Proper hydration prior to, during and after endurance sports competitions is critical for optimal performance as well as recovery from extended endurance exercise. Research has demonstrated that a reduction in body weight of only a few pounds (1-2% of your body weight) has a detrimental effect on endurance athletic performance. For example, if you are a 150 pound athlete and lose 3 pounds you have lost 2% of your weight due to fluid loss. It is equally important not to over hydrate. The purpose of this article is to assist endurance athletes to determine the optimal hydration strategy for races and training.
Your body has three mechanisms for cooling:
Conduction: The body loses a small amount of heat when the skin contacts a surface with a lower temperature (i.e., when resting on a cold ground).
Radiation: The body loses heat due to infrared rays, similar to the sun heating the earth (heat transfer without touching). The skins temperature must be higher than the environment for this method to work.
Convection and/or evaporation: The body loses heat when in contact with water or air molecules. When the environmental temperature rises, the primary mechanism for cooling the body is through sweating and evaporation.
All three cooling mechanisms depend on a temperature gradient between the skin and the environment. Your body has a reduced capacity to cool itself as the air temperature and humidity rise because the gradient between the skin and the environment declines. Proper hydration is critical to maintain the blood flow to the skin and to maintain sweat flow. Failure to properly hydrate will result in reduced performance as the body must work harder to cool the core. Athletes can lose up to 2 liters of water per hour exercising in hot climates or when over-dressed for the environment, i.e. running or hiking up a mountain with too many layers thus trapping heat and encouraging water loss.
Dehydration degrades endurance sports performance because the body has reduced circulatory capacity in both maximum cardiac output and peripheral circulation. The body will re-direct blood flow from the working muscles to the peripheral circulation or skin to aide in cooling the body. The reduction in blood flow to the working muscles reduces oxygen and, thus, performance.
Tips for staying hydrated for optimal performance:
- Adopt a drinking system for hydration that is easy to use and encourages drinking. Hydration packs provide a convenient method for "hands free" drinking and enable a schedule for hydration instead relying on thirst as the sole indicator of when to drink. Research has demonstrated that thirst alone is not a reliable method of determining when to drink. Hydration systems come in packs, belts, and other easy to use delivery mechanisms experiment in practice and determine what works best for you.
- Determine a hydration schedule for your race or training event based upon documented weight loss. Weight yourself prior to training events (long trail runs, cycling, etc.) and record your weight. Re-weigh yourself after training and calculate the delta. Example: if you weigh 150 prior to training and upon returning from a 1 hour workout you weigh 148, you have lost 2 pounds and require 32 ounces of liquid to re-gain your weight lost. Your schedule for a similar event would be 8 ounces every 15 minutes to maintain your weight.
- Pre-hydrate. Similar to ensuring you have high glucose levels before an ultra or 24 hour adventure race or mountain bike race, pre-hydration ensures you are not beginning the competition in a deficit. It is good practice to consume fluids prior to the event to prolong your proper hydration level, but do not over hydrate. Use your weight as an indicator and adjust accordingly.
- Monitor your hydration. Examine the color of your urine prior and after training and competitions. if it's light yellow, like lemonade, that's usually a sign of good hydration. Crystal-clear urine often indicates over-hydration and the need to cut back. Dark urine (like the color of apple juice) signals dehydration and the need to drink more.
- Over hydration [hyponatremia]. Finally, it is equally important to not over hydrate by drinking too much water and dangerously diluting your electrolyte levels. Consuming large amounts of water while exercising for prolonged periods of time can have an equally detrimental effect as a failure to hydrate properly. "Over hydrating can lead to a dangerous condition called hyponatremia, or low blood sodium levels," states Maharam, a sports medicine specialist practicing in New York City (medical director of the New York City Marathon and the Country Music Marathon).
Winter Exercise and Hydration: Winter and the cold temperatures athletes experience during training and competition provide additional complications to maintaining proper hydration. Athletes training and racing in cold temperatures rarely feel like drinking any water or performance beverages. More over, colder temperatures can render your hydration pack's water reservoir useless with a frozen line and bite value--if not the entire reservoir. Here are a couple of tips to overcome the challenges and remain hydrated:
- Use an insulated bladder or place the bladder close to your body
- Blow the water back through the drinking tube into the bladder to reduce the water that can freeze during cold races
- Fill the bladder with warm water prior to the race
- Most performance beverages lower the freezing temperature of water, but you are faced with the post training cleaning task
- Use pipe insulation from a hardware store to cover the drinking tube
- Keep the drinking tube inside your insulating layer and close to your body and pull it out only to drink
- You can purchase "winterized" hydration packs, but many people already have a fair investment in their current packs and the above tips help you use them effectively in the winter
Beneficial Effects of Fluid Replacement:
- Improves regulation of body temperature: sweat rate and skin blood flow are increased and core body temperature is decreased.
- Improves cardiovascular function; plasma and stroke volumes are higher and heart rate is lower.
- Performance in hot environments may be increased following recommended hydration techniques.
The bottom line:
- Weigh yourself prior to and after workouts to determine actual fluid loss. Calculate the amount of fluid loss and determine the amount of fluid you must consume every 15 minutes.
- Schedule your fluid intake similar to your fueling schedule to maintain blood glucose levels (see above to determine how much).
- Experiment with and choose a hydration system that works for you.
- Pre-hydrate prior to your event.
- Combine proper hydration with carbohydrate supplementation to maintain blood glucose levels.
- Cool to tepid liquids are easier to absorb by the body than cold fluids.
- Acclimate to heat prior to competition.
- Wear light colored clothing that wicks moist away from the body which aides in improving cooling.
Hydration Packs and Hydration Gear:Hydration packs are not new, but CamelBak, Nathan and others are constantly refining their designs. The drinking tube coming from the main bladder enables the wearer to drink from the internal water bladder without removing the pack. This design concept facilitates easier and hopefully more frequent drinking leading to better overall hydration and athletic performance.
Exercise Physiology: Theory and Application to Fitness and Performance, by Scott K. Powers and Edward T. Howley.