25 Jun 2015

Heat, Exercise and Heart Health

From Our Changing World, 9:06 pm on 25 June 2015

By Alison Ballance

“Heat is part of exercise. And it’s probably an important part of exercise. It can adapt various things in the cardiovascular system.”
Jim Cotter, School of Physical Education, Sports and Exercise Science, University of Otago

Cycling as fast as you can on an exercycle, in a room that is heated to 40°C at 60 per cent humidity, isn’t most people’s idea of fun, but PhD student Ashley Akerman at the University of Otago is asking volunteers to do just that, as part of a study looking at cardiovascular adaptations to heat.

PhD student Ashley Akerman (standing) supervises triathlete Rob Creasy who is undertaking a strenuous work-out on an exercycle in a room heated to 40 degrees Celsius with 60% humidity.

PhD student Ashley Akerman (standing) supervises triathlete Rob Creasy who is undertaking a strenuous work-out on an exercycle in a room heated to 40 degrees Celsius with 60% humidity. Photo: RNZ / Alison Ballance

Ashley's supervisor, exercise scientist Jim Cotter, says that heat affects the cardiovascular system in a number of ways.

“It can help adapt the blood vessels, and keep them in better condition and slightly larger than they might otherwise be. It can help adapt the heart and protect it chemically against becoming short of blood, so can help protect against heart attack. And it can help increase blood volume and lower blood pressure. For example you can have 5% more blood volume the day after your exposure to exercise [and heat].”

Ashley has already tested a number of people of average fitness, to see if exercising in a hot environment has different results to exercising in a more temperate environment. More recently he has been testing super-fit athletes, such as triathlete and fellow PhD student Rob Creasy, who already has an extremely well adapted cardiovascular system.

“We don’t yet know whether it’s just the fluid part of the blood, the blood plasma, that increases [after exercising and heat exposure], or whether it manages to increase the red call component, the oxygen carrying part, as well,” says Jim. “Some studies are indicating that it is increasing red cell volume and therefore it may take over from altitude training for athletes. But we haven’t seen any evidence of that.”

When asked if living and working in a hot climate predisposes people to have better cardiovascular health Jim says there’s no evidence of that, but he also says that perhaps training in hot climates will have a better outcome than exercising in temperate climates. He mentions that a training institute in Qatar has set itself up as a heat camp to investigate whether training in the heat might replace altitude training. He also says it’s possible that exposure to heat might be beneficial to people who are unable to exercise.

“Heat no doubt has a lot of benefits,” says Jim, “And it’s a question of how wide those benefits go, and how much maybe should they take the place of exercise. Because exercise is free and freely available to almost everybody. But to what extent do we want to add [heat] onto exercise? Or for people who genuinely can’t exercise, how effective is it?”

Rob Creasy is investigating the reason that triathletes competing in very hot environments sometimes find it difficult to finish races even when they were highly motivated. “We found there was a lot of stuff going on with the brain, and blood flow and oxygenation to the brain.”

Jim says that humans shed heat by sweating and moving blood to the peripheries, rather than by shallow panting, which is what many animals do. Heavy breathing can lead to hyperventilation. “We blow the carbon dioxide out of our blood, and it reduces our brain blood flow. So when people faint in the heat it’s sometimes a combination of lack of blood pressure because of vasodilation and blood going to their skin, and partly because they have constricted brain blood vessels.”

Jim Cotter’s work on dehydration and exercise has previously featured on Our Changing World.