HYDRATION STRATEGIES OF MARATHON RUNNERS: WHAT DOES THE EVIDENCE SAY?

Sports nutrition and sports hydration, in particular, is a widely discussed and a hot topic in the field of sports1. Many researches have demonstrated that dehydration impairs performance in most events, and athletes should be well hydrated before exercise2,3,4,5. As per the International Olympic Committee Consensus 6,7 statement, sufficient fluid should be consumed during exercise to limit dehydration to less than 2% of body mass. Sodium should be included when sweat losses are high, especially if exercise lasts more than about 2 hours. During recovery from exercise, rehydration should include replacement of both water and salts lost in sweat.

This article reviews the various strategies that may be followed in order to achieve maximal performance. Also, we will try to understand the potential impact of dehydration on performance. The strategies mentioned in this review may be used by the coaches, athletes and marathon enthusiast to optimize their health and performance.

It is now clear that any amount of dehydration of more than or equal to 2% of body weight is detrimental to the performance of a middle and long-distance runner and they are affected the most. Optimal hydration reflects a physical state of having normal body water and electrolytes and it is assumed as the starting point for most of the recommendation and strategies8. An athlete can very well self assess the day to day hydration requirement by the cues from the body. It is a necessity that the athlete should be aware of this, as too much water drinking may be detrimental to the health and may lead to Exercise-Induced Hyponatremia9. WUT is such a strategy where the reduced body Weight (W), dark colour Urine (U) and feeling Thirsty (T) gives an indication of hydration needs. A daily loss of body weight (W) greater than 0.5 to 1.0 kg, a small volume of dark coloured urine (U; apple juice or darker), and the noticeable sensation of thirst (T) are all the symptoms of dehydration. When two or more symptoms are present, dehydration is very likely8. It is recommended that all three WUT symptoms should be assessed upon waking each morning. The total sweat loss is another factor to be considered to meticulously plan the hydration needs. The primary factors that influence sweat loss include body size, exercise intensity, exercise duration, the environment and choice of clothing10. At minimum, the athletes must replace body water and electrolyte losses daily. Failure to do so can lead to dehydration, poor training, and competition outcomes8. Dehydration also affects mental readiness. It has a negative effect on mood state and there is alteration in perceived tiredness, alertness, confusion, fatigue, anger or depression. It can also produce unpleasant and distractive symptoms, such as dry mouth, thirst and headache2.

It is very well stated that optimal day to day hydration is most important for optimizing training and competition for all track and field athletes8. The use of thirst to guide drinking behavior is probably sufficient for optimizing hydration particularly in a familiar setting, but when the training and competition are in unfamiliar settings a more programmed approach is recommended11. As marathon runners intend to compete, replacement planning should be part of the strategy.

The practical strategies8 to reduce dehydration may be as follows-

1. WUT- First-morning weight, Urine color, and thirst sensation to guide day to day adequacy of water and electrolyte consumption.
2. Incorporate Electrolytes- Rehydrate with meals and include sodium and potassium-rich foods.
3. Personalize fluid needs- Estimate personal sweat losses from changes in body weight pre-to post-exercise.
4. Train as you compete- Incorporate a competition drinking strategy into training.
5. Improve thermal management- Train during the coolest times of the day, consider indoor air-conditioned training in extreme heat and consider the use of active cooling (e.g. cold towels, cold showers)
To conclude, we can see that to optimize the performance it is necessary for the athletes to maintain an adequate fluid and electrolyte balance both during training and competition. If the athlete is training and competing in hot environmental conditions then a more programmed approach is a must. Given the individual nature of sweating responses with training and competition, each athlete should assess should assess their own individual fluid requirements and determine if these are likely to be a cause for a concern8.`

References-
1. CotterJ.D.ThorntonS.N.LeeJ.K.& LaursenP.B.(2014). Are we being drowned in hydration advice? Thirsty for more?Extreme Physiology & Medicine3(1) 18.
2. CheuvrontS.N.& KenefickR.W.(2014). Dehydration: Physiology, assessment, and performance effects. Comprehensive Physiology4(1) 257–285.
3. EvansG.H.JamesL.J.ShirreffsS.M.& MaughanR.J.(2017). Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. Journal of Applied Physiology122(4) 945–951.
4. McDermottB.P.AndersonS.A.ArmstrongL.E.CasaD.J.CheuvrontS.N.CooperL.… RobertsW.O.(2017). National Athletic Trainers’ Association position statement: Fluid replacement for the physically active. Journal of Athletic Training52(9) 877–895.
5. WittbrodtM.T.& Millard-StaffordM.(2018). Dehydration impairs cognitive performance: A meta-analysis. Medicine & Science in Sports & Exercise50(11) 2360–2368.
6. IOC consensus statement on sports Nutrition 2003. (2004) Journal of Sports Sciences, 22 (1).
7. IOC consensus statement on sports Nutrition 2010. (2011) Journal of Sports Sciences, 29 (Suppl. 1), S3-S4.
8. Casa, D. J., Cheuvront, S. N., Galloway, S. D., & Shirreffs, S. M. (n.d. ). Fluid Needs for Training, Competition, and Recovery in Track-and-Field Athletes, International Journal of Sports Nutrition and Exercise Metabolism, 29(2), 175-180.
9. Goublet EDB(2013), British Journal of Sports Medicine;47:679-686.
10. Gagnon D.JayO.& KennyG.P.(2013). The evaporative requirement for heat balance determines whole-body sweat rate during exercise under conditions permitting full evaporation. The Journal of Physiology591(11) 2925–2935.
11. KenefickR.W.(2018). Drinking strategies: Planned drinking versus drinking to thirst. Sports Medicine 48(Suppl. 1) 31–37.

About the Author:
Dr Sudeep Satpathy
Consultant Sports Medicine & Human Performance
MBBS (Gold Medal), MD (Phy), Dip Sports Medicine(IOC)
MFSEM (Royal College of Surgeons)