Wk 6 - Thermoregulation and thermal stress, exercise and altitude

Question 1

Describe our body core temperature:

Answer 1

-> Humans are homeotherms. Normal resting core temperature: 36.5-37.5C. Cold temperature is defined as: Temperature of the hypothalamus, the thermoregulatory centre of the body. In the heat, core temperature can safely increase up to 40C. In the cold, core temperature can safely drop to 35C. The posterior and anterior hypothalamus acts as a thermostat in the brain to be able to control the temperature of the body.

Question 2

How can core temperature be assessed?

Answer 2

-> Oesophageal temperature, Rectal temperature, Stomach temperature (swallowed telemetry pill), Oral temperature and Tympanic temperature.
-Body temperature -> Core + skin temperature (skin temperature ~32-25C). Cool mean skin temp = <30C. Warm mean skin temp = 30-34.9C. Hot mean skin temp = >35C. The thermal gradient is the heat transferred from high to low temperature.

Question 3

What is temperature regulation?

Answer 3

The homeostatic maintenance of body temperature requires the operation of temperature sensors (peripheral and central thermoreceptors) and regulated effectors.

Question 4

Draw the physiological control of thermoregulation

Answer 4

-Found in thermoregulation notes

Question 5

What is heat balance?

Answer 5

-> Body temperature is maintained by balancing heat gain and heat loss.
* Heat conservation/ production -> Shivering thermogenesis, voluntary muscular activity, non-shivering thermogenesis
* Heat loss -> Blood reaching the skin, sweating

Question 6

What is heat balance during exercise?

Answer 6

-> Metabolic reactions during exercise lose ~75% of energy as heat

Question 7

What is heat exchange and balance? and draw the equation

Answer 7

S = heat storage (kcal/min or watts)
M = metabolic heat production (kcal/min or watts)
Cv = convective heat loss or gain (kcal/min or watts)
Cd = conductive heat loss or gain (kcal/min or watts)
R = radiant heat loss or gain (kcal/min or watts)
E = evaporative heat loss (kcal/min or watts)

Question 8

What is heat exchange?

Answer 8

-> Between the body and environment governed by biophysical properties. Biophysical properties dictated by the surrounding temperature, humidity and air motion, sky and ground radiation and clothing. There is a shift in heat generation and demand.

Question 9

What is the most challenging environment?

Answer 9

-The most challenging environment for exercise is hot and humid. This is because you cannot sweat as much due to the moisture in the air (alters the gradient).
-Aerobic performance is impaired when undertaken in a hot, humid environment.

Question 10

Why is exercise performance affected by hot ambient conditions?

Answer 10

-When performing aerobic exercise in a hot environment, there is an increase in demand on heat loss mechanisms (skin blood flow and sweating) and a Reduced gradient between core and skin – therefore, core temperature increases
-There is competition from the brain and heart as well as the working muscles (especially during exercise)
-There is an increase in cardiovascular strain

Question 11

What is dehydration?

Answer 11

-Dehydration = loss of fluid from the body. Decreases sweat rate and plasma volume. Further decreased cardiac output, maximal oxygen uptake, muscle strength and work capacity. As soon as a threshold is reached, the sweat production is reduced in order for the body to maintain the fluids in the body.

Question 12

Why is prolonged high-intensity exercise markedly impaired by a hot environment?

Answer 12

This is because:
* Competing regulatory demands for blood flow between thermoregulation, working muscle and CNS
* Heat-related changes in skeletal muscle function and metabolism

Question 13

Draw the heat-related health impacts

Answer 13

-Found in thermoregulatory notes

Question 14

How do you mitigate the impact of heat stress?

Answer 14

• Before – Heat acclimation and aerobic training
• Immediately before – Pre-cooling, hydration status
• During – Hydration, clothing and cooling

Question 15

Draw the table for heat acclimatization:

Answer 15

-Found in thermoregulatory notes

Question 16

What is hypothermia?

