Evidence that women meeting physical activity guidelines do not sit less: an observational inclinometry study

Abstract

Background: The inactivity physiology paradigm proposes that sedentary behaviors, including sitting too much, are independent of the type of physical activity delineated for health in the Physical Activity Guidelines for Americans. Thus, we hypothesized that, when accounting for behaviors across the entire day, variability in the amount of time spent sitting would be independent of the inter-and intra-individual time engaged in sustained moderate-to-vigorous physical activity (MVPA).

Methods: Ninety-one healthy women, aged 40-75 years, completed a demographic questionnaire and assessment of height and weight. Participants wore the activPAL activity monitor for one week and time (minutes/day) spent sitting, standing, stepping, and in sustained bouts (bouts ≥10 minutes) of MVPA were quantified. The women were then stratified into groups based on weekly sustained MVPA. Additionally, each day of data collection for each participant was classified as either a "sufficient" MVPA day (≥ 30 min of MVPA) or an "insufficient" MVPA day for within-participant analyses.

Results: Time spent sitting, standing, and in incidental non-exercise stepping averaged 64, 28, and 11 hrs/week, respectively, and did not differ between groups with individuals meeting/exceeding the current exercise recommendation of 150 min/week of sustained MVPA in ≥10 minutes bouts (M = 294 min/week, SD = 22) compared to those with none or minimal levels (M= 20 min/week, SD = 4). Time spent sitting (M = 9.1 hr/day, SD = 0.19 vs. M = 8.8 hr/day, SD = 0.22), standing (M = 3.9 hr/day, SD = 0.16 vs. M = 3.9 hr/day, SD = 0.15), and in intermittent stepping (M = 1.6 hr/day, SD = 0.07 vs. M = 1.6 hr/day, SD = 0.06) did not differ between days with (~55 min/day) and without recommended MVPA.

Conclusions: This study provides the first objective evidence that participation in sustained MVPA is unrelated to daily sitting duration in relatively healthy, middle and older-aged women. More research is needed to extend these findings to other populations and to inform distinct behavioral recommendations focused on sedentary time.

Figure 1

The accumulative weekly time spent engaged in physical activity as recommended in the federal guidelines for aerobic exercise. Women were stratified to represent 3 levels of aerobic exercise duration: 1) None/Low Exercise , accumulating < 60 min/week of exercise; 2) Intermediate , accumulating some exercise but not meeting recommendations (i.e., accumulating 60–149 min/week of exercise) and, 3) Meeting or Exceeding Exercise Recommendations by accumulating ≥ min/week of sustained moderate-vigorous physical activity. Values are expressed as mean with SEM bars. * p<0.001 vs. None/Low Exercise , † p<0.001 vs. Intermediate.

Figure 2

Time spent sitting, standing, incidental stepping when not exercising (non-exercise stepping), and exercising as defined by the federal physical activity guidelines. Panels A and B illustrate the results for a cross-sectional comparison between subjects for the mean daily duration of each behavior (A) and the sum of all behaviors accumulated over an entire week (B) for the 3 groups stratified by time spent exercising. Panels C and D illustrate the within subject analysis results comparing the days that subjects had Insufficient exercise (<30 minutes) compared to days where they perform at least 30 minutes of aerobic exercise. Values are expressed as means with SEM bars. * p<0.001 vs. None/Low Exercise or Insufficient Exercise , † p<0.001 vs. Intermediate.

Figure 3

Relationship between the total time spent engaged in exercise as defined in the federal guidelines for sustained physical activity with the 3 non-exercise behaviors, including sitting, standing, and intermittent non-exercise stepping.