What is altitude?

Altitude is the vertical distance above sea level measured normally in metres (spelled 'meters' in the USA) or feet. A particular sea level is set as the 'zero reference', and so the 'altitude' there is 0 metres. So all topography that rises above sea level has a positive altitude reading. All points below sea level have either a minus sign in front or may simply be in a different colour. Some parts of Holland for example are below sea level! Colloquially though, we speak of 'height' instead of 'altitude'.

If you get out your cycling map of the French Alps, you will see that the tops of the mountains, and the passes between the peaks, have height readings. For example, the famous Mont Blanc is around 4,600m above sea level. This is very high and is in fact the highest mountain in Europe.

Mont Blanc mountain

How does altitude affect me?

The pressure at any point in the atmosphere obeys the laws of physics concerning any 'fluid'; simply:

PRESSURE = DEPTH X DENSITY

This means that as we climb up through the atmosphere there is less 'Depth' above us, and so the pressure falls. Of particular importance to human beings is that the efficient transfer of oxygen from the air in the lungs through to the red blood cells, depends on something called the "partial pressure" of oxygen.

As a cyclist climbs higher and higher up a mountain, this reducing partial pressure of oxygen will result in there being less oxygen present to the heart and lungs to fuel the muscles. The consequence of this inefficiency is an ever-decreasing performance the higher the cyclist climbs.

Now we can start to understand how to use altitude to improve our performances back at sea level. The next few pages are aimed at cyclists who have probably been to altitude for a brief visit, but now want to return with the aim of improving their fitness for racing.

Adaptation to altitude

To combat the performance decrease from altitude, it is important that the body somehow adapts to the environmental stress. It is well documented in the research literature that in order to perform well at altitude athletes should ''acclimatise'' by remaining at the desired altitude for several weeks, depending on the cyclist's previous exposure level. As a broad guideline, approximately 2 weeks are required to adapt to altitudes up to 2300m. In general, the research says that the higher the altitude from this height upwards, the longer the adaptation period required.

In my experience, I stayed at 2000m for around four weeks. I feel that most research literature over-estimates how high you need to go to get good adaptations from altitude exposure. Others and myself have felt the effects of altitude at even lower altitudes than this.

The most fundamental aspect of altitude 'oxygen restriction' training is the body's natural process of synthesising red blood cells (erythrocytes) in blood fluid (plasma) to make up for the oxygen deficit at altitude. The erythrocyte synthesis comes from the increased release of the hormone erythropoietin (EPO) from the kidneys. An increase in erythrocytes means more oxygen is available to convert to energy and performance.

Within this process, there is an increase in hematocrit (the ratio of red blood cells to total blood fluid) at altitude. This means that a greater percentage of special 'transporting' cells can carry oxygen in the blood. There are also a few other positive adaptations:

1. An increase in capillary density, which means more pathways for the blood to reach the muscle cells. With more blood to the muscle cells, there is more oxygen to convert to energy. So with improved oxygenation of the muscles, there is consequently an increase in athletic performance.

2. An increase in the density of mitochondria. These are the ''power houses'' of the cells where oxygen is converted to energy. So a greater volume of mitochondria means oxygen can be converted to energy more efficiently in the muscle cells.

It can therefore be expected that altitude acclimatisation improves the capacity for aerobic exercise at altitude. And, on a simple basis it might be anticipated that on returning to sea level there would be quite a large increase in athletic performance. But to our simple model we must add the following complications that could offset the positive physiological effects:

1. A decrease in maximum heart rate and cardiac output. The resulting decreased oxygen availability 'slows down' the athlete, preventing him from training his muscles at his normal maximum intensity levels. It is important to realise here, that even though the cyclist may adapt well to the workload, he will ALWAYS be working at a lower % of VO2max at any given intensity level compared to his sea-level intensities - even after 3 weeks of acclimatisation at altitude. The athlete consequently 'de-trains'.

2. A decrease in both body mass and composition. Experts say that long-term exposure to high altitude produces a significant loss in lean body mass and body fat. The magnitude of weight loss is directly related to the terrestrial elevation. This is due to fat being the main fuel for exercise at altitude and the carbohydrate metabolism is seemingly dramatically changed. A loss of lean muscle mass and body fat may mean a loss of athletic strength and power in the muscles.

3. Loss of heat acclimatisation from training in cooler temperatures at altitude. Cyclists normally train for major events that occur in the summer months. Whilst the ambient early afternoon temperature at a typical near-sea level location on Continental Europe may be around 33 deg Celsius, going to an intermediate altitude of say 2000m in August in the Alps the temperature is only just above freezing most nights and only around 15 deg Celsius during the day.

Continued article on next page...

|home| next page>