Answer 16

-Hypothermia -> Core temperature below 35C
- 2C drop associated with maximal shivering
- 4C drop with ataxia and apathy
- 6C drop with unconsciousness
- Further drop associated with ventricular fibrillation, reduced brain blood flow, asystole, death

Question 17

How does heat loss exceed heat production?

Answer 17

Conduction, convection, radiation and evaporation. It is important to protect against heat loss and maintain the core temperature.

Question 18

Effects of exercising in a cold environment:

Answer 18

• Cold acclimatisation/ acclimation – results in lower skin temperature at which shivering begins. Increases non shivering thermogenesis
• Maintains higher hand and foot temperature – improved peripheral blood flow
• Improved ability to sleep in the cold – due to reduced shivering
• Adaptations begin in 1 week

Question 19

Draw the table for physiological responses to exercise in the cold:

Answer 19

-Found in thermoregulatory notes

Question 20

What are the effects of altitude on performance in short races e.g. 1964 Tokyo and 1968 Mexico Olympics:

Answer 20

The lower air density at altitude offers less resistance to high-speed movement, and sprint performances are either not affected or are improved. Short term anaerobic performance - lower PO2 at altitude should have no effect on performance – O2 transport does not limit performance.

Question 21

What are the effects of altitude on performance in long races e.g. 1964 Tokyo and 1968 Mexico Olympics:

Answer 21

Performance demands is more dependent on oxygen delivery to muscle. Long-term anaerobic performance – lower PO2 results in poorer aerobic performance- dependent on oxygen delivery to muscle.

Question 22

What is barometric pressure and altitude?

Answer 22

• Boyle’s Law – gas volume inversely proportional to it’s pressure. As you increase air pressure, there are less particles which means that the air is less dense and more ‘spread out’.
• High altitude – same percentages of O2, CO2 and N2 in the air. Lower Partial pressure of O2, CO2 and N2.
• Atmospheric pressure – decreases at higher altitude
• Hypoxia – low PO2 (altitude)
• Normoxia – normal PO2 (sea level)
• Hyperoxia – high PO2
• Hypoxaemia – low levels of oxygen in the blood

Question 23

What is the effect of altitude on environmental and physiological variables?

Answer 23

-> Exposure to hypoxia directly results in a reduction in arterial oxygen pressure (PaO2). This disruption in homeostasis triggers neuroendocrine responses that help regulate important adjustments in key physiological systems. As you ascend, there is a decrease of the partial pressure of oxygen in the blood, the consequence is the saturation of blood also decreases.

Question 24

What is the time of useful consciousness at altitude?

Answer 24

We would be awake and conscious for only a minute if we were dropped off at the top of Mt. Everest (8848m), due to the lack of oxygen at the high altitude.

Question 25

What is oxygen transport cascade?

Answer 25

Ambient air, lungs, haemoglobin, cardiac output, muscle blood flow, oxygen extraction, cellular metabolism. We are less capable of doing work in this zone (~40 PO2) because there is less oxygen extraction to do work with.

Question 26

What are short term adjustments to altitude?

Answer 26

* Immediate response – get in more O2 molecules * Ventilation changes – hyperventilation (chemoreceptors), raises alveolar O2, lowers alveolar CO2, causes alkalosis and diuresis (HCO3-) * Cardiovascular changes – increased resting heart rate and cardiac output * Cold/ dry air (reduced humidity), dehydration, UV light (sunstroke, blindness)

Question 27

What are changes in VO2 max with increasing altitude?

Answer 27

-> No adverse events for events <2mins (as its using ATP systems, so altitude is not involved). There is a linear relationship with the ability to perform with aerobic power and with altitude. The less altitude there is, the higher the aerobic power there is able to be performed.

Question 28

What is the effect of altitude on the ventilatory response to sub-maximal exercise?

Answer 28

Increased ventilation for same workload. This is because there is less oxygen, so you will breathe more in order to get the oxygen to the working muscles and into the body.

