Blood pressure response to bicycle exercise testing in athletes

It is common medical thinking that the combination of being involved in sports activities, regular exercise training and a healthy lifestyle would result in a lower incidence of hypertension and cardiovascular hard events. Fagard summarized all available published evidence and concluded that training for three to five times per week during 30–60 min per session at an intensity of about 40–50% of net maximal exercise performance appeared to be effective with regard to blood pressure (BP) reduction [1]. The former may hold true in the population at large but there has always been a vivid debate in literature on the validity of that claim in higher intensity training and even more for highly trained endurance athletes. It is justified by the common belief that increased BP is the first-in-line revealed abnormality in preparticipation cardiac screening of athletes. In the meta-analysis of 34 studies by Berge et al.[2], the reported prevalence of hypertension in athletes ranged from 0 to 83% in heavy weightlifters. As expected, the prevalence of left ventricular (LV) hypertrophy in trained individuals increased with their BP level but the mechanistic issue definitely remains a matter of debate. The interested reader will find an in-depth discussion of the topic in the ‘Recommendations for Echocardiography in Hypertension’ by Marwick et al.[3]. A typical example of a sport discipline at high risk of attaining high BP response and developing hypertension is American-style football with even substantial higher risk for their linemen [4]. However, reports in other less demanding disciplines clearly counterbalanced the concept of accrued risk of hypertension by high-intensity sports activities. For instance, a recent cross-sectional survey in a large European cohort (>2000) of competitive athletes (not including any American football players) showed a relatively low prevalence of hypertension (3% for a mean age of 25 years) [5]. A multivariable regression model incriminated two factors influencing the prevalence of hypertension: a family history of hypertension and the BMI. However, absence of hypertension does not necessarily mean absence of cardiovascular risk [6]! The combination of exercise testing and echocardiography is increasingly used, also in sports medicine. Exercise testing offers two opportunities in addition to exploring cardiovascular risk: a more quantitative estimation of the cardiovascular adaptations to strenuous efforts and guidance of training schedules. It is obvious that a sex-specific reference frame is required. In 2016, Caselli et al.[7] derived reference values and upper limits of BP response to ECG-monitored graded bicycle exercise testing in 1876 elite athletes. In their hands, upper limits of BP response were 220 mmHg in men and 200 mmHg in women. A total of 7.5% of their athletes were classified as ‘high BP responders to exercise’ and were characterized as those participating in endurance/mixed sport disciplines, those showing increased BMI and having increased baseline SBP in the absence of overt cardiac and metabolic abnormalities. In this issue of the Journal Pressler et al.[8] described the BP and heart rate responses during individually customized bicycle exercise testing in 2419 apparently healthy athletes (27% women) for preparticipation screening or preventive purposes. In essence, SBP significantly increased during the test (particularly in male endurance athletes) whereas DBP minimally changed. The study was sufficiently powered to allow for calculation of sex-specific upper normative limits for maximal SBP response during exercise testing: 247 mmHg for men and 214 mmHg for women. It is a pity that follow-up data are not presented to answer the tingling question whether exceeding the upper normative limits for exercise SBP in athletes and highly fit individuals will increase the risk of incident hypertension and hard endpoints. How to interpret an ‘exaggerated’ exercise BP in an athlete: a benign adaptive escape from ‘normal’ physiology or is it living in the vicinity of an impending volcanic eruption? An athlete's BP response to exercise differs from the nonathlete's response. The far most prevailing hypothesis claims a relative benign condition reflecting better physiological adaptation mechanisms to higher loads. In the general population, cardiorespiratory fitness modifies BP response in a somewhat different way: higher fitness lowers SBP response during exercise in ‘normal’ physiology. A significant portion of the athletes in Pressler's [8] study achieve SBP responses far exceeding the upper limits of 220 mmHg in men and 200 mmHg in women proposed by Caselli et al.[7] whose athletes apparently did not exercise till complete exhaustion (mean age of 25, mean maximal heart rate of 167). Next to a better training status and more excellent coping with higher intensity levels, top athletes more frequently develop a higher cardiac output (higher VO2max), and are more frequently free of overt cardiometabolic comorbidities [9]. In dynamic-type of sports activities, fat-free mass may significantly contribute to the maximal attained SBP during exercise testing. In their earlier research, Pressler et al.[10] incriminated increased peripheral resistance for the increases in maximal attained DBP in regular intensive strength training. According to Currie et al.[11], exaggerated BP response in athletes was not associated with latent dysfunctions such as impaired sympathetic reactivity, LV dysfunction or increased arterial stiffness. These authors suggested a compensatory mechanism to cope with the high peripheral blood flow demands. Given, however, the relatively high prevalence of masked hypertension [12] and the occurrence of exaggerated BP response in endurance athletes [13] one should not a priori deem that condition as innocuous. What is the prognostic value of maximal SBP response during bicycle exercise testing or of exercise-induced hypertension? The studies by Fagard et al.[14,15] in hypertensive men did not suggest a huge incremental value of BP response during exercise testing beyond that of office BP. In a meta-analysis, Schultz et al.[16] condensed the evidence from nine studies: a hypertensive response to moderate exercise-intensity exercise stress testing significantly predicted cardiovascular outcome whereas SBP at maximal workloads did not. In the young adults of the CARDIA cohort BP during exercise predicted 5-year risk of incident hypertension. Participants with an exaggerated BP response had slightly higher baseline SBP (1–3 mmHg) but were 1.70 times more likely to develop hypertension than individuals with normal BP responses [17]. Does the ability to perform beyond ‘normal’ limits guarantee longer life expectancy free of cardiovascular morbidity? Recently Antero-Jacquemin et al. documented a 6.5-year longevity gain in French Olympic Games athletes (1912–2012) [18]. However, the overall major driver of the advantage was lower risk of fatal cancer and of interest, the endurance athletes had a comparable risk of cardiovascular disease-related death as the population at large. Thus, a word of caution might be needed for the cardiovascular disease-related mortality in endurance athletes despite their unmistakable ‘supernormal’ heart in terms of cardiac performance. In this issue of the Journal, Pressler et al.[8] provided sex-specific upper normative limits of SBP response to maximal dynamic exercise in apparently healthy competitive athletes. These upper limits are considerably higher than earlier suggested values in literature. ‘Exaggerated’ BP responses were mostly observed in male endurance athletes. Elite endurance athletes undeniably have ‘supernormal’ hearts and their performances and BP peaks escape ‘normal’ physiology when compared with their age-matched and sex-matched counterparts from the general population. Recent studies have reiterated the epidemiological evidence that longevity will be secured in a large portion of highly trained athletes but future studies will have to answer the tantalizing question whether an endurance athlete's ‘exaggerated’ BP response to dynamic exercise will not compromise the cardiovascular disease-related part of his/her otherwise excellent prognosis. ACKNOWLEDGEMENTS Conflicts of interest There are no conflicts of interest.