People with heart failure may be able to improve their endurance during exercise using hot water baths, according to recent research led by Griffith University.
The study found that after immersing the lower limbs in hot water for 45 minutes, the walking distance of participants increased by an average of 201 meters (659 feet).
Lead researcher Fergus O’Connor said the research highlights the potential of passive heating as a simple and non-pharmacological strategy to enhance exercise performance in people with heart failure.
“By improving blood flow and oxygen delivery, lower-limb heating may help patients get more out of their rehabilitation programs,” O’Connor said.
Heart failure is a considerable issue in Australia, with around 144,000 adults living with the condition 2022. It can be life-threatening and usually develops gradually, worsening over time.
Healing Powers of Heat
Heat causes vasodilation—widening of blood vessels—especially in the skin and muscle tissue. The widened vessels allow the body to direct more blood to heated areas.
O’Connor told The Epoch Times that vasodilation increases blood flow through the femoral artery, which is located in the upper thigh.
Consequently, more oxygen-rich blood reaches the muscles, theoretically improving muscle oxygenation, and possibly translating to the observed increase in walking distance.
The participants in the study suffer from reduced ejection fraction, meaning their heart fails to pump enough blood to meet the needs of the body.
Therefore, the capacity for heat to restore blood flow in patients with reduced ejection fraction is a promising strategy to boost exercise capacity.
What Is Reduced Ejection Fraction?
Ejection fraction (EF) refers to the proportion of blood the heart pumps out with each beat.
Normal EF ranges from 55–70 percent, but heart failure with reduced ejection fraction (HFrEF) causes EF to drop below 40 percent.
“While everyone has an EF, reduced EF is a hallmark of this particular type of heart failure. It’s estimated that HFrEF accounts for about 50 percent of all heart failure cases,” O’Connor said.
“The other major subtype is heart failure with preserved ejection fraction (HFpEF), where the EF is normal but the heart has impaired filling due to stiffened muscle.”
Trialed Temperatures
The study tested the exercise capacity of participants following baths of two temperatures: 30°C (86°F), as a control condition, and 42°C (107.6°F) to explore the effect of heating.
O’Connor said the control temperature was an important consideration in the research design, and 30°C was selected rather than room temperature because of water’s high thermal conductivity.
“Using room temperature water (e.g., 22°C [71.6°F]) would likely result in a cooling effect,” he said.
“Instead, we chose a temperature approximating skin temperature, which in theory would have no thermal influence on the immersed limbs.”
Although the normal temperature of human skin sits between 32-34°C (90-94°F), the average temperature of the lower extremities at their base is around 30°C.
O’Connor said that at this stage, the study only tested heating at 42°C, but exploring the effects of lower water temperatures remains an important avenue for future research.
Demographics Represented
The study examined the exercise capacity of 22 participants, who ranged in age from 50 to 80 years old, using an endurance test—similar to the beep test.
The absence of younger people is consistent with the condition as heart failure mainly occurs in older individuals, and usually arises at 65.
Heart failure risk increases with age, with more than 10 percent of people over 70 years old affected by the condition.
The participant pool mainly represented the male demographic, as only one female participant completed the study.
“While there is lower representation of women in HFrEF, it limits the generalisability of our findings,” O’Connor said.
“As noted, larger studies, particularly with more balanced sex representation, are needed before drawing broader clinical conclusions,” he said.
Further Investigation Points
The study serves as a proof-of-principle, meaning that although the participant number is relatively small, it was statistically powered to detect differences in walking distance between conditions.
However, O’Connor said larger-scale randomised trials are needed before clinical recommendations can be made.
“For instance, while our results show that a single bout of lower-limb heating improves exercise endurance in individuals with HFrEF, it’s unclear how this could be applied in practice,” he said.
“Future research should explore whether pre-rehabilitation heating could enhance training adaptations over a complete cardiac rehabilitation program.”
The long-term benefits of the passive heating strategy have not yet been explored.