Question 29

What is the effect of acute exposure to altitude on the CV response to sub-maximal exercise?

Answer 29

Heart increased during submaximal exercise – lower oxygen content and increased SNA. There is an increase in heart rate during acute exposure and this is stimulated by the hypoxic environment.

Question 30

What is the effect of high altitude on the heart rate response to maximal exercise?

Answer 30

* At max, cardiac strain is reduced – lactate production also isn’t higher at altitude at maximal effort (lactate paradox) * Maximal heart rate response to exercise is attenuated at altitude. At altitude during exercise, the ability to produce lactate is reduced (lactate paradox). * Evidence that activation of parasympathetic nervous system limits maximal heart rate response to exercise at altitude. Parasympathetic blockade (glycopyrrolate) restores maximal heart rate response to exercise

Question 31

What are the benefits and detriments of high altitude training?

Answer 31

-Beneficial effects of acclimatisation -> As people spend time in altitude, the ability to increase the oxygen uptake improves -Acute acclimatisation and ventilatory responses to exposure -> The ability to ventilate increases during acclimatization, which can be around ~50%.

Question 32

What are the effects of altitude acclimatisation on the CV response to sub-max exercise?

Answer 32

CO falls. Ficks equation: VO2 = cardiac output x a-vO2 difference. More O2 in the blood improves O2 extraction capacity = less reliance of central delivery (i.e. less cardiac strain). Individuals become less hypoxic. There is also less plasma volume, which allows more blood to be taken, however it means that performance decreases at the same time.

Question 33

What are blood changes from high altitude training?

Answer 33

* Polycythaemia due to increased erythropoietin (EPO) -> O2 carrying capacity of blood normally 200mL/litre. Peruvians at altitude 260mL/litre. Extreme acclimatization 310mL/litre. * Increased red blood cell production in the red bone marrow, which enables an increase in blood oxygen * Decreased plasma volume (helps haemoglobin) * Hyperventilation causes alkalosis which shits ODC to left * Increase in 2,3 DPG in RBC’s shifts ODC to right and causes increased Bohr shift

Question 34

What are vascular/ cellular changes from high altitude training?

Answer 34

* Increased capillarisation – in large part from reduction of muscle mass * Increased myoglobin in muscles * Increased aerobic enzymes (citrate synthase) * Muscle mitochondrial density does not increase * a-vO2 difference during exercise, falls with short-term exposure, but widens following acclimatisation * Increased lactate consumption and oxidation by active muscle

Question 35

What are the longer-term adjustments to altitude hypoxia? -Pulmonary acid-base, cardiovascular, haematologic and local

Answer 35

-Pulmonary acid-base -> hyperventilation and excretion of base (HCO3 via kidneys) -Cardiovascular -> HR increased, SV decreased, CO unchanged or slightly decreases, maximal CO decreased -Haematologic -> decreased plasma volume and increased haematocrit, haemoglobin and RBC number -Local -> increased skeletal muscle capillarization, increased RBC 2,3, increased mitochondria density, increased oxidative enzyme activity and loss of body weight and lean body mass

Question 36

Benefits, detriments and solution to high altitude training:

Answer 36

* Benefits – Blood changes (red cell mass), some cellular changes, some circulatory changes * Detriments – Blood changes (viscosity), cardiovascular changes, loss of training intensity, reduced muscle mass and increased ventilatory response * Solution – Tents (hypoxicators) believed by many to be an effective performance enhancer If you increase haemoglobin mass, you can increase VO2 max. Enabling performance to then be increased.

Question 37

What is 'live high, train low'?

Answer 37

* Live at high altitude – may elicit an increase in red blood cells mass (via EPO and leads to an increase in VO2 max) * >22hr/ day at 2000-2500m required – or stimulated altitude of 2500-3000 for 12-16hr/day * Intermittent hypobaric hypoxia – for example, 3hr/day for 5 days/wk at 4000-5000m * Then, train at low altitude to maintain high interval training velocity