Variability of Objectively Measured Sedentary Behavior.

Introduction: The primary purpose of this study was to evaluate variability of sedentary behavior (SB) throughout a 7-day measurement period and to determine if < 7-days of SB measurement would be comparable to the typical 7-day measurement period.

Methods: Retrospective data from Ball State University’s Clinical Exercise Physiology Laboratory on 293 participants (99 men, 55+/-14 years, BMI = 29+/-5 kg/m2; 194 women, 51+/-12 years, BMI = 27+/-7 kg/m2) with 7 consecutive days of data collected with Actigraph accelerometers were analyzed. Time spent in SB (either < 100 cpm or <150 cpm) and breaks in SB were compared between days and by sex using a 2-way repeated measures ANOVA. Stepwise regression was performed to determine if < 7-days of SB measurement were comparable to the 7-day method; using an adjusted R2 of >=0.9 as criterion for equivalence.

Results: There were no differences in daily time spent in SB between the 7 days for all participants. However, there was a significant interaction between sex and days, with women spending less time in SB on both Saturdays and Sundays than men when using the 100 cpm cut-point. Stepwise regression showed using any 4 days would be comparable to a 7-day measurement (R2>0.90).

Conclusion: When assessed over a 7-day measurement period, SB appears to be very stable from day-to-day, although there may be some small differences in time spent in SB and breaks in SB between men and women, particularly on weekend days. The stepwise regression analysis suggests that a measurement period as short as 4 days could provide comparable data (91% of variance) to a one-week assessment. Shorter assessment periods would reduce both researcher and subject burden in data collection.