Effects of the Environment on Performance Kacey, Newelly, Mick, Skunk and Mimmi

Our Lab will cover… Thermoregulation Physiological Responses to Heat Stress Body fluid Balances Transfer of Body heat Effects of Humidity Aims of the test

What is Thermoregulation? Humans are Homoeothermic, with less 25% of energy used for physiological functions, the rest is converted to heat. Thermoregulation is a process where the thermoregulatory control system in the hypothalumus, (the brain) readjusts the bodies temperatures in response to changes in our environment. Normal Core temperature is 36.1C to 37.8C. Although temperatures do vary, changes are no more than 1.0 C.

Physiological Responses to Heat Stress A Thermally neutral environment in considered to be somewhere between C. The cardiovascular system The cardiovascular system is placed under immense stress whilst exercising in hot conditions (24C+). - Circulatory system continues to transport blood to working muscles but also to the skin to transfer heat away from the body. -This results in an ↑ Q. -Heart rate Increases, Stroke volume decreases. -Shunting of blood from non- essential Organs.

Physiological Responses to Heat Stress Demand for blood flow and oxygen to muscles ↑ Working muscle blood flow, Same Body temperature ↑ Cardiac output ↑ Oxygen uptake ↑ Heart rate ↑ Stroke volume ↓ Overall blood volume, Same End diastolic volume ↓ Volume of blood returning to the heart ↓

Physiological Responses to Heat Stress Body Fluid Balance -Sweating will increase during exercise in heat -Leads to Dehydration and electrolyte loss if not attended to. -3 to 4 litres of sweat loss per hour can occur, 6-10% of body weight for endurance athletes, this can only be sustained for a number of hours. - Can lead to a decrease in blood volume.

Transfer of body heat HEAT GAIN- conduction and convection Conduction The transfer of heat through direct molecular contact with solid object. Movement of an electrical impulse, such as through a neuron. During exercise- not much because source of heat exchange is little because the body surface area in contact with solid objects is small. Convection Transfer of heat or cold via the movement of gas or liquid across an object, such as the body. The heat molecules in the air are transferred over the skin. The greater rate of movement the quicker the exchange can happen. In cooler temps convection doesn’t allow the heat to leave the body. Constantly removes metabolically generated heat from the body when the air temperature is lower than the skin temp.

HEAT LOSS – radiation and evaportation Radiation Radiation is the transfer of heat at through electromagnetic waves. In a body at rest, radiation is the primary method for discharging the resting body’s excess heat. At normal room temperature (21-25°C), the nude body loses about 60% of its excess heat by radiation. The heat is given off in the form of infrared rays, which are a type of electromagnetic waves. Evaporation Evaportation is heat loss through the conversion of water (such as sweat) to vapor. Evaporation accounts for about 80% of the total heat loss when one is physically active and is therefore an important avenue for heat loss. As body core temperature increases, sweat production increases. As sweat reaches the skin, it is converted from a liquid to a vapor, and heat is lost from the skin in the process.

Effect of Humidity Water vapor in the air plays a major role in evaporative heat loss. Relative humidity is more commonly used and relates to the water vapor pressure of the air to that of fully saturated. Expressed as a percentage. Fully saturated=100% humidity. High humidity: water molecules in the air is high High humidity: means that the air will struggle to accept more water or in the case of exercise sweat from an athlete. Therefore Low sweat evaporation will result in Low heat loss. Low humidity on the other hand will result in High sweat loss. While it is ideal to compete and exercise in low humidity environments, for ideal sweat evaporation and heat loss, this sweating can lead to dehydration.