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Compensation or displacement of physical activity in middle-school girls: the Trial of Activity for Adolescent Girls.

Baggett CD, Stevens J, Catellier DJ, Evenson KR, McMurray RG, He K, Treuth MS - Int J Obes (Lond) (2010)

Bottom Line: Each additional minute of MVPA was associated with 1.85 min less of inactivity on the same day (95% CI: -1.89, -1.82).Daily MVPA was also negatively associated with inactivity the following day.Our results, based on 6 days of observational data, were not consistent with the 'activitystat' hypothesis, and instead indicated that physical activity displaced inactivity, at least in the short term.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. cbaggett@email.unc.edu

ABSTRACT

Objective: The 'activitystat' hypothesis suggests that increases in moderate-to-vigorous physical activity (MVPA) are accompanied by a compensatory reduction in light physical activity (LPA) and/or an increase in inactivity to maintain a consistent total physical activity level (TPA). The purpose of this study was to identify the evidence of compensation in middle-school girls.

Subjects: Participants were 6916, 8th grade girls from the Trial of Activity for Adolescent Girls (TAAG).

Design: Inactivity and physical activity were measured over 6- consecutive days using accelerometry (MTI Actigraph). A within-girl, repeated measures design was used to assess associations between physical activity and inactivity using general linear mixed models.

Results: Within a given day, for every one MET-minute more of inactivity, there was 3.18 MET-minutes (95% confidence interval (CI): -3.19, -3.17) less of TPA (activity >2 METS) on the same day. Daily inactivity was also negatively associated with TPA on the following day. Each additional minute of MVPA was associated with 1.85 min less of inactivity on the same day (95% CI: -1.89, -1.82). Daily MVPA was also negatively associated with inactivity the following day.

Conclusion: Our results, based on 6 days of observational data, were not consistent with the 'activitystat' hypothesis, and instead indicated that physical activity displaced inactivity, at least in the short term. Longer intervention trials are needed, nevertheless our findings support the use of interventions to increase physical activity over discrete periods of time in middle-school girls.

Show MeSH
Demonstration of “activitystat.” As MVPA increases across the three days, there is a compensatory decline in LPA and an increase in inactivity in order to maintain the set-point for total physical activity.
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Figure 1: Demonstration of “activitystat.” As MVPA increases across the three days, there is a compensatory decline in LPA and an increase in inactivity in order to maintain the set-point for total physical activity.

Mentions: Figure 1 is a graphic illustration of how the “activitystat” could maintain a set-point total physical activity level. In this example, as minutes (y-axis) of moderate to vigorous physical activity (MVPA) increases across the three days, light physical activity (LPA) decreases, and total physical activity, expressed in terms of intensity weighted minutes, is unchanged across the three days. As can be seen in Figure 1, the total amount of physical activity is not affected by the inactivity level. Despite total physical activity remaining constant, inactivity varies on each of the three days to compensate for the changes in LPA and MVPA. The “activitystat” results in compensation for the periods of inactivity through increases in the intensity of activity during the rest of the day in order to maintain the total physical activity set-point.


Compensation or displacement of physical activity in middle-school girls: the Trial of Activity for Adolescent Girls.

Baggett CD, Stevens J, Catellier DJ, Evenson KR, McMurray RG, He K, Treuth MS - Int J Obes (Lond) (2010)

Demonstration of “activitystat.” As MVPA increases across the three days, there is a compensatory decline in LPA and an increase in inactivity in order to maintain the set-point for total physical activity.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2902636&req=5

Figure 1: Demonstration of “activitystat.” As MVPA increases across the three days, there is a compensatory decline in LPA and an increase in inactivity in order to maintain the set-point for total physical activity.
Mentions: Figure 1 is a graphic illustration of how the “activitystat” could maintain a set-point total physical activity level. In this example, as minutes (y-axis) of moderate to vigorous physical activity (MVPA) increases across the three days, light physical activity (LPA) decreases, and total physical activity, expressed in terms of intensity weighted minutes, is unchanged across the three days. As can be seen in Figure 1, the total amount of physical activity is not affected by the inactivity level. Despite total physical activity remaining constant, inactivity varies on each of the three days to compensate for the changes in LPA and MVPA. The “activitystat” results in compensation for the periods of inactivity through increases in the intensity of activity during the rest of the day in order to maintain the total physical activity set-point.

Bottom Line: Each additional minute of MVPA was associated with 1.85 min less of inactivity on the same day (95% CI: -1.89, -1.82).Daily MVPA was also negatively associated with inactivity the following day.Our results, based on 6 days of observational data, were not consistent with the 'activitystat' hypothesis, and instead indicated that physical activity displaced inactivity, at least in the short term.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. cbaggett@email.unc.edu

ABSTRACT

Objective: The 'activitystat' hypothesis suggests that increases in moderate-to-vigorous physical activity (MVPA) are accompanied by a compensatory reduction in light physical activity (LPA) and/or an increase in inactivity to maintain a consistent total physical activity level (TPA). The purpose of this study was to identify the evidence of compensation in middle-school girls.

Subjects: Participants were 6916, 8th grade girls from the Trial of Activity for Adolescent Girls (TAAG).

Design: Inactivity and physical activity were measured over 6- consecutive days using accelerometry (MTI Actigraph). A within-girl, repeated measures design was used to assess associations between physical activity and inactivity using general linear mixed models.

Results: Within a given day, for every one MET-minute more of inactivity, there was 3.18 MET-minutes (95% confidence interval (CI): -3.19, -3.17) less of TPA (activity >2 METS) on the same day. Daily inactivity was also negatively associated with TPA on the following day. Each additional minute of MVPA was associated with 1.85 min less of inactivity on the same day (95% CI: -1.89, -1.82). Daily MVPA was also negatively associated with inactivity the following day.

Conclusion: Our results, based on 6 days of observational data, were not consistent with the 'activitystat' hypothesis, and instead indicated that physical activity displaced inactivity, at least in the short term. Longer intervention trials are needed, nevertheless our findings support the use of interventions to increase physical activity over discrete periods of time in middle-school girls.

Show MeSH