Heart Failure and Exercise: New Insights on Muscle Fatigue
"Discover how heart failure affects muscle endurance during exercise, challenging previous beliefs about fatigue and cardiac function."
Chronic heart failure (CHF) often leads to reduced exercise capacity, impacting individuals' ability to perform daily activities. While central hemodynamic factors like cardiac output and muscle perfusion play a role, the direct effects of CHF on skeletal muscle function are increasingly recognized. Understanding these effects is crucial for developing effective exercise strategies for those living with CHF.
Traditionally, studies have focused on isometric contractions, where muscles generate force without changing length. These studies suggested increased muscle fatigue in CHF. However, everyday activities often involve isotonic contractions, where muscles shorten during movement. This type of muscle activity places different demands on energy metabolism, potentially influencing fatigue development.
Recent research has investigated how CHF affects muscle function during isotonic exercise, challenging previous findings. The results reveal surprising insights into how muscles adapt (or fail to adapt) during shortening contractions, offering new perspectives on exercise tolerance and the potential for rehabilitation.
The Scale of Fatigue and Functional Loss
Heart failure currently affects an estimated 6.2 million U.S. adults and approximately 2% of people globally. In chronic heart failure, performance in activities of daily living was reported as 30% lower than in controls, and this limitation was related to reduced aerobic capacity. Evidence also indicates that patients experience skeletal muscle fatigability in the lower extremities during single-limb tasks.
Exercise Training and Its Limits
Exercise prescription for heart failure commonly combines aerobic and resistance training. Practical guidelines report that resistance exercises can generally be added within 2–4 weeks of starting aerobic exercise, or sooner according to clinical judgment. However, impaired oxygen transport is a major determinant of reduced physical capacity and maximal oxygen uptake, and patients with heart failure may reach less than 50% of the maximal cardiac output attained by healthy people during peak exercise.
From Cardiac Dysfunction to Skeletal Myopathy
Early descriptions by Egyptian, Greek, and Roman physicians contributed to the historical understanding of cardiac dysfunction. Modern accounts define heart failure as a condition in which the heart does not pump as well as it should, potentially limiting the oxygen available to the body. Research on symptom origins further identified skeletal myopathy as a cause of fatigue and a contributor to breathlessness, while regular activity has been associated with improved circulation and muscle strength.
Challenging Traditional Views of Muscle Fatigue in Heart Failure
Past studies using isometric contractions indicated that individuals with CHF experience faster muscle fatigue. However, isotonic exercises, involving muscle shortening, have revealed a different picture. A study published in PLOS ONE examined fatigue development in rats with induced CHF during isotonic contractions. The results showed that, contrary to expectations, muscles from CHF rats didn't necessarily fatigue faster; in some aspects, they performed better than those from healthy rats.
- Isometric vs. Isotonic: Isometric exercises involve muscle contraction without changing length (e.g., holding a weight), while isotonic exercises involve muscle shortening (e.g., lifting a weight).
- Energy Demand: Isotonic contractions require significantly more energy than isometric contractions.
- Study Design: The study used a rat model of CHF, with muscles stimulated to shorten against a constant load.
Muscle Dysfunction and Exercise Benefits
A 2023 review describes established and newer mechanisms contributing to heart-failure-induced skeletal muscle wasting and weakness. A 2025 review examines clinical benefits of exercise training across heart failure subtypes and focuses on clinical trials and their key outcomes. A separate review reports that combined exercise training, aerobic training, and inspiratory muscle training significantly improved fatigue in patients with heart failure.
Safety Requires Individualized Exercise
The Rush guidance states that people living with heart failure can exercise safely and improve their health by following simple guidelines. This supports exercise as a feasible part of care rather than treating heart failure as an automatic reason to avoid physical activity. At the same time, the source frames safety as dependent on following appropriate guidance, so exercise should not be approached as an unsupervised or one-size-fits-all intervention.
Resistance Training Versus Broader Exercise Strategies
A 2024 systematic review concludes that resistance training offers several advantages for people with chronic heart failure, with restoration of muscle strength identified as a notable benefit. In heart failure with preserved ejection fraction, exercise capacity is described as markedly reduced because of cardiac, vascular, and skeletal factors. These findings suggest that resistance training addresses an important muscle-specific limitation, while broader exercise strategies may need to account for multiple contributors to reduced capacity.
Rethinking Exercise Strategies for Heart Failure
These findings suggest that exercise recommendations for individuals with CHF should consider the type of muscle contraction involved. While isometric exercises might exacerbate fatigue, isotonic exercises could be better tolerated and more effective for improving muscle function. The study's authors suggest that patients with CHF may tolerate cycling (isotonic exercise) better than stair climbing (which relies more on isometric force development).
Practical Exercise Guidance
Guidance for people with heart failure emphasizes good practice when exercising, particularly for those who feel worried or anxious about physical activity. The cited educational video presents six tips intended to support exercise with heart failure. Its focus is practical rather than a new clinical trial, so the material is best understood as exercise guidance rather than definitive evidence about muscle-fatigue mechanisms.
Tracking Muscle Function and Activity
A 2025 review identifies changes in muscle function and composition as important determinants of prognosis in heart failure patients and highlights the effectiveness of resistance exercise as an area of interest. Separately, Johns Hopkins researchers reported that each 750 MET-minutes-per-week increase in exercise over six years was associated with a 16% reduction in heart failure risk. The American Heart Association also emphasizes monitoring weight and tracking fluid intake as lifestyle measures that can improve quality of life, suggesting that future care may combine exercise exposure with broader self-monitoring.
Breathlessness, Exhaustion, and Deconditioning
The British Heart Foundation notes that heart failure can leave people feeling breathless, tired, or even exhausted. Its guidance explains that keeping the body moving can help the muscles and lungs. This highlights a practical challenge: symptoms that make activity difficult may also make continued movement important, requiring exercise approaches that account for fatigue and breathlessness.
Demonstrating Safe Activity
A Sharp HealthCare exercise physiologist, Alex Angeli, MA, demonstrates safe exercises after heart failure. The example places exercise instruction in a real-world rehabilitation context rather than presenting activity only as an abstract recommendation. It also illustrates the role of trained professionals in showing patients how exercise can be approached after a heart-failure event.
Further research is needed to fully understand the mechanisms behind these differences and to determine the optimal exercise prescriptions for individuals with CHF. Investigating the balance between muscle fiber types, energy metabolism adaptations, and the role of calcium handling could provide valuable insights. The team suggests further experiments are needed to know the mechanistic details.
Ultimately, this research highlights the complexity of muscle function in heart failure and the need for personalized exercise strategies that account for the specific demands of different activities. By understanding how muscles respond to various types of contractions, healthcare professionals can develop more effective rehabilitation programs to improve the quality of life for individuals with CHF.