6/11/15

The dehydrated athlete


It surprises me how many athletes assume they are just fine just "getting by" in workouts by not fueling or hydrating during the workout.
Could you be underfueling and more importantly, underhydrating during your workout?

Maintaining adequate hydration during workouts and especially in races is one of the most important nutrition strategies for optimizing performance and for keeping the body in good health. 

Every athlete knows that even losing a small percentage of body weight can affect health and can impair performance so why even think twice about going for a swim, bike or run without adequate fluids?

I find myself spending a lot of my time educating athletes on what they are not doing well (or consistently) which could be sabotaging workouts and one area is speaking to triathletes and runners to try to get them to consume adequate fluids during workouts.
With so many athletes coming to me looking to boost performance, improve health or to reach body composition goals, you wouldn't believe how many of these athletes (runners or triathletes) struggle to remember (or make an effort) to put on a fuel belt when they run or bring a bottle to a swim workout or stay on top of fluids during a long bike. They will easily put in the work training but taking a few minutes to fill a bottle and drink from it during a workout can be quite difficult (or it's an afterthought).

With so many hydration belts, packs and handhelds on the market, it really saddens me that athletes don't think more about the physical and health consequences of dehydration. 

Let's talk first about sweating and thirst. 
When we sweat, we experience a decrease in plasma volume and an increase in plasma osmolality. 
As vascular pressure receptors and hypothalamic osmoreceptors respond to the increase in sodium and chloride concentrations in blood plasma, ADH (antidiuretic hormone) is released from the pituitary gland, renin releases from the kidneys and aldosterone and angiotensin II increase water and sodium retention by kidneys and ultimately, we feel thirsty. Yes, all that happens before we "feel" thirsty. 

There has been a lot of talk lately about athletes not needing to drink during workouts or that athletes should simply rely on natural thirst mechanism to let us know when to drink when we workout or race. Because of this advice, athletes will many times train and race underhydrated and express afterward "but I didn't feel thirsty" or "but I didn't feel like I needed it."

Relying on thirst may work for the average fitness enthusiast but when it comes to athletes, it can be quite difficult to offset the large volume of sweat that we lose AND meet carbohydrate and electrolyte needs without risking GI issues by "just waiting" until we are thirsty.
More so, many athletes go into workouts in a dehydrated state which doesn't make it any easier to train consistently in a training cycle.

Before I give some basic hydration tips for athletes to help ensure that you are making an effort to meet hydration needs, consider the following: 

-To assure rapid gastric emptying of fluids/electrolytes/carbohydrates, you need a comfortable volume of fluid in the stomach (pre and during workouts/races)

-It's very easy to get distracted, feel you don't need it or to consider carrying fluids as a nuisance so thirst signals may be ignored or overlooked. 

-If fluids are not available, it won't be convenient to act on your thirst. Whereas on race day, with ample aid stations, you may find yourself acting too often, in too large of amounts. 

-Based on plasma osmolality, there is a specific amount of fluid that needs to be lost from the body before thirst is stimulated so it is true that by the time thirst is perceived, the body may already be dehydrated.

-Carbohydrate stimulates rapid water absorption in the small intestines with sodium, chloride and potassium replacing electrolytes.

-Sodium plays a critical role in maintaining the osmotic drive to drink and provides an osmotic stimulus to retain fluid in extraceullar space (plasma and interstitial fluid compartments).

-Drinking plain water dilutes sodium concentration in blood and removes the osmotic drive to drink.
 Drinking plain water as a means to stay hydrated during long duration or intense activities causes premature satiation of thirst which results in a decrease in fluid intake before adequate fluid has been ingested. OR the opposite happens. Excessive water intake (or consuming low sodium/low carb sport drinks) can quickly dilute plasma sodium concentrations. This can lead to hyponatremia or more serious, water entering the brain as the osmotic balance across the blood-brain barrier becomes disrupted. 

-Drinking plain water during long distance or intense exercise will cause plasma osmolality to decrease which suppresses thirst and increase urine output. When sodium is added to drinks, the osmotic drive to drink is maintained and urine production is decreased. 

-Plain water can quench thirst but is not adequate to serve as a rehydration beverage during or post workout. 

-A properly formulated sport drink (one that contains carbohydrates, sodium, chloride and potassium) not only improves palatability but also helps maintain an osmotic drive for drinking, reduces the amount of sodium that the blood has to supply to the intestine prior to fluid absorption, helps maintain plasma volume during exercise and serves as a primary osmotic impetus for restoring extracellular fluid volume after exercise. Carbohydrates will provide sweetness in a drink to improve palatability, will help fuel muscles and will stimulate fluid absorption from intestines. 

In my next post I will give some tips to help with hydration before, during and post workout. 

Information in this blog collected from Sport Nutrition: A practice manual for professionals. By Christine A Rosenbloom, PhD, RD, CSSD and Ellen J Coleman MA, MPH, RD, CSSD.