Consequences of short interruptions of bouts walking on estimates of compliance to physical activity guidelines

Current guidelines on physical activity suggest that 30 min of moderateintensity physical activity can be accumulated in continuous bouts of atleast 10 min. It has been shown by use of activity monitoring that it isdifficult to achieve 10 min of completely uninterrupted walking in thefree-living urban environment where we have obstacles such as roads tocross. The aim of this study was to examine the effect of shortinterruptions in walking on the rate of oxygen uptake (ml . kg .min(-1)) to determine if walking with short interruptions can still beconsidered continuous. This leads to a more meaningful understanding asto what is a physiological break in activity. This is an importantconsideration for measurement of physical activity especially whenexploring measurement by accelerometry.In a laboratory setting a repeated measure design was used to replicateinterrupted walking in urban setting. Healthy volunteers (N = 10) walkedon a treadmill with walking interruptions of 10 s, 50 s and 100 s.Oxygen uptake was measured using a gas analysis system.10 s interruptions in walking had no significant effect on the VO2 . kg. min(-1). However two breaks of 50 s or 100 s introduced into a 5 minbrisk walking bout showed a significant reduction in oxygen uptakerequirements and metabolic equivalent of task (MET) (p < 0.001) comparedto continuous walking for the same amount of effective walking, but onlythe 100 s walking period could not be considered greater than 3 METduring the interval.Short periods of brisk walking interrupted by 10 s breaks can beconsidered continuous physical activity, but when walking is interruptedby longer breaks e.g. 50 s, there is a significant reduction in oxygenuptake requirement suggesting that it is not continuous anymore andshould be considered as fragmented.