Relative‐Intensity Physical Activity and Its Association With Cardiometabolic Disease

Abstract

Aerobic guidelines from the US Department of Health and Human Services recommend at least 150 min/wk of moderateintensity physical activity, 75 min/wk of vigorousintensity physical activity, or an equivalent combination of moderatetovigorous intensity physical activity (MVPA).1 MVPA intensity is defined either in terms of absolute intensity or relative intensity. Absolute intensity refers to the energy required to perform an activity and does not take into account an individual’s exercise capacity. Relative intensity is when the level of effort is relative to a person’s exercise capacity.2,3 For adults aged 18 to 64 years, US Department of Health and Human Services guidelines are based on an absoluteintensity scale. There is limited evidence on whether it is better to assess MVPA on a relative scale to promote and maintain health. Addressing this question has important implications about how individuals should monitor their MVPA intensity, how physicians should prescribe MVPA, and whether current MVPA guidelines should be modified. Accelerometerderived MVPA intensity is estimated on an absolute scale. Using data from a large observational study, we investigated the prospective association between relativeintensity MVPA and incident hypertension, incident diabetes mellitus, and waist circumference (WC), and compared our results with those obtained using absoluteintensity MVPA. Participants were from the CARDIA (Coronary Artery Risk Development in Young Adults) study, an ongoing cohort study of 5115 Black and White men and women aged 18 to 30 years at baseline in 1985 to 1986.4 In 2005 to 2006 (year 20), an ancillary CARDIA Fitness Study was performed on 2760 participants aged 38 to 50 years who wore accelerometers for 1 week. Previously,2 we modeled the relationship between accelerometer counts and rating of perceived exertion3 during the year 20 treadmill test to calculate personspecific accelerometer cut points corresponding to relativeintensity MVPA. Participants were reexamined in 2010 to 2011 (year 25) and 2015 to 2016 (year 30). Incident hypertension was defined as systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of hypertension medication, at year 25 or year 30. Incident diabetes mellitus was defined as hemoglobin A1c ≥6.5%, fasting glucose ≥126 mg/dL, 2hour glucose ≥200 mg/ dL, or use of diabetes mellitus medication, at year 25 or year 30. We excluded those who did not have accelerometer data (n=399) or who wore the accelerometer <4 days (n=241). Those with missing or prevalent year 20 hypertension (n=395) and diabetes mellitus (n=197) were excluded from the hypertension and diabetes mellitus analyses, respectively. Also excluded were participants with missing outcomes: incident hypertension (n=88), incident diabetes mellitus (n=105), year 30 WC (n=262), or missing year 20 covariates (n=23). The study was approved by the Institutional Review Boards at all sites. Participants provided written informed consent. Data and methods used in this analysis are available on request (http://www.cardia.dopm. uab.edu/conta ctcardia). Analyses were performed using R (version 4.0.3). We used generalized additive models5 to examine nonlinear relationships of average daily minutes of MVPA with time to hypertension, time to diabetes mellitus, and year 30 WC, stratified by sex. Separate models were fit using MVPA on relativeand absoluteintensity