By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Physical exercise at high elevations following rapid travel from sea level to the mountains has become common with the luxuries of modern travel. Some examples of high-altitude exercise include running the Colorado Pike’s Peak marathon (elevation 14,110 feet), rock climbing or backcountry skiing on Wyoming’s Grand Tetons (elevation 13,770 feet), and alpine skiing or snowshoe hiking at Utah’s Snowbird ski resort (elevation 11,000 feet).
Does a rapid ascension to these types of elevations have a restrictive effect on athletic performance? Absolutely!
Studying the Effects of High-Altitude Exercise
The increased stress of altitude on exercise began to be scientifically investigated following the 1968 Olympic Games in Mexico City (elevation 7,546 feet). For the first time in history, no world records were established in Olympic events lasting longer than 2.5 minutes, while African runners who trained regularly at high altitudes dominated the endurance events.
Consequently, most Olympic, professional and collegiate teams now take altitude adjustments into consideration during their training prior to competitions. Prior to the 1988 NFL American conference championship football game in Denver’s stadium (elevation 5,280 feet), for instance, the Cleveland Browns practiced for one week at the University of New Mexico (elevation 5,314 feet).
Altitude training for several days was not quite enough, however. The Browns ran out of gas in the final minutes of the game, and the Broncos won 38 to 33.
High-Altitude Exercise, Oxygen and Reduced Barometric Pressure
The human body requires a continuous supply of oxygen to the body’s tissues to maintain the process of metabolism (the use of substrate for energy to maintain life-sustaining biological processes). The source of this oxygen is ambient air where the percentage of oxygen remains fixed at 20.93%, regardless of altitude.
Ascent to a higher altitude, however, causes a reduction in barometric pressure and induces a partial decrease in the pressure of oxygen of inhaled air. For example, if you ascended from sea level to the top of the tram at Snowbird’s 11,000-foot Hidden Peak near Salt Lake City in Utah, the average barometric pressure decreases and the pressure of the air you inhale partly decreases as well.
This oxygen enters the body through the lungs where it binds with hemoglobin in the bloodstream for transport to the tissues. A reduced pressure of oxygen impairs the oxygenation of blood that flows through the lungs. A bloodstream with a reduced oxygen saturation will consequently deliver a diminished oxygen supply to your muscles.
At the muscle tissue level, oxygen is released from the blood and enters the cells of the working muscles to sustain aerobic metabolism. The preferred fuel for exercise at altitude appears to be fat, due to a dramatic decrease in carbohydrate metabolism.
This complex shift in substrate utilization is not well understood, but it may be due to the fact that a reduced oxygen supply already causes a higher lactic acid level in the muscles and blood. As a result, carbohydrate consumption should be curtailed by athletes working out in high-altitude locations.
Lactate is only produced during carbohydrate (not fat) breakdown. Ultimately, high-altitude exercise results in reduced maximal aerobic power, diminished endurance and faster muscular fatigue.
How the Body Compensates for High-Altitude Environments
Fortunately, the body adapts to minimize the effects of reduced oxygen delivery to the tissues. Many of these adaptations occur quite early after high-altitude exposure and include shifts in pulmonary ventilation, the cardiovascular system, and the cellular composition of the blood.
The body’s ventilation rate (the total amount of air moving in and out of the lungs) is stimulated at high elevations by an increase in breath frequency. This increase in breathing raises oxygen availability to the alveoli in the lungs, which extract oxygen from inhaled air and transfer it to the bloodstream.
Unfortunately, hyperventilation also causes excess carbon dioxide to be expelled from the body, which disrupts the acid-base balance of the tissues and contribute to altitude sickness. Considerable body water is also lost, with high ventilation rates leading to dehydration.
Airplane flights to higher altitudes also strongly contribute to dehydration because the relative humidity of airplane cabins and mountainous regions are generally low. A low-humidity environment continually draws precious moisture from the body, which must be replaced by fluid consumption.
High altitudes also stimulate an increase in heart rate and cardiac output (the total amount of blood pumped by the heart) to increase blood circulation to the muscles. During this process, the circulatory system unloads oxygen, picks up carbon dioxide and moves the blood back to the alveoli for more oxygen. This process compensates for the blood’s reduced oxygen saturation but also stresses the heart, which may affect persons predisposed to heart disease.
The composition of the blood changes after about two weeks of altitude exposure by producing more red blood cells and hemoglobin (the iron-protein compound that transports oxygen). Bone marrow stimulation to increase hematocrit (the percentage of red cells in the blood) in addition to an increase in plasma volume serves to increase total blood volume.
The benefits of blood adaptation in the weeks following high-altitude exposure includes reducing the cardiac output required for oxygen delivery during rest and submaximal exercise and increasing maximal oxygen transport during strenuous exertion. The body also gains a larger fluid reserve for sweating.
Effects of High-Altitude Exercise on Athletic Performance
Several studies investigating the effect of high- and low-altitude training on exercise performance have been conducted. Competitions at laboratories such as the Olympic Training Center at Colorado Springs (elevation 6,500 feet) have concluded that exercise at altitude can be severely restricted following conditioning at sea level.
