Hydration & Athletic Performance (2)- What Happens To Our Body When We Are Dehydrated?

Welcome back to our series on hydration and its effects on exercise and athletic performance!  In Part 1 we discussed how dehydration can compromise many aspects of our workouts, especially the results that we work so hard to achieve!  We also detailed strategies on how to determine if your body is well-hydrated or if it is showing signs and symptoms of dehydration.  Being familiar with the red flags our body raises when we are in a state of hypohydration and consuming enough fluid to remain properly hydrated, especially when we are going to embark on any kind of physical activity, is key to performance, results and avoiding injury.  In this Part 2, we are going to delve into the biology of what happens in different systems of our body when we are dehydrated, specifically the musculoskeletal and cardiovascular systems – the systems that are most involved in physical activity.  And although exercise is a type of “good” stress that keeps us healthy and strong, it can quickly backfire if we aren’t consuming our daily fluid needs.  


How Dehydration Affects Your Muscles 

Water is the main component of the body and represents approximately 76% of muscle mass.  A review of the effects of dehydration on athletic performance found that it negatively impacts muscle strength, power, and high-intensity anaerobic capacity*.  Cheuvront and Kenefick (2014) reported that even mild dehydration also impaired endurance exercise performance mediated by body water volume loss. If you’re into exact numbers, according to a meta-analysis by Savoie et al. (2015), hypohydration caused muscle strength to fall by 5.5% and anaerobic power fell by 5.8%. This suggests alterations in total body water can affect both the quality and quantity of your workouts.  For example, you may not be able to lift as much weight when strength training or run as fast or as far when dehydrated.  

Physiologically, the water in your muscles is distributed in the extracellular (outside the cell) and intracellular (inside the cell) compartments.  When there is an imbalance due to dehydration between the inside of the muscle cell and the outside of the muscle cell, this leads to cellular dehydration. When your cells are dehydrated there are severe consequences in both muscle structure and function and may ultimately result in muscular damage.  It is also important to note that muscle strength is the main determinant of functional capacity (how well you’re able to physically function), which is pertinent to longevity – both your healthspan and lifespan. In older people, muscle strength depends more on muscle quality than on muscle quantity (or muscle mass). Proper intracellular water content means better muscle quality!  


How Dehydration Affects Your Joints  

 Because of the lubricating effect water has on the joints, dehydration can directly cause joint pain. Synovial fluid, the thick lubrication located between the joints provides a cushion so the bones don’t come in contact with each other. This fluid is located in the joints throughout your body – knees, feet, shoulders, hands and hips.  If you are properly hydrated, then this gel-like liquid provides the necessary shock-absorption, lubrication and cushioning in the joints. Hydration also helps to reduce friction in the cartilage, which is 70 – 80% water in its content. Without good fluid status the motion in the joints is no longer smooth, which may lead to the development of joint pain and joint injury.  But keep in mind, just because you are experiencing joint pain doesn’t necessarily mean that your pain is caused by dehydration. A lack of hydration has been found to contribute to joint pain, but it might not be the root cause of the pain. If you notice mild pain in your joints, then try increasing your water intake for a week or two to see how the pain is affected. 


How Dehydration Affects Your Bones

Far from being dry and brittle, healthy bones contain about 31% water. Most people probably don’t associate hydration with bones, but dehydration can lead to serious diseases such as osteoporosis – a disease characterized by reduced bone density that leads to increased bone fragility and risk of fracture.  It is well-known that our bones need calcium and other key nutrients to stay in a healthier condition. Now, of course, having a diet rich in such nutrients is important. If these nutrients fail to reach the bones due to dehydration, the bones will get nutritionally deficient, losing mass and strength because water is essential to carry calcium and other nutrients throughout the body and make up for the lost minerals, which happens naturally. Toxins in our body, if not removed, build up in the bones. This manifests in several problems, including inflammation, weakening, and loss in bone density. Water is needed here to eliminate these toxins.


How Dehydration Affects Your Heart 

The function of our heart and cardiovascular system also depend on proper hydration. When you are dehydrated, your blood volume – , or the amount of blood circulating through your body -, decreases. To compensate, your heart has to beat faster, increasing your heart rate and your blood pressure. Also, when you are low on fluids, your blood retains more sodium, which can “thicken” your blood and make it harder for your blood to circulate through your body. When circulation is affected, the delivery of nutrients to our cells is also jeopardized.  Keeping your body hydrated helps your heart pump blood more easily and allows oxygen to reach your muscles, which helps the muscles work efficiently.  When we exercise and we put more stress on our cardiovascular system, being in a state of dehydration can be even more pronounced.  


Dehydration – Just Don’t Do It!

With all the problems and stress that dehydration puts on our bodies, it is no wonder being low on fluids puts additional stress on the systems that become more stressed during exercise.  It is absolutely a “must” that if we are to embark on any physical activity endeavor that we, number one, recognize the signs and symptoms of dehydration and number two, ACT to rehydrate so we do not injure ourselves.  Being properly hydrated allows us to get the best results from our workout and good hydration affects blood volume and circulation, which can help to reduce recovery times. Additionally, every cell, tissue and organ in your body needs water to work properly so being hydrated is a foundational practice to help you stay healthy. !Good news is it’s never been so easy to  monitor our water intake and educate ourselves on hydration benefits and best practices!




  1. Cheuvront S, Kenefick R. Dehydration: Physiology, assessment, and performance effects. Compr Physiol. 2014;4:257–285.
  2. Judelson DA, Maresh CM, Anderson JM, Armstrong LE, Casa DJ, Kraemer WJ, Volek JS. Hydration and muscular performance: Does fluid balance affect strength, power and high-intensity endurance? Sports Med. 2007;37:907–921.
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723611/
  4. http://www.heart.org/en/healthy-living/fitness/fitness-basics/staying-hydrated-staying-healthy
  5. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/water/art-20044256
  6. UPMC (University of Pittsburgh Medical Center): https://share.upmc.com/2014/09/importance-hydration-heart/
  7. We also recommend the Strength Running Podcast “The Big Hydration Episode, With Sports Scientist Andy Blow”. (July 9, 2020)


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