HIIT vs Moderate Cardio Benefits Heart Failure Fitness

HIIT and Moderate Cardio Deliver Equal Benefits for Heart Failure Patients’ Fitness and Muscle

For patients with stable heart failure, a six-week cardiac rehabilitation program that includes high-intensity interval training improves walking distance, muscle mass, and oxygen uptake as effectively as traditional moderate continuous training. A study from Ankara City Hospital found both methods are viable for combating sarcopenia and boosting functional capacity, with no clear winner in clinical outcomes.

HIIT Matches Steady-State Training for Critical Functional Gains

Researchers led by Dr. Merve Sönmez at Ankara City Hospital randomly assigned heart failure patients to either a high-intensity interval training (HIIT) or moderate-intensity continuous training (MCT) group. Both groups exercised three days per week for six weeks. The results, published in Acta Cardiologica, showed significant and nearly identical gains in several key areas.

After the program, patients in both groups could walk about 50 meters farther in the six-minute walk test. Their quadriceps muscle thickness increased by approximately 8-10%, and handgrip strength improved. Most importantly, VO₂ max—a gold standard measure of cardiovascular fitness—rose significantly. “There was no statistical difference in treatment-related change between the two protocols,” the authors concluded. This challenges the assumption that HIIT is inherently superior for improving functional capacity in this clinical population.

The study’s protocol was relatively short at six weeks, and longer-term adherence and effects remain to be seen. However, the results provide strong evidence that both training styles are potent tools in cardiac rehabilitation.

Exercise Benefits Muscle Without Altering Key Circulating Signals

A surprising finding from the Turkish study was the lack of change in specific muscle-derived signaling proteins, or myokines. The team measured blood levels of myostatin, which inhibits muscle growth, and brain-derived neurotrophic factor (BDNF), which supports nerve and muscle health. Neither HIIT nor MCT altered these circulating levels.

This suggests the impressive improvements in muscle thickness and strength—direct counters to sarcopenia—are mediated by mechanisms other than systemic changes in these particular myokines. Benefits may come from local muscle adaptations, improved blood flow, or changes in other unmeasured factors. It’s a reminder that a single blood biomarker rarely tells the full story of exercise’s complex effects. The body’s response is highly integrated, involving cardiovascular, muscular, and metabolic systems working in concert. For more on how different training affects overall fitness, see our analysis on the Polarized Training Model for Endurance Athletes.

Ketosis May Amplify Vascular and Oxygen-Carrying Adaptations

Separate physiology research points to a dietary factor that could influence how the body adapts to exercise. A multinational team from KU Leuven and the University of Ljubljana investigated how a state of ketosis affects vascular function and the response to training stimuli.

Their preliminary work, noted in The Journal of Physiology, indicates that exogenous ketosis can enhance blood vessel function and angiogenic signaling—the process of building new capillaries. This is critical for delivering oxygen and nutrients to muscles. Furthermore, ketosis appeared to strengthen the erythropoietic response, which is the body’s production of new red blood cells in reaction to exercise and hypoxia (low oxygen).

While this research is in early stages and primarily explores mechanisms, it opens a compelling question: Could nutritional strategies that promote ketosis work synergistically with endurance or interval training to improve vascular efficiency and oxygen delivery? This connects to a broader conversation on how metabolic state influences training adaptation, a topic also explored in our article on how Altitude Adjusts Zone 2 Training.

Applying the Evidence to Training Prescription

For coaches, athletes, and individuals managing heart health, these studies offer practical clarity and new avenues for inquiry. The Ankara study strongly supports that exercise intensity can be personalized. A patient who enjoys and adheres to steady cycling will see similar functional benefits to one who prefers short, intense intervals. Adherence is often the greatest predictor of long-term success in rehabilitation.

The ketosis research, while not yet prescriptive, highlights the importance of the metabolic environment for adaptation. It suggests that what you eat and when you eat it could influence how effectively your blood vessels and blood composition adapt to your training load. This aligns with growing interest in how dietary patterns support endurance, as discussed in resources like Autophagy Fasting Benefits Heart Health & Aging on our partner site.

It is essential to note that the heart failure study involved medically supervised patients. Those with cardiovascular conditions should always consult a doctor before beginning a new exercise program. For the general population seeking metabolic fitness, the principle of equivalency holds: consistency with either HIIT or moderate aerobic exercise yields major dividends for health and functional capacity.

The evidence confirms that both high-intensity intervals and moderate continuous exercise are powerful for improving fitness and combating muscle loss in vulnerable populations. The choice may rightly depend on individual preference and sustainability, not a presumed hierarchy of effectiveness. Future research will clarify how dietary strategies like ketosis can be integrated to potentially enhance these physiological adaptations.

Sources:
https://pubmed.ncbi.nlm.nih.gov/42200871/
https://pubmed.ncbi.nlm.nih.gov/42200706/