The influence of bout interruptions on measured and predicted physical activity during treadmill walking and running
Howe, Stephanie Marie
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The importance of daily physical activity (PA) has been established as a means of decreasing risk for chronic diseases. However, the presence of bout interruptions ((BI), defined as a brief pause (< 2 min) PA), can complicate measures of PA. This study was designed to evaluate the influence of different BI rules on PA during treadmill locomotion. Fifteen runners (6 women, 9 men) completed a series of walking (53.6, 107.2 m/min) and running (160.8 m/min) trials while using a metabolic measurement system to measure actual activity energy expenditure (AEEA) and four activity monitors to measure predicted AEE (AEEP). Treadmill speeds were selected to elicit light (L), moderate (M), and vigorous (V) PA intensities. Both AEEA and AEEP, were calculated as the sum within and between the start and end of each defined trial using 3 BI rules: 1) without an allowance for a BI (BI0), 2) or a 1-min BI allowance (BI1), 3) or a 2-min BI allowance (BI2). TA and TP were defined as the time spent at or above a moderate intensity during each PA bout for BI0, BI1, and BI2. Values of AEEA and AEEP for each BI definition and PA intensity were compared within intensities categories using a 2-factor RMANOVA, while data for all three PA intensities were evaluated simultaneously using a RMANOVA. Similarly, values of TA and TP for each BI definition were compared using the same multivariate RMANOVA model. Mean AEEA and AEEP for BI0 were significantly lower than those for BI1 and for BI2 at all PA intensities (p<0.05). When expressed as a percentage, the increase in AEEA and AEEP between BI0 and BI1, or BI1 and BI2, was 0.3-3.9% and between 5.5-11.0% for TA and TP across all intensities. Allowing for 1- or 2-min BIs within a PA bout significantly influences AEE and time during locomotion. These results suggest that rules for the number of BIs allowed should be established since an increase in BIs will cause PA outcome variables to become more dependent on the BIs than the PA itself.