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Hydration in Athletes

Original Editor - Alicia Fernandes|

Top Contributors - Alicia Fernandes, Angeliki Chorti, Kim Jackson and Khloud Shreif  

Introduction

Athletes, running, hydration

Hydration plays an important role in competitive athletic performance, injury prevention and recovery. [1] Athletes need to keep fluid levels adequate, in order to train and compete at top levels. From a physiotherapist's perspective, understanding the importance of hydration, the methods of assessing hydration status, and individualised hydration strategies is essential for optimising athlete performance and health.

Importance of Hydration

Proper hydration is vital for maintaining physiological functions, thermoregulation, and optimal performance. Dehydration can lead to decreased endurance, increased fatigue, impaired cognitive function, and a higher risk of heat-related illnesses. A reduction of more than 2-4% in body mass due to dehydration can significantly compromise endurance performance. [2][3]

Methods of Assessing Hydration Status

Accurately assessing hydration status is critical for developing effective hydration strategies. Common methods include: [4]

  • Plasma/Serum Osmolality: Measures solute concentration in the blood and is considered a gold standard but can be influenced by various factors.[5]
  • Urine Analysis: Urine color, specific gravity, and osmolality are practical and non-invasive methods, although they may not be as accurate as blood tests.[5][6]
  • Sweat Rate and Electrolyte Analysis: Determining sweat rate and sweat sodium concentration helps tailor hydration plans to individual needs.[7]

Use of Technology in Assessing Hydration

Apart from hydration status monitoring, assessment of rehydration, and the ability to use non-laboratory measurements that address issues of portability in sport settings are also important when looking at athletic performance and prevention of illnesses. [8] Athletes may have different habitual fluid intakes and this may have an effect on their hydration status but not their body water compartments due to homeostatic mechanisms. [9]

Some authors propose the development of novel techniques that monitor hydration in real time and are non-invasive, portable, safe, and customised to the individual athlete. [10] [11] With these considerations in mind, real-time data from wearable sensors have been used to accurately estimate mild dehydration in athletes, [8] and machine learning has been used to distinguish hydration status and fluid balance characteristics in elite adolescent athletes.[11]

Hydration Strategies

Effective hydration strategies are personalised, taking into account individual sweat rates, exercise intensity, and environmental conditions. Key strategies include:

  • Pre-Exercise Hydration: Ensuring athletes are well-hydrated before exercise is crucial. This can be achieved by drinking fluids ad libitum in the hours leading up to exercise. [2]
  • During Exercise: Athletes should aim to drink enough to prevent significant body mass loss while avoiding overhydration. Drinking to thirst and using marked bottles to monitor fluid intake can help manage hydration levels. [7]
  • Post-Exercise Rehydration: Consuming fluids and electrolytes after exercise aids recovery. Including sodium in post-exercise meals and drinks can enhance rehydration.[3]

Establishing a Hydration plan

As follows:[12]

Guiding Question
Steps to Correct
Implementation Example
Are athletes in a state of optimal hydration? Assess hydration status Have scales available before and after practice to assess fluid deficits - Measure fluid needs via sweat rate
Is the exercise prolonged or intense? Increase availability of palatable fluids Have more breaks during longer practices or more intense exercise - Allow longer duration breaks |
Is the exercise being performed in environmental conditions that lead to greater fluid losses? Establish breaks based upon environmental conditions Modify practice schedules utilizing WBGT to establish work-to-rest ratios that allow for adequate fluid intake
Is fluid available throughout the entire duration of exercise? Fluid is made readily available for athletes Provide free access to fluids during practice<br>- Ensure athletes utilise breaks to rehydrate when opportunities are limited
Are there individuals with intrinsic risk factors? Identify individuals with high sweat rates or other limits to optimal hydration Test sweat rates of individuals who have issues with hydration - Develop individual hydration plans for high-risk athletes
Are there sport-specific factors that need to be considered? Counsel athletes on health and performance risks of utilising dehydration for weight loss Assess hydration status alongside weight measurements to promote healthy weight management

Use of Technology in Managing Hydration

Artificial Intelligence (AI) in sports applications have come to change the landscape of sports hydration. Water trackers and water drink reminders are some examples of commonly used hydration apps that gamify water intake and make hydration more fun and effective. What is more interesting though is that athletes are able to identify patterns in their fluid concentration levels with the help of AI and make use of personalised hydration plans. Some companies have actually created platforms to deliver personalised hydration plans that fit the athletes' exercise routines. For example, athletes' sweat content measurements have been used by a programme that produces a personalised drink formula to replenish lost nutrients. "Smart caps” on water bottles have also been developed to keep track of fluid intake, with the aim to manage hydration more effectively during exercise.

