This case study provides 'the most definitive illustration that a sufficiently intense and prolonged dose of exercise (in this case, 24 h of intense cycling) can result in acute heart failure,' while also demonstrating complete recovery by 5 months post-attempt.
Key Findings
Results
24 hours of intense cycling resulted in acute heart failure with pulmonary edema in a highly trained ultra-endurance athlete.
The athlete was in acute respiratory distress and showed signs of acute pulmonary edema immediately following the 24-hour attempt.
The 24-hour attempt was a world-record-setting effort completed in March 2018 when the athlete was 42 years old.
This outcome contrasted sharply with the 12-hour attempt, after which the athlete was physically exhausted but showed no signs of respiratory distress or heart failure.
The findings represent what the authors describe as 'the most definitive illustration of an exercise dose threshold that resulted in acute heart failure in a highly trained endurance athlete.'
Results
Cardiac biomarkers were markedly elevated following the 24-hour attempt compared to the 12-hour attempt.
After the 24-hour attempt, BNP was 561 ng/L and cardiac troponin-I (cTnI) was 394 ng/L.
After the 12-hour attempt, BNP was 166 ng/L and cTnI was 64 ng/L.
Both BNP and cTnI elevations following the 24-hour attempt were described as 'pronounced,' compared to 'moderately increased' following the 12-hour attempt.
Cardiac biomarkers measured included B-type natriuretic peptide (BNP) and cardiac troponin-I (cTnI).
Results
Biventricular ejection fraction and myocardial strain were markedly reduced following the 24-hour attempt.
After the 24-hour attempt, left ventricular (LV) ejection fraction was 37% and right ventricular (RV) ejection fraction was 32%.
After the 24-hour attempt, LV strain was -14.2% and RV strain was -13.8%.
After the 12-hour attempt, LV ejection fraction was 43% and RV ejection fraction was 43%, with LV strain of -12.2% and RV strain of -13.4%.
Cardiac imaging included echocardiography and rest and exercise cardiac magnetic resonance imaging (CMR).
Reductions following the 24-hour attempt were described as 'marked' compared to 'moderately reduced' following the 12-hour attempt.
Results
Cardiac function fully recovered by 5 months following the 24-hour attempt, though only partial recovery was observed at 18 days.
Cardiac function 'only partially recovered 18 days postattempt but had completely normalized by 5 mo postattempt' following the 24-hour cycling bout.
In contrast, all cardiac parameters recovered within 14 days following the 12-hour attempt.
The authors note that 'the absence of persistent myocardial injury highlights the resilience of the heart to acute stress.'
Complete normalization by 5 months was observed despite the acute heart failure presentation immediately post-attempt.
Results
The 12-hour cycling attempt produced moderate but transient cardiac dysfunction without clinical heart failure.
Following the 12-hour attempt, BNP was 166 ng/L and cTnI was 64 ng/L, described as 'moderately increased.'
LV ejection fraction was 43% and RV ejection fraction was 43%, both described as 'moderately reduced.'
All parameters recovered within 14 days of the 12-hour attempt.
The 12-hour attempt was completed in March 2017 when the athlete was 41 years old and was also a world-record-setting effort.
The athlete was 'physically exhausted but demonstrated no signs of respiratory distress or heart failure' after the 12-hour attempt.
Results
A dose-response threshold between 12 and 24 hours of intense cycling was identified for triggering acute heart failure.
12 hours of intense cycling produced moderate, fully reversible cardiac fatigue without clinical heart failure.
24 hours of intense cycling exceeded a threshold resulting in acute heart failure with pulmonary edema.
The study used comprehensive evaluation including cardiac imaging (echocardiography and CMR), cardiac biomarkers, and clinical evaluation before and at several timepoints following both attempts.
The authors describe this as 'the most definitive illustration of an exercise dose threshold that resulted in acute heart failure.'
What This Means
This research followed a single highly trained ultra-endurance athlete who attempted two world-record cycling events: 12 hours in 2017 and 24 hours in 2018. Researchers measured heart function, heart stress markers in the blood, and clinical symptoms before, immediately after, and at multiple follow-up points after each event. After the 12-hour ride, the athlete was exhausted and showed some signs of cardiac strain — reduced heart pumping function and elevated blood markers of heart stress — but had no breathing problems and fully recovered within two weeks. After the 24-hour ride, however, the athlete developed acute respiratory distress and signs of pulmonary edema (fluid in the lungs), which are hallmarks of acute heart failure. Blood markers of heart stress were dramatically higher, and heart pumping function was substantially reduced in both the left and right ventricles.
This research suggests there is a threshold somewhere between 12 and 24 hours of intense cycling beyond which the heart can be pushed into a state of acute heart failure, even in an elite athlete whose heart is highly adapted to endurance exercise. The right ventricle — which pumps blood to the lungs — appeared particularly affected in both attempts, consistent with prior research suggesting the right side of the heart is especially vulnerable during prolonged endurance exercise.
Despite the severity of the acute heart failure after the 24-hour attempt, the athlete's heart function had completely returned to normal within 5 months, with no evidence of lasting damage. This research suggests the heart has remarkable resilience to even extreme acute stress, but also underscores that there are real physiological limits to prolonged intense exercise, and that adequate recovery time after extreme endurance events is important for allowing the heart to heal.
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Foulkes S, Anderson M, Janssens K, Beaudry R, Carey A, Mitchell A, et al.. (2026). From healthy to heart failure in 24 hours: defining the upper limit of exercise-induced cardiac fatigue.. Journal of applied physiology (Bethesda, Md. : 1985). https://doi.org/10.1152/japplphysiol.00140.2026