title: New relative intensity ambulatory accelerometer thresholds for elderly men and women: the Generation 100 study.
abstract: BACKGROUND
  Public health initiatives world-wide recommend increasing physical activity (PA) to improve health. However, the dose and the intensity of PA producing the most benefit are still debated. Accurate assessment of PA is necessary in order to 1) investigate the dose-response relationship between PA and health, 2) shape the most beneficial public health initiatives and 3) test the effectiveness of such initiatives. Actigraph accelerometer is widely used to objectively assess PA, and the raw data is given in counts per unit time. Count-thresholds for low, moderate and vigorous PA are mostly based on absolute intensity. This leads to largely inadequate PA intensity assessment in a large proportion of the elderly, who due to their declining maximal oxygen uptake (VO2max) cannot reach the moderate/vigorous intensity as defined in absolute terms. To resolve this issue, here we report relative Actigraph intensity-thresholds for the elderly.
  
  
  METHODS
  Submaximal-oxygen-uptake, VO2max and maximal heart rate (HRmax) were measured in 111 70-77 year olds, while wearing an Actigraph-GT3X+. Relationship between VO2max percentage (%), counts-per-minute (CPM) and gender (for both the vertical-axis (VA) and vector-magnitude (VM)) and VO2max% and HRmax% was established using a mixed-regression-model. VM-and VA-models were tested against each other to see which model predicts intensity of PA better.
  
  
  RESULTS
  VO2max and gender significantly affected number of CPM at different PA intensities (p < 0.05). Therefore, intensity-thresholds were created for both men and women of ranging VO2max values (low, medium, high). VM-model was found to be a better predictor of PA-intensity than VA-model (p < 0.05). Established thresholds for moderate intensity (46-63 % of VO2max) ranged from 669-3367 and 834-4048 CPM and vigorous intensity (64-90 % of VO2max) from 1625-4868 and 2012-5423CPM, for women and men, respectively. Lastly, we used this evidence to derive a formula that predicts customized relative intensity of PA (either VO2max% or HRmax%) using counts-per-minute values as input.
  
  
  CONCLUSIONS
  Intensity-thresholds depend on VO2max, gender and Actigraph-axis. PA intensity-thresholds that take all these factors into account allow for more accurate relative intensity PA assessment in the elderly and will be useful in future PA research.
  
  
  BACKGROUND
  (ClinicalTrials.gov Identifier: NCT02017847, registered 17. December 2013).
authors.affiliation: K.G. Jebsen Center of Exercise in Medicine at Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. nina.zisko@ntnu.no.
authors.forename: Nina
authors.initials: N
authors.lastname: Zisko
authors.affiliation: K.G. Jebsen Center of Exercise in Medicine at Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. trude.carlsen@ntnu.no.
authors.forename: Trude
authors.initials: T
authors.lastname: Carlsen
authors.affiliation: Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. oyvind.salvesen@ntnu.no.
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Salvesen
authors.affiliation: Institute for Science in Sport, Norwegian University of Science and Technology, Trondheim, Norway. nils.petter.aspvik@svt.ntnu.no.
authors.forename: Nils Petter
authors.initials: NP
authors.lastname: Aspvik
authors.affiliation: Institute for Science in Sport, Norwegian University of Science and Technology, Trondheim, Norway. jan.ingebrigtsen@svt.ntnu.no.
authors.forename: Jan Erik
authors.initials: JE
authors.lastname: Ingebrigtsen
authors.affiliation: K.G. Jebsen Center of Exercise in Medicine at Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. ulrik.wisloff@ntnu.no.
authors.forename: Ulrik
authors.initials: U
authors.lastname: Wisløff
authors.affiliation: K.G. Jebsen Center of Exercise in Medicine at Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway. dorthe.stensvold@ntnu.no.|Liaison Committee between the Central Norway Regional Health Authority (RHA) and the Norwegian University of Science and Technology (NTNU), Trondheim, Norway. dorthe.stensvold@ntnu.no.
authors.forename: Dorthe
authors.initials: D
authors.lastname: Stensvold
mesh_terms: D061725:Accelerometry / Q000295:instrumentation / Q000379:methods; D000368:Aged; D000375:Aging / Q000502:physiology*; D015308:Anaerobic Threshold / Q000502:physiology; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D015577:Geriatric Assessment / Q000379:methods; D006801:Humans; D007702:Kinetocardiography / Q000295:instrumentation / Q000379:methods; D008297:Male; D064797:Physical Conditioning, Human / Q000379:methods* / Q000502:physiology