Comparison Of Intensity And Variability In Accelerometer-measured Activities Between Two Laboratory Visits And Free-living

Accelerometer validation studies often involve participants completing activities in a research laboratory. Participants may perform activities differently in the laboratory compared to free-living (FL) environments (e.g., their home), but there may also be variability in how individuals complete the same activity in the same setting but on different occasions. Understanding variability in performance of activities may influence the development of accelerometer validation protocols leading to more accurate physical activity measurement. PURPOSE: To determine reliability in how adults perform activities during two laboratory visits on different days and compared to FL. METHODS: Participants (N = 25; age = 21.1 ± 3.7y) wore an accelerometer at the dominant (DW) and nondominant wrist (NDW) and right hip (RH) during two 1.5-hr laboratory visits, separated by one FL day. During each laboratory visit and the FL day, participants completed ~10 representative daily activities. Start and stop times were recorded by a research assistant in the laboratory, and by the participant in FL. A mixed effects model was used to compare the mean and standard deviation (SD) of Euclidian Norm Minus One (ENMO; mg) for each activity between the two laboratory visits, and between the first laboratory visit and FL (fixed effects) with participant as a random effect. Significance was indicated when p < 0.05 after Tukey adjustment. Activities completed across all three settings were included for analyses. RESULTS: Mean ENMO was higher in the laboratory compared to FL for resistance exercise (NDW: +118.3 mg) and stairs (NDW: 79.4 mg, RH: 56.0 mg), while walk brisk was higher in FL compared to the laboratory (RH: 52.0 mg). SD ENMO was higher in FL compared to the laboratory for cooking (NDW: 34.2 mg, DW: 40.9 mg) and walk (RH: 28.1 mg), but SD ENMO was lower in FL compared to the laboratory for stairs (RH: 21.0 mg, NDW: 40.1 mg). Mean ENMO did not differ between laboratory visits, but SD ENMO differed for self-care (NDW: 64.5 mg) and sit (RH: 22.2 mg). CONCLUSIONS: Overall, differences were minimal across settings. There were more differences between laboratory and FL (5/14 activities) than there were between laboratory visits (2/14 activities), suggesting that participants perform some activities differently in a FL setting compared to the laboratory.