Evidence of direct cardiac damage following high-intensity exercise in chronic energy restriction: a case report and literature review

Introduction: Following AQ4 prolonged endurance events such as marathons, elevated levels of cardiospecific biomarkers are commonly reported. Although transiently raised levels are generally not considered to indicate clinical myocardial damage, comprehension of this phenomenon remains incomplete. The popularity of high-intensity interval training highlights a paucity of research measuring cardiac biomarker response to this type of exercise. This a posteriori case report discusses the elevation of cardiac troponins (cTn) associated with short interval, high-intensity exercise.
Case summary: In this case report, an apparently healthy 29-year-old recreationally active female presented clinically raised cTn I levels (>0.04 ng/mL), after performing high-intensity cycle ergometer sprints. As creatine kinase (CK) is expressed by multiple organs (e.g., skeletal muscle, brain, and myocardium), cTnI assays were performed to determine any changes in total serum CK levels not originating from skeletal muscle damage. 
A posteriori the individual’s daily energy expenditure indicated chronically low-energy availability. Psychometric testing suggested that the individual scored positive for disordered eating, highly for fatigue levels, and low in mental health components. 
Conclusion: The current case report provides novel evidence of elevated cTnI occurring as a result of performing short duration, high intensity, cycle ergometer exercise in an individual with self-reported chronically depleted energy balance. A schematic to identify potentially “at risk” individuals is presented. Considering this as a case report, results cannot be generalized; however, the main findings suggest that individuals who habitually restrict their calorie intake below their bodies’ daily energy requirements, may have elevated biomarkers of exercise induced myocardial stress from performing high-intensity exercise.
Abbreviations: ATP = adenosine triphosphate, BMI = body mass index, BNP = B-type natriuretic peptide, CI = confidence interval, CK = creatine kinase, cTn = cardiac troponin, EAT = exercise associated thermogenesis, EDE-Q 6.0 = Eating Disorder Examination (28 Item) Questionnaire, Mg2+ = magnesium, NAT = nutritional analysis tool, NEAT = nonexercise associated thermogenesis, NHS = National Health Service, SF36v2 = Short Form Health Survey 36 version 2, TDEE = total daily energy expenditure, URL = upper reference limit, WHO = World Health Organization.