Effects of Altitude on Fueling and Hydration
By Neal Henderson MS, CSCS

Traveling to higher altitude for a training camp is a method used by many elite athletes to help improve performance in sea level competition. Ideally, an altitude training camp should last for 3 to 4 weeks to receive an optimal amount of exposure to high altitude. Most studies indicate that performance can be increased by 1-2% when using altitude training. For that average Joe, that doesn’t sound like much but for a high performance athlete, the margin between 1st and 4th place can be less than 1%. Typically, staying at a moderate elevation of 5,000-8000 feet allows for maintenance of relatively high training volume and moderately high training intensity. At very high elevations, training stimulus will be reduced significantly while using a lower elevation may not cause any positive adaptations in red cell mass or hemoglobin concentration. Another reason that you might be traveling to higher altitude is for a competition that is held at high altitude, such as the Leadville 100 Mountain Bike Race or Boulder Peak Triathlon. Whether for a training camp or a competition, there are several changes to your typical nutrition habits that will improve your body's ability to adapt to the stress to moderate to high altitude. The primary concerns are changes in resting metabolic rate, increased use of carbohydrate, changes in fluid balance requirements, and iron status.

Resting Metabolic Rate and Carbohydrate Use

First, there are initial responses to altitude, which cause an increase in stress hormones such as epinephrine and nor-epinephrine. The hormones that are associated with the "fight or flight" syndrome that causes your body to use more carbohydrate than it would normally use. As a result, it is important to slightly increase your carbohydrate intake at higher altitude as compared to normal. This is both true at rest, and during exercise. At any intensity of effort, you will be using a higher percentage of carbohydrate to fuel your exercise at altitude. Being conscientious about replenishing your glycogen stores following long or intensity training sessions is critical at higher altitudes, as well as fueling yourself during long distance races at altitude. (Also see First Endurance Carbohydrate Newsletter for more tips on Carbohydrate needs with exercise.) In the first week or two, there is also a slight increase in your resting metabolic rate. Many athletes that I see going to a training camp at altitude also increase their training volume, so accounting for the increased total caloric needs, and again - especially carbohydrate, is critical.

Fluid Balance

A second major concern related to moderate altitude is an increase in fluid needs. Most moderate and high altitude environments are relatively dry - with relative humidity of 15-30% the norm. This means that your sweat will evaporate into the air more readily than it would in a location with higher humidity. It also means that your body actually needs to hydrate the air that you are breathing in and out each minute to get it to body temperature, pressure, and water vapor saturation (or BTPS). At higher breathing rates (over 100 liters of air per minute), it will take nearly half a liter of fluid just to hydrate the air that you are breathing in during exercise lasting an hour! That fluid amount also doesn't take into account your actual sweat losses of fluid. Most endurance athletes lose between .5 and 1.5 liters of fluid per hour through sweat - though some folks reach extremes of over 3 liters of sweat per hour. In a dry high altitude environment, sweat evaporates rapidly and therefore it is more difficult to track your actual fluid loss. One simple trick is to measure body weight pre- and post-training to get an idea of their actual fluid loss. Many folks are surprised that they are actually sweating over 1 liter of fluid per hour. Using pre and post-weight checks to identify their fluid loss needs is an excellent way to stay on top of your own personal fluid needs. (See also the First Endurance Electrolyte Newsletter for more tips on hydration needs.)

Iron Status

Finally, for those who live at high altitude or are planning a several week long training camp at altitude, you should ensure that your iron levels prior to going to altitude are good and that you are taking in adequate iron while at altitude. You should discuss the appropriate tests with your physician, but typically a serum iron test, iron binding capacity, ferritin, and complete blood count (CBC) tests will ensure a proper look at the entire iron spectrum of currently available iron and your iron stores. By paying attention to these special concerns for altitude training or competition, you can ensure your best training situation or race performance.

Reference:

"Altitude Training and Athletic Performance" by Randall Wilbur. Human Kinetics Publisher (2004)