- The body limits hyperthermia through skin blood flow, etc.
- In heat, the body rises to the metabolic challenge through adaptation.
- Cardiac output rises to meet the demands of heat, but the heart cannot meet the maximal demands of cooling AND exercise without limits. Blood pressure is maintained at the expense of all else. Training will suffer before cardiac output.
- Heat acclimatization has many benefits, but primary among them is reduced risk of heat illnesses.
- Acclimatization: Repeated exposure to a naturally hot environment during exercise.
- Acclimation: Improved ability to exercise in heat due to repeated exposure in an artificially created environment.
- Adaptation: Long-term adjustments made physiologically to adapt to heat.
- HA=Heat Acclimatization.
- Most HA factors plateau within 6-9 days after exposure to a hot environment.
- All adaptation is complete within 14 days.
- Variables influenced by HA:
- Heartrate goes down
- VO2 Max goes up.
- Blood Plasma volume goes up.
- Skin blood flow goes up.
- Sweatrate goes up in 8-14 days.
- Core temperature at the onset of sweating goes down.
- Skin temperature goes down.
- Decreased risk of heat illness.
- Applications to Sport:
- Acclimate for 7-10 days if possible.
- If 7-10 impossible, 5 days will give 90% of the benefits.
- Take 1-2 days to re-acclimate if out of the environment for a short period.
- In high school, give less talented runners MORE time to acclimate.
- The Golden Guidelines for Heat Acclimatization:
- Reduce the time and intensity of warm-up.
- Some HA is better than none.
- Gradually increase the time and intensity of exercise in heat.
- HA is best facilitated at 50% of VO2 max (60% in elite athletes).
- HA will improve performance in cold weather through improved exercise economy.
- Assure proper sodium (Na) initially.
- Put hardest workouts in the AM or PM.
- Moderate and easy workouts in hottest heat.
- Once HA is achieved, then increase intensity in the heat.
- Adjust practice and hydration according to sweatrate.
- Know temperature and humidity of your race location.
- Arrive 6 weeks before competition if it is your livelihood, 10 days if it is important, and 4-5 days before if time milts you.
- Underestimate your ability in heat.
- Avoid fatigue (loss of sleep, dehydration, etc.) during HA.
- Untrained athletes HA more slowly.
- Stay well-hydrated throughout HA.
- Be aware of individual differences in HA.
- Acclimatization (natural) is preferable to acclimation (artificial) if possible.
- Minimize clothing during HA.
- Fitness accounts for 50% of response to heat, HA the other 50%, so get fit first.
- Watch for heat illness in high-risk athletes.
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