Exercising in the Heat

Exercising in the heat can cause dizziness and fatigue so with summer is in full swing, Jennifer Brown, Fitness Coach at the Australian Institute of Fitness NSW, explains how to reduce your risk of heat stroke. Studies have shown that exercising in the heat can cause minor disruptions to the body, including sweating, or obvious fatigue; to major disruptions to the body like nausea, dizziness or even death (in extreme cases). Heat stress or heat exhaustion can occur from prolonged exposure to hot temperatures, and not being able to produce enough sweat to cool the body, or sweat evaporating due to the high humidity. Heat exhaustion is a physiological response to blood pressure, whereby it drops quickly and becomes postural hypotension’.

Signs and symptoms of heat stroke

• Nausea
• Fatigue
• Light headedness, dizziness
• Confusion
• Loss of skill and coordination/clumsiness or unsteadiness
• Collapse
• Aggressive or irrational behaviour
• Ashen grey or pale skin
• Altered consciousness.

How to reduce the risk of heat stroke

• Choose a time of the day when the heat isn’t at its strongest
• Reduce the intensity of the activity
• Reduce the duration of the activity
• Have adequate fluids before, during and after activity
• Wear light coloured, loose fitting clothing
• Adapt to conditions during training for the activity
• Wear a hat, long sleeve shirt, and apply sunscreen often
• Get enough sleep before the session.

When exercising in the heat, the skeletal muscles require an increase in blood flow to allow for heat dissipation. This in turn helps to keep the body’s core temperature at an average of 37C. Sweat can’t always be used as a guide. Women typically sweat less, and lose fewer electrolytes, than men. Hydration can play a major role in heat stress. For example, according to ACSM’s Foundation of Strength Training and Conditioning, an elite marathon runner can lose up to 6-10% of total body mass or up to 5L. Dehydration can affect the function of the cardiovascular system, exercise performance, and can increase heat storage. By losing 4.3% of body mass, a person’s VO2max can fall by up to 22%.

The best temperatures to exercise

Ambient Temperature	Relative Humidity	Risk of Illness
15-20C		Low
21-25C	Exceeds 70%	Low-Moderate
26-30C	Exceeds 60%	Moderate-High
31-35C	Exceeds 50%	High-Very High
36C and above	Exceeds 30%	Extreme

It is crucial that a person puts steps in place to reduce their risk as much as possible, and have an action plan in place. The following resources are great for further information on this topic.

• Fitness Australia’s Outdoor Training guidelines’
• Sunsmart UV exposure and heat illness guide’
• Sports Medicine Australia Beat the Heat’ fact sheets