Staying Hydrated: What You Need To Know!

Read on to discover five tips to help keep cool in the heat.

Imagine the beautiful desert sun beating down your neck as you begin your training. In a rush, you have forgotten your camelback full of sports drink. As you continue, you start to notice a muscle cramp developing in your calf which soon turns into an annoying muscle twitch.

At last, a water fountain arrives. You take a few sips and continue on. Unfortunately, the unpleasant cramp returns and suddenly, your breathing starts to act up almost as if you are having an asthma attack. Even though that potent sun continues to beat down your neck, you start to get the chills. A bout of dizziness follows, causing you to stumble over a rock.

As you try to get up, your heart starts to race and you lose consciousness. These symptoms are associated with a fluid and electrolyte imbalance, which can be extremely dangerous with respect to health and can have a profound negative impact on endurance performance. Read on to discover five tips to help keep cool in the heat.

Don't Wait Until Your Thirsty To Start Drinking!

Perhaps the biggest mistake endurance athletes make is waiting until they are thirsty to start drinking.

Upon the onset of thirst, an athlete is already 3% dehydrated which reduces maximal performance capability by 15%. This adds up to be a large chunk of time when looking at such endurance events as marathons, long-course triathlons, and adventure races.

In fact, one study discovered a 6-7% reduction in 5k and 10k running speed in athletes who were 2% dehydrated. This would be equivalent to adding 2 minutes 48 seconds to a 40 minute 10k. Dehydration becomes life-threatening when 10-20% of body weight is lost.

To prevent dehydration, it is best to sip on fluids throughout the day until urine flows clear to pale yellow. Daily fluid needs vary depending on the body composition and total weight of the athlete. The following equation can be used to estimate daily fluid needs in ounces:

Body weight (in pounds) / 2 = Daily Fluid Needs in Ounces

Note that these fluids should be non-carbonated and non-caffeinated, as caffeine and carbonation tend to increase gastric emptying of fluids.

Tap Off Your Fluid Tank Before Training.

The American College of Sports Medicine (ACSM) recommends that athletes fortify themselves with at least 16 ounces of non-carbonated and non-caffeinated fluids about an hour prior to exercise.

For those who have trouble holding fluids, try sipping on a sports drink containing sodium that last hour rather than drinking all 16 ounces at once. The sodium in the sports drink will help increase absorption of the water into the cells.

Stay On Top Of Your Fluids During Your Workout.

Maintaining fluid balance during exercise requires replacement of fluids that are lost via sweat and urine by drinking such hydrating beverages as water and sports drinks.

The American College of Sports Medicine recommends drinking 5-12 ounces of fluid every 15-20 minutes of exercise. If the exercise bout is under an hour, water is an appropriate fluid replacement beverage. Beyond an hour, a sports drink containing a 7% concentration of carbohydrates will help enhance performance.

In order to get a more exact estimate of your fluid needs, determination of sweat rate is necessary. To determine sweat rate, weigh in both immediately pre- and post-exercise on several different occasions. Every pound of body weight lost during exercise is equivalent to approximately 16 ounces of fluid.

For example, if you consistently lose 1 pound of body weight on a 30-minute run where you are not drinking anything, your hourly fluid needs are 32 ounces per hour. Use the card below to jot down your hourly fluid needs in different conditions (hot & humid versus cold & dry; intense intervals versus long run).

Don't Neglect Electrolytes In Exercise Lasting >1 Hour.

In addition to fluid replacement, replacement of electrolytes becomes instrumental in endurance bouts lasting longer than 1 hour, especially when completed in hot and humid conditions.

The principle electrolytes include sodium (generally bound to chloride), potassium, magnesium, and calcium. These electrolytes are involved in metabolic activities and are essential to the normal function of all cells, including muscle function.

An electrolyte imbalance has reported symptoms similar to dehydration: nausea, vomiting, muscle weakness, muscle cramping, muscle twitching, overall fatigue, labored breathing, "pins and needles", and confusion. The table below displays the function of the principle electrolytes and goal dosing patterns during exercise and performance daily intake (PDI) recommendations for athletes.

A potentially life-threatening condition can occur if an athlete fails to use an electrolyte-replacement drink during exercise bouts lasting longer than an hour. There have been several incidences of "water intoxication" in athletes, which causes blood sodium levels to drop dangerously low, causing an electrolyte imbalance and triggering seizures, coma, and even death.

Initial symptoms are similar to dehydration and include confusion, disorientation, vomiting, and muscle weakness. So remember: For the long haul, use a sports drink containing the electrolytes displayed in table 1.

Electrolyte Primary Roles Dose per 8-12 ounces of fluid Performance Daily Intake (PDI)
Sodium Muscle contraction Nerve transmission 150-250 mg 1,500-4,500 mg
Chloride Peak muscle function 45-75 mg
Potassium Muscle contraction Nerve transmission Glycogen formation 50-80 mg 2,500-4,000 mg
Magnesium Muscle relaxation ATP (energy) production 20-30 mg 400-800 mg
Calcium Bone health Nerve transmission Muscle contraction 10-15 mg 1,200-1,600 mg

Table 1. Electrolytes to replace during exercise.

Rehydrate Upon Completion Of Training.

For every pound of body weight lost during exercise, consume 16-24 ounces of fluid as means to rehydrate and enhance recovery from exercise. Sports drinks are desirable for post-workout rehydration due to the sodium (which increases fluid absorption) and carbohydrate (replenishes lost glycogen) content.

On a final note, it is important to be careful out there especially if you are training alone. Increased heat and humidity makes optimal fluid and electrolyte replacement challenging.

If you start to experience any symptoms associated with dehydration (nausea, vomiting, cramps, fatigue, and goose bumps), it is to the benefit of your health and wellness to stop and aggressively replace your fluids and electrolytes with a sports drink.

About The Author

Kim Brown, MS, RD is a registered sports dietitian and competitive endurance athlete who provides nutritional counseling and meal planning to athletes all around the world. For more info on her services, go to You can contact her at