title: Validation of Cut-Points for Evaluating the Intensity of Physical Activity with Accelerometry-Based Mean Amplitude Deviation (MAD).
abstract: OBJECTIVE
  Our recent study of three accelerometer brands in various ambulatory activities showed that the mean amplitude deviation (MAD) of the resultant acceleration signal performed best in separating different intensity levels and provided excellent agreement between the three devices. The objective of this study was to derive a regression model that estimates oxygen consumption (VO2) from MAD values and validate the MAD-based cut-points for light, moderate and vigorous locomotion against VO2 within a wide range of speeds.
  
  
  METHODS
  29 participants performed a pace-conducted non-stop test on a 200 m long indoor track. The initial speed was 0.6 m/s and it was increased by 0.4 m/s every 2.5 minutes until volitional exhaustion. The participants could freely decide whether they preferred to walk or run. During the test they carried a hip-mounted tri-axial accelerometer and mobile metabolic analyzer. The MAD was calculated from the raw acceleration data and compared to directly measured incident VO2. Cut-point between light and moderate activity was set to 3.0 metabolic equivalent (MET, 1 MET = 3.5 ml · kg-1 · min-1) and between moderate and vigorous activity to 6.0 MET as per standard use.
  
  
  RESULTS
  The MAD and VO2 showed a very strong association. Within individuals, the range of r values was from 0.927 to 0.991 providing the mean r = 0.969. The optimal MAD cut-point for 3.0 MET was 91 mg (milligravity) and 414 mg for 6.0 MET.
  
  
  CONCLUSIONS
  The present study showed that the MAD is a valid method in terms of the VO2 within a wide range of ambulatory activities from slow walking to fast running. Being a device-independent trait, the MAD facilitates directly comparable, accurate results on the intensity of physical activity with all accelerometers providing tri-axial raw data.
authors: The UKK Institute for Health Promotion Research, Tampere, Finland.
authors: Henri
authors: H
authors: Vähä-Ypyä
authors: The UKK Institute for Health Promotion Research, Tampere, Finland.
authors: Tommi
authors: T
authors: Vasankari
authors: The UKK Institute for Health Promotion Research, Tampere, Finland.
authors: Pauliina
authors: P
authors: Husu
authors: The UKK Institute for Health Promotion Research, Tampere, Finland.
authors: Ari
authors: A
authors: Mänttäri
authors: Haaga-Helia University of Applied Sciences, Vierumäki, Finland.
authors: Timo
authors: T
authors: Vuorimaa
authors: The UKK Institute for Health Promotion Research, Tampere, Finland.
authors: Jaana
authors: J
authors: Suni
authors: The UKK Institute for Health Promotion Research, Tampere, Finland.
authors: Harri
authors: H
authors: Sievänen
mesh_terms: D000054:Acceleration; D061725:Accelerometry / Q000379:methods; D000328:Adult; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008124:Locomotion / Q000502:physiology; D008297:Male; D018670:Monitoring, Ambulatory / Q000379:methods; D009043:Motor Activity / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D012420:Running / Q000502:physiology; D016138:Walking / Q000502:physiology