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Heat Balance in a Hot Environment.

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Sam Dainty - Sports Science and Physiology 012-003-266 Heat Balance in a Hot Environment Practical Write-up Group 1- Monday a.m Heat Balance in a Hot Environment Introduction Changes in metabolic requirements of the human body are reflected by changes in ventilation rate accompanied by corresponding changes in oxygen consumption and carbon dioxide production. Using a Douglas bag, expired air can be collected over a set period of time so that the rate of ventilation can be calculated, and, after analysis of the expired air with the composition of inspired air, oxygen consumption and carbon dioxide production can be calculated. This method is technically called open circuit indirect calorimetry. It has been used in many studies of metabolism covering a wide range of physical activities, but now due to modern technology, sensitive gas analysers that are very rapid in response are used to calculate ventilation. The "integrative centre" in the hypothalamus compares the body core temperature to the ambient temperature through a number of thermoreceptors. It then regulates heat loss and heat production to maintain the body core temperature at the "set point". Heat loss from the skin is regulated through control of cutaneous vasomotor activity and sweating which evaporates from the skin and decreases body core temperature. ...read more.


After 30 minutes the subject was quickly taken out of the hot room and was weighed. Exercise was then immediately resumed for another 30 minutes at the same rate and the temperatures and the expiration volumes were also measured. After the last 30 minute period the subject was removed from the hot room and weighed. Results See attached Excel spreadsheet: Following the observations seen in the spreadsheet the following calculations were made to create a more accurate set of results: M(metabolic rate) = VO2 x 21.2 x 1000 60 x S.A(m2) 21.2 = The energy that 1 litre of oxygen provides (kJ) 1000 = Converts kJ into J. 60 = Converts J per min to J per second. S.A = Surface Area of body (m2) Measured using the surface area nomogram W(mechanical energy) = Load(kp) x revs per min x 0.978 S.A (m2) H = (T skin - T air) (Rd) x S.A T skin = Mean skin surface temperature T air = Air temperature Rd = Thermal resistance of clothing (0.07 in light clothing) S.A = Surface area of body (m2) E(evaporative heat loss) ...read more.


These glands are coiled regions in the dermis which secrete sweat on stimulation via cholinergenic sympathetic nerves or the circulation of adrenaline or noradrenaline. Due to the anomalous result that was identified, the heat balance curve that has been plotted has a sharp decrease at the beginning of exercise. From analysis of all the other values that were recorded it is seen that there should not be a large decrease in heat balance but there should be a gradual decline in heat balance which gives a smooth curve on the graph. The values of heat loss and heat loss via evaporation show that all heat loss at rest is via other mechanisms rather than sweating but during exercise the main avenue for heat loss is through evaporation because the values for E are greater than that for H in the exercise stage of the experiment. As seen in 'Heat Balance Components' the body was in heat balance in only the rest stage of the experiment. The heat production was equal to heat loss. To improve the accuracy of the experiment the subject should not be removed from the temperature controlled room to get weighed. There should be scales in the room. The temperature could also be recorded at more frequent intervals so that a more accurate curve can be plotted. 1 ...read more.

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