Aggiornamento: 9 ott 2020
by Gursharan Chana, PhD
We all know maintaining good hydration contributes significantly to peak physical and mental performance. However, knowing when you have drunk enough fluid to achieve optimal hydration is not clear cut, and relying on your body’s thirst response can lead to significant underestimation in fluid requirements.
Why is maintaining fluid balance so important?
Water is the main constituent of the human body, comprising 60% of total body weight, with the vital organs (heart, lungs, brain, liver, kidneys) and muscles composed of greater than 75% water (1). Fluid loss, including water and electrolytes, during exercise of greater than 1% bodyweight begins to impact cognition and decision making (2). Fluid loss greater than 2% results in reduced muscular strength and endurance and increases the risk of heat-related injury. The higher the degree of dehydration, the more pronounced and consistent the impact on physical and mental performance.
While a certain amount of fluid loss is expected during training or competition, if an athlete begins exercising in a fluid deficit, dehydration and reduced performance will occur faster, with chances of injury increasing with duration of exercise. Therefore, ensuring athletes manage their hydration so that they start training or competition fully hydrated can help maintain performance by providing a buffer to the adverse effects of exercise related dehydration.
Tracking hydration for an athlete is a continuous challenge, so pre-exercise preparation needs to be coupled with adequate and appropriate hydration during exercise and then effective rehydration and recovery post-exercise.
How much and what fluid to consume?
While guidelines on fluid replacement for athletes exist (3), fluid requirements, including water and electrolytes vary greatly between individuals, based on age, gender, weight, muscle mass, diet, fitness level, environment and level of activity.
Tracking Fluid and Electrolyte Loss
Plasma osmolarity represents one of the most accurate methods for assessing fluid balance being reflective of total body water content (TBW). However, as a measure of hydration it is invasive and impractical for routine use, with many athletes not keen to continuously give blood samples for analysis.
BODYWEIGHT – Body Mass Loss (BML)
Assessing changes in nude bodyweight before and after exercise represents an accurate measure of fluid loss, termed body mass loss (BML). While BML is simple and non-invasive, simply requiring a scale (accurate to ±0.1kg), there is significant inconvenience due to measurements requiring to be undertaken nude, with changes associated with urine and sweat present on the body also needing to be considered. In addition, as significant fluctuations in bodyweight can occur from day to day, the utility of BML as a pre-exercise measure is limited.
Although urine colour and urine specific gravity (USG) have been the mainstay of hydration testing utilized by professional teams and athletes, offering a relatively easier method for tracking hydration when compared to plasma, these measures are often inappropriately applied and interpreted. For instance, to utilise USG correctly, a first morning, mid-stream sample is required ensuring a valid measurement of hydration status. This is often not practical and usually very little control is enforced on collection of the sample. This had led to teams utilising USG measurements for conducting hydration spot checks of athletes. This can lead to both under- and overestimation of hydration status (4), with younger players being wise to the tactic of consuming large amounts of water 30-45minutes prior to being tested. While this allows them to return a very hydrated score, the measurement is simply reflective of the body flushing out excess fluid that cannot be absorbed.
Saliva represents a simple, convenient and non-invasive fluid to assess hydration status. Until recently, the routine use of saliva to measure hydration status through estimation of salivary osmolarity (SOSM) was uncommon due to the requirement of specialized laboratory equipment, termed an osmometer, to conduct measurements.
Our company, MX3 Diagnostics, has developed a solution to overcome this problem. We have developed a handheld osmometer, the MX3 LAB, that uses disposable test strips, allowing SOSM measurements to be made rapidly and conveniently to measure hydration status.
Measurements can be made by sampling inserting a test strip into the device, tapping it on a user’s tongue. The SOSM results related to the athlete’s hydration status is then displayed and recorded in the App. The accuracy of our system in estimating SOSM has been independently validated by the US Air Force.
Increases in SOSM during exercise have been found to be significantly correlated with changes in nude body mass loss (BML) (5). Therefore, tracking SOSM allows an athlete to track their fluid balance relative to activity to ensure they are optimally hydrated before training or competition and additionally to track their rehydration and recovery.
While tracking fluid balance provides one part of the hydration equation, the second part relates to being able to accurately measure what electrolytes an athlete is losing. This can be determined via assessing their sweat sodium concentration, with sodium the predominant electrolyte lost during exercise. The conventional and most accurate approach to measuring sweat sodium relies on using a sweat patch to collect sweat and then analysing the content of the patch using a laboratory electrolyte analyser. While a sweat patch can certainly be obtained easily, having access to an expensive electrolyte analyser limits the use of this method of sweat sodium testing. We have developed a sweat test strip that can measure sweat sodium levels as accurate as an electrolyte analyser but do so rapidly and conveniently so that athletes can develop personalised rehydration plans.
The MX3 sweat test kit represents the first laboratory grade sweat testing system that is significantly reduced in cost, thereby making it much more accessible to coaches, trainers, nutritionists, and athletes.
REHYDRATION – A Shift in Thinking
Over the last decade there has been a significant shift in thinking related to drinks for optimal rehydration and recovery. There has been a move away from high fructose, high calorie beverages that were traditionally the mainstay of sports drinks, to drinks with more of an emphasis on electrolyte replacement while providing just enough carbohydrates for absorption of fluid and energy replacement. In addition, there has been a greater focus by professional teams and athletes on personalised rehydration strategies to maximize performance. This paradigm shift will inevitably continue to be adopted by larger numbers of athletes and teams as tools to track fluid and electrolyte replacement become more accessible.
1 Elia, M. Body composition analysis: an evaluation of 2 component models, multicomponent models and bedside techniques. Clin Nutr 11, 114-127, (1992).
2 Ganio, M. S. et al. Mild dehydration impairs cognitive performance and mood of men. Br J Nutr 106, 1535-1543, (2011).
3 McDermott, B. P. et al. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train 52, 877-895, (2017).
4 Cheuvront, S. N., Kenefick, R. W. & Zambraski, E. J. Spot Urine Concentrations Should Not be Used for Hydration Assessment: A Methodology Review. Int J Sport Nutr Exerc Metab 25, 293-297, (2015).
5 Munoz, C. X. et al. Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration. Eur J Clin Nutr67, 1257-1263, (2013).
Gursharan Chana is the Director of Biomedical Science at MX3 Diagnostics, a Company based in Austin (Texas, USA), Minneapolis (Minnesota, USA) and Melbourne (Australia).
Originally a neuroscience researcher he now drives MX3's physiology studies aimed at developing and validating point-of-care technologies for tracking performance and health and wellbeing.