Risks of Hyperhydration

While preventing dehydration is critical, overhydration, or hyperhydration, can lead to exercise-associated hyponatremia (EAH), a potentially life-threatening condition characterised by low blood sodium levels. [13] Preventing EAH involves educating athletes to avoid excessive fluid intake and to drink based on thirst and sweat rates. [3]

Intrinsic Factors Affecting Fluid Loss in Athletes

  • Larger individuals tend to have higher sweat rates, necessitating greater fluid intake. For example, football linemen exhibit some of the highest recorded sweat rates .[14]
  • An individual’s thirst drive can influence drinking behavior during exercise, but it may not align with actual fluid needs. Athletes often experience voluntary dehydration due to a mismatch between fluid losses and drinking habits. Conversely, excessive drinking due to heightened thirst can lead to hyponatremia. [15][16][17]
  • Heat-acclimatised athletes generally sweat more, which increases the risk of hypohydration. Although this increased sweat rate aids in heat dissipation, it requires additional fluid intake to maintain hydration.[18]
  • Women may be more susceptible to exercise-induced hyponatremia, influenced by factors such as lower body weight, excess water consumption, and longer exercise durations.[19] This risk is not significantly linked to higher estradiol levels or other female sex hormones affecting thirst and sodium regulation.  [20] 

Effects of Hydration Changes on Neuromuscular Function in Athletes

  • Impact of Hydration on Neuromuscular Function:Neuromuscular function is highly sensitive to hydration status. Dehydration can lead to neuromuscular fatigue, characterised by alterations in electromyographic (EMG) activity. A decrease in mean power frequency (MPF) towards lower frequencies has been associated with muscular fatigue due to reduced muscle fiber conduction velocity . This suggests that dehydration affects the excitability of muscle membranes, thereby impairing muscle function. [21]
  • Effects of Increased Water Intake: Increasing water intake over a short period can improve hydration status and potentially enhance neuromuscular function. The H2OAthletes project aims to determine if athletes with a low habitual water intake (WI) can benefit from increased WI over four days. Improved hydration is expected to reduce muscle fatigue and enhance performance by maintaining muscle fiber conduction velocity and motor unit activity. [7]
  • Neuromuscular Adaptations to Dehydration:Dehydration protocols often reveal EMG changes such as a decrease in MPF and an increase in average rectified value (ARV), indicating fatigue and central regulation of motor unit activity. Athletes may compensate for dehydration-induced fatigue by increasing motor command, leading to higher motor unit recruitment and firing rates. This adaptation is more pronounced at lower contraction levels due to greater recruitment capacity. [21]
  • Hormonal and Psychological Factors:Dehydration can increase plasma arginine vasopressin (AVP) levels, indicating intracellular dehydration. Psychological factors such as increased perception of fatigue, tension, and anxiety also play a role in neuromuscular function during dehydration. The H2OAthletes project includes mood state assessments to explore these associations. [7]

Conclusion

Proper hydration is critical for athletes, influencing performance, recovery, and overall health. From a physiotherapist's perspective, assessing hydration status and developing individualised strategies are key components of optimising athletic performance. Effective hydration strategies should account for factors such as exercise intensity, environmental conditions, and individual sweat rates. Pre-exercise hydration, maintaining hydration during exercise, and rehydration post-exercise are essential practices. Additionally, understanding the risks of hyperhydration and the impact of hydration on neuromuscular function can help in creating comprehensive hydration plans. By addressing these elements, physiotherapists can help athletes achieve optimal hydration and enhance their performance.

