Read some of the cards laid around the room. What’s this lesson about? Use the cards to make a large flow diagram to show how the body does this.

Thermoregulation How the body regulates temperature Effect of temperature changes on exercise performance Cardiovascular drift

Complete your A3 thermoregulation flow diagrams

Methods of Heat Loss Conduction Convection Radiation Evaporation Which of the above does the body rely on for thermoregulation during exercise?

Vasodilation Arterioles contain smooth muscle that can contract to reduce the blood vessel diameter, or relax to increase the diameter Pre-capillary sphincters can also contract or relax Sympathetic nervous stimulation; muscle metabolites e.g. CO2, H+ What do you think would make the arterioles and sphincters relax? and other factors including ATP, ADP, Histamine, Nitric Oxide

Sweating 1-2 Litres lost per hour (although some people can lose up to 3L per hour) Sweat contains water and ions including sodium, potassium and chloride (why is this important?) Heat from the body is transferred to the water in the sweat, causing it to evaporate as water vapour. This removes heat from the body, cooling it. Sweating is affected by the humidity of the air – humid air reduces the water potential gradient, so less water will evaporate and less heat will be lost (as a result….?) Sweating is also affected by ambient temperature, exercise intensity and the athlete’s fitness

Affect of rising temperature on performance Increasing temperature has a detrimental effect on performance: Subjects exercising at 70% VO2 max had a mean exercise duration of 158 mins at 10°C, but only 53 mins at 30°C The effect of rising body temperature on performance is complex but… Fatigue occurs if core temperature rises above 39.5°C (why?) Parameters such as muscle blood flow, fuel utilisation and OBLA seem uneffected. Read section titled ‘Body temperature regulation during exercise’ in text to find answer to why we fatigue quicker.

Acclimatisation Significantly helps reduce temperature related fatigue Subjects exercising at 50% VO2 max in 40°C heat could exercise for 48 mins before acclimatisation, and 80 mins after 10 days acclimatisation.

Pre cooling / heating To examine the effect of initial body temperature [esophageal temperature (Tes) = 35.9 ± 0.2, 37.4 ± 0.1, or 38.2 ± 0.1 (SE) °C induced by 30 min of water immersion], seven cyclists (maximal O2 uptake = 5.1 ± 0.1 l/min) performed three randomly assigned bouts of cycle ergometer exercise (60% maximal O2 uptake) in the heat (40°C) until volitional exhaustion. Despite different initial temperatures, all subjects fatigued at an identical level of hyperthermia (Tes = 40.1–40.2°C, muscle temperature = 40.7–40.9°C, skin temperature = 37.0–37.2°C) and cardiovascular strain (heart rate = 196–198 beats/min, cardiac output = 19.9–20.8 l/min). Esophageal temperature (A), mean skin temperature (B), heart rate (C), and skin blood flow (D) during exercise in heat (40°C, 17% relative humidity) during precooling, control, and preheating trials. Skin blood flow is referenced to resting baseline values obtained on arrival at the laboratory (0.2–1.2 V;n = 4). Values are means ± SE for 7 subjects. * Significantly different from control, P < 0.05. González-Alonso J et al. J Appl Physiol 1999;86:1032-1039

Cardiovascular Drift

Cardiovascular Drift Cardiovascular drift is a phenomenon whereby some CV responses begin a continuous time-dependent change, or "drift," after ~10 min of prolonged moderate intensity exercise (e.g., 50-75% VO2max) in a neutral or warm environment. It is characterized by a progressive decline in stroke volume and pulmonary and systemic mean arterial pressures and a parallel increase in heart rate whereas cardiac output is maintained nearly constant

Cardiovascular Drift

Cardiovascular Drift These changes occur because: Vasodilation during exercise increases blood flow to the skin to increase heat loss This means less blood returns to the heart so stroke volume decreases Sweating causes blood plasma to decrease in volume (water lost in sweat), further reducing the volume of blood returning to the heart and ultimately increasing viscosity Heart rate increases to compensate for the decrease in stroke volume to maintain cardiac output at the level required to meet the demands of the activity.