Hydration for Endurance Athletes by M. Tribble

Participation in endurance athletics over the last 5-10 years has risen significantly. The term endurance athletics is meant to describe [Untitled] an athletic endeavor that lasts 2 hours or longer. This includes activities such as adventure races, triathlons, ultra-marathons, cycling, hiking, etc. These activities require that one not only be “in-shape”, but that one properly fuel the body. The purpose of this article is to discuss properly fueling the body in terms of hydration during prolonged physical exertion. The article will discuss briefly the basic rules for proper hydration as well as the effects of improper hydration, i.e. under-hydration and over-hydration.

During intense activity the body produces substantial heat in the chemical breakdown of fuel (glycogen, fats, etc). In order to maintain the body’s core temperature, the body produces sweat. Sweat on the skin carries away excess heat during the evaporation process. With a finite amount of water in the body to help cool it, it is easy to see that water lost through sweat needs to be replaced if one is to maintain a level of activity. Else, the body will suffer the detrimental effects of not being able to operate in an ideal temperature range. On average, the body loses approximately one liter of water per hour during exercise. This number will vary depending on one’s level of fitness, temperature and humidity of ambient conditions, and intensity of exercise. Unfortunately, the body cannot absorb at the same rate it can expel. Thus the athlete’s dilemma, “how much do I need to drink during exercise?” Studies have shown that the body can absorb as little as 50% of the amount lost. So, over an hour of exercise if you lost one liter (1000ml) of water through sweat, your body could very well only reabsorb 500ml of ingested fluid.. Again, this number varies depending on one’s level of fitness and physiology. Sweat tests are popular for elite athletes to help determine their sweat rate and re-absorption rates. For most of us who aren’t elite athletes, the rule of thumb is to drink 500ml-700ml per hour to help maintain the body’s water reserves. It is best to space this quantity of fluid replacement equally over an hour, say 150ml every 15 minutes. In order to determine the optimal hydration rate for your body, experiment during your next training session by starting with these values and tweak as necessary.


[Untitled]While a fluid replacement strategy can seem like a simple task on paper, many athletes get distracted during exercise and particularly during races. If you fail to replenish the body’s fluids the body can quickly over-heat and performance suffers. Studies have shown that at 1%-2% of body weight water loss performance levels will begin to decline. At 4%, performance levels drop off by 20%-30%. And by 7%, collapse is likely. One simple method to determine whether or not you hydrating appropriately is to weigh yourself before your training sessions and after and calculate your loss. 2% loss is considered typical and normal. Any more is considered under-hydration (or dehydration). An equal weight or more is considered over-hydration.

As with many things in life, less can be more. This can be true with hydration when it comes to fluid replacement. Many athletes who participate in long course events suffer from drinking too much fluid per hour in effort to reduce their risk or fear of dehydration. Recall that the body has limited capacity to re-absorb fluids. The potential consequence of drinking too much is a condition call hyponatremia. This condition arises when an athlete drinks excess fluids effectively diluting the body’s [Untitled]sodium and electrolyte balances. Effects of hyponatremia are as serious as de-hydration effects.

Hopefully this article has helped you to start thinking about you hydration strategy for your next workout or event. A properly executed plan will help you to achieve your potential. Poor plans or poorly executed plans will certainly lead to a disappointing day. Also note that this article has just focused on the basics of fluid replacement. An effective nutrition plan also considers mineral and calorie replacement. These two topics are beyond the scope of this article, but will hopefully be addressed in future articles.

Happy Trails!

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