Reference

  1. ↑ Judge LW, Bellar DM, Popp JK, Craig BW, Schoeff MA, Hoover DL, Fox B, Kistler BM, Al-Nawaiseh AM. Hydration to Maximize Performance and Recovery: Knowledge, Attitudes, and Behaviors Among Collegiate Track and Field Throwers. J Hum Kinet. 2021 Jul 28;79:111-122.
  2. ↑ 2.0 2.1 Goulet ED. Dehydration and endurance performance in competitive athletes. Nutr Rev. 2012 Nov;70(suppl_2):S132-S136.
  3. ↑ 3.0 3.1 3.2 Königstein K, Niess AM, Carlsohn A, Treff G. Hydration management in sports. Dtsch Z Sportmed. 2022;73(4):137-141.
  4. ↑ Cleary MA. What are the Most Practical, Valid Methods of Measuring Hydration Status in Athletes?. InQuick Questions Heat-Related Illness 2024 Jun 1 (pp. 151-156). Routledge.
  5. ↑ 5.0 5.1 Barley, O.R., Chapman, D.W. & Abbiss, C.R. Reviewing the current methods of assessing hydration in athletes. J Int Soc Sports Nutr 17, 52 (2020). 1-6
  6. ↑ Smith BR. Urine Color as a Marker of Change in Hydration Status Produced by Land-Versus Water-Based Exercise. University of Wyoming; 2024.
  7. ↑ 7.0 7.1 7.2 7.3 Ayotte, D., Corcoran, M.P. Individualized hydration plans improve performance outcomes for collegiate athletes engaging in in-season training. J Int Soc Sports Nutr 15, 27 (2018)
  8. ↑ 8.0 8.1 Kamran F, Le VC, Frischknecht A, Wiens J, Sienko KH. Noninvasive Estimation of Hydration Status in Athletes Using Wearable Sensors and a Data-Driven Approach Based on Orthostatic Changes. Sensors (Basel). 2021 Jun 29;21(13):4469.
  9. ↑ Francisco R, Jesus F, Nunes CL, Cioffi I, Alvim M, Mendonca GV, Lukaski H, Sardinha LB, Silva AM. Athletes with different habitual fluid intakes differ in hydration status but not in body water compartments. Scand J Med Sci Sports. 2023 Jul;33(7):1072-1078.
  10. ↑ Armstrong LE. Assessing hydration status: the elusive gold standard. J Am Coll Nutr. 2007 Oct;26(5 Suppl):575S-584S.
  11. ↑ 11.0 11.1 Suppiah HT, Ng EL, Wee J, Taim BC, Huynh M, Gastin PB, Chia M, Low CY, Lee JKW. Hydration Status and Fluid Replacement Strategies of High-Performance Adolescent Athletes: An Application of Machine Learning to Distinguish Hydration Characteristics. Nutrients. 2021 Nov 15;13(11):4073.
  12. ↑ Belval LN, Hosokawa Y, Casa DJ, Adams WM, Armstrong LE, Baker LB, et al Practical hydration solutions for sports. Nutrients. 2019;11(7):1550. .
  13. ↑ Maughan RJ, Meyer NL. Hydration during intense exercise training. Nestle Nutr Inst Workshop Ser. 2013;76:25-37.
  14. ↑ Sawka M, Burke L, Eichner R, Maughan R, Montain S, Stachenfeld N. American College of Sports Medicine exercise and fluid replacement position stand. Med. Sci. Sport. Exerc. 2007;39:377-90.
  15. ↑ Hosseinlou A, Khamnei S, Zamanlu M. The effect of water temperature and voluntary drinking on the post rehydration sweating. International Journal of Clinical and experimental medicine. 2013;6(8):683.
  16. ↑ Passe D, Horn M, Stofan J, Horswill C, Murray R. Voluntary dehydration in runners despite favorable conditions for fluid intake. International journal of sport nutrition and exercise metabolism. 2007 Jun 1;17(3):284-95.
  17. ↑ Hew-Butler T, Rosner MH, Fowkes-Godek S, Dugas JP, Hoffman MD, Lewis DP, Maughan RJ, Miller KC, Montain SJ, Rehrer NJ, Roberts WO. Statement of the third international exercise-associated hyponatremia consensus development conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine. 2015 Jul 1;25(4):303-20.
  18. ↑ Tyler CJ, Reeve T, Hodges GJ, Cheung SS. The effects of heat adaptation on physiology, perception and exercise performance in the heat: a meta-analysis. Sports medicine. 2016 Nov;46:1699-724.
  19. ↑ Almond CS, Shin AY, Fortescue EB, Mannix RC, Wypij D, Binstadt BA, Duncan CN, Olson DP, Salerno AE, Newburger JW, Greenes DS. Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine. 2005 Apr 14;352(15):1550-6.
  20. ↑ Ishunina TA, Swaab DF. Vasopressin and oxytocin neurons of the human supraoptic and paraventricular nucleus; size changes in relation to age and sex. The Journal of clinical endocrinology & metabolism. 1999 Dec 1;84(12):4637-44.
  21. ↑ 21.0 21.1 Francisco R, Jesus F, Nunes CL, Santos P, Alvim M, Campa F, et al. H2OAthletes study protocol: effects of hydration changes on neuromuscular function in athletes. Br J Nutr. 2024;131(9):1579-90.
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