Development and validation of an activPAL accelerometry count-based model of physical activity intensity in adults.
Level 4 - case-series / case-control
Measurement and calibration validation study without a randomized design (graded by design analogy)
PubMed 34479692 · doi:10.1016/j.medengphy.2021.07.014
What was done
Researchers developed and cross-validated an activPAL tri-axial accelerometry count-based model to estimate physical activity metabolic equivalents (METs) in 40 healthy adults (mean age 25 ± 6 years). Participants completed a 7-stage progressive treadmill protocol with indirect calorimetry as the criterion measure. A regression model relating vector magnitude counts to METs was developed in a subset (n = 20) and cross-validated in the remaining participants (n = 20). Additionally, 32 participants wore the activPAL alongside a criterion PiezoRxD monitor during free-living conditions over 192 total days.
What was found
In the calibration group, the counts-METs regression model achieved R² = 0.76. Cross-validation in the laboratory yielded an absolute percent error of 18 ± 13%, with equivalence to indirect calorimetry demonstrated at the slowest (1.5 mph) and fastest (4.0–4.5 mph) treadmill stages. In free-living conditions, the model accurately quantified light- and moderate-intensity activity but significantly underestimated vigorous-intensity physical activity (6.5 ± 11.3 vs. 5.5 ± 20.8 mins/day; p < 0.001).
Why it matters
Using tri-axial acceleration counts rather than stepping cadence alone improves the activPAL's ability to estimate light and moderate physical activity intensity in both laboratory and daily living environments.
Limits
The study sample was small (n = 40) and restricted to young adults (mean age 25), limiting generalizability to older or clinical populations. Laboratory testing was limited to treadmill locomotion, and the model significantly underestimated vigorous-intensity activity in free-living conditions.
Cited by
- supports Standard metabolic equivalent of task (MET) categories classify light activity as 0 to 3 METs, moderate activity as 3 to 6 METs, and vigorous activity as greater than 6 METs.