Environment and Exercise

Thermoregulation

Body temperature

• Different temperatures:– Surface / Skin– Core body– Tympanic– Esophogeal– Rectal– oral

Regulation

• Regulated by hypothalamus to within 1 degree (37 + or – 1)

• Fig 11.5 a and b pg 258, 259• Negative feedback loopThermal receptors in the skin Temperature changes in blood

Mechanisms of Heat Loss/gainMechanisms of Heat Loss/gain• Radiation

– The release of heat via electromagnetic heat waves

• Conduction– Direct transfer of heat through contact with a

liquid, solid, or gas

• Convection– Carrying heat on air currents

• Evaporation– Provides the major physiologic defense

against overheating

Primary mechanisms??

• At rest?

• During exercise??

Mechanisms of Heat Conservation

Mechanisms of Heat Conservation

• Vascular adjustments– Vasoconstriction of

peripheral blood vessels

• Muscular activity– Voluntary physical

activity– Involuntary- Shivering

• Hormonal output– Increased secretion of E,

NE, thyroxine

Mechanisms Facilitating Heat Loss

Mechanisms Facilitating Heat Loss

• Circulatory adjustments

• Evaporation

• Hormonal adjustments

Circulatory AdjustmentsCirculatory Adjustments

• Two competitive cardiovascular demands exist during exercise in the heat– Oxygen delivery to muscles must increase to

sustain exercise energy metabolism– Peripheral blood flow to the skin must

increase to transport metabolic heat from exercise for dissipation at the body’s surface

Evaporation depends on

• Surface exposed to environment

• Temperature and humidity of air

• Convective air currents

Clothing

• Cloth traps air next to skin and warms it to provide insulation

• However if sweat is not absorbed and drawn away from skin to be kept dry, clothing loses 90% insulating property

Exercise in the Heat

Heat

• Beijing

• Fig 11.6 shows that compared to thermoneutral environments, HR higher SV lower in hot conditions

• 40-41 degrees- brain sends signals to stop exercise

Consequences of DehydrationConsequences of Dehydration

• Reduced plasma volume

• Increased submaximal heart rate

• Reduced rate of sweating

• Impaired ability to thermoregulate

hyperthermia

• Prevention– Avoid holding competition when temp >28

degrees– Drink fluids before and after and have breaks

every 15-30 mins– clothing

• Treatment– Immerse in ice bath/ cold water

Clothing for the heat

• Cover as little SA as possible

• Loose fitting to allow convective air currents near skin

• Wet allows increased evaporation

• Colour– Dark = absorbs radiant

heat– Light – reflects radiant heat

Factors Affecting Heat Tolerance

Factors Affecting Heat Tolerance

• Acclimatisation

• Exercise training

• Age

• Gender

• Body composition

• Hydration

Acclimatisation to heat

• Physiologic adaptive changes that improve heat tolerance

• Training increases heat tolerance• As does 9-14 days of exercising

in heat– Lower Heart rate– Lower skin temp– Lower core body temp – Increased plasma volume– Double sweating capacity (volume),

Greater area of the body is used for sweating, More dilute

– Sweat response earlier in exercise session

during exercise

Exercise in the Cold

Cold

• Physiological– Peripheral Vasoconstriction – Non shivering thermogenesis– Shivering

• Behavioural adjustments– Huddle– Voluntary movement– Put more clothes on– Exercise indoors

Exercise in water in the cold

• Body loses heat 4 x as fast in cool water as in air the same temperature

Shivering

• Swimming in 18degrees as opposed to 26 degrees = 500 ml/min more o2

Exercise in the cold

• Increased consumption o2 to compensate for that used in shivering

• Increased mobilisation FFA’s for fuel– If low blood glucose reduced shivering

reduced temperature

• Cold muscle = decreased contractile force– Particularly when fatigued– Large inner muscles insulated and protected– Peripheral muscles decreased dexterity

Dry Mouth

• Air is warmed and humidified by the bronchial tract 27/30 degrees

• When air is humidified it takes moisture from the respiratory tract

• Especially during exercise• Therefore

– Dry mouth– Burning throat– Irritation respiratory passages

Evaluating cold stress

S/A node in heart slow HR

Frostbite warning signs• Tingling & numbness

fingers and toes• Burning sensation –

nose & ears

Acclimatisation to cold

• Genetic- Eskimo

• Habituation- Repeated exposure of extremities to cold increased peripheral blood flow to reduce possibility of frostbite

Exercise in Pollution

Pollution

• Carbon monoxide, sulfur oxides, nitrogen oxides, ozone, peroxyacetyl nitrate, aerosols, soot, dust and smoke

• Large particles and highly soluble gases are usually filtered out in nasal passages

Effects

• Irritation of the upper respiratory tract

• 30 min submax exercise = smoking a pack of cigarettes

• Carbon monoxide - reduces the blood’s capacity to transport oxygen to the tissues.

• Asthma attacks

Beijing 2008•Pollution levels 2-3 x higher than those deemed safe by WHO

• Trial to take 1 million cars off the road to see if pollution levels go down

Exercise and AltitudeExercise and Altitude

Exercise at AltitudeExercise at Altitude

– Reduced barometric pressure

– Reduced partial pressure of oxygen (Po2)

– Reduced relative humidity

– Reduced ambient temperature

Immediate adjustments to altitude above 2300 m

Immediate adjustments to altitude above 2300 m

• Hyperventilation– Chemoreceptors detect that not getting

enough oxygen– Increase ventilation to compensate evaporation fluids respiratory tract

• Cardiovascular– Increased HR and cardiac output– At rest and during submaximal exercise

Exercise Capacity at AltitudeExercise Capacity at Altitude

• Aerobic capacity– Progressively decreases as altitude increases– 1-3.5% reduction Vo2 max every 300m

increase from 1500 m– Greater rate decline for trained athletes

• Circulatory factors– Decreased MHR and SV

Acclimatisation

• Adaptive responses to improve one’s tolerance to altitude

• 2 weeks to adapt to 2300 m

• Additional 610 m = 1 week

• Cellular adaptations– Increased capillary density– Increased mitochondrial densities

• Blood volume- – Plasma volume decreases– Erythropoietin released increase RBC

• Acid-base adjustment- Ambient air at altitude contains very little Co2- Affects gradient of o2/Co2 volumes- Combined with hyperventilation causes low

Co2 increased pH

Longer-Term AdjustmentsLonger-Term Adjustments

Altitude TrainingAltitude Training

• Acclimation to altitude improves one’s capacity to exercise at altitude

• However inability to train at equivalent intensity no improvement Vo2 max on return to sea level

Live High, Train Low

SummarySummary

• Environment critical to optimal performance

• Be aware of environment in case of negative effects

• Use to your advantage– Heat

• Humidity

– Cool– Pollution– Altitude