Comparing methodologies for reallocating time between physical behaviours

Reallocating 60 minutes from sitting to standing and to stepping was associated with lower BMI, waist circumference and triglycerides, and higher HDL-cholesterol using both methodologies.

We utilised two methodologies for modelling the reallocation of time spent in one behaviour with time spent in another. To do this, cross-sectional data were combined from three RCTs. Physical behaviour data were collected using the activPAL3, a thigh-worn accelerometer. Both isotemporal substitution modelling and compositional isotemporal modelling were utilised to assess the associations of reallocating 60 minutes of sitting to standing or to stepping. 

As results from both methodologies were broadly similar, the decision as to which methodology to use should be based on the data and the research question stipulated, with a consideration of the interpretation of results.

Minor differences were observed in the symmetry of associations, suggesting these methodologies may diverge to a greater extent when larger amounts of time are reallocated, limiting the comparability of methodologies to smaller reallocations of time.

What next?

Future research should consider using either or both methodologies. These decisions should be driven by the data and the aim of the study.

Understanding possible mechanism(s) underpinning the differences in symmetry of results is crucial to making more informed decisions, whether that be statistical or physiological.

Citation details

Biddle GJH, Henson J, Biddle SJH, Davies MJ, Khunti K, Rowlands AV, Sutton S, Yates T, Edwardson CL. Modelling the Reallocation of Time Spent Sitting into Physical Activity: Isotemporal Substitution vs. Compositional Isotemporal Substitution. International Journal of Environmental Research and Public Health. 2021; 18(12):6210. DOI: 10.3390/ijerph18126210.


The authors would like to thank the participants who volunteered for these studies. This research was funded by National Institute for Health Research (NIHR) Collaborations for Leadership in Applied Health Research and Care (CLAHRC) East Midlands and was supported by the National Institute for Health Research (NIHR) Leicester Biomedical Research Centre.

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Greg Biddle

Dr Greg Biddle

Research Associate, GP standing desk research