s2 w9 exercise in the heat

process of heat loss

radiation

conduction

convection

evaporation

process of heat gain

metabolic heat

environmental heat (conduction, convection and radiation)

physiological responses to exercise in the heat

thermoregulatory control by preoptic anterior hypothalamus-thermoreceptors detect changes

vasodilation and sweat response

CV function: Increased cardiac output, decreased stroke volume—> increased HR (CV drift)
heart cannot provide sufficient blood flow to heart and skin, decreased performance

sweating leads to decreased blood volume and decreased cardiac output

heat adaptation

hot baths

warm weather camps

heat chambers

potential dangers of exercising in the heat

in extreme conditions core temperature will continue to ris despite compensatory mechanisms

In severe cases exertional heatstroke (EHS)occurs (>40.5°C) – can ultimately lead to death if not treated correctly​

heat cramps-muscle cramps, sweating

heat exhaustion-nausea

heatstroke-no sweating

treatment for heat related illness

Measuring heat stress can assess the conditions​

cold water immersion most effective

strategies employed by sports when athletes exercise in the heat

consider cancellation >28 degrees

practice early mornings/late night

breaks in play

minimise amount of clothing worn

education about EHS

heat acclimation

temperature monitoring

alert levels

reasons for exercising in the heat

climate change

location of events

more likely to get medals at a higher core temp

measuring body temperature

• core temperature – Tc​

• Skin temperature – Tsk​

• Whole body sweat rate​

• Local sweat rate​

• HR​

• VO2/ VCO2​

• Plasma volume changes​

• Performance​

• Thermal comfort​

• RPE​

• Blood flow​

body temperature regulation

temperature maintained in a narrow range-36.1-36.8)

extreme cases cause body temperature to deviate from the normal range-exercise, fever, hot/cold conditions

performance in the heat

8 males cycled to exhaustion at 70% max

inverted U with best performance at 11 degrees

Fatigue at 31°C not substrate dependent + decreased temp gradient​

4°C – reduction in mechanical efficiency?

worst performance at 31 degrees

running

performance improves in sprint events

no difference in middle distance events

performance decreases in long distance events

conditions that decrease time to exhaustion

heat

humidity

solar radiation

fluid intake and core temp

montain and coyle 1992

8 trained cyclists for 2 hours at 62-67%

large fluid attenuated hyperthermia

-increased skin blood flow

Fluid intake maintains or reduces the decrease in plasma volume arising from fluid lost as sweat​

• Helps maintain stroke volume and cardiac output ​

• Therefore maintain or preventreduction in performance​

heat acclimation

Physiological changes occur over a short period of time​

• a period of heat acclimation athletes can become develop beneficial physiological changes and adaptations that may help maintain or prevent reductions in performance​

• The heat acclimation period can vary in duration, methods, intensity​

• Often performed before competitions or military deployment​

5 days after, increased plasma volume, decreased heart rate, steady thermal comfort

sweating rate and exercise capacity stabilises at 11-12 days

heat acclimatisation

Physiological changes as a result of living in a hot climate for months/years​

methods of heat acclimation

Isoprogressive​- Maintaining Tc =38.5°C​

Fixed duration​ e.g. 90 min in heat at50% VO2peak​

Exercise until a Tc reached e.g. 38.5°C​

short term​ e.g. 5 days​

Long term​ e.g. 14 days​

Repeat baseline testing​ e.g. heat stress test​ 30 min monitoring T