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The importance of pre-hydration: Are you drinking enough before race day?

Pre-hydration Strategy

Before exercise, athletes often fail to hydrate effectively (2) and begin exercise in a hypohydrated state (i.e. dehydrated), which refers to the state of being in a negative water balance. As little as a 2-3% body mass deficit is enough to adversely effect physical and mental performance during exercise, especially when the exercise is undertaken in hot conditions (1).

When you sweat you lose fluids and key electrolytes, such as sodium, potassium, magnesium, chloride and calcium – crucial to maintaining performance. When racing or training, it is therefore important to replace both fluids and electrolytes if you want to avoid the affects of dehydration. When dehydrated, your total blood volume decreases, thereby causing a reduced blood flow to your skin and muscles. Collectively, these responses result in higher body temperatures, reduced sweat rates, increased muscle glycogen use, increased perception of effort and higher heart rates, all of which contribute to reduced concentration, skill and physical performance. Given the negative effects of dehydration, it is therefore crucial that you begin your training session or race already in a hydrated state.



Research has suggested that athletes may achieve euhydration prior to exercise by consuming a fluid volume equivalent to 5–10 ml per kilo of body mass in the 2 to 4 hours before exercise (1). It is recommended that an athlete should achieve urine that is pale yellow in color while allowing for sufficient time for excess fluid to be voided from the body (1,2,4).

Sodium plays a key role in hydration, helping absorb and retain fluid in the body (1,3,5). The concentration of sodium in our bloodstream is normally tightly regulated within a concentration of 135-145 mmol/L. When the blood sodium level drops below the range, this is known as hyponatremia (6). The solute content of sweat is influenced by a number of factors, including the sweating rate and acclimatization status of the individual (6). Some athletes are ‘salty’ sweaters, which is highly individual. For these athletes especially, increasing sodium levels in the diet (particularly pre-exercise) is important to maintain performance in the heat and/or for prolonged periods of time.

Follow this example plan for a 70kg athlete preparing for a competition:

  1. Wake up – 250-500 ml fruit juice/water with breakfast
  2. 3-4 hours prior – 500-750 ml SiS GO Electrolyte
  3. 30-60 minutes prior– 250 ml SiS GO Hydro (at this stage your urine output should have reduced and any urine passed should be pale yellow)


As always, you should practice your pre-hydration in training before trying in competition.



  1. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Medicine and Science in Sports and Exercise, 48(3), 543.
  2. Shirreffs, S. M., & Sawka, M. N. (2011). Fluid and electrolyte needs for training, competition, and recovery. Journal of sports sciences, 29(1), 39-46.
  3. Casa, D. J., DeMartini, J. K., Bergeron, M. F., Csillan, D., Eichner, E. R., Lopez, R. M., & Yeargin, S. W. (2015). National Athletic Trainers’ Association position statement: exertional heat illnesses. Journal of Athletic Training, 50(9), 986-1000.
  4. Armstrong, L. E., Herrera Soto, J. A., Hacker Jr, F. T., Casa, D. J., Kavouras, S. A., & Maresh, C. M. (1998). Urinary indices during dehydration, exercise, and rehydration. International Journal of Sport Nutrition, 8(4), 345-355.
  5. Stachenfeld, N. S. (2014). Sodium Ingestion, Thirst and Drinking During Endurance Exercise. Sports Science Exchange, 27(122), 1-5.
  6. Lara, B., Gallo-Salazar, C., Puente, C., Areces, F., Salinero, J. J., & Del Coso, J. (2016). Interindividual variability in sweat electrolyte concentration in marathoners. Journal of the International Society of Sports Nutrition, 13(1), 31.
Written By

Ben Samuels

Ben is a Performance Nutritionist at Science in Sport