Hot to go - Guidelines fOR Exercise in THE HEat

It’s well documented that exercising in extremely warm temperatures can elicit adverse changes in physiology and health. It’s also been well documented that training in the heat can improve performance. Read on for the full story…\

As temperatures increase, athletes become at risk for conditions such as heat exhaustion and heat stroke due to the effects of a core body temperature increase. From a physiology point of view, core temperature is tightly regulated, under the control of the hypothalamus, which acts as the body’s internal thermostat.

The body regulates core temperature through two main mechanisms - vasodilation - that is, the body’s blood vessels widen close to the skin, diverting blood away from internal organs and towards extremities to offload heat through radiation and conduction.

When conditions become warm this can be accompanied by an elevated heart rate, both at rest and during exercise, to help expedite this process.

The body also controls core temperature through the process of sweating - as moisture evaporates from the skin, a cooling effect is provided.

When exercise is undertaken during hot conditions, performance is impacted as both the mercury and the humidity rises. Increased humidity prevents the effective evaporation of fluid from the skin, which affects the ability for the body to naturally control core body temp.

Layering endurance exercise on top of a heat stressed body forces the cardiovascular system to try and cope with both the demands of the exercise (increased oxygen) and the body’s requirement to divert blood flow to the skin for cooling.

Therefore, exercise, as well as environmental conditions can precipitate potentially life threatening heat related illnesses, such as heat stroke, heat exhaustion, hyponatraemia (a drop in blood sodium levels caused by drinking excessive amounts of plain water, whilst losing body slats through sweating) as well as exertion heat injury conditions, such as rhabomyolysis and acute liver and kidney damage. The more intense exercise is, the higher the risk.

Dehydration is also a big risk factor - as even mild dehydration will reduce cardiac output - and thus the body’s ability to self cool.

Susceptibility to heat illness varies amongst the general population, but generally, the older the athlete, the higher the risk. Other risk factors include hydration status, lack of acclimatisation, recent acute and chronic illnesses. It should be noted that several medications can impact how an individual may develop a heat related illness through a variety of different pathways such as decreasing HR, impairing sweating, altering kidney function etc.

However, the good news is that some of this risk can be mitigated by a heat acclimization strategy over a period of ten to fourteen days. Interestingly, recent research has also pointed to heat acclimatisation training boosting training adaptations - most notably due to a plasma volume increase that occurs to reduce heart rate at sub maximal workloads. When an athlete returns to training or racing at optimal temperatures, these adaptations persist for a finite period.

This research has also shown that active heat exposure is better than passive heat exposure - that if someone exposes themselves to heat while exercising, the adaptations are superior to simply being exposed to higher temperatures without moving.

A typical active heat acclimation session is one hour - keeping the heart rate within endurance zones and acclimatisation begins to improve with approximately eight to fourteen exposures - these can be done on consecutive days or up to four times per week.

It’s crucial to pay attention to hydration - due to a high sweat rate with these activities - as well as consider ingesting an electrolyte solution to help offset sodium loss. This loss varies amongst individuals and one of the best ways to ascertain this is by undertaking a sweat loss test with an accredited Sports Dietitian.

In terms of hydration and to prevent hyponatremia and maintain cardiac output, consuming 500-700mg sodium per litre of fluids will help combat this as well as dehydration - using an electrolyte mix in water such as Hydralyte or Gatorade is recommended. Athletes who are aware they sweat heavily may need more. We will all have different sweat rates, a good idea to monitor dehydration is by checking urine colour regularly.

TAKE HOME MESSAGES

• Approach intentional exercise in the heat with caution, particularly if you are a master’s athlete, unfit or suffer from chronic conditions

• Use/wear equipment suitable for the session - light coloured clothing that is breathable, use sunscreen

• Use cooling strategies such as placing ice in the end of some panty hose, tying a knot and stuffing it down your jersey (if you’re a cyclist) or an ice vest if you have one

• Exercise during the coolest parts of the day and keep intensity low to reduce risk

• Drink plenty of fluids before, during and after exercise - ensure you use electrolyte mixes, not just plain water, to avoid hyponatraemia which is life threatening

Reduce risk of heat related illnesses by exercising early!

TIPS FOR ACCLIMATIZATION

• Keep sessions short and low intensity to begin with - can progress these gradually

• If you’re in a colder climate and wanting to access the changes to physiology by trying heat exposure, consider training in a heated room or wearing extra layers of clothing.

• Maintain a decent level of endurance fitness, which helps mitigate some danger.

• If travelling to an extremely warm destination for a race/event, do some heat acclimation work at home prior to your departure, and arrive at least a week before your event to help further acclimatise you to conditions.

OTHER RESOURCES: Sports Medicine Australia, in conjunction with Sydney University, have developed a “Sports Heat Tool” and comprehensive, evidence based guidelines to assess risk in hot weather conditions. Check it out here.

Questions? Feel free to email me at hello@liznelson.com.au

REFERENCES:

Sports Medicine Australia - Sports Heat Tool

Tyler CJ, Reeve T, Hodges GJ, Cheung SS. The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Med. 2016 Nov;46(11):1699-1724.

Maunder E, Plews DJ, Wallis GA, Brick MJ, Leigh WB, Chang WL, Watkins CM, Kilding AE. Temperate performance and metabolic adaptations following endurance training performed under environmental heat stress. Physiol Rep. 2021 May;9(9):e14849