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 moderate intensity physical activity can be accumulated in continuous bouts of at least 10 min. It has been shown by use of activity monitoring that it is difficult to achieve 10 min of completely uninterrupted walking in the free-living urban environment where we have obstacles such as roads to cross. The aim of this study was to examine the effect of short interruptions in walking on the rate of oxygen uptake (ml · kg · min^-1) to determine if walking with short interruptions can still be considered continuous. This leads to a more meaningful understanding as to what is a physiological break in activity. This is an important consideration for measurement of physical activity especially when exploring measurement by accelerometry. In a laboratory setting a repeated measure design was used to replicate interrupted walking in urban setting. Healthy volunteers (N  =  10) walked on 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 min brisk walking bout showed a significant reduction in oxygen uptake requirements and metabolic equivalent of task (MET) (p  <  0.001) compared to continuous walking for the same amount of effective walking, but only the 100 s walking period could not be considered greater than 3 MET during the interval. Short periods of brisk walking interrupted by 10 s breaks can be considered continuous physical activity, but when walking is interrupted by longer breaks e.g. 50 s, there is a significant reduction in oxygen uptake requirement suggesting that it is not continuous anymore and should be considered as fragmented.