Altitude is typically defined as being at an elevation above 2,600 meters. Higher elevations reduce the amount of oxygen available in the air and create a state of hypoxia, in which the rate of oxygen supply cannot meet demands of the muscles. This forces the muscles to rely heavily on pathways of anaerobic metabolism such as the creatine-phosphate energy system and anaerobic lactate energy system. Currently, most scientists suggest that living at a higher altitude and training at low altitudes is best for enhancing performance. Whether living, competing, or training at altitude, special nutritional considerations should be taken to ensure optimal performance.
Training at elevation can decrease exercise capacity by 3% for every 300m above 1,500 m. Weight loss is common among athletes training at altitude. Appetite is suppressed at altitude, decreasing calorie intake and resulting in weight loss. Athletes training or competing at altitude must ensure optimal calorie intake to maintain performance and prevent losses in lean body mass. Higher-altitude environments increase the amount of fluids lost through the urine and ventilation. These environments cause the kidneys to increase urine production, which speeds the loss of fluids, and puts athletes at a much higher risk of dehydration. Dehydration can have multiple detrimental effects on the athlete including decreases in physical and cognitive performance and increased risk of injury. As little as 1%-2% losses in body water can equate to 5%-15% drops in performance. A combination of adequate fluid and electrolyte intake will ensure athletes are staying well hydrated. As the body is forced to rely more heavily on anaerobic metabolism, optimal carbohydrate intake is of even greater importance. Athletes will need to rely heavily on carbohydrate and muscle glycogen stores at altitude and will deplete stores much more quickly during training and competition. Altitude will also increase the total stress of training or competition since athletes will produce greater amounts of stress hormones and free radicals than normal due to the hypoxic conditions. Training or competing at high altitude can also result in poor sleep and slow recovery. Athletes should put extra thought into training volumes and intensities to account for these changes.
Nutritionally, athletes must focus on calorie and carbohydrate intake as well as fluids, electrolytes, and possibly higher intakes of antioxidants such as vitamins E and C. Weight loss is common but can be prevented if calorie needs are met. Calorie recommendations are similar at altitude verses at sea at sea level, and scientists believe reduced appetite and calorie intake are responsible for the weight loss commonly experienced by athletes. Caloric intake should emphasize carbohydrates. Roughly 65% of caloric intake should come from high-carbohydrate foods since athletes will rely heavily on anaerobic pathways of metabolism and use carbohydrates and glycogen stores extensively. Recommendations for carbohydrate intake during exercise at altitude are speculative. It is obvious that needs significantly increase from the recommended 22-45 g of carbohydrates/ hour of activity recommended for athletes at sea level. Remaining on the higher end of these recommendations and consuming slightly more—45-75 g/hour of activity—is advised. Consuming 3-5 L/day of fluid is recommended. Keeping fluid volumes high, especially with meals when adequate amounts of electrolytes such as sodium and potassium are provided in foods will assist with absorption. Athletes should also aim to consume an electrolyte beverage when drinking fluids alone without food. No altitude-specific recommendations are available for fluid intake during exercise; general guides for athletes at sea level should be applied. Adding support by using antioxidant supplements lacks a significant amount of scientific data to make definitive recommendations; however,some evidence exists to suggest benefits from supplementation with antioxidant vitamins and minerals, including vitamin A, vitamin E, vitamin C, selenium, and zinc.