Validity of relationships between heart rate reserve and oxygen uptake reserve percentages in cycling and running exercise prescription

Abstract

Introduction: The relationship between the percentage of heart rate reserve (%HRR) and percentage of oxygen uptake reserve (%VO2R) has been recommended for prescribing aerobic exercise intensity due to the supposed relation of equivalence of 1:1. However, this relationship was derived from progressive maximal exercise testing data and the accuracy of the relationship during prolonged exercise at a constant work rate has not been established. Objective: The present study investigated the relationship between %HRR and %VO2R during a cardiopulmonary exercise test (CPET) and discrete bouts of isocaloric cycling and treadmill running. Methods: Thirty physically active men [mean (minimum –maximum): age, 24 (18-34) yr; height, 181 (163-198) cm; body mass, 84 (59-116) kg; body mass index, 25 (20-30) kg.m-2; percentage body fat, 18% (9%-27%) visited the laboratory three times for anthropometrical and resting VO2 assessments, and perform cycling and running CPETs. Ten men visited the laboratory twice more to investigate the validity of the %HRR-%VO2R relationships during isocaloric bouts of cycling and running at 75% VO2R with energy expenditures of 400 kcals. Results: The %VO2R was significantly lower than the %HRR in the CPETs, especially during running (P < 0.001). During isocaloric exercise bouts, mean %HRR-%VO2R differences of 6.5% and 7.0% were observed for cycling and running, respectively (P = 0.007 to P < 0.001). The %HRR and %VO2R increased over time (P < 0.001), the rate of which was influenced by exercise modality (P < 0.001). On average, heart rate was 5 (P = 0.007) and 8 (P < 0.001) beats·min-1 higher than predicted from the second time quartile for cycling and running, respectively; however, observed VO2 was lower than predicted during all quartiles for cycling, and the first quartile for running. Consequently, time to achieve the target energy expenditure was greater than predicted (P < 0.01). Conclusion: The %HRR-%VO2R relationship observed during CPET data did not accurately transpose to prolonged isocaloric bouts of cycling and running. Additionally, work rates defined by the ACSM equations for cycling and running overestimated VO2 and energy expenditure.