Are wearable heart rate measurements accurate to estimate aerobic energy cost during low-intensity resistance exercise?

Victor M Reis,Tiago M Barbosa,André L Carneiro,Jeferson M Vianna,Felipe J Aidar,Jefferson Novaes,Nuno Garrido,Jose Vilaça Alves

doi:10.1371/journal.pone.0221284

Abstract

The aim of the present study was to assess the accuracy of heart rate to estimate energy cost during eight resistance exercises performed at low intensities: half squat, 45° inclined leg press, leg extension, horizontal bench press, 45° inclined bench press, lat pull down, triceps extension and biceps curl. 56 males (27.5 ± 4.9 years, 1.78 ± 0.06 m height, 78.67 ± 10.7 kg body mass and 11.4 ± 4.1% estimated body fat) were randomly divided into four groups of 14 subjects each. Two exercises were randomly assigned to each group and subjects performed four bouts of 4-min constant-intensity at each assigned exercise: 12%, 16%, 20% and 24% 1-RM. Exercise and intensity order were random. Each subject performed no more than 2 bouts in the same testing session. A minimum recovery of 24h was kept between sessions. During testing VO2 was measured with Cosmed K4b2 and heart rate was measured with Polar V800 monitor. Energy cost was calculated from mean VO2 during the last 30-s of each bout by using the energy equivalent 1 ml O2 = 5 calorie. Linear regressions with heart rate as predictor and energy cost as dependent variable were build using mean data from all subjects. Robustness of the regression lines was given by the scatter around the regression line (Sy.x) and Bland-Altman plots confirmed the agreement between measured and estimated energy costs. Significance level was set at p≤0.05. The regressions between heart rate and energy cost in the eight exercises were significant (p<0.01) and robustness was: half squat (Sy.x = 0,48 kcal·min-1), 45° inclined leg press (Sy.x = 0,54 kcal·min-1), leg extension (Sy.x = 0,59 kcal·min-1), horizontal bench press (Sy.x = 0,47 kcal·min-1), 45° inclined bench press (Sy.x = 0,54 kcal·min-1), lat pull down (Sy.x = 0,28 kcal·min-1), triceps extension (Sy.x = 0,08 kcal·min-1) and biceps curl (Sy.x = 0,13 kcal·min-1). We conclude that during low-intensity resistance exercises it is possible to estimate aerobic energy cost by wearable heart rate monitors with errors below 10% in healthy young trained males.

Highlights

Aerobic exercise intensity and its energy cost (EC) are often assessed with the use of wearable heart rate monitors
Relative errors, when expressed to the measured energy cost at 24% 1-RM exercise intensity, were all up to 10% (Table 1)
We found that the standard errors of the regression between energy cost and heart rate varied between 0,08 kcal min-1in triceps extension exercise and 0,59 kcal min-1 in leg extension exercise

Summary

Introduction

Aerobic exercise intensity and its energy cost (EC) are often assessed with the use of wearable heart rate monitors. This procedure relies on the good agreement between heart rate, exercise intensity and EC in low- to moderate-intensity steady-state aerobic exercise. Resistance exercise (RE), when performed at low-intensities, presents bioenergetics that are quite like those described for aerobic steady-state exercise, with a major aerobic contribution to energy release [4]. Due the growing interest of low-intensity RE (i.e. to address the elderly or some pathologies) it is necessary to accumulate data on the specific energy cost of the most popular exercises and, in the future, to use such data to build technology that enables accurate calorie count during RE.

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