Hydration is a key component to consider when partaking in any form of exercise. During exercise, sweat evaporates from the skin's surface which causes us to lose fluid and can potentially result in dehydration. Although sweating is an effective biological mechanism for cooling down the heat produced from working muscles, we must ensure this fluid is replenished. The amount of fluid lost through sweat can vary between individuals, with maximum sweat rates being between 2-3 litres per hour, resulting in body mass reductions of 2-3%. Not replenishing this lost fluid and causing dehydration to occur can be detrimental to our health and our exercise performance.
Dehydration happens when the overall water volume within the body is reduced, changing from a steady condition of normal levels of body water to less than normal. These significant decreases effect our physiological functioning since our bodies are made up of approximately 65% water. For example, dehydration causes our blood volume to decrease which is compensated for by an increase in heart rate. Additionally, it can effect our muscle functioning which greatly impacts our endurance capacity, making it extremely bad news for endurance athletes performance. Basic signs and symptoms of dehydration include feeling dizzy or lightheaded, feeling exhausted and having a dry mouth, but it can escalate to experiencing cramps, chills or vomiting/nausea. In order to restore our water balance, the primary method is through fluid and food ingestion, demonstrating why fuelling during long, endurance sessions is important.
What should I drink to hydrate?
Water is always the obvious first choice to grab for when feeling dehydrated. However, it has been found that water alone is not the optimum fluid to consume during endurance exercise like running. Evidence shows that drinks with added electrolytes are more effective in improving our performance. Having said that, this can vary depending on the intensity, duration and type of exercise being carried out. Many athletes opt for sports drinks during sessions which contain a variety of nutrients and other substances alongside water. The key ingredients are most commonly water, carbohydrate and sodium and the main aim of their use is to speed rehydration, stimulate fast fluid absorption and promote recovery post-workout.
Choosing which type of drink is best, however, largely depends upon the scenario it is needed. Sports drinks consisting of high carbohydrate concentrations are ideal if an energy source is required during exercise since it increases delivery to the site of absorption in the small intestine. In addition, carbohydrates cause better maintenance of blood glucose which is used by exercising muscles. Yet, this increased carbohydrate concentration would also reduce the amount of fluid available for absorption meaning the likelihood of dehydration could be temporarily increased. On the other hand, increased levels of sodium stimulates sugar and water intake in the small intestine which helps to combat dehydration and maintains our drive to drink. Although, drinks containing higher sodium content can often be unpalatable. Therefore if an energy boost is your requirement, be sure to opt for a sports drink higher in carbohydrate, but if the aim is rehydration then choose one with increased levels of sodium.
It is worth noting that plain water has also been found to improve performance and undeniably combats the effects of dehydration. Thus plain water is still a viable option to stay hydrated during exercise, there are just increased performance improvements found when carbohydrates and electrolytes are also consumed. For example, one study demonstrated that the added nutrients in a sports drink preserved cyclists leg force considerably more after prolonged cycling in the heat than water alone. Alongside this, replacing water loss with solely water creates higher rates of urine flow and formation compared with sports drinks, which can contribute to less than optimal performance.
What are the effects of dehydration on my exercise performance?
Based upon previous research, an important level of dehydration that begins to hinder exercise performance is losing 2% of body mass. Whether bodily water loss occurs during exercise of before exercise, the performance outcomes are extremely similar. A loss of water is consistently found to cause a decrease in endurance exercise performance, although the amount of decrease is variable. For example, performance has been found to be particularly reduced when carried out in temperatures exceeding 30 degrees Celsius. In addition, the most decrease is seen in exercise lasting 90 minutes or more, with exercise less than this duration demonstrating smaller decreases in endurance performance. Notably, this diminishing performance effect is not commonly found when examining sprint running performance, suggesting dehydration has considerably more impact upon endurance exercise.
This decline in performance is a result of a dehydrated individual suffering hypothermia due to a lack of heat escaping the body, a consequence of impaired skin blood flow and sweating response. Ultimately, this added stress upon the body causes cardiovascular strain, characterised by a reduction in cardiac output. During times of dehydration, our sweat response can be compromised due to reduced stimuli from the central nervous system to our sweat glands. In turn, this results in failing to keep our bodily temperature down, wreaking further havoc for our exercise performance and overall health.
What is the ideal way to rehydrate after exercise?
To optimise recovery post-exercise, water and sodium should be consumed in a greater quantity than the amount lost from the body during. Although plain water is sufficient to rehydrate ourselves, we lose both water and sodium through our sweat meaning our sodium levels also need replenishing in order to recover effectively. Therefore, electrolytes should again be considered post-exercise.
Interestingly, one study found a yoghurt drink to be effective in replenishing the electrolytes lost in athletes during exercise, providing a low-cost, alternative solution to proper rehydration. Blood sugar levels were even found to be more stable with the yoghurt drink compared to a sports drink or water alone. Although, in terms of restoring urine electrolytes such as sodium and chloride, the yoghurt drink was comparable to the effects of a sports drink after strenuous exercise. In addition, as mentioned in one of my previous posts, chocolate milk is an extremely common choice by athletes for exercise recovery. This doesn't mean ditching a good glass of plain ol' H20 after exercise, since the benefits of this are indisputable. But, if maximising recovery efficiency is your key objective there may be other things to take into account, so be sure to consider the specific electrolytes and nutrients your body will require for this process.
Do you have any tips and tricks to combat dehydration during long, endurance sessions? Be sure to share them in the comments below!