Effects of Environment on Performance Damien Hirst Alicia Rady Bonnie Spry Liam Hawkey

-Physiological Responses to Heat Overview of Lesson Basic overview of Theory: -Thermoregulation -Physiological Responses to Heat -Methods of Heat Loss -Effects of Humidity Practical Component: 3 Females will be running for 30 minutes at 9km/hr in three different environmental conditions. These include heated room, cold room and a neutral conditions. Everyone will be assigned a job to monitor the effects of the specific environment Class Discussion on results will conclude lesson

Thermoregulatory control Thermoregulation is based around keeping the body temperature constant even when the environmental temperature changes. For this process to be effective the body needs to keep a balance between heat loss and heat gain. Heat gain comes from environmental heat and metabolic heat as over 75% of energy from ATP used in physiological functions is converted into heat. During rest the majority of heat is lost through radiation and during exercise the majority is lost through evaporation. If this control is successful the body will deviate within the normal range of 36.1 to 37.8`C.

Thermoregulatory control Where and how does all this happen? This first starts with sensory receptors called thermoreceptors located in the skin and brain. These thermorecptors detect changes and relay this information to the region of the brain referred to as the preoptic-anterior hypothalamus (POAH). In response to these receptors the hypothalamus activates mechanisms that regulate heating or cooling of the body.

Thermoregulatory control These are the steps involved with hyperthermia which are outlined in (Wilmore et al., 2008): 1. Increased blood and internal temperature 2. Increased temperature is sensed by thermorecptors and relayed to hypothalamus 3. Vasodilation occurs in skin blood vessels so more heat is lost from skin. 4. Sweat glands become active, increasing evaporative heat loss 5. Body temperature decreases

Physiological response to heat The body experiences physiological responses to heat, these are even more obvious during exercise. To reduce the effects of muscle heat production the body reacts in 3 main ways to remain within the limits of internal body temperature. The hypothalamus and various glands sense changes in body heat, they release hormones or impulses send signals to control the release heat. A circulatory adjustment increases blood flow to the skin and away from nonessential areas. Blood vessels dilate known as skin vasolidation which occurs to aid heat dissipation to the environment, this allows the blood to cool faster. Eccrine sweat glands all under the bodies’ skin are triggered by the hypothalamus to begin to release sweat through a tubular duct onto the skins surface. The sweat cools if the environmental temperature is lower then the bodies’, this mechanism of facilitating heat loss accounts from up to 80% of total heat loss during exercise.

Four methods of heat regulation Conduction Convection Radiation Evaporation

Conduction (C) Conduction involves the transfer of heat through direct contact with another solid object. Example: When holding a hot cup of coffee in your hand, the heat is transferred from the cup to your hands from the direct contact, which in turn warms your hands. For conduction to have any effect on core body temperature, the objects need to be in contact for a prolonged period of time. In terms of the body, the object needs to be in contact for prolonged period of time so that the heat can be transferred from the skin to the blood, enabling the heat to circulate around the body and hence raising core body temperature. Conduction is somewhat negligible in sport as contact with other solid objects is considerably small.

Convection (K) Convection involves the transfer of heat via movement of a gas or liquid across an object, such as the body(Wilmore et. al, 2008). As the gas or liquid moves across the object, it either takes heat away or gives heat to the object. Example: When a cool breeze blows across your face or you dive into a cold body of water, the molecules move across your body and take the heat away with them.

Radiation (R) Radiation involves the transfer of heat through electromagnetic (heat) waves from one object to another. The body gives off such waves to objects around it and can also receive heat from objects surrounding it that are warmer. If the temperature of objects around the body are warmer, the body receives a net heat gain. Example: When you open the door to a freezer, you send electromagnetic (or heat) waves to that freezer. As The freezers’ temperature is lower than your body temperature this makes your body cooler. At rest, Radiation is the primary method of heat regulation for the body.

Evaporation (E) Evaporation involves the heat loss through the conversion of water to vapour, such as the liquid sweat. As the core body temperature rises, so too does sweat production. However, for sweating to have any effect on heat regulation, the sweat must evaporate from the skin’s surface. Example: When the body temperature rises, sweat is produced in the form of a liquid. This liquid evaporates from the skin, taking the heat away with it from the change from liquid to vapor. 80% of body heat is lost through evaporation when physically active, while at rest it is responsible for 10-20% of heat dissipation. Humidity has a significant affect of the effectiveness of evaporation as a mean of heat regulation.

Effects of humidity When humidity levels are high the air contains an increased amount of water molecules, which decreases the bodies sweat evaporation. When exercising in humid whether it’s important to: Drink plenty of fluids, dress appropriately and take time to adjust to the environment.

Discussion Question Relationship of results based on the graph? Any change in core temperature during the testing? Why/Why not? What physiological mechanisms would have occurred during the test to control heat regulation in the hot and cold conditions?

Conclusion What have we learnt about thermoregulatory control during exercise in various ambient temperatures? What physiological changes occur during exercise in various ambient temperatures? What mechanisms are used to maintain homeostasis during exercise?