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Hypoxia is the restriction of oxygen supply to the whole body or part of the body. Hypoxic training is used to improve endurance exercise through improving oxygen delivery and utilization. Some of the positive adaptations from hypoxic training that can influence endurance performance include at a cellular level increased tissue oxygen extraction, increased myoglobin and oxidative capacity, and in the blood, increases in erythropoietin, haematocrit and haemoglobin concentrations.

In athletics training, hypoxia and can be elicited by exercising at altitude or simulated altitude, or by restricting breathing such as breath holding or controlled frequency breathing. These techniques are used in training for sports requiring high levels of aerobic endurance, such as running or swimming, or sports where access to air is restricted, such as in underwater sports.

Training At Altitude

There are benefits from training at altitude (or simulated altitude), where the air still contains the same amount of oxygen, but due to the lower atmospheric pressure, the air is "thinner" and less oxygen is available in each breath.

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After a period of training at altitude, when returning to compete at lower altitude, the higher concentration of red blood cells and improved tissue oxidative capacity can give the athletes a competitive advantage. Altitude training is not always practical or cost-effective, as training facilities are not always available at high altitudes, and the lower levels of oxygen mean the training intensity may be decreased.

Breath Holding Training (BHT)

There is another way of inducing hypoxia, by breath hold training (BHT). This method is used by some athletes to increase their tolerance for oxygen deprivation and improve oxygen delivery. This method, which often involves breath holding underwater, is mostly used for swimmers and other athletes involved with water-based activities. The benefits of this technique are not large, and considering the health risks, it is not commonly used.

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Related Pages

• All about Aerobic Endurance Fitness
• Breathing During Exercise — nose or mouth breathing?
• Altitude Nutrition — Nutritional considerations for training at altitude
• 'VO_2max and arterial O₂ saturation at sea level and at 610m altitude
• Breath Hold Fitness test — how long can you hold your breath?
• What are the highest-ranking endurance sports?