Intra-individual and inter-individual variability in daily sitting time and MVPA

Objectives: Little is known about how much variability exists in free-living sitting time within individuals. The purpose of this study was to examine intra-individual variability of objectively determined daily sitting time and to determine if this variability was related to weekly averages of sitting duration or recommended moderate-vigorous physical activity (MVPA). Also., this study determined the reliability of free-living sitting and MVPA time as it useful for guiding researchers in determining how many days of monitoring are needed. Design: An activPAL monitor was worn for 7 consecutive days by 68 women (52 +/- 8 years). Methods: Intra-individual range of daily sitting time was calculated. Generalizability theory analysis determined the reliability of daily sitting and recommended MVPA. Results: Mean sitting time was 9.0 +/- 1.8 h/day and the within individual weekly mean range was 4.5 +/- 1.7 h/day. Similarly, there was a 4.5 h/day difference in sitting time between the mean of the lowest sitting (6.7 +/- 0.8) and highest sitting (11.3 +/- 1.1 h/day) quartiles. The intra-individual range in daily sitting did not differ among quartiles of sitting time (i.e., 4.9 +/- 1.9, 4.1 +/- 1.9, 5.1 +/- 1.5, 3.9 +/- 1.1 h/day for the 1st-4th quartiles) nor among quartiles of MVPA (i.e., 4.2 +/- 1.8, 4.7 +/- 2.0, 4.6 +/- 1.5, 4.4 +/- 1.3 h/day for the I st-4th quartiles. A reliability coefficient of 0.80 was achieved with 4 days of objectively measured sitting time and 7 days for MVPA. Conclusions: The findings suggest exposure to relatively high levels of sedentary time may occur in people regardless of weekly averages in sitting and regular exercise due to the high day-to-day variation in daily sitting time (4.5 h/d range within a week). (C) 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.