By Annie Bothma, 25 September 2022
STAY ON TOP OF YOUR HYDRATION
Athletes should aim to be fully hydrated before they train or compete because the body cannot adapt to dehydration. If you don't start exercise in a well-hydrates state your training quality will suffer and so will your performance on race day.
EFFECTS OF DEHYDRATION ON PERFORMANCE
Dehydration will significantly impact the athletes performance by:
Reducing blood-volume
Decreasing blood-flow to the skin
Decreasing sweat-rate
Decreasing heat dissipation
Increasing body core temperature
Increasing the rate of muscle glycogen use
A decrease in performance will be noticed at around 2-3% of body-fluid loss. Severe dehydration will increases the risk of developing heat illness and may cause an athlete to end up in the medical tent on race day.
EFFECTS OF DEHYDRATION ON THE GASTROINTESTINAL SYSTEM
Dehydration will also have negative effects on the gastrointestinal system such as:
Nausea
Vomiting
Stomach pain
Bloating
Decreased appetite
Dehydration will increase GI distress during prolonged exercise in the heat which will result in less blood flow to the intestine by reducing total blood volume. This will further impact the athlete’s ability to fuel and hydrate sufficiently creating this vicious cycle of depletion and accelerating the increase in dehydration. Of course, this will also significantly impact the athletes performance and may even lead to a dreaded DNF.
DRINKING TO THIRST VS DRINKING WITH A PLAN
Relying on feeling thirsty as the signal to drink is unreliable because a considerable degree of dehydration can certainly be sufficient to impair athletic performance and may occur before the desire to ingest fluids. This is why athletes should become accustomed to consuming fluid at regular intervals with or without being thirsty during training sessions leading up to a major event, to lessen the change of GI discomfort during competition. Ideally, athletes should consume enough fluids during activity that body weight remains fairly constant before and after exercise. However, don't over-drink as this can lead to hyponatremia (diluted blood sodium concentrations), which can have serious and even potentially threatening consequences.
SPORT DRINKS VS PLAN WATER
I recommend athletes to use sport drinks instead of just water alone to counteract fluid losses. Sports drinks that contain sodium and other electrolytes, as well as carbohydrates, This is ideal since the presence of small amounts of glucose and sodium tends to cause an increase in the rate of water absorption compared with pure water alone. Sodium and other electrolytes that are added to sports drinks don't just replace lost electrolytes, but also provide the following benefits:
Increase palatability
Maintain thirst (and therefore promote drinking)
Prevent hyponatremia (diluted blood sodium)
Increase the rate of water uptake
Increase the retention of fluid
SWEAT RATES:
Sweat rates vary widely among individuals under the same ambient conditions. So, it is difficult to prescribe the specific amount a person should ingest without knowing the person’s sweat rate under the prevailing weather conditions.This is why it is helpful for athletes to determine their own individual sweat rate so they can fine-tune their hydration strategy leading into race day.
HOW TO ESTIMATE YOUR SWEAT LOSSES AND SWEAT RATES:
1) Measure body mass both before and after at least one hour of exercise under
conditions similar to competition or a hard practice.
2) Take these body mass measurements wearing minimal clothing and while bare footed.
Towel dry after exercise and obtain body mass as soon as is practical after exercise (Do it right after you finished your exercise, before eating, drinking or going to the toilet)
Example: Pre-exercise weight = 74.5 kg
Post-exercise weight = 72.8 kg
Fluid deficit = 1.7 kg
3) Estimate the weight of any fluid or foods you have consumed during the workout.
Example: 800 ml of fluid = 800 g or 0.8 kg)
4) Sweat loss (Liters) = Body mass before exercise (in kg) - Body mass after exercise
(kg) + weight of fluids/foods consumed (kg).
Example: 74.5 kg – 72.8 kg = 1.7 kg deficit
+ 0.80 kg (800 ml fluid) = sweat loss of 2.5 kg or 2500 ml.
To convert to a sweat rate per hour, divide by the exercise time in minutes and multiply by 60.
5) Your weight deficit at the end of the session provides a guide to how well you
hydrated during the session, and how much you need to rehydrate afterwards.
To convert kg to % body mass, divide the weight deficit by starting body mass and
multiply by 100:
Example: 1.7 kg/74.5 X 100 = 2.3%
* Note: 2.2 pounds equals 1.0 kg and converts to a volume of 1.0 liter or 1,000 ml or 34
ounces of water.
* Test more than one time and try to mimic the race conditions as closely as possible in terms of weather conditions and your exercise intensity.
PRACTICAL WAYS TO ASSES AND MANAGE YOUR HYDRATION
1. Develop good daily hydration practices
The aim is to develop fluid practices over the day and consume extra for the losses from exercise or when training in hot environments. As your losses change, so should drinking practices - some days you may need more, others less. It is better to spread fluid intake over the day rather than trying to play catch up at the end of the day. Drinking more than you need in the later part of the day can mean you'll interrupted sleep due to toilet breaks.
2. Start the session well hydrated.
If you are passing urine less often than normal, you may be dehydrated. If urine color becomes darker then what is normal for you, then you may not be drinking enough.Take note that the color pigments of certain fruits and vegetables, as well as certain vitamins (like B-vitamins), may effect your urine color.
* Note: The aim should NOT be for your urine to be as pale as possible. Drinking too much can be harmful like explained above.
3. Develop a personalized drinking plan for training and competition that is right for you.
Your plan should be based on several pieces of information including your typical sweat losses, the opportunities to drink in your sport, GI comfort and thirst sensations.
4. Monitor your sweat losses and the success of your drinking plan during training sessions in different situations:
How did you feel?
How did you perform?
How was your GI discomfort?
What was your weight loss over the session? *
* Note: This should generally not exceed about 1-2% of body mass. If you lost
more than this, you probably did not drink enough. Drink more next time. If you lost less, you might have drunk too much.
4. Assess if you you are a “salty sweater”
You may need drinks with more salt and may need more salt in food when sweat losses are high. To check whether you are a salty sweater, you can do a sweat test to analyze your individual sweat composition. High salt losses may be a contributing factor in some cases of muscle cramps. Sports drinks with higher salt (sodium) levels may help reduce muscle cramps in certain athletes. Sweat composition does vary greatly amongst individuals and can be up to 5g electrolytes lost in certain individuals. The key electrolytes you lose in your sweat include: sodium, chloride, potassium, magnesium and calcium.
KEY TAKE AWAYS:
2-3% dehydration will significantly impact the athletes performance.
Dehydration will increase gastrointestinal distress.
Drink to a plan, not just to thirst in longer events.
Choose sports drinks over plain water.
Avoid hyponatremia by not over consuming fluids.
Develop good daily hydration practices
Start the session well hydrated.
Determine your own individual sweat rate.
Access if you are a salty sweater
Create your own hydration plan.
Practice and asses your hydration strategy during training.
Get on top of your hydration now before it is too late and you are already dehydrated! Use the weeks leading up to your race to determine your individual sweat rate and fluid needs. Creating an individual hydration plan that is right for you and the specific race you are training for will help you perform to your best!
READ MORE:
Sport Nutrition, Third Edition. (2019) by Asker Jeukendrup, Micheal Gleeson