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. 2020 Feb;52(2):398-407.
doi: 10.1249/MSS.0000000000002153.

Individualized Relative-Intensity Physical Activity Accelerometer Cut Points

Juned Siddique  1 , David Aaby  1 , Samantha E Montag  1 , Stephen Sidney  2 , Barbara Sternfeld  2 , Whitney A Welch  1 , Mercedes R Carnethon  1 , Kiang Liu  1 , Lynette L Craft  3 , Kelley Pettee Gabriel  4 , Bethany Barone Gibbs  5 , Jared P Reis  6 , Patty Freedson  7
Affiliations

Individualized Relative-Intensity Physical Activity Accelerometer Cut Points

Juned Siddique et al. Med Sci Sports Exerc. 2020 Feb.

Abstract

Purpose: Physical activity (PA) intensity is expressed as either absolute or relative intensity. Absolute intensity refers to the energy required to perform an activity. Relative intensity refers to a level of effort that takes into account how hard an individual is working relative to their maximum capacity. We sought to develop methods for obtaining individualized relative-intensity accelerometer cut points using data from a maximal graded exercise treadmill test (GXT) so that each individual has their own cut point.

Methods: A total of 2363 men and women 38 to 50 yr old from the CARDIA fitness study wore ActiGraph 7164 accelerometers during a maximal GXT and for seven consecutive days in 2005-2006. Using mixed-effects regression models, we regressed accelerometer counts on heart rate as a percentage of maximum (%HRmax) and on RPE. Based on these two models, we obtained a moderate-intensity (%HRmax = 64% or RPE = 12) count cut point that is specific to each participant. We applied these subject-specific cut points to the available CARDIA accelerometer data.

Results: Using RPE, the mean moderate-intensity accelerometer cut point was 4004 (SD = 1120) counts per minute. On average, cut points were higher for men (4189 counts per minute) versus women (3865 counts per minute) and were higher for Whites (4088 counts per minute) versus African Americans (3896 counts per minute). Cut points were correlated with body mass index (rho = -0.11) and GXT duration (rho = 0.33). Mean daily minutes of absolute- and relative-intensity moderate to vigorous PA were 34.1 (SD = 31.1) min·d and 9.1 (SD = 18.2) min·d, respectively. RPE cut points were higher than those based on %HRmax. This is likely due to some participants ending the GXT before achieving their HRmax.

Conclusions: Accelerometer-based relative-intensity PA may be a useful measure of intensity relative to maximal capacity.

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Conflict of interest statement

CONFLICT OF INTEREST

Dr. Freedson has served as a paid consultant for ActiGraph. The remaining authors have no conflicts of interest to disclose. Results of the present study do not constitute endorsement by ACSM. Results are presented clearly (as possible), honestly, and without fabrication, falsification or inappropriate data manipulation. The views expressed in this manuscript are those of the authors and do not necessarily represent the views of the NHLBI; the National Institutes of Health; or the U.S. Department of Health and Human Services.

Figures

Figure 1:
Figure 1:
Participant flow diagram of CARDIA Fitness study participants
Figure 2:
Figure 2:
Scatter plot of accelerometer cts/min and heart rate as a percentage of maximum (%HRmax) (left panel) and rating of perceived exertion (RPE) (right panel) at each stage of the CARDIA treadmill test. In both panels, the solid line is a smoothed non-parametric estimate of the relationship.
Figure 3:
Figure 3:
Average weekly minutes of MVPA on a relative intensity scale (y-axis) versus an absolute intensity scale (x-axis). In the left panel, the cut-points for classifying relative intensity MVPA were estimated using heart rate as a percentage of maximum heart rate (%HRmax) from the treadmill test. In the right panel, the cut-points for classifying relative intensity MVPA were estimated using rating of perceived exertion (RPE) from the treadmill test. In both panels, the 45 degree line identifies the region where both absolute and relative intensity MVPA minutes are the same. The vertical dotted line identifies those participants who averaged more or less than 21 minutes of MVPA per day on an absolute intensity scale. The horizontal dotted line identifies those who averaged more or less than 21 minutes of MVPA per day on a relative intensity scale.
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