title: Intensity Thresholds on Raw Acceleration Data: Euclidean Norm Minus One (ENMO) and Mean Amplitude Deviation (MAD) Approaches.
abstract: OBJECTIVE
  (1) To develop and internally-validate Euclidean Norm Minus One (ENMO) and Mean Amplitude Deviation (MAD) thresholds for separating sedentary behaviours from common light-intensity physical activities using raw acceleration data collected from both hip- and wrist-worn tri-axial accelerometers; and (2) to compare and evaluate the performances between the ENMO and MAD metrics.
  
  
  METHODS
  Thirty-three adults [mean age (standard deviation (SD)) = 27.4 (5.9) years; mean BMI (SD) = 23.9 (3.7) kg/m2; 20 females (60.6%)] wore four accelerometers; an ActiGraph GT3X+ and a GENEActiv on the right hip; and an ActiGraph GT3X+ and a GENEActiv on the non-dominant wrist. Under laboratory-conditions, participants performed 16 different activities (11 sedentary behaviours and 5 light-intensity physical activities) for 5 minutes each. ENMO and MAD were computed from the raw acceleration data, and logistic regression and receiver-operating-characteristic (ROC) analyses were implemented to derive thresholds for activity discrimination. Areas under ROC curves (AUROC) were calculated to summarise performances and thresholds were assessed via executing leave-one-out-cross-validations.
  
  
  RESULTS
  For both hip and wrist monitor placements, in comparison to the ActiGraph GT3X+ monitors, the ENMO and MAD values derived from the GENEActiv devices were observed to be slightly higher, particularly for the lower-intensity activities. Monitor-specific hip and wrist ENMO and MAD thresholds showed excellent ability for separating sedentary behaviours from motion-based light-intensity physical activities (in general, AUROCs >0.95), with validation indicating robustness. However, poor classification was experienced when attempting to isolate standing still from sedentary behaviours (in general, AUROCs <0.65). The ENMO and MAD metrics tended to perform similarly across activities and accelerometer brands.
  
  
  CONCLUSIONS
  Researchers can utilise these robust monitor-specific hip and wrist ENMO and MAD thresholds, in order to accurately separate sedentary behaviours from common motion-based light-intensity physical activities. However, caution should be taken if isolating sedentary behaviours from standing is of particular interest.
authors.affiliation: Department of Health Sciences, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.
authors.forename: Kishan
authors.initials: K
authors.lastname: Bakrania
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Yates
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|Alliance for Research in Exercise, Nutrition and Activity (ARENA), Sansom Institute for Health Research, Division of Health Sciences, University of South Australia, Adelaide, Australia.
authors.forename: Alex V
authors.initials: AV
authors.lastname: Rowlands
authors.affiliation: National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, Leicestershire, United Kingdom.
authors.forename: Dale W
authors.initials: DW
authors.lastname: Esliger
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Bunnewell
authors.affiliation: National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, Leicestershire, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: Sanders
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.
authors.forename: Melanie
authors.initials: M
authors.lastname: Davies
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care - East Midlands (CLAHRC - EM), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.
authors.forename: Kamlesh
authors.initials: K
authors.lastname: Khunti
authors.affiliation: Diabetes Research Centre, University of Leicester, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.|National Institute for Health Research (NIHR) Leicester-Loughborough Diet, Lifestyle and Physical Activity Biomedical Research Unit (BRU), Diabetes Research Centre, Leicester General Hospital, Leicester, Leicestershire, United Kingdom.
authors.forename: Charlotte L
authors.initials: CL
authors.lastname: Edwardson
mesh_terms: D061725:Accelerometry / Q000295:instrumentation / Q000592:standards; D056044:Actigraphy / Q000295:instrumentation / Q000592:standards*; D000328:Adult; D015444:Exercise; D005260:Female; D006615:Hip / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture / Q000502:physiology; D012372:ROC Curve; D057185:Sedentary Behavior; D014953:Wrist / Q000502:physiology*; D055815:Young Adult