New relative intensity ambulatory accelerometer thresholds for elderly @entity1 and XXXX : the Generation 100 study.

@entity2270 @entity1 @entity26
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 @entity26 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- @entity26 -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 @entity2270 ( @entity2270 ) and vector-magnitude (VM)) and VO2max% and HRmax% was established using a mixed-regression-model. VM-and @entity2270 -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 @entity1 and @entity1 of ranging VO2max values (low, medium, high). VM-model was found to be a better predictor of PA-intensity than @entity2270 -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 @entity1 and @entity1 , 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. CONCLUSION: 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. TRIAL REGISTRATION: (ClinicalTrials.gov Identifier: NCT02017847 , registered 17. December 2013).