Physical activities begin to be affected at about 4,500 feet (depending on the fitness level of an athlete) due to reductions in ventilatory and cardiac efficiency. Endurance (aerobic) events are affected by altitude much more than sprinting or weight training (anaerobic) events.
Training acclimatization time for athletes needs to be longer as the altitude becomes higher. Training for 14 days at 6,500 feet and 28 days at 8,000 feet are currently the best recommendations.
Altitude chamber studies have indicated that full body acclimatization at 7,500 feet is possible after a continuous stay of four weeks, while complete adaptation to the extreme altitude of 13,000 feet is possible after a continuous stay for 14 months. Athletes can generally maintain the same exercise intensity, but they should increase their rest periods by decreasing exercise duration and increasing the frequency of their workouts.
Training at altitude, however, is only beneficial prior to competitions conducted at high altitudes. Competitions at a lower altitude have shown no advantage to altitude training.
How to Help Your Body Adjust to High-Altitude Exercise
If you’re planning a skiing trip or other exercise in a high-altitude location, here are some guidelines:
1. Take it easy and only do light physical activity on your first day in a high altitude. The major variables that effect your body’s reaction to high-altitude exercise include your rate of ascent, the altitude you attain, the length of acclimatization, and the intensity, duration, and mode of your exercise. Although individual responses to high altitudes vary considerably, use common sense and curtail strenuous exercise on your first day, especially if you are doing an activity (such as skiing or rock climbing) that you do not normally do at sea level.
Be particularly attentive to the signs of fatigue (rapid heart rate, shortness of breath, light-headedness, and muscle soreness) and reduce your activity appropriately. On the other hand, do not loaf around and sleep upon arrival because light physical activity speeds the adaptation process.
2. Be aware that ascension to a mountainous region often involves other stressors such as cold, wind chill and jet lag. The cumulative effects of several environmental stressors amplify the effects of high-altitude exercises.
3. Compensate for any difficulty in sleeping, which is a common complaint following an ascent to high altitudes. Taking a 10-minute sauna or whirlpool hot bath (standard equipment at most ski resorts) before going to bed will increase the quality and quantity of your sleep.
Many ski lodges will deliver a humidifier to your room upon request; using a humidifier will increase water content of the air in your room and relieve dried-out sinuses. Putting a dab of petroleum jelly on the tip of your nose and inhaling steam over a hot water sink may also bring some temporary sinus relief.
4. Be alert for the symptoms of mountain sickness or pulmonary edema. The symptoms of acute mountain sickness include headache, difficulty sleeping, decreased appetite, nausea, vomiting and dizziness. Acetazolamide (diamox) at a dosage of 250 milligrams three times a day is commonly prescribed to people suffering from mountain sickness or pulmonary edema.
High-altitude pulmonary edema (a buildup of fluid in the lungs) begins with symptoms of extreme lethargy and may lead to coughing up pink sputum, fever, rapid heart rate, and cyanosis. High-altitude illnesses have life-threatening potential because they alter the pH of the body, so consult a physician immediately.
5. Protect yourself from ultraviolet rays. Ultraviolet (UV) radiation increases by about 5% for every 1,000 feet of elevation, which means that you will be exposed to 55% more UV rays at the top of a mountain’s summit as compared to sea level. Using sunscreen and wearing UV-sensitive sunglasses or goggles to protect your skin and eyes during high-altitude exercise is especially important due to the sun’s reflection off the snow.
6. Drink more liquids and avoid alcohol in high-altitude environments. A low-humidity environment at high elevations continually sucks moisture from your body, but you may not notice it due to evaporation before sweat can form. Consuming plenty of fluids and avoiding alcohol is very important in high-altitude environments.
Be sure to monitor your body weight and drink enough water to regain any lost weight (consuming one pint of fluid will replenish one pound of water weight loss). Be sure to consume a healthy diet as well. Vacation diets sometimes involve a shift to more fatty foods, which affect fluid retention and your energy level.
7. If you are moderately sensitive to monosodium glutamate (MSG), stay aware from foods that contain it, since people who are moderately sensitive to monosodium glutamate at sea level become hypersensitive at high altitudes. Simply staying away from the wrong food may prevent medical problems from ruining your vacation.
8. Give your body enough time to properly acclimate to high-altitude exercise. If you ever attempt to climb Mount Everest (elevation 24,029 feet) or Mount McKinley (elevation 20,320 feet), begin your ascent at less than 10,000 feet if you arrive by aircraft or motor vehicle and keep your daily ascent rate to less than 1,000 feet.
Several expeditions of climbers have reached the Everest summit without using supplementary oxygen, due to the acclimatization process that occurred during a months-long ascent. World-renowned climbers Peter Habeler and Reinhold Messner once said of climbing Everest, “Every 15 steps we collapsed into the snow to rest as we approached the summit, then we crawled on again.”
If you’re thinking of taking a shortcut by using a helicopter to reach the Everest summit, forget it. You would pass out immediately after leaving the pressurized cabin without oxygen support and without acclimatization. It’s better to give your body the time it needs to adapt to high-altitude exercise, as well as consuming plenty of water and eating a healthy diet.