The ≥85% maxHR threshold for defining maximal exercise effort showed 91% sensitivity but only 13% specificity compared to the metabolic reference of RER >1.05, misclassifying 33% of tests.
Cohort (n=211)
Does the ≥85% maxHR threshold reliably indicate maximal physiological effort compared to RER >1.05 during cardiopulmonary exercise testing?
The conventional threshold of ≥85% age-predicted maximum heart rate is an inaccurate marker of maximal exertion during exercise testing, especially in patients on beta-blockers, and should not replace metabolic criteria like RER.
Abstract Background The practice of defining an exercise test as "maximal" once 85% of the age-predicted maximum heart rate (maxHR) is reached stems from submaximal protocols of the 1960s–1970s, where this threshold acted as a safety limit rather than a marker of maximal exertion. Despite this, it is still widely used to judge effort adequacy. In contrast, cardiopulmonary exercise testing (CPET) uses the respiratory exchange ratio (RER 1.05) as an indicator of true metabolic maximality. Aim To assess whether the ≥85% maxHR threshold reflects maximal effort, using RER 1.05 as the metabolic reference. Methods We analysed a consecutive cohort undergoing CPET. The population included competitive athletes and individuals with cardiovascular disease, including those receiving beta-blockers(BB). Tests were performed on a cycle ergometer using personalised ramp protocols designed to elicit maximal effort within 8–13 minutes. Breath-by-breath gas exchange was collected. Maximal effort was defined by a Borg score of 19–20 and RER 1.05, while achieving ≥85% of maxHR represented the conventional criterion. Results We included 211 individuals (median age 40 years, 71.6% male). Indications were suspected cardiomyopathy(48%), follow-up in cardiomiopathy(21%), coronary disease evaluation(7%), premature ventricular(4%) or supraventricular arrhythmias(2%), adult congenital heart disease(8%), coronary anomalies(2%), and performance assessment in healthy athletes(8%). Overall, 46% were athletes and 31% received BB. Peak HR was 164 (144–179) bpm, corresponding to 91% (82–96%) of maxHR, and peak RER was 1.12 (1.08–1.16). At 85%, RER was 1.02 (0.96–1.06), indicating that most had not reached metabolic maximality. Among those on BB, 66% did not reach ≥85%, yet 88% achieved RER 1.05. Findings were similar in athletes and non-athletes, with submaximal RER at 85% in both groups (1.01 vs 1.04). Using RER 1.05 as reference, the ≥85% threshold showed 91% sensitivity but 13% specificity, misclassifying as maximal 33% of tests, and as submaximal 61% among those receiving BB. Conclusions The ≥85% maxHR threshold does not reliably indicate maximal physiological effort or reflect true metabolic intensity. Heart rate alone is not an appropriate marker of test adequacy. Maximal testing requires guiding individuals to their highest capacity, supported by perceived exertion. Figure 1. The scatter distribution illustrates that RER-defined maximal effort is frequently reached at heart rates either well below or above the 85% maxHR threshold. RER, respiratory exchange ratio; HR, heart rate.Figure 1For image description, please refer to the figure legend and surrounding text.
Graziano et al. (Mon,) conducted a cohort in Cardiovascular disease and healthy athletes (n=211). ≥85% maxHR threshold vs. RER >1.05 was evaluated on Maximal effort defined by RER >1.05. The ≥85% maxHR threshold for defining maximal exercise effort showed 91% sensitivity but only 13% specificity compared to the metabolic reference of RER >1.05, misclassifying 33% of tests.