INTRODUCTION & SUMMARY
To exercise at high altitude means working in an environment with reduced atmospheric pressure. The oxygen tension of the inspired air is therefore decreased, that is, there is atmospheric hypoxia. Exercise increases oxygen requirements which must now be met in the face of this decreased oxygen driving pressure. The initial handicap is less complete oxygenation of blood within the lung. In an effort to preserve oxygen delivery, a greater volume of blood is circulated, that is, cardiac output is increased. However, this pattern of compensation is only temporary. Within days, hemoconcentration increases the oxygen-carrying capacity of the blood, and as a consequence, less cardiac output is required to maintain oxygen delivery. In fact, cardiac output decreases to levels lower than existed prior to ascent. This reduction in cardiac output results primarily from a decrease in stroke volume due to less venous return secondary to the smaller blood volume produced by hemoconcentration. The hypoxia of high altitude produces sustained stimulation of the sympathetic nervous system. Initially, this increases heart rate, but, with time, the responsiveness of the heart decreases, so the initial tachycardia may not be sustained. Other consequences of sympathetic stimulation include an increase in resting metabolic rate, a shift away from glycogen toward free fatty acids as primary energy sources, and bone marrow stimulation to increase red cell production. The parasympathetic nervous system may also be stimulated at high altitude, which may explain the reduction in maximum heart rate. Upon arrival at high altitude, aerobic working capacity is reduced. Although this may or may not be attenuated following adaptation, endurance capacity does seem to improve. Several parallels therefore emerge between adaptation to the hypoxia of high altitude and adaptation to the struggle for oxygen created by exercise training at low altitude. Sympathetic stimulation is common to both forms of hypoxic stress, and similar responses, particularly metabolic, result. Not surprisingly, then, exercise training provides an advantage to adaptation to high altitude.
EFFECT ON PERFORMANCE
The body’s adaptation to high altitude helps significantly but doesn’t fully compensate for the lack of oxygen. There is a drop in VO2 max of 2% for every 300 m elevation above 1500 m even after allowing for full acclimatization. I know that this is a difficult concept to believe because so many programs have touted the benefits of high altitude training.To fully appreciate this realize that there aren’t any world record times at high altitudes. Think about this a moment. The air density is much lower, thus wind resistance is much lower. Wind resistance is the cyclists biggest barrier to speed. If all other factors were equal, then there must be faster times at higher altitudes. Because there aren’t, means that something else must have decreased. That something is the engine — the human engine.
Furthermore, while adaptation to high altitude makes you better at high altitude it hasn’t proved useful for making you faster at sea level. There is a lot of mysticism that surrounds the belief of enhanced sea-level performance after altitude training, but the current scientific evidence is lacking. The reason is that some of the adaptive responses at high altitude are actually a hindrance at lower altitude. As more research is done then perhaps a training regimen that shows definitive improvement will emerge. The best advice as of 1994 is that high-altitude training is like “magic shoes” — If it works for you then wear them.
There is some more recent evidence to suggest that a “train-low, sleep high” approach may confer some advantages. In this scenario, training is carried out at low altitude to push anaerobic threshold, and VO2 max –but sleeping is done at high altitude so that the hypoxic stress increases red cell mass. Certainly a creative approach and one which might yield excellent results, because it may give the athlete the “best of both worlds”. In a practical sense it may be difficult to construct, but if you are lucky enough to live in a situation that allows this type of training, it is worthy of consideration.
BENEFITS OF ALTITUDE EXPOSURE
Exposure to high altitude could theoretically improve an athlete’s capacity to exercise. Exposing the body to high altitude causes it to acclimatise to the lower level of oxygen available in the atmosphere. Many of the changes that occur with acclimatisation improve the delivery of oxygen to the muscles -the theory being that more oxygen will lead to better performance.
For any type of exercise lasting longer than a few minutes, the body must use oxygen to generate energy. Without it, muscles simply seize up and can become damaged. This type of exercise is called aerobic exercise, meaning with oxygen.
The body naturally produces a hormone called erythropoetin (EPO) which stimulates the production of red blood cells which carry oxygen to the muscles. Up to a point, the more blood cells you have, the more oxygen you can deliver to your muscles. There are also a number of other changes that happen during acclimatisation which may help athletic performance, including an increase in the number of small blood vessels, an increase in buffering capacity (ability to manage the build-up of waste acid) and changes in the microscopic structure and function of the muscles themselves.
