Cardiovascular responses to heat exposure training in athletes with SCI


Lay summary by Annie Zhou

Edited by Crystal Han

This is the lay summary of the original article by Dr. Christopher West, and his colleagues Cameron Gee, Melissa Lacroix, Wendy Pethick, Patrick Côté, Trent Stellingwerff. Read the original article here.

What is heat acclimatization, and how is it related to spinal cord injury?

Heat acclimation (HA) is an artificial exposure to heat during exercise to stimulate physiological adaptations and is a proven method of improving exercise performance. Athletes with high-thoracic and cervical level spinal cord injuries (SCI) find exercising in the heat extremely challenging because their sweat glands and blood vessels do not respond appropriately during exercise. Without the proper sweat gland function, heat is retained in the body of the athlete, and cannot be dissipated, which may result in increased fatigue. Thus, athletes with high-level SCI put themselves at greater risk of extreme levels of fatigue when exercising in the heat, compared to those without an SCI. By allowing these individuals to adapt to controlled heat stress, HA training is a potential strategy that can improve the heat tolerance, and therefore the performance and health, of athletes with an SCI.

What was the purpose of the study?

The purpose of this study was to investigate a 5-day HA training plan, and its effect on the blood profiles, resting cardiac function, and the left-ventricular function (LV) in elite wheelchair rugby athletes with SCI. The left ventricle is the largest chamber of the heart, and is responsible for pumping oxygenated blood to the rest of the body, so investigating the functions of the left ventricle will give the researchers a good outlook of the athlete’s overall heart function. Researchers wanted to test the hypothesis that HA intervention in athletes with SCI would lead to a decrease in resting heart rate. Additionally, they hypothesized that HA intervention could also result in an increase in total resting stroke volume (SV), and plasma volume (PV). Plasma volume is the amount of plasma, a component found in our blood, in a set amount of blood. Stroke volume is the total blood volume pumped from the left ventricle of the heart per heartbeat.

An increase in the SV allows athletes with an SCI to increase the amount of blood flowing through their body, and enhances their exercise output capacity and oxygen delivery to working muscles. Thus, this study aimed to determine whether HA training would induce cardiovascular adaptation and performance improvements in elite wheelchair rugby athletes with an SCI.

How was the research conducted?

11 Paralympic wheelchair rugby athletes with an SCI were assessed 5 days before and after HA training. The HA training involved raising and maintaining the gastrointestinal temperature (Tc) at 38.5ºC, via circuit training or track sprints. If Tc exceeded 38.5ºC, cooling strategies were implemented. Each HA session was 60 minutes long.

Exercise intensity was monitored through questionnaires that rated perceived exertion (how hard the athlete thinks their body is working), thermal tolerance (how manageable is the level of heat), and thermal sensation (how warm or cool the athlete feels).

To investigate the blood profiles and resting cardiac function, resting blood samples from the veins were drawn to analyze changes in blood components to calculate for the percentage change in PV before and following HA.

What were the results of the study?

The researchers observed an increase in both PV and SV, but due to the limited sample size, it was likely that this increase occurred due to variation. The researchers noted that a larger sample size could have created more meaningful results. Researchers also noted a decrease in the resting heart rate of the participants, which did not occur by chance.

Why are the findings important?

This was the first study to demonstrate that short-term HA training is a practical method to introduce positive changes in the resting dynamics of blood flow and left-ventricular function in elite wheelchair rugby athletes with SCI. Individuals with an SCI are unable to increase SV in response to exercise, and thus are faced with severe cardiovascular limitations. However, the capacity of the cardiovascular system is important in determining the performance of athletes with an SCI. An increased SV following HA training would result in the enhancement of exercise capacity and performance.

Additionally, HA can also help reduce the heat injury risk in individuals with SCI by reducing heat stress, which proves to be vital for their health and safety. Therefore, HA intervention, which helps maintain cardiovascular stability during heat strain, has the potential to improve the performance and health of athletes with an SCI.

What are the limitations of the study?

It is important to note that this research only studied elite athletes. Thus, any extrapolation to non-athletic individuals with SCI should be performed with care.

Definition of specific terms:

Plasma volume: total volume of plasma, a substance of our blood, found in the blood.

Stroke volume: volume of blood pumped from left ventricle of the heart, per heartbeat.