Polar Opposites: Effects of Thermal Stress on Physiology and Performance

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Polar Opposites Effects of Thermal Stress on
Physiology and Performance

• Stephen S. Cheung, Ph.D.
• Associate Professor
• Dalhousie University

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Appeals of Environmental Research

• Pushing the human envelope
• Direct application of research
• Lab work is fun!

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Convergence of Basic /Applied Science

• Hydration
• Cardiovascular control
• GI/Renal physiology
• Sports drinks
• Cold-Shock
• Respiratory control
• Offshore survival

• Hyperthermia fatigue
• Thermoregulatory control
• Exercise heat waves
• Cold cognition
• Information processing
• Search rescue

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Convergence of Disciplines

• Physiology
• Psychology
• Ergonomics
• Engineering
• Mathematics

• Health and safety
• Training
• Policy

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EEL Research Themes
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Sudden Cold Water Immersion
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Real Breath-hold Capacity

• Breath-hold capacity of actual offshore
  population
• Actual offshore population (n 228)
• Warm water (25oC)
• Ideal conditions
• Breath-hold ltltlt Requirement!
• 10-120 s range
• 37 s mean, 39 median

Cheung et al. 2001
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Need for Supplemental Air!

• Conclusions
• Offshore population DO NOT possess adequate
  breath-hold capacity to ensure reasonable
  survival probability in helicopter ditchings
• End Result
• Natural Resource Council new policy requiring
  supplemental air source for all marine helicopter
  passengers

Brooks et al. 2000, Cheung et al. 2001, Brooks
and Cheung 2001
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HYPOTHERMIA
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Manual Dexterity in Cold

• Need for insulation AND dexterity
• Rapid time course of impairment (Cheung et al.
  2003)
• Thermal monitoring in non-uniform thermal
  environments (Thornley et al. 2003)

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Rewarming from Hypothermia

• Cranial/Neck rewarming
• High blood flow
• High heat loss site
• Targeting brain rewarming
• Minimise afterdrop from skin rewarming
• Maintain shivering

Wright M.Sc.
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Thermal Stress Cognition
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Mental Cognition Thermal Stress

• Rethinking of thermal stress limits? (Hancock
  1998)
• Task performance critical criterion, not
  physiological tolerance
• Merging of physiological psychological
  parameters vital

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Tea, anyone?
Richardson M.Sc. 2002 Richardson et al.
(Submitted)
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Current / Future Work

• Vigilance spatial attention
• Body cooling (Cheung et al. Submitted)
• Body heating (Marsh B.Sc.K.)
• Cold distraction (Ojah B.Sc.K.)

• Hypothermia navigation/mapping (Payne M.Sc.)
• Search Rescue
• Hyperthermia on cognition (Flouris Ph.D.?)
• Effects of age
• Effects of fitness
• Immunology
• Pharmaceutical countermeasures?

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Exercise-Heat Stress
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Critical Internal Temperature Hypothesis
Effects of hydration, fitness, heat acclimation
on heat tolerance during uncompensable heat stress
Consistency of Tre at fatigue Effect of fitness
Cheung McLellan 1998
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Heat Stress and Exercise

• Direct effect of temperature on exercise
  performance
• Ambient temp (Galloway Maughan 1997)
• Core temperature (Gonzalez-Alonso et al. 1999,
  Gregson et al. 2002)
• Heat storage (Gonzalez-Alonso et al. 1999)
• Pacing (Marino et al. 2004)

• Fatigue from a variety of mechanisms
• Cardiovascular collapse
• Hydration fluid imbalance
• Endotoxemia
• Psychological

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Pre-cooling as Ergogenic Aid

• Effective with endurance exercise
• ? physiological strain (Lee and Haymes 1995)
• ? 30 min run distance (Booth et al. 1997)
• Head pre-cooling (Palmer 2002)
• Effective pre- and during prolonged running
• Benefits to sprinting? (Cheung Robinson 2004,
  Duffield et al. 2003, Sleivert et al. 2001, Drust
  2000)
• Cooling of active muscle?
• Confounding with warmup?

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Ongoing Work

• Microclimate cooling
• Thermal Control Suit
• Pre-cooling strategies
• Endurance exercise
• Sprinting exercise (Cheung Robinson 2004)
• Endotoxemia and immunological response (New
  Zealand)

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EEL Summary

• Effects of thermal stress on physiology
  performance
• Fundamental science application of research
• Athletic
• Occupational
• Equipment design

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Thanks for your time!
Stephen S. Cheung, Ph.D. stephen.cheung_at_dal.ca 902
-494-6499