title: Moderate intense physical activity depends on selected Metabolic Equivalent of Task (MET) cut-off and type of data analysis.
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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: van Remoortel
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Carlos Augusto
authors.initials: CA
authors.lastname: Camillo
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Daniel
authors.initials: D
authors.lastname: Langer
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Miek
authors.initials: M
authors.lastname: Hornikx
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Heleen
authors.initials: H
authors.lastname: Demeyer
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Chris
authors.initials: C
authors.lastname: Burtin
authors.affiliation: Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Marc
authors.initials: M
authors.lastname: Decramer
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Rik
authors.initials: R
authors.lastname: Gosselink
authors.affiliation: Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Wim
authors.initials: W
authors.lastname: Janssens
authors.affiliation: Faculty of Kinesiology and Rehabilitation Sciences, Department of Rehabilitation Sciences, Katholieke Universiteit Leuven, Leuven, Belgium ; Respiratory Division and Rehabilitation, UZ Gasthuisberg, Leuven, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Troosters
mesh_terms: D061725:Accelerometry / Q000592:standards* / Q000706:statistics & numerical data; D003430:Cross-Sectional Studies; D006801:Humans; D016013:Likelihood Functions; D009043:Motor Activity / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013147:Spirometry; D018709:Statistics, Nonparametric; D013997:Time Factors