|THE EFFECTS OF ALTITUDE|
Two World Cups have been played at altitude (1970 & 1986 - both in Mexico). It is well established that exercising at high altitude affects playing performance, especially at a physiological level. Thus, the ability to perform the intense intermittent exercise required when playing soccer will be impaired. The altitude in Mexico City where the World Cup matches were played is 2.3 Km. Hypoxia (reduced oxygen availability) at this level will lead to:
Maximum oxygen uptake (VO2 Max) being impaired
by about 15% compared to at sea level due to the reduced arterial oxygen
content (from lower oxygen pressure which makes it more difficult for
oxygen to diffuse across the alveolar membranes in the lungs and into
the blood). For
every 305 metres ascent above sea level, VO2 Max
will decrease by 1 percent.
- Decrease in running performance over a distance of 5km by about 8%.
- Heart rates being much higher for the same bout of exercise at altitude as is the breathing rate. During recovery, heart rate also takes longer to return to normal.
- Blood lactate levels are generally greater for the same given exercise as is the time for the lactate levels to reduce after exercise. The anaerobic system is generally called into play at a relatively lower work rate due to a deficit in oxygen uptake.
- When arriving, mountain sickness can occur meaning headaches, vomiting, physical and mental fatigue, sleep and digestive disorders. Onset of symptoms typically occurs within hours to three days after arrival at altitude. These symptoms tend to be resolved after several days but can sometimes persist for up to two weeks.
Generally, during match play, soccer players cannot work at the same rates than at sea level and will need to pace themselves better by working for shorter periods, at less intensive levels or increase the number of rest periods.
Athletes are recommended to have an acclimatisation period of around 2-3 weeks. After a 1 month acclimatisation period, although improvements compared to the initial few days are seen, VO2 Max is still impaired by about 6% and the 5km running time still slightly reduced although individuals do often demonstrate different physical responses.
These improvements are due in part to an increased haemoglobin concentration/pulmonary ventilation, the development of greater blood capillary volumes, better usage of body fats and sparing of muscle glycogen. Altitude training will also stimulate an increase in the concentration of 2,3-diphosphoglycerate (2,3 DPG) levels in red blood cells (rbc). This chemical allows oxygen, carried by rbc, to be released or dissociated from the cell more easily and to a greater extent. The increase in oxygen dissociation allows more oxygen to reach the working muscles.
There is a loss of water and sodium during the body's attempt to acclimatize to altitude. This places the individual at risk of dehydration, especially when high-intensity exercise is involved. Proper nutrition during this period is thus critical to facilitate optimal blood growth, maintain health, and to aid in maximal recovery. Particular attention to fluid intake at altitude is crucial. Drinking a greater volume of fluids than usual (as well as carbohydrate drinks) is recommended. Players also need adequate rest and sleep..
Iron supplements taken before and during ascent can be useful in preventing anaemia. Researchers have observed that athletes who arrive at altitude with deficient iron stores experience impaired adaptation responses and are at greater risk of anaemia.
Evidence shows that players can also prepare at sea level for altitude by wearing training equipment to simulate hypoxic conditions. The Danish National Team prepared in this way for the 1986 World Cup. Hypobaric chambers can also be used although this type of equipment may be expensive.
It seems from various scientific studies that performance capacity at sea level after prolonged exposure at altitude is not improved. Evidence shows that living at altitude and training at sea level may be more advantageous. Generally, training at altitude improves exercise performance at altitude but not at sea level. Below demonstrates a general example of a four week acclimatization period which can be adjusted by the fitness trainer for his own needs:
Week 1: Players should arrive at altitude in a optimum physical condition. They should be well rested and fed and understand the effects of altitude. If not, the atmospheric conditions may have a greater effect on performance in poorly prepared players. Volume and intensity should be low to medium, allowing them to adjust to the new environment.
Week 2: Volume and intensity should be increased to medium-high amounts.
Week 3: High volume and intensity during this period.
Week 4: Volume and intensity is lowered again to allow for recovery although the volume is increased by 10% from the first week. Special detail to tactical practice may be useful at this time.
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