JMIR Publications

ABSTRACT

Background:

Resting heart rate (HR) and routine physical activity are associated with cardiorespiratory fitness levels. Commercial smartwatches permit remote HR monitoring and step count recording in real-world settings over long periods of time, but the relations of smartwatch-measured HR and daily steps to cardiorespiratory fitness remain incompletely characterized in the community.

Objective:

We examined the association of non-active HR and daily steps measured by a smartwatch with a multi-dimensional fitness assessment via cardiopulmonary exercise test (CPET) among participants in the electronic Framingham Heart Study (eFHS).

Methods:

eFHS participants were enrolled at a research exam (2016-2019) and provided with a study smartwatch that collected longitudinal HR and physical activity data for up to 3 years. At the same exam, participants underwent CPET on a cycle ergometer. Multivariable linear models were used to test the association of CPET indices with non-active HR and daily steps.

Results:

We included 662 participants (mean age 53±9 years, 59% women, 91% White, mean non-active HR 73±6 beats/minute) with a median of 1,836 HR records and a median of 128 watch-wearing days for each individual. In multivariable-adjusted models, lower non-active HR and higher daily steps were associated with higher peak oxygen uptake (VO2), % predicted peak VO2, and VO2 at the ventilatory anaerobic threshold (VAT), with false discovery rate-adjusted p-values (FDR-P) <0.001 for all. Reductions of 2.4 beats per minute in non-active HR, or increases of nearly 1000 daily steps corresponded to a 1.3 ml/kg/min higher peak VO2. In addition, ventilatory efficiency (VE/VCO2), % predicted maximum HR, and systolic blood pressure-to-workload slope (SBP/W slope) were associated with non-active HR (FDR-P<0.05) but not associated with daily steps (FDR-P>0.05).

Conclusions:

Our findings suggest the feasibility of simple smartwatch-based assessments as indicators of a broad array of cardiorespiratory fitness responses in the community, including measures of global fitness (peak VO2), ventilatory efficiency, and blood pressure response to exercise. Metrics captured by wearable devices offer a valuable opportunity to utilize extensive data on health factors and behaviors to provide a window into individual cardiovascular fitness levels.