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Dehydration and Heat Conditions (Part 2 of 3)

Dehydration and Heat Conditions (Part 2 of 3)

Last time I talked (briefly) about the importance of water for proper physiological functioning, how and why we lose water, and what happens when we enter a dehydrated state. This post will pick up where we left off and take a more in depth look at dehydration in athletes, what can happen when it becomes serious and some preventative steps we can take.

Dehydration is a state in which our bodies experience a dynamic loss of fluid and it can be caused by a number of different factors

e.g.  prolonged heat exposure, vomiting, diarrhea, excessive intake of caffeine, and/or alcohol

For today however, I will be focusing on exercise induced dehydration and what that can look like for the athlete.

Under normal condition we lose between 2-3L of water/day through different mechanisms - respiration, sweating and excretion - but under extreme conditions (exercise and/or high temperatures) this amount increases significantly. Which means that when exercising, it is important for athletes to increase fluid intake in order to match/offset the fluids lost through perspiration and respiration. If they don’t, they will experience increasing levels of dehydration and a sharp decline in performance.  

When we are dehydrated, blood volume decreases (blood is ~ 83% water); which means our heart must pump harder/faster to compensate. In addition to increasing our heart rate, dehydration impairs our ability to thermoregulate (sweating) and the more dehydrated we get, the harder it becomes to maintain our core temperature. Now this may not seem like a big deal

“I experience changes in body temperature all the time”,

but there is a big difference between temporary temperature changes in our extremities (e.g. cold hands, or feet) and a shift our overall core temperature.

Dehydration and Heat related conditions, nine times out of ten, these two go hand in hand; and while they both have the potential to turn fatal, they can be easily prevented with the right precautions. So What Do the Different Stages Look Like?

Early Stage(s)

Mild Dehydration and Muscle Cramps

Ever had a calf cramp, or maybe a charlie horse?  Muscle cramps are one of the earlier signs that something is not right and that something is related to fluid deficiency, electrolyte imbalances and/or neuromuscular fatigue. At this point, dehydration is still minor and non life-threatening; but to prevent it from progressing further, it is important to increase intake of fluids and electrolytes in order to reestablish a normal hydration status.

Headaches, Light-Headedness and Heat Syncope

Headaches, dizziness and heat syncope (fainting) are just a few conditions associated with dehydration and the more dehydrated we are, the worse these symptoms will become. Athletes training or competing in extreme/unfamiliar climates are at particular risk of temporary loss in consciousness, because their bodies need time to acclimatize (adjust) to their new environment. Proper hydration, staying cool and (in the case of travel) allowing the body a few extra days to adjust to the climate can help minimize the effects.

Later Stage(s)

Exercise Induced Heat Exhaustion

Heat exhaustion is what can happen when dehydration goes untreated for too long and the combination of depleted body water, electrolyte imbalances, and elevated core temperature make exercising not only difficult, but also dangerous. The symptoms of heat exhaustion include (but are not limited to):

  • excessive sweating, pale/clammy skin, persistent cramps, weakness, fainting, headaches, increased respiration, nausea, lack of appetite, diarrhea, decreased urine output and an increased core temperature (up to 40⁰C).
  • While it is more commonly to see heat exhaustion in hot, humid climates and endurance athletes, it does not discriminate. If any athlete presents with the above symptoms, it is important that they stop exercising immediately, get out of the sun/heat, and drink electrolyte containing fluids to help reduce temperature and reestablish proper hydration levels. It is possible to treat mild to moderate heat exhaustion without medical attention; however if left untreated, it can progress to a level that requires medical treatment and is potentially fatal.

    Exercise Induced Heat Stroke

    Heat stroke is the most severe form of dehydration and heat-related condition and is characterised by extreme dehydration and dangerously elevated core body temperatures (over 40⁰C). Many symptoms of heat stroke are similar to those we might see in someone suffering from heat exhaustion

  • e.g. increased heart rate, cramps, hyperventilation, diarrhea, temporary loss of consciousness (fainting)
  • However, these symptoms are usually far more severe and may also be accompanied by

  • severely altered mental status/confusion, seizures, prolonged losses in consciousness, coma and even death.
  • Furthermore, whereas people suffering from heat exhaustion often sweat excessively (as the body tries to cool itself off), the skin of people suffering from heat stroke will often be dry and hot to touch, because they have reached a state dehydration so severe, they cannot even sweat. Any athlete who has progressed this far along the dehydration and hyperthermia spectrum will require medical attention as soon as possible, because when the body’s core temperature is so high there is an increased risk of developing complications due to:

  • severe lactic acidosis (accumulation of Lactic acid in the blood)
  • hyperkalemia (excessive potassium in the blood)
  • acute renal failure and Rhabdomyolysis (destruction of skeletal muscle associated with exercise)
  • disseminated intravascular coagulation (bleeding disorder in which blood clots cannot form)
  • and the longer the core temperature remains elevated the greater the chance of morbidity is.


    Last but not least, before we get into avoiding and treating dehydration there is one more hydration related condition I want to talk about. ‘Exertional Hyonatremia’ (aka water toxicity) is essentially the reverse of severe dehydration; and it can occur when excessive amounts of water is consumed (often in an attempt to rehydrate), but no salt/electrolytes (sodium in particular) are taken with water. When we sweat, we lose water and sodium, and in order to rehydrate we need to replenish our stores of both (not just water). If we don’t, sodium concentrations within the body become dangerously low (<130mmol/L) and this in turn can cause a redistribution of fluid within the body and intracellular swelling. Symptoms of hyponatremia include:

    • disorientation, altered mental status, heachaches, vomiting, lethargy, swelling of extremities, pulmonary and cerebral edemas and seizures

    Just like heat stroke, hyponatremia can be fatal; which is why it's important to make sure we are rehydrating properly and not just flooding our bodies with water.

    Now, obviously these are extreme examples/worst case scenarios of what can go wrong; and (hopefully) most of us will only have to deal with mild-moderate levels of dehydration. However, given that even mild dehydration can be detrimental to physical performance; and just how easy it is for mild dehydration to become severe, it's worth being informed so you know how to avoid dehydration, what to look for, and how to treat it; which is exactly what will be discussed in my next post, so stay tuned.References & Further Reading
  • Berardi, John.The Essentials of Sport and Exercise Nutrition.
    1. Binkleyl Helen M., Beckett, Josepth., Casa, Douglas J., Kleiner, Douglas M., Plummer, Paul E.National Athletics Trainers’ Association Position Statement: Exertional Heat Illnesses. Retrieved from <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC164365/>
    2. Decker, Meredith.Current and Potential Practices in Athletic Training: The Effects of Hydration on Athletic Performance. Retrieved from <https://www.kon.org/urc/v10/athletic-training/decker.html>
    Kidd, Simon.An Athlete’s Guide to Hydration: When, What and How Much.Retrieved from <breakingmuscle.com/nutrition/an-athlete-s-guide-to-hydration-when-what-and-how-much>
    About the Author
    Taryn Haggerstone is a Competitive Olympic Weightlifter, CrossFit Athlete and Coach based out of Vancouver, B.C., Active from a young age, Taryn’s passion for health and fitness led her to obtain an undergraduate degree in kinesiology and she has been working in the industry since graduating in 2012. Find her on instagram (@tarynemilyh), follow her twitter (@tarynhaggerston) and check out her blog www.gohardgetstrong.com



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