Abstract
Background: Intervention studies observing the effects of physical activity on health often use accelerometry to quantify periods of sedentary behaviour and non-sedentary behaviour as well as the number of interruptions in sedentary behaviour, known as breaks. Previous studies have a transition from sedentary behaviour to non-sedentary behaviours such as standing or walking to classify a break in sedentary time. In contrast, a group of light to moderate intensity activity breaks such as light treadmill walking and callisthenic exercises have been shown to acutely improve markers of cardiometabolic health in laboratory studies. Longer term studies are needed to confirm these breaks have meaningful impacts on longer term health. However, measuring compliance to the intensity of breaks is not possible using existing accelerometer thresholds.
Objective: To develop accelerometer count thresholds that can be used to identify an intensity that is similar to that of activity breaks shown to improve short term cardiometabolic health in laboratory studies
Design: Twenty young, healthy weight university students completed a single 2 hour laboratory session where they performed two sets of six different 2-3 minute duration activity breaks, each separated with 5 minutes of sitting while wearing ActiGraph, activPAL and heart rate monitors. The activity breaks included walking at 3.2 km/h, 6 km/h, self-selected pace, stair walking at a self-selected pace, and two different combinations of resistance exercises. ActiGraph count data were used to develop count thresholds for each of the six activity breaks and sitting, while activPAL and heart rate data were used as comparisons.
Results: The overall count threshold found to correspond to an intensity similar to the activity breaks used in a laboratory setting was 981 counts per minute (cpm) using vector magnitude counts. The thresholds for grouped walking and resistance activity breaks were 1122 cpm and 981 cpm respectively, and individual activity break thresholds ranged from 981 cpm (SRA 1; half-squat/knee raise/glute-contraction/calf-raise) to 3384 cpm for 6.0 km/h walking. Estimated activPAL MET values ranged from 1.8 ± 0.1 MET for resistance activity breaks to 3.6 ± 0.2 MET for 6.0 km/h walking. Heart rate was highest for self-selected pace stair walking at 138 ± 19 bpm and lowest for 3.2 km/h walking at 94 ±14 bpm.
Conclusion: A 1000 cpm threshold will identify an intensity of activity similar to the intensity of activity breaks found to impart acute metabolic benefit when performed in a laboratory setting. This threshold will be particularly useful for measuring compliance to activity breaks in longer-term interventions that are aimed at determining their effects on long term health outcomes.