Many factors affect the amount of energy and the ratio of carbohydrates to fats used when training. Being aware of how the environment may effect metabolic changes in hot and cold weather can better help athletes train in these conditions more efficiently. The human body will do what it needs to keep its internal temperature at normal ranges and these actions may need to be looked at more closely to make sure the proper amount of nutritional requirements are met. The purpose of this article is to address any necessary approaches needed to help increase performance in these conditions through nutrition and hydration.
Environment & Nutrition
The advantage that humans have in relationship to physical performance is that we have the abilities to adapt to training stimuli. This allows an athlete to increase his/her athletic ability and have somewhat of a control over their performance in a particular sport. This involves an adaptation of strength and conditioning parameters (power, strength, endurance), physiology, and metabolism. Although this is very beneficial with regards to performance, one limitation can impair training, and it is referred to as homeothermy, or the balance of internal temperatures. This involves an ongoing “battle” ones body temperature has with environmental temperatures. The body must maintain normal temperatures (37 degrees C or 98.5 degrees F) within a relatively narrow range in order for optimal functioning to occur. Several defense mechanisms that occur in order to allow for this are shivering, sweating, vasodilatation or vasoconstriction. Research has shown repeatedly that when the capability of these physiological defense mechanisms are exceeded and body core temperature drops below 35 degrees C (95 degrees F) or rises above 41 degrees C (106 degrees F), both physical and mental performance deteriorates. Because athletes and coaches have no control over the environment, precautions must be taken in order to reduce the detrimental effects of the environment.
Heat & Sports Participation
Sports participation in either cold or hot environments causes physiological and metabolic changes that alter fluid balance, nutritional requirements, and can ultimately have a negative effect on performance if not controlled for. Exercising in the heat has been of particular interest to the sports communities with reference research and application. Activities in the heat can result in an increased sweat response, which can lower plasma volume in the blood. If not replaced, a loss of body fluids of as little as 1 to 2% of total body weight can negatively impair performance in an athletic event (strength, power, endurance). However, intense thirst is commonly not experienced by the athlete until perhaps a loss of 2-4% body weight due to dehydration. This represents a danger to the athlete in terms of relying solely of subjective feelings of thirst. If a larger gap between feelings of thirst and dehydration exists, then the athlete is in particular danger of the effects of losing body fluids. A consistent intake of fluids is therefore strongly recommended, particularly during periods of practice or competition in the heat. The guidelines of fluid intake are for an athlete to consume 150 to 200 mL of fluids every 15 to 20 minutes of exercise. This appears to be sufficient to prevent the occurrence of dehydration.
Exercising in the heat not only creates a possible fluid imbalance, but also can affect substrate, or fuel oxidation during activity, with an increased reliance on carbohydrates for fuel. Numerous studies have shown that muscle glycogenolysis (the breakdown and use of muscle glycogen), liver glucose production, and the respiratory exchange ratio (relationship of carbon dioxide to oxygen utilization that depicts fuel use) is all higher during exercise in a hot environment. The accumulation of lactate within skeletal muscle is also increased, indicating an increased rate of carbohydrate oxidation. The possible processes responsible for this shift lie within the central nervous system. Increases in body core temperature, and increased sweating responses, perhaps cause an increase in catecholamine (epinephrine/norepinephrine) secretion. Epinephrine at the cellular level causes an increased uptake and oxidation of glucose for fuel, and therefore causes a shift away from fat or adipose tissue oxidation.
Physiological consequences of the effects of heat on performance may result in a faster depletion of carbohydrates or glycogen stores. If carbohydrate oxidation is increased during training in the heat, such as during multiple pre-season practices, muscle glycogen may become prematurely depleted, causing the onset of fatigue to occur sooner. Numerous studies have examined the effects of carbohydrate intakes on exercising in the heat, and the results largely show that if adequate carbohydrate amounts are consumed, this premature depletion of glycogen stores can be somewhat prevented. This involves adequate pre-and post-exercise carbohydrate consumption to properly fuel and restore muscle glycogen, but also to maintain an adequate blood glucose level during training. Carbohydrate/electrolyte drinks can provide the necessary energy to help reduce the onset of hypoglycemia, or diminished blood glucose. Research has shown that the adequate volumes and rates of ingestion are approximately 15 to 20g of simple carbohydrates every 15 to 20 minutes of exhaustive exercise.
Cold & Sports Participation
A decrease in environmental temperature can also have an effect on metabolism during sports and exercise. On average the energy expenditure of an activity performed in cold environments can increase the energy requirements of the exercise session by 10 to 15%. Energy requirements in a cold environment are influenced by the intensity of the cold, wind-speed, and physical difficulties. Although the energy costs of exercise increases in the cold, the rates and types of substrate (fuel) use is not affected.
Few studies have dealt specifically with nutrient requirements in the cold. The limited research available supports the concept that cold does not cause a greater demand for any other nutrients besides calories. There have occurred anecdotal reports of increases in hunger during intense exercise in cold weather. However, none have been justified through research or clinical studies. A more important topic with regards to sports participation in the cold is adequate fluid intakes. Any change in the environment, and as a result a change in physiology or metabolism, could alter an athlete’s subjective feelings with regards to thirst. It is recommended that the athletes be properly educated on adequate fluid intakes during cold environments, and the possible changes in thirst or hunger that may occur. This is to help prevent any occurrences of hypohydration or decreased water intake.
In conclusion, training in different environments calls for different nutritional needs to help the body maintain a balanced internal temperature. In hotter conditions, the body sweats and uses more of its glycogen stores for fuel. In this case, carbohydrate/electrolyte drinks can provide the necessary energy to help reduce the onset of hypoglycemia, or diminished blood glucose in the amounts of approximately 15 to 20g of simple carbohydrates every 15 to 20 minutes of exhaustive exercise. As for training in colder environments, the increased calorie expenditure of 10 to 15% due to the increased metabolic rate to warm the body back to it’s internal temperature, needs to be addressed when determining calorie needs to make sure those needs are accounted for when training in that environment. Download Paper
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