A: What one thing can affect your heat tolerance, heart rate, mental function, motor control, gastric emptying, physical performance, and recovery?
If you answered hydration state then you would be correct!
A less than optimal hydration state can:
• Decrease your ability to tolerate heat
• Increase your submax heart rate
• Increase your perceived exertion level
• Impair mental function and concentration
• Impair motor control
• Slow gastric emptying
• Impair physical performance
• Hinder recovery from training
It doesn’t take much in the way of a less than optimal hydration state for these effects to be seen and felt. A loss of fluid equivalent to 1-2% of bodyweight can have a large impact.
In certain sports, like running, you would think that taking in fluids may seem like a no brainer but optimizing your hydration with regards to how much, when, and what type can take some careful preparation. Your body is composed of 60-80% water. Body temperature regulation, blood volume, and heart rate are all affected by hydration status.
Showing up to a race not optimally hydrated will start you off behind the eight ball and this is something you will not be able to make up. During a race it is generally recommended that fluid intake during the event be about 5-6 ounces every 15 minutes.
In order for fluids to best facilitate hydration/rehydration carbohydrate and electrolytes must be present. Depending on exercise modality (running, cycling etc) a sports drink that is 4-8% carbohydrate will allow for optimal gastric emptying and therefore enhance fluid delivery.
The addition or inclusion of electrolytes also aids in fluid replenishment. In order for hydration status to be maintained it is suggested that sodium levels be moderately high with the possible inclusion of potassium. Sweat composition is different from person to person, but in general it contains much more sodium than potassium. For this reason sodium inclusion in hydration fluids is essential. Beverages should contain 110-200mg sodium per 8oz fluid.
Without the inclusion of adequate electrolytes maintenance of hydration is futile. In fact, drinking beverages with suboptimal electrolytes can lead to increased urine output. Simply stated, a further increase in fluid loss, leaving you further dehydrated.
Sports beverages are specifically designed to meet the carbohydrate and electrolyte needs of athletes needing hydration and rehydration.
Consuming plain water can actually blunt the thirst response causing further dehydration while beverages with citrus flavors often increase fluid consumption.
Regardless of exercise modality- resistance or endurance- dehydration at any level can and will affect performance. Fluid consumption during (when necessary) and after exercise is essential for adequate performance in subsequent exercise sessions.
One easy way to assess how much fluid needs to be replaced is to weigh before and after a training session. Each kg (body weight) lost is the equivalent of 1 liter of fluid needing to be replaced.
Whew, so why the long dissertation before the answer to your question?
So you will understand why coconut water may not be an optimal choice for hydration. Coconut water, albeit ‘natural’, has very little carbohydrate and an even smaller amount of sodium. Remember, those two things are absolutely necessary when it comes to improving and maintaining hydration during and after exercise.
The carbohydrates contained in the sports drinks are essential to aiding in rehydration, but not muscle glycogen resynthesis. It is imperative that you do not mistake the two. Be sure to read Everything you want to know about hydration.
So in a coconut shell, if you’d like to enjoy coconut water as a low calorie beverage then that's great! However, in a sports setting for hydration or rehydration coconut water might not be the best choice.
Maughan R. Leiper J. Shirreffs S. Factors influencing restoration of fluid and electrolyte balance after exercise in the heat. Br J Sports Med. 1997 September; 31(3): 175–182
Everything you want to know about hydration
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