Purpose We investigated the cardiovascular individual response to 6 weeks (3×/week) of work-matched within the severe-intensity domain (high-intensity interval training, HIIT) or moderate-intensity domain (moderate-intensity continuous training, MICT). In addition, we analyzed the cardiovascular factors at baseline underlying the response variability. Methods 42 healthy sedentary participants were randomly assigned to HIIT or MICT. We applied the region of practical equivalence-method for identifying the levels of responders to the maximal oxygen uptake (V̇O2max) response. For investigating the influence of cardiovascular markers, we trained a Bayesian machine learning model on cardiovascular markers. Results Despite that HIIT and MICT induced significant increases in V̇O2max, HIIT had greater improvements than MICT (p < 0.001). Greater variability was observed in MICT, with approximately 50% classified as “non-responder” and “undecided”. 20 “responders”, one “undecided” and no “non-responders” were observed in HIIT. The variability in the ∆V̇O2max was associated with initial cardiorespiratory fitness, arterial stiffness, and left-ventricular (LV) mass and LV end-diastolic diameter in HIIT; whereas, microvascular responsiveness and right-ventricular (RV) excursion velocity showed a significant association in MICT. Conclusion Our findings highlight the critical influence of exercise-intensity domains and biological variability on the individual V̇O2max response. The incidence of “non-responders” in MICT was one third of the group; whereas, no “non-responders” were observed in HIIT. The incidence of “responders” was 11 out of 21 participants in MICT, and 20 out of 21 participants in HIIT. The response in HIIT showed associations with baseline fitness, arterial stiffness, and LV-morphology; whereas, it was associated with RV systolic function in MICT.

Purpose: Sudden cardiac death [SCD] in competitive athletes is caused by a diverse set of cardiovascular diseases such as hypertrophic and dilated cardiomyopathy [HCM/DCM], myocarditis, coronary anomalies or even coronary artery disease. In order to identify potential risk factors responsible for SCD, elite athletes underwent cardiac magnetic resonance [CMR] imaging. Materials and Methods: 73 male [M] and 22 female [F] athletes (mean age 35.2???11.4 years) underwent CMR imaging. ECG-gated breath-hold cine SSFP sequences were used for the evaluation of wall motion abnormalities and myocardial hypertrophy as well as for quantitative analysis (left and right ventricular [LV, RV] end-diastolic and end-systolic volume [EDV, ESV], stroke volume [SV], ejection fraction [EF] and myocardial mass [MM]). Furthermore, left and right atrial sizes were assessed by planimetry and delayed enhancement imaging was performed 10 minutes after the application of contrast agent. Coronary arteries were depicted using free-breathing Flash-3?D MR angiography. Results: The quantitative analyses showed eccentric hypertrophy of the left ventricle (remodeling index [MM/LV-EDV]: M 0.75, F 0.665), enlargement of the RV volumes (RV-EDV: M 122.6???19.0?ml/m?, F 99.9???7.2?ml/m?) and an increased SV (LV-SV: M?64.7???10.0?ml/m?, F 56.5???5.7?ml/m?; RV-SV; M?66.7???10.4?ml/m?, F 54.2???7.1?ml/m?). Abnormal findings were detected in 6 athletes (6.3?%) including one benign variant of coronary anomaly and abnormal late gadolinium enhancement in 2 cases. None of the athletes showed wall motion abnormalities or signs of myocardial ischemia. Conclusion: CMR imaging of endurance athletes revealed abnormal findings in more than 5?% of the athletes. However, the prognostic significance remains unclear. Thus, cardiac MRI cannot be recommended as a routine examination in the care of athletes. Key points: Citation Format:

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Intensive endurance training can induce abnormal ECG patterns at rest. These alterations are differentiated into minor, mildly or distinctly abnormal ECG patterns. Echocardiographic data imply a correlation between the extent of these alterations and cardiac parameters like cardiac volume or wall thickness. In comparison to echocardiography, cardiac magnetic resonance imaging (MRI) is characterized by high reproducibility and accuracy. The aim of this study was to investigate the correlation between ECG alterations and cardiac parameters in highly trained asymptomatic male endurance athletes as assessed using cardiac MRI. Forty-five asymptomatic male endurance athletes (mean age 40 ± 8.9 years., range 19-59 years., 13 ± 5 h of training per week) underwent a cardiac MRI examination in addition to a resting ECG. Based on the ECG patterns at rest, the athletes were divided into groups with normal or minor (group 1) and mild or distinct (group 2) alterations. Steady-state free-precession cine MRI was used to calculate left and right ventricular end-diastolic volume, end-systolic volume, stroke volume, ejection fraction, and myocardial mass (MM). Late enhancement imaging was used to exclude structural alterations or myocardial scarring. Athletes in group 1 and 2 did not differ significantly in terms of age, height, body weight, body mass index or hours of training per week. Athletes with mildly or distinctly abnormal ECG patterns showed a significantly higher MM than athletes with minor ECG alterations at rest or normal resting ECG values (156.4 ± 18.4 g vs. 140.5 ± 20.0 g; p = 0.0103). The differences persisted when the values were corrected for body surface area (80.0 ± 7.4 g/m² vs. 73.4 ± 8.3 g; p = 0.0093). All other assessed cardiac parameters did not differ between the two groups. Pathological myocardial enhancement was detected only in one patient with a minor abnormal ECG. Male asymptomatic endurance athletes with mildly or distinctly abnormal ECG patterns at rest are characterized by a higher myocardial mass than comparable athletes with minor alterations or normal ECG at rest. Thus, the extent of ECG-abnormalities seems to be mainly the result of an increase in myocardial mass. Additionally, the absence of mild or distinct ECG alterations does not exclude the presence of pathological late gadolinium enhancement.

"Athlete's heart" is characterized by an increase in ventricular chamber sizes and myocardial mass (MM), and is mainly observed in endurance athletes. At present, it remains unclear whether cardiac adaptations in long-distance runners differ from those in triathletes. Twenty male triathletes (mean age 38.7 ± 6.2 years) and 20 male marathon runners (mean age 44.1 ± 7.9) underwent cardiac magnetic resonance imaging to calculate left and right ventricular end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), and MM. Late-enhancement (LE) imaging was used to exclude structural alterations or myocardial scarring. EDV, ESV, SV, and EF for the left and right ventricles, as well as MM, did not differ between long-distance runners and triathletes, although the weekly training volume was significantly higher in triathletes (17.05 vs 9.95 h/week, P < 0.0001). There was a significant correlation between weekly training volume and right and left EDV, right and left ESV as well as MM within the study group. Myocardial LE was absent in all athletes. Highly trained male long-distance runners and triathletes have comparable cardiac parameters. However, the extent of physical training seems to be associated with the degree of cardiac adaptation in endurance athletes. The absence of LE supports the idea that athlete's heart is a nonpathological adaptation of the cardiovascular system.