2013-11-11T00:00:00Z, Ruch, Nicole, Joss, Franziska, Jimmy, Gerda, Melzer, Katarina, Hänggi, Françoise, Mäder, Urs

Awareness of being monitored can influence participants' habitual physical activity behavior. This reactivity effect may threaten the validity of physical activity assessment. The aim of this study was to investigate whether physical activity outcomes measured by accelerometer devices differ From measurement day to measurement day, and whether the day of the week and the day on which measurement started influence these differences.