Moderate intense physical activity depends on selected Metabolic Equivalent of Task (MET) cut-off and type of data analysis

PLoS One. 2013 Dec 20;8(12):e84365. doi: 10.1371/journal.pone.0084365. eCollection 2013.

Abstract

Background: Accelerometry data are frequently analyzed without considering whether moderate-to-vigorous physical activities (MVPA) were performed in bouts of >10 minutes as defined in most physical activity guidelines. We aimed i) to quantify MVPA by using different commonly-applied physical activity guidelines, ii) to investigate the effect of bouts versus non-bouts analysis, and iii) to propose and validate a MVPA non-bouts cut-point to classify (in-) active subjects.

Methods: Healthy subjects (n=110;62±6yrs) and patients with Chronic Obstructive Pulmonary Disease (COPD) (n=113;62±5yrs) wore an activity monitor for 7 days. Three Metabolic Equivalent of Task (MET) cut-offs and one individual target (50% VO₂ reserve) were used to define MVPA. First, all minutes of MVPA were summed up (NON-BOUTS). Secondly, only minutes performed in bouts of >10 minutes continuous activity were counted (BOUTS). Receiver operating characteristic (ROC) curve analyses were used to propose and (cross-) validate new MVPA non-bout cut-points based on the criterion of 30 minutes MVPA per day (BOUTS). Likelihood ratios (sensitivity/[1-specificity]) were used to express the association between the proposed MVPA non-bout target and the MVPA bout target of 30 min*day⁻¹.

Results: MVPA was variable across physical activity guidelines with lowest values for age-specific cut-offs. Selecting a METs cut-point corresponding to 50% VO₂ reserve revealed no differences in MVPA between groups. MVPA's analyzed in BOUTS in healthy subjects were 2 to 4 fold lower than NON-BOUTS analyses and this was even 3 to 12 fold lower in COPD. The MVPA non-bouts cut-point of 80 min*day⁻¹ using a 3 METs MVPA threshold delivered positive likelihood ratios of 5.1[1.5-19.6] (healthy subjects) and 2.3[1.6-3.3] (COPD).

Conclusion: MVPA varies upon the selected physical activity guideline/targets and bouts versus non-bouts analysis. Accelerometry measured MVPA non-bouts target of 80 min*day⁻¹, using a 3 METs MVPA threshold, is associated to the commonly-used MVPA bout target of 30 min*day⁻¹.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Accelerometry / standards*
  • Accelerometry / statistics & numerical data
  • Cross-Sectional Studies
  • Humans
  • Likelihood Functions
  • Motor Activity / physiology*
  • Pulmonary Disease, Chronic Obstructive / physiopathology*
  • ROC Curve
  • Retrospective Studies
  • Sensitivity and Specificity
  • Spirometry
  • Statistics, Nonparametric
  • Time Factors

Grants and funding

This research was supported by FWO Vlaanderen (G.0598.09N). CAC is supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico/Brazil (204525/2011-8). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.