Exercising Outdoors in a Cold and Hot Environment

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Table of Contents

Hypothermia
Physiological Responses to Cold Environment
Individual Factors and Exercise in Cold Environment
Heat Acclimation and Endurance Performance
References

Hypothermia

Hypothermia is a medical emergency state of a human body that occurs when the organism cannot produce heat at sufficient speed. That corresponds to a dangerously low body temperature; usually, 35 C^ois considered the upper limit for this dangerous situation, while the average is about 36.6 C^o. Cold injuries may happen when the human organism decreases the blood flow to the shell and triggers peripheral vasoconstriction, especially in the hands and fingers. If the person does not increase the insulation from the environment by adding layers of clothes, they may experience the loss of manual dexterity, frostbite, and, possibly, permanent damage to the skin, muscle, and nerve tissues.

Physiological Responses to Cold Environment

Peripheral vasoconstriction happens when there is a need to decrease heat loss to the environment due to the low ambient temperatures. The organism limits the blood flow to the skeletal muscles to increase the insulation between the internal organs and the environment. The peripheral shell tissues may experience cold injuries if the temperature stays low for a significant amount of time. The core response may be affected by an individuals body composition and anthropometric characteristics.

Voluntary muscle activity, such as physical exercise or active movement, helps maintain the organisms safe core temperature. However, if it cannot be performed, the shivering, or involuntary contraction, begins. The process involves increasing the whole-body oxygen intake and intensifying the thermogenesis with the severity of cold stress. It is similar to the muscles performing the work, but the main aim is to release the heat. While shivering helps the body decrease the negative effect of the cold environment, it is a sign of a stressful state for the organism.

Exercise in a cold environment presents several challenges to athletes. First, the organism would not be able to deliver sufficient amounts of oxygen to the muscles since the blood flow does not reach them at the usual rate. For activities, it would mean a 5-6% decrease in VO₂ max per C^odrop of the core temperature. However, the maximal heart rate generally does not change much during cold exposure. Since aerobic metabolism is no longer reliable under these conditions, the anaerobic one begins to play a more significant role. It is less efficient, as a single glucose molecule generates only 2 ATP during anaerobic glycolysis, whereas subsequent oxidative metabolism yields 34 ATP. In other words, it would be enough to maintain the essential functions of the human body, but not for its peak performance.

Anaerobic glycolysis and metabolism produce lactic acid as a by-product. It could be used as emergency energy during strenuous exercises by the heart and slow the muscle contraction speed leading to lower peak performance levels of an athlete. The higher sugar level in the blood allows it to retain the heat better as it is reaching the muscles. The glucose levels drop in a cold environment as it is used for energy to remain at the body temperature, but is not replaced at a sufficient rate. Besides, the human bodies go into the survival or endurance mode, and the muscles start to engage the type II, or slow fibers, responsible for the consistent activity performed over an extended period.

Individual Factors and Exercise in Cold Environment

Anthropometry has an effect on individual tolerance to low temperatures. It follows the laws of physics: if the heat loss takes place through the skin surface, the smaller is the surface to a persons mass ratio, the longer they can support operating temperatures in the cold environment. Acclimatization happens when individuals spend at least several weeks at an unusual climate and altitude. When the group members have a similar body size, composition, fat amount, and physical activity habits, those who had trained in the cold conditions will be using 20-30% less oxygen at the 5 C^o than the other group. This was determined through a volitional fatigue test but correlates with any physical exercises performed at temperatures below the 11 C^o.

The persons fitness level defines how prepared their body is for physical activity, including one in a cold environment. Since the heart is already trained to pump larger volumes of oxidized blood and muscles contain more fiber than non-athletes, performing below comfortable temperatures would be easier for those who regularly engage in sports activities. Still, their results will be less impressive than those in moderate conditions.

Age and gender affect acclimatization, but not as much as the previously mentioned factors. Some evidence shows that female athletes are a little slower in adapting to the temperature changes, but that may be happening partially because of their smaller size and weight on average. Children have more problems performing in the cold due to their dimensions and still developing anatomically. At the same time, the cardiovascular systems of older people would be their weak spot. Depriving the peripheral skeletal muscles of sufficient blood flow in the cold environment leads to dexterity loss in the hands. Using appropriate insulating gloves decreases the effects of low temperatures on hand functions.

Hypothermia is a dangerous condition that causes physiological changes in human bodies due to low environmental changes. They may lead to discomfort and negative consequences for muscle and nerve tissues. For athletes, that generally means low peak performance and potential risk of injury; however, the effects can be minimized through appropriate clothing and training.

Heat Acclimation and Endurance Performance

Hyperthermia

Hyperthermia is a heat-related condition in which the persons internal temperature rises to dangerous levels because of external factors. Heat injuries happen when the persons body does not have enough resources to regulate its temperature through sweating and capillary expansion. The potential problems include dehydration, headaches, heart problems, fainting, and even death. They may be prevented through water intake, air circulation, and ambient temperature decrease. Athletes risk overheating due to increased muscle work as they train and perform. The human body adapts to the training conditions, including the temperatures and humidity, to optimize resource usage. In moderate conditions, the muscles will not adjust the oxygen intake and glucose breakdown levels for the hotter environment. However, moving the performance to a place with a high temperature would result in worse performance due to potential overheating and increased sweating. When the level of electrolytes and moister in the human body is low, the blood and respiratory systems may fail.

Heat acclimation occurs when significant time spent living and training in high temperatures leads to better thermal regulation of the human organism. Sports conditioning in a hot environment for about two weeks can lead to cardiovascular adaptations. It is especially beneficial for endurance athletes since their performance depends heavily on oxygen consumption levels. Heat acclimation allows the heart to pump more oxygen-induced blood through the muscles and use the fats and carbohydrates for fuel more efficiently by increasing the VO₂ max. This state could be achieved through high-intensity interval training (at 80-90% of the maximum heart rate).

Exercising in extreme heat is stressful for athletes, especially the endurance ones since they have to perform for a significant amount of time. Overheating may cause dehydration, headaches, and, eventually, serious health problems. Proper clothing, water availability, and acclimation are beneficial for the health and performance levels of endurance athletes when their environment changes from moderate to hot and humid.

References

Baker, L. (2019). Physiology of sweat gland function: The roles of sweating and sweat composition in human health. Temperature, 6(3), 211-259.

Castellani, J.W. (2020). Running in cold weather: Exercise performance and cold injury risk. Strength and Conditioning Journal, 42(1), 83-89. Web.

Institute of Medicine (US) Committee on Military Nutrition Research. (1996). Nutritional Needs in Cold and in High-Altitude Environments: Applications for Military Personnel in Field Operations. National Academies Press.

Muller, M.D., Kim, C.-H., Bellar, D.M., Ryan, E.J., Seo, Y., Muller, S.M., & Glickman, E.L. (2012). Effect of cold acclimatization on exercise economy in the cold. European Journal of Applied Physiology, 112, 795-800.

Nimmo, M. (2004). Exercise in the cold. Journal of Sports Sciences, 22, 898-915.

The Physiological Society. (2019). Physiology of Aerobic and Dexterity Performance in the Cold [Video]. YouTube.

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