This is an interview with Dr. Koen Levels. Dr. Levels is an assistant professor at the VU University in Amsterdam. Here is a list of all his research articles and here is a link to the article on endurance sports hydration discussed below. Here is an article ‘Hydration Guide for Swimmers’ by Kevin Iwasa-Madge.
1. Please introduce yourself to the readers (how you started in the profession, education, credentials, experience, etc.).
My name is Koen Levels. In 2014 I received my PhD degree on pacing strategies during exercise in the heat. The focus of my research is on optimizing aerobic exercise performance in conditions of extreme heat stress. At this moment, I’m employed as an assistant professor at the VU University Amsterdam, Faculty of Human Movement Sciences.
2. You recently published an article on endurance sports hydration performance. What is the theory of why hypohydration decreases aerobic exercise performance?
During exercise a substantial blood flow to the exercising muscles is needed to ensure adequate oxygen delivery and removal of waste products. However, also an increase in blood flow to the skin is needed to facilitate heat dissipation, mainly by the evaporation of sweat. When an individual is hypohydrated (= lowered body water content), blood plasma volume is reduced which leads to both cardiovascular and heat strain. This strain can ultimately result in a lower exercise intensity and thereby decrease exercise performance. This is especially true for long-lasting (aerobic) exercise, as greater cumulative strain is placed on the body.
3. What did your study look at?
In this study we investigated if drinking to the dictates of thirst during a 40-km cycling time trial in the heat can counteract the negative effects of starting hypohydrated. The participants in this study were dehydrated before starting the 40-km cycling time trial by performing light exercise for approximately 50 minutes in 30ºC.
The current guidelines of the American College of Sports Medicine(ACSM) on fluid replacement during exercise state that a fluid loss of >2% body mass should be prevented during exercise. Therefore, we also considered providing the cyclists with sufficient fluid to prevent body mass losses >2%. However, as in real-life competition thirst is the most relevant signal for drinking, we found drinking to the dictates of thirst more practically relevant to investigate.
5. What were the results of your study?
The employed dehydration protocol prior to the cycling time trial in the heat resulted in mild hypohydration. Surprisingly, this mild hypohydration did not result in a reduced 40-km time trial performance. Because of this, whether or not participants drank during the time trial did not influence their performance. It appears that it is not that detrimental to performance to be mildly hypohydrated at the start of prolonged exercise in the heat as long as there is enough opportunity to dissipate heat during the exercise. In this study participants had a considerable airflow (=wind) over their body which facilitated heat loss.
6. What were the practical implications from your study?
The results from this study indicate that it is not too bad to be mildly hypohydrated during exercise as long as there is enough opportunity to dissipate heat. For outdoor sports this means that the advantages of weighing less due to mild hypohydration may even outweigh the disadvantages of a reduced body water content with regards to cardiovascular and thermoregulatory strain. The ACSM guidelines should therefore be interpreted differently based on the possibility of an individual to lose heat.
7. Do you think these results would be different for each sport, particularly swimmers?
The results will definitely be different for other sports, mainly because of differences in the amount of heat that is produced and the speed of travel and associated wind speed. In swimming, the importance of hydration status seems to be even less relevant than in other sports. The duration of swimming exercise is usually relatively short and heat is easily transferred from the body to the (cool) water. Therefore, heat can easily be dissipated and hypohydration appears to be of little effect on performance. A lower body weight might even be beneficial for performance.
8. Are there any other methods you’d recommend for measuring hydration?
Determining body weight changes is the easiest way to measure hydration. New methods are now on the market that are being advertised to measure hydration status. However most of these methods still need to be validated. One example of these methods is a device measuring concentrations of salivary proteins. However, at this moment my advise would be to measure the change in body weight during exercise and use this as a guide for future exercises of similar length and intensity. In other words, it is important to train drinking behavior.
9. What is the best endurance sports hydration strategy?
Based on scientific literature my advise would be to drink according to the sensation of thirst. If it comes to endurance performance hydration, this appears to be an adequate method to keep the performance optimal. Individuals generally become thirsty if 1% of body mass is lost. Starting with drinking at this moment appears to be sufficient to maintain performance.
10. What research or projects are you currently working on or should we look from you in the future?
At this moment we are studying the interactive effect of hypohydration and heat on endurance exercise performance. The main question that we try to answer is if severe hypohydration degrades performance to a greater extent in the heat than in thermoneutral environments. If this is true, environmental temperature should be taken into account when interpreting drinking guidelines.