Queensland, Australia. scant@hms.uq.edu.au
Trost
Stewart G
SG
D000328:Adult; D001930:Brain Injuries / Q000150:complications / Q000503:physiopathology*; D004734:Energy Metabolism; D005260:Female; D020233:Gait Disorders, Neurologic / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods*; D009043:Motor Activity; D010101:Oxygen Consumption; D015203:Reproducibility of Results; D016138:Walking