Abstract
PurposeThe aim of this study was to analyze the effect of epoch length on intensity classification during continuous and intermittent activities.MethodsTen active students exercised under controlled conditions on a treadmill for four 5-min bouts by combining two effort intensities (running and walking) and two physical activity (PA) patterns (continuous or intermittent). The testing session was designed to generate a known level of moderate to vigorous PA (MVPA) for each condition. These PA levels were used as criterion measures to compare with the accelerometer measures. Data obtained from the accelerometer were reintegrated into 1-sec, 10-sec, 30-sec and 60-sec epochs. Equivalence testing was used to examine measurement agreements between MVPA values obtained with the different epochs and the reference values. Mean absolute percent errors (MAPE) were also calculated to provide an indicator of overall measurement error.ResultsDuring the intermittent conditions, only the value obtained with the 1-sec epoch was significantly equivalent to the reference value. With longer epochs the difference increased for both intermittent conditions but in an opposite way: with longer epochs, MVPA decreased during walking but increased during running. Regarding the measurement accuracy, the pattern of variations according to the epoch length selected during the intermittent conditions was identical between walking and running: MAPE increased with the increase in epoch length. MAPE remained low only for the 1-sec epoch (7.6% and 2.7% for walking and running, respectively), increased at 31.3% and 34% for the 10-sec epoch and until near 100% with the 30- and 60-sec epoch lengths.ConclusionThis study highlighted the misclassification of exercise intensity based on accelerometer measurement and described for the first time the extent and the direction of this misclassification. Moreover, we can confirm that the shorter epochs are more accurate to measure the real exercise intensity during intermittent PA whatever the intensity.
Highlights
Accelerometers are useful tools to assess objectively physical activity (PA) level in a wide range of population
The pattern of variations according to the epoch length selected during the intermittent conditions was identical between walking and running: Mean absolute percent errors (MAPE) increased with the increase in epoch length
MAPE remained low only for the 1-sec epoch (7.6% and 2.7% for walking and running, respectively), increased at 31.3% and 34% for the 10-sec epoch and until near 100% with the 30- and 60-sec epoch lengths
Summary
Accelerometers are useful tools to assess objectively physical activity (PA) level in a wide range of population (i.e., children and adolescents [1], adults [2] or elderly [3]). Several studies evaluated their validity to assess PA intensity compared to indirect calorimetry or doubly labeled water in adults [4,5,6,7,8] or in children [9]. The moderate-to-vigorous PA (MVPA) duration, an essential variable in terms of health used as a basis of the guidelines for the world public health authorities, appears to be strongly affected during this kind of activity pattern
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