EFFECTS OF DEHYDRATION

When dehydrated, your total blood volume decreases, thereby causing a reduced blood flow to your skin and muscles. This can result in:

  • higher body temperature
  • reduced sweat rate
  • increased muscle glycogen use
  • increased perception of effort
  • higher heart rate

 

All of which contribute to reduced concentration, skill, and physical performance. Given the negative effects of dehydration, it is crucial that you begin your training session or race already in a hydrated state.

PRE-EXERCISE HYDRATION

Athletes should aim to commence exercise and competition in a hydrated state to minimize the potential adverse effects of fluid loss during exercise. Although there are no specific guidelines on how to achieve this, all athletes should assess any potential signs of dehydration and correct these prior to exercise. To do this, the ‘WUT’ method below can be used to assess the three main tell-tale signs of dehydration. If signs of dehydration are present, consuming approximately 500 ml water with an additional 200-300 mg sodium will begin the rehydration process prior to exercise.

 

WEIGHT

As athletes are typically able to maintain a day-to-day stable body weight, body mass loss greater than 1% may be a sign of dehydration as this amount of weight-loss goes beyond normal day-to-day variations in total body water. If your body weight upon waking is unusually low, this may be a potential sign of dehydration.

URINE COLOUR

As urine is comprised of water and various other substances, dehydration results in urine becoming more concentrated and of a darker color. As a result, urine color can be used as a practical indicator of hydration status whereby dark-colored urine correlates favorably with dehydration.

THIRST

Although the absence of thirst does not indicate adequate hydration, the desire for water does coincide with dehydration and should be combined with body weight and urine to provide an indication of your hydration status.

DURING-EXERCISE HYDRATION

Given that fluid losses during exercise are highly individual and can be influenced by a number of factors, fluid intake recommendations should be bespoke to each individual athlete. To do this, athletes will need to estimate their whole body sweat rate during the specific conditions they are training/competing in. This assessment is based on the premise that body mass lost during exercise is reflective of fluid loss. As such, change in body mass before and after exercise can be used to estimate whole body sweat loss during exercise (whereby a 1 g body mass loss represents 1 mL of sweat loss).

 

SWEAT LOSS CALCULATIONS

Equation 1: WBSL (L) = [Body Mass PRE-EX – (Body Mass POST-EX – Fluid Intake EX + Urine Output EX)]

Equation 2: WBSR (L/h) = WBSL / Exercise Duration

 

EX = during exercise

PRE-EX = pre-exercise

POST-EX = post-exercise

WBSL = whole-body sweat loss

WBSR = whole-body sweating rate

 

Once your individualised sweat rate has been calculated, the goal should be to drink enough fluid to keep body mass loss to a minimum. It has been shown that as little as a 2-3% reduction in body weight, due to fluid loss, is enough to adversely affect physical and mental performance during exercise, therefore this should be closely considered. E.g., a 60 kg endurance runner with an estimated fluid loss of 2.4 L (equating to 4%) would be required to consume a minimum of 1.2 L of fluid during exercise to prevent body mass losses of greater than 2%.

Given that our sweat contains key electrolytes such as sodium, magnesium, potassium, and calcium (all of which play a vital role in muscle function), the addition of these electrolytes to your fluid via a sports drink such as Hydro, will ensure these losses are replaced, and performance is maintained throughout.