Proper drinking is one of the cornerstones of a healthy diet. The state of hydration of our body has a direct influence on a wide range of physical and mental functions and thus plays an important role in the context of sports performance. In today's article, we will focus on how and whether to replenish fluids at all during endurance performance itself.
During endurance and especially ultra-endurance exercise, we naturally lose body water through sweat, which can lead to dehydration to a greater or lesser extent. This increases the risk of overheating, the perception of pain, but also, for example, worsens the mood - which can significantly affect sports performance, even lasting several hours.
Most often, it is stated that body weight should not drop by more than 2% during the exercise. In contrast, however, Hoffman et al. (2018) state that this rule cannot be applied to ultra-endurance athletes, for example. According to the authors, their losses are physiologically much higher during such extreme performances. Thus, if there is an attempt to keep losses to 2%, this could lead to hyperhydration, which can cause complications associated with hyponatremia with potentially fatal consequences. Duvillard et al. (2004) report fluid intake in excess of 1.5 L of fluid every hour during surgery as a risk. The appropriate fluid intake for exercises over 60 min then, according to various recommendations, ranges from 400 to 800 ml/h, but some state an upper limit of up to 1200 ml/h.
Similarly, there is no clear consensus in the professional community on how best to replenish fluids during exercise. There are proponents of two basic strategies - programmed drinking and drinking to thirst.
During programmed planning, it is almost precisely determined in advance what volume of fluid is to be taken and at what intervals during the procedure. The amount of fluid is determined by the estimated sweat rate, which is determined by systematically recording the individual's pre- and post-exercise weight. The limitation here, as mentioned above, is that there is not a complete consensus on what percentage of weight loss we should stick to. Furthermore, another and probably the main limitation of this strategy is that many endurance sports are not performed in constant conditions. So temperature, humidity, course profile, and our physical and mental state, for example, play a big role. It is therefore very difficult to determine exactly the right fluid volume. For example, Kenefick (2018) cites planned fluid intake as the optimal method, especially for high-intensity, high-temperature performances lasting longer than 90 min.
The second approach is drinking to thirst. This is, of course, a much simpler intuitive approach. However, increased attention is needed in cases where the thirst sensation is not properly formed - e.g. in swimmers, the elderly or under increased psychological stress.
Whether using one approach or the other, fluid repletion for exercises lasting less than 60 minutes does not significantly affect performance. Conversely, for exercises longer than 60 minutes, fluid repletion is no longer desirable. In this case, we will also benefit from supplementing plain water with carbohydrate and electrolyte intake. For this purpose, e.g. ionic drinks or energy gels can serve well.
Let's remember that if we go for a few kilometres under normal conditions, we certainly don't have to carry water. If we have a more intense training session or a race lasting more than 60 minutes, we should definitely drink and not rely on plain water alone. With higher intensities and longer periods of exercise, the importance of planning fluid intake increases - at least to some extent. Most athletes of all levels will then be perfectly comfortable managing their fluid intake based on their sense of thirst. Of course, the feeling of thirst is a very subjective concept, so you need to work with yourself and feel your body and feelings. Especially athletes know their body, or at least should know it, very well. Then we should be able to make an appropriate estimation of how much fluid to take in ourselves without causing any digestive discomfort and at the same time being adequately hydrated.
Literature
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