Validity of Accelerometry for Measurement of Activity in People With Brain Injury

Purpose To evaluate the validity of a uni-axial accelerometer (MTI Actigraph) for measuring physical activity in people with acquired brain injury (ABI) using portable indirect calorimetry (Cosmed K4b²) 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 K4b² 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 [Lt] 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 [Lt] 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.

Link to Abstract: http://www.ncbi.nlm.nih.gov/pubmed/16177597