The subjects (9 obese, 11 lean, 1 overweight; 28 ± 5 kg/m2; 29 ± 11 kg body fat, 35 ± 9% body fat) continued their usual activities throughout the duration of the protocol. Of the 21 subjects, one identified herself as Black and another identified himself as Asian. The remaining subjects were Caucasian (n=11) or designated themselves as unknown/other. The 210 days the 21 subjects wore PAMSs were classified as work and leisure days (129 work days and 75 leisure days), with a total of 6 days (3%) omitted due to incomplete work shifts. Each day analyzed represents 172,800 lines of data (since data are collated each half second). Since data were gathered for ten axes, the total data set was comprised of 352,512,000 discrete movements. There was the expected positive relationship between fat-free mass and BMR (r2 =0.84). Considering the limited size of the study, the 21 subjects were broadly representative of office workers; 14 of the jobs were, “Entirely Sedentary” and seven were “Semi-Sedentary”.
The data supported our hypothesis that subjects sit more on work days than leisure days (). At work people sat longer compared to leisure days (597 ± 122 min/day c.f. 484 ± 83 min day; P<0.0001). The mean difference in sitting time between work days and leisure days was 110 ± 99 min/day. Leisure days were associated with more standing and walking (417 ± 101 min/day) compared to work days (341 ± 97 min/day; P=0.002). The average difference in standing and walking time between work and leisure days was, 76 ± 96 minutes. Thus, work is associated with more sitting time and less walking/standing time compared to leisure days.
Posture allocation per day for 21 subjects. Values are presented as means ± standard error of the mean (ANOVA and post hoc paired t-tests; * p=0.02, ** p = 0.004, ***p = 0.0001).
Since leisure days were associated with more standing and walking time than work days, it might be expected that the subjects move more on leisure days. However, these data do NOT suggest that to be the case. We compared daily movement (from the accelerometers) between the subjects while they were at work and at leisure. We found that total daily acceleration was similar between work days (3811 ± 767 AU/day) and leisure days (3938 ± 877 AU/day) (the data were gathered in duplicate with 99% concordance). We plotted individuals’ daily acceleration for work and leisure days. We found that there was a positive within subject correlation (r = 0.66; P<0.001), suggesting that subjects who were more active during work days, were also more active on leisure days.
To estimate the energetic implications of our findings, we examined all the walks that people took; (validated in, (8
)). Comparing work days to leisure days, the number of walking bouts did not differ significantly (46 ± 9 vs. 42 ± 9 walking bouts/day). On work days, the mean free-living velocity of a walk was 1.08 ± 0.28 mph and on leisure days was 0.94 ± 0.24 mph (P=0.03). The average time spent walking was 322 ± 91 minutes on work days and 380 ± 108 minutes on leisure days (P=0.03). Estimates (validated in, (9
)) of the daily energetic cost of walking approximated, 527 ± 220 kcal/day for work days and 586 ± 326 kcal/day for leisure days (r=0.72, P<0.001).
Although gender-specific differences were not the principal focus of this paper, we compared posture allocation for men and women. There were no significant differences between men and women (work day sitting time for men 623 + 111 min/day min/day and women, 568 + 138 min/day and leisure day sitting time for men, 491 + 84 min/day cf women, 476 + 98 min/day). The data for the obese (n=9; 5 M:4 F, 39 ± 5 yr, 33 ± 1.8 kg/m2, 98 ± 11 kg) and lean (n=11, 6 M:5 F, 36 ± 10 yr, 24 ± 0.9 kg/m2, 71 ± 9.5 kg) subjects were also compared. In both groups, work days were associated with significantly greater sitting time compared to leisure days. For the obese subjects, standing & walking time was 80 + 73 minutes greater than for work days (P=0.01). For the lean subjects, standing & walking time was 83 ± 113 minutes greater than for work days (P=0.04). The converse was true for sitting. The differences between work and leisure days were not accounted for by obesity. Thus lean and obese people show similar quantitative differences between work and leisure days.