Exercise Physiology Chapter 12

16 Questions

What may happen if the body core temperature goes above 45°C?

Destroy proteins and enzymes

What is the normal core temperature of the human body?

37°C

Evaporation is the most important means of heat loss during exercise.

True

Humans are considered __________, which means they maintain a constant body core temperature.

homeotherms

Match the following means of heat loss with their descriptions:

Radiation = Transfer of heat via infrared rays Conduction = Heat loss due to contact with another surface Convection = Heat transferred to air or water Evaporation = Heat from skin converts sweat to water vapor

Define the following terms: (1) homeotherm, (2) hyperthermia, and (3) hypothermia.

Homeotherm: an organism that maintains a relatively constant body temperature. 2) Hyperthermia: abnormally high body temperature. 3) Hypothermia: abnormally low body temperature.

Why does a significant increase in core temperature represent a threat to life?

A significant increase in core temperature can lead to denaturation of proteins, heat exhaustion, heat stroke, and potentially death.

How is body temperature measured during exercise?

Body temperature can be measured during exercise using a thermometer placed orally, rectally, in the ear, or on the skin.

List and define the four mechanisms of heat loss. Which of these avenues plays the most important part during exercise in a hot/dry environment?

The four mechanisms of heat loss are radiation, convection, conduction, and evaporation. Evaporation plays the most crucial role during exercise in a hot/dry environment.

Briefly discuss the role of the hypothalamus in temperature regulation. How do the anterior hypothalamus and posterior hypothalamus differ in function?

The hypothalamus regulates body temperature by controlling mechanisms like vasoconstriction, sweating, and shivering. The anterior hypothalamus is responsible for heat loss responses, while the posterior hypothalamus triggers heat conservation responses.

Discuss the two general categories of heat production in people.

Heat production in people can be categorized as either physiological or biochemical. Physiological heat production includes physical activity, while biochemical heat production involves metabolic reactions.

What hormones are involved in biochemical heat production?

Thyroid hormones, adrenaline, and noradrenaline are involved in biochemical heat production.

Briefly outline the thermal events that occur during prolonged exercise in a moderate environment. Include changes in core temperature, skin blood flow, sweating, and skin temperature.

During prolonged exercise in a moderate environment, core temperature gradually increases and may plateau. Skin blood flow and sweating increase to dissipate heat, while skin temperature rises. These processes help regulate body temperature.

Calculate the amount of evaporation that must occur to remove 400 kcal of heat from the body.

Approximately 1 gram of water requires 0.58 kcal to evaporate. Thus, 400 kcal / 0.58 kcal ≈ 690 grams of water or 690 ml of sweat must evaporate to remove 400 kcal of heat.

Discuss the physiological changes that occur in response to chronic exposure to cold.

Chronic exposure to cold triggers adaptations like increased nonshivering thermogenesis, improved blood flow to extremities, and better tolerance to cold temperatures, all aimed at maintaining core temperature and preventing hypothermia.

How might exercise in a cold environment affect dexterity in skills such as throwing and catching?

Exercise in a cold environment can decrease dexterity due to reduced blood flow to the extremities, leading to slower nerve conduction and muscle responses.

Study Notes

Temperature Regulation

Humans are homeotherms, maintaining a constant body core temperature (37°C) despite changes in environmental temperature.
Heat loss must match heat gain to maintain a constant core temperature.
Normal core temperature range: 37°C (above 45°C can be fatal, and below 34°C can cause slowed metabolism and arrhythmias).
Thermal gradient: from body core to skin surface, ideal gradient is ~4°C.

Temperature Measurement During Exercise

Deep-body (core) temperature: measured at rectum, ear, or esophagus in a laboratory setting.
Skin temperature: measured using thermistors at various locations, including forehead, chest, forearm, thigh, calf, abdomen, and back.

Heat Production

Voluntary heat production: exercise (70-80% energy expenditure appears as heat).
Involuntary heat production: shivering (increases heat production by ~5x), and non-shivering thermogenesis (thyroxine, catecholamines).

Heat Loss

Radiation: transfer of heat via infrared rays (60% heat loss at rest, can be a method of heat gain).
Conduction: heat loss due to contact with another surface.
Convection: heat transferred to air or water (example: fan pushing air past skin).
Evaporation: heat loss from skin converting water (sweat) to water vapor (25% heat loss at rest, most important means of heat loss during exercise).

The Body's Thermostat—Hypothalamus

Anterior hypothalamus: responds to increased core temperature, commencing sweating and increased skin blood flow.
Posterior hypothalamus: responds to decreased core temperature, inducing shivering and increased norepinephrine release.

Exercise in the Heat

Increased exercise intensity increases heat production, leading to a linear increase in body temperature.
Mechanisms of heat loss during exercise: evaporation, convection, radiation, and conduction.
Heat acclimatization: adaptations occur within 7-14 days, including increased plasma volume, earlier onset of sweating, and reduced sodium chloride loss in sweat.

Exercise in a Cold Environment

Enhanced heat loss reduces the risk of heat injury but increases the risk of hypothermia.
Cold acclimatization: adaptations occur within one week, including lower skin temperature at which shivering begins, maintained higher hand and foot temperature, and improved peripheral blood flow.

This quiz covers the concept of temperature regulation during exercise, including heat balance, core temperature, and means of increasing body temperature. Test your knowledge of human physiology in this fitness and performance context.

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