Validity of the Actical Accelerometer Step-Count Function

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Purpose:To assess the validity of the new Actical accelerometer step count function.Methods:Actical step counts were compared according to two criterion standards. 1) Eight Acticals were assessed using a mechanical shaker table under six different testing conditions. 2) Thirty-eight volunteers (aged 9-59 yr) wore eight Acticals and eight Actigraphs during treadmill walking (50 and 83 m·min−1) and running (133 m·min−1) for 6 min at each speed. Steps were counted during the second and fourth minutes of each speed by a trained observer.Results:The correlation between Actical step counts and the mechanical shaker step counts was excellent (r = 1.0). Compared with visually counted steps, both the Actical and Actigraph step counts were significantly different at 50 m·min−1; however, no significant differences were evident at 83 and 133 m·min−1. The criterion-related validity correlations (r) for the Actical and Actigraph, respectively, were 0.73 and 0.52 at the slow walk condition and 0.99 and 0.99 at the normal walk and run conditions.Conclusion:The new step count function of the Actical accelerometer provides valid estimates of step counts at 83 and 133 m·min−1 on a range of healthy participants.

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