Research has shown that sedentary behavior is an independent risk factor for chronic disease. It is not known whether people who are regularly physically active will alter their physical activity behavior in response to imposed sedentary time.
PURPOSE: The objective of the current study was to determine whether imposing 10 hours of sedentary time per week for 8 weeks would alter the typical physical activity profiles of physically active adults.
METHODS: Participants were sixteen healthy young adults (age 21.6 years ± 1.4, 10 males) who met physical activity guidelines (≥ 150 minutes moderate- to- vigorous- physical activity, MVPA, per week). Eight participants were randomized to the sitting group (SIT), with 10 hours of imposed sedentary time per week for 8 weeks. The other 8 participants were randomized to the no-intervention control (CON) group. Physical activity and diet were measured at baseline, 4 weeks, and 8 weeks. At each time point, diet was self-reported using a 3-day diet record, and physical activity was assessed via 7-day accelerometry (Actical worn at the wrist).
RESULTS: At baseline, the participants spent 736.8 ± 235.2 minutes in sedentary behavior and 170.8 ± 87.9 minutes in MVPA per day. There were no statistically significant differences, either between or within groups, in step counts (CON = 615.1 ± 3019.1, SIT= -1158.0 ± 3373.0 steps, p = 0.287) minutes of sedentary (CON = -57.0 ± 176.6, SIT = 5.3 ± 66.3 mins, p = 0.366), light (CON = 71.5 ± 146.0, SIT = 11.1 ± 56.2 mins, p = 0.293), moderate (CON = 1.1 ± 43.9, SIT = -8.1 ± 36.1 mins, p = 0.656) or vigorous (CON = 0.9 ± 4.3, SIT= -0.1 ± 6.0 mins, p = 0.701) physical activity when comparing the participants’ typical week to imposed sitting week. Chi-square analyses showed a greater proportion of SIT participants decreased their steps (4/8) compared to CON (1/8) during the period of imposed sedentary behavior (χ 2 = 10.3, p = 0.001).
CONCLUSION: Despite imposing 10 hours of sedentary time per week, healthy, physically active young adults did not significantly change weekly physical activity behaviors. Due to the high variability in physical activity change within this small sample, larger studies are needed to investigate potential compensation in responses to imposed sedentary behavior.