LET YOUR BODY ADJUST
Even National Football League players struggle to play in football games in places like Denver. This is because their bodies struggle to process the oxygen that is coming in during the game. It’s nearly impossible for someone to enter into a high altitude and start working out immediately. Because of this, you shouldn’t even try it. To prevent oxygen deprivation from happening in your body, don’t exercise the first day that you’re in a new higher altitude. Rather, let you body naturally adjust to the air at that altitude. Give your body some time to process it and see what it feels like to exist in a high altitude before you push it too much.
WHAT IS MOUNTAIN SICKNESS ?
Mountain sickness is the name given to a cluster of symptoms that occurs in some individuals after rapid ascent to high altitude. Mild forms of the illness may affect up to 50% of people traveling to altitudes above 14,000 ft. Severe forms of the illness may be life threatening because of pulmonary or cerebral edema.
Symptoms of headache, malaise, and decreased appetite are fairly common amongst individuals traveling to altitudes greater than 8,000 ft — although this can occur at lower altitudes. The mild forms of mountain sickness can usually be treated with rest, hydration, analgesics (eg. ibuprofen), and alcohol avoidance. If you are already experiencing these symptoms do not go to higher altitudes. There is a medication that can help prevent this illness. Individuals who have already experienced an episode of mountain sickness are at risk for future trips and should seek medical advice.
Severe forms are characterized by severe shortness of breath, cough, severe headache, confusion, or hallucinations. This may progress to coma and death. This is a medical emergency. Immediate descent to lower altitude, administration of oxygen, and medical attention are required.
Although the heart has to work harder during exercise even at sea level, at higher altitudes the demand on the heart is even greater. According to Curtin University, during rest and submaximum exercise, cardiac output is increased at higher altitudes. Cardiac output is the amount of blood which is pumped out of the heart each minute. Cardiac output increases to transport oxygen throughout the body.
DEHYDRATION OCCURS FASTER
Air at high altitude is often cool and dry, which can contribute to dehydration, especially while exercising. Due to the lower air pressure, moisture evaporates from the skin faster than it does at sea level. Increased respiratory rate also causes your body to lose moisture faster.
INCREASE IN RED BLOOD CELL PRODUCTION
Since less oxygen is available at higher altitudes, the body has to compensate. One way it compensates is by producing more red blood cells, which carry oxygen to the various tissues and organs of the body. When the body senses it is getting less oxygen, production of erythropoietin increases, which causes more red blood cells to be produced. A possible downside to increased red blood cell production is thicker blood, which can mean that blood flow becomes a bit slower.
INITIAL BODY RESPONSE
During the first few days at a higher altitude with thinner air that contains less atmospheric oxygen, one’s body will respond as follows:
- Breathing rate (ventilation) increases
- Blood pH decreases, becoming more acidic
- Muscle pH also decreases and becomes more acidic
- Use of carbohydrates as an energy source increases
- Use of fat as an energy source decreases
These changes lead to a slight increase in basal metabolic rate (BMR), the amount of energy needed to keep your body working correctly at rest for 24 hours. Research studying this phenomena have found between a 6 – 28 percent increase in overall BMR in women and men at high altitudes. With time, the increase in BMR lowers, but does not return completely to baseline, so metabolism is slightly elevated at higher altitudes.
LIVE HIGH – TRAIN HIGH
Maximum exposure to altitude. Evidence of a positive effect at sea level is controversial, and there is less support for this method amongst experts.
LIVE LOW – TRAIN HIGH
The idea behind this regime is that the athlete is exercising in a low oxygen environment, whilst resting in a normal oxygen environment. There have been some interesting findings suggesting that this technique might work, but there are no good studies showing that the technique makes any difference to the ultimate competitive performance of the athlete at sea-level. Additionally, training intensity is reduced so some athletes may find that they actually lose fitness using this regime.
LIVE HIGH – TRAIN LOW
The theory behind this regime is that the body will acclimatize to altitude by living there, whilst training intensity can be maintained by training at (or near) sea level. Hence, the beneficial effects of altitude exposure are harnessed whilst some of the negative ones are avoided. However, residence at altitude must be for more than 12 hours per day and for at least 3 weeks. With this technique, improvements in sea-level performance have been shown in events lasting between 8 and 20 minutes. And interestingly, athletes of all abilities are thought to benefit.