No evidence of reactivity in accelerometry-based measurement of physical activity and sleep

Accelerometry provides more objective estimates of physical activity and sleep parameters than self-report data. However, the use of accelerometry may suffer from reactivity to measurement, that is, changes in behaviour under study due to the awareness of being observed.

In two field-experimental studies, we examined reactivity to measurement in physical activity and sleep parameters estimated with accelerometry. We used within-subjects designs and manipulated if participants were made aware of the measurement intention or if it was concealed.

During a 2-week study, participants received a red accelerometer for one of the weeks and were informed that their physical activity would be monitored in this week. In the other week, participants received a black accelerometer and were informed that it would monitor sleep. In fact, both the red and the black accelerometers monitored both physical activity and sleep.

We consistently found no evidence for reactivity to measurement for any indicator of physical activity (moderate to vigorous physical activity, steps) or sleep (duration, efficiency).

Accelerometry can provide unbiased measures of indicators of physical activity and sleep and is therefore a valuable addition to the common use of self-report data.