Differences among physical activity actigraphy algorithms in three chronic illness populations.

OBJECTIVES: In three chronic illness populations and in a combined sample, we assessed differences in two algorithms to determine wear time (WT%) and four algorithms to determine: Kilocalories, light physical activity (PA), moderate-to-vigorous PA (MVPA), and metabolic equivalents (METs).

METHODS: Data were collected from 29 people living with HIV (PLHIV), 27 participants recovering from a cardiac event, and 15 participants with hypertension (HTN). Participants wore the ActiGraphTM wGT3X-BT for > 3 days on their hip. Analysis of variance (ANOVA) was used to assess differences among the algorithms.

RESULTS: No differences were found between the two algorithms to assess WT% or among the four algorithms to assess kilocalories in each of the chronic illness populations or in the combined sample. Significant differences were found among the four algorithms for light PA ( p  < .001) and METs ( p  < .001) in each chronic illness population and in the combined sample. MVPA was significantly different among the four algorithms in the PLHIV ( p  = .007) and in the combined sample ( p  < .001), but not in the cardiac ( p  = .064) or HTN samples ( p  = .200).

DISCUSSION: Our findings indicate that the choice of algorithm does make a difference in PA determination. Differences in algorithms should be considered when comparing PA across different chronic illness populations.