Does light-intensity physical activity moderate the relationship between sitting time and adiposity markers in adolescents?

Background:While the relationship between sedentary time and adiposity markers may be independent of moderate-to-vigorous intensity physical activity(MVPA) among adolescents,little is known about the role of light-intensity physical activity(LIPA) in this relationship.The aim of this cross-sectional study was to examine whether device-measured LIPA and MVPA moderate the associations between objectively measured sitting time and adiposity markers(body mass index(BMI)) and waist circumference(WC)) among adolescents.Methods:This study included accelerometer and inclinometer data obtained from 219 adolescents(age=14.9±1.6 years,mean± SD),collected during 2014 and 2015 in Melbourne,Australia.ActiGraph GT3 X accelerometers were used to determine time spent in total-LIPA(101 counts/min to 3.99 metabolic equivalents(METs)) was dichotomized into low-LIPA(101-799 counts/min) and high LIPA(800 counts/min to 3.99 METs),and MVPA(> 4 METs).The average time spent sitting was obtained from activPAL inclinometers.Anthropometric measures were assessed by trained staff.Interactions between sitting and total-LIPA,low-LIPA,high-LIPA,and MVPA on BMI z-score(zBMI) and WC z-score(zWC),respectively,were examined using linear regression,adjusting for age and sex;and moderation by total-LIPA,low-LIPA,high-LIPA,and MVPA were examined by adding interaction terms.Significant interaction effects were probed by comparing associations at the mean and at 1 SD below and above the mean.Results:Total-LIPA significantly moderated the association between sitting time and zBMI,and low-LIPA significantly moderated the association between sitting time and zBMI and zWC.No other associations were found for total-LIPA,high-LIPA,or MVPA.Specifically,at high levels of total-LIPA(+1 SD),there is a negative association between sitting time and zBMI.In addition,at high levels of low-LIPA(+1 SD),there is a negative association between sitting time and zBMI and zWC.Conclusion:Associations between sitting and adiposity depended on time spent in total-LIPA and low-LIPA,but not high-LIPA or MVPA.Results suggest that increasing time spent in LIP A may provide protection from the deleterious effects of sitting on adiposity markers among adolescents.Experimental evidence is needed to support these conclusions.