In the context of sports nutrition, hydration is an often overlooked component of a healthy diet. Water performs many functions in the body:
- It maintains the health and integrity of cells.
- It serves as a transportation system for nutrients, oxygen, and other elements, as well as waste and byproducts.
- It lubricates joints and absorbs shocks within the brain, spinal cord, and eyes.
- It aids in the digestion and biochemical breakdown of other nutrients.
- It keeps mucous membranes healthy.
- It regulates body temperature.
Hydration isn’t just about water, though: electrolytes are an essential part of hydration as well. Electrolytes are minerals that form electrically charged particles, or ions, in body fluids. In the body, electrolytes help to regulate nerve and muscle function, blood pH, and hydration. Five key electrolytes are essential for optimal function among athletes:
Together, these electrolytes help maintain fluid balance, conduct nerve impulses, and play a role in muscular contraction and metabolism. Because electrolytes regulate how much water is available for cell use, it’s important to maintain the proper concentrations of electrolytes in the body.
During exercise, fluids and electrolytes are lost through sweat; the extent to which they are lost depends on a number of factors, including air temperature, the intensity and duration of exercise, body size, gender, genetics, and fitness level. Neglecting to replace lost fluids and electrolytes during and after exercise makes performing at your optimal level and recovery near impossible.
Dehydration occurs when you lose more fluid than you take in, and normal physiological processes are disrupted. Specifically, dehydration results in a reduction of blood volume, decreased blood flow to the skin, decreased sweat rate and heat dissipation, and increased core temperature. These physiological shifts result in a reduced maximal cardiac output: as water from your blood is drawn away to help cool you down, your blood volume decreases and your blood’s viscosity thickens. As a result, your heart has to work harder and faster to deliver the same amount of oxygen to cells.
The severity of symptoms depends on the amount of fluid you lose, but with respect to sports performance, dehydration has been shown to adversely affect performance by increasing the perceived difficulty of exercising; reducing maximal aerobic power and endurance; and impairing reaction time, judgement, and decision making.
It’s a commonly held belief that dehydration and electrolyte loss can also lead to cramping, as an imbalance of fluids and electrolytes increases the excitability of nerves. New research indicates that cramping may have little or nothing to do with dehydration: when ten individuals exercised with their non-dominant limbs (cramp testing was performed on their dominant limbs to eliminate the confounder of muscle fatigue and damage) for four hours in hot conditions, reaching an average dehydration of 4.7%, there was no difference in cramp susceptibility or intensity. According to the researchers, cramping is tied to “altered neuromuscular function,” which includes muscle fatigue, not tapering enough, and a genetic predisposition. But because cramping is linked to muscle fatigue, and dehydration also plays a role in muscle fatigue, dehydration may play an indirect role in cramping.
There are no one-size-fits-all guideline for staying hydrated. Staying hydrated or rehydrating involves simply replacing the water and electrolytes lost during exercise for an individual person, but these are very difficult to measure in a sports setting; in addition, these factors vary even within individuals depending on the environment, acclimatization state, duration and intensity of exercise, and amount of rest.
Three main goals to keep in mind regarding hydration and sports performance:
- Delay physical and mental fatigue. Dehydration forces your heart and muscles to work harder, tiring you out faster; staying hydrated allows you to play harder for longer.
- Regulate body temperature (especially in hot climates). Exercise generates heat through both mechanical energy and through anaerobic and aerobic metabolic reactions. To counter the effects of heat production, water regulates body temperature by redistributing heat from active muscles to skin and through sweating. Dehydration challenges these processes by reducing blood flow to the skin and reducing the sweat rate.
- Promote quick recovery following practice and tournaments. Because water plays an important role in a number of physiological functions that also affect recovery – muscle repair, protein synthesis, nutrient absorption, waste removal – hydrating post-workout is just as essential as consuming enough protein and carbohydrates.
The National Athletic Trainers’ Association Recommends The Following Hydration Guidelines For Exercise
- 2-3 hours pre-exercise: 17 to 20 fluid ounces of water or sports drink
- 10-20 minutes pre-exercise: 7 to 10 ounces of water or sports drink
- During exercise: Fluid replacement should approximate sweat and urine loss and maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces of water or sports drink every 10 to 20 minutes. Include carbohydrates in the beverage if the exercise is intense or lasts more then 45-50 minutes. Water alone will suffice and save calories if the exercise is moderate or less than 45-50 minutes.
- Post-exercise: Athletes should weigh themselves nude before and after workouts to learn how much weight is lost from sweat (water and salt).They should then ingest fluid equal to 150% of the weight loss, ideally within two hours and no more than four to six hours after the event. Including sodium in the drink allows fluid volume to be better conserved and increases the drive to drink. Carbohydrate (a component in many sports rehydration/energy drinks) included in the drink will improve the rate of intestinal absorption of the fluid and replenish glycogen (energy) stores in the muscles and liver.
- The volume of fluid in the stomach is critically important for proper hydration. Maintaining 12 to 20 ounces of fluid in the stomach will optimize digestive function and prevent dehydration. Concentrations of 4 to 8% of carbohydrates should be used if they are included in the fluid (for example, Gatorade and other energy drinks). Concentrations higher than 8% slow the rate of fluid absorption, while 6 to 8% concentrations is optimal for hydration and performance. So athletes should monitor the amount of carbohydrates in hydration source carefully.
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