Your Heart Can’t See What Sneakers You Are Wearing: Exercise Training Load in Endurance Athletes Is Inadequately Quantified in Sports Cardiology

BACKGROUND: Training load may be an important factor underlying the (patho-)physiologic cardiovascular adaptations from endurance exercise. Yet, quantifying training load remains challenging due to the complexity of its components (Frequency, Intensity, Time, and Type [FITT]). In this systematic review we evaluate how training load has been quantified in sports cardiology studies and provide recommendations for how this can be improved. METHODS: A comprehensive search was conducted across PubMed and EMBASE up to October 2024. Studies involving "sports cardiology," "training load," and "endurance sport" were included. Data extraction included study characteristics, training load assessment methods, cardiovascular outcomes, and athlete profiles. RESULTS: A total of 62 studies with 1,060,700 participants were included in our review. The majority of studies (59.7%) focused on exercise-induced cardiac remodelling, with other topics being cardiac arrhythmias (12.9%), cardiac autonomic adaptation (3.2%), exercise dose-response (6.5%), and coronary heart disease (17.7%). Training load was primarily quantified by questionnaires (58.1%), whereas heart rate monitoring, a more objective measure, was used in only 1.6% of the studies. All studies reported exercise type, but only 19.4% measured all FITT components. CONCLUSIONS: There is a lack of uniformity in the assessment of key FITT variables to quantify training load within the field of sports cardiology, with many studies relying on subjective or incomplete methods. As cardiology moves into the precision medicine era, researchers and clinicians should seek to obtain objective training load information from their athletes according to the FITT framework, and data from use of objective wearable devices represent the optimal way to do this.