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Flashcards in Ex. Phys. Environmental Physiology Deck (18):

basic human responses to environmental stressors

-the environment presents stressors that disrupt homeostasis in our internal environment
-each type of environment requires a unique set of adaptive responses
-people may lack or have sufficient hereditary abilities to adapt to any or all environments
-people vary in how they respond to the same environmental stressor, which produces different outcomes
-environmental stressors can positively or negatively affect a person's ability to meet physical or psychosocial demands
-environmental stressors are strongly mediated by psychological factors
--if the stressors are not viewed as harmful or alarming, they may produce small or even opposite physiological responses
-physiological responses to environmental stressors at times can be excessive, inappropriate, inadequate, or disordered
-physiological behavioral changes sometimes occur before an environmental stressor has been applied


what is the necessary adaptation time to any environment
-time for deacclimation

8-14 days for most people
deacclimation within 14-28 days following removal from environment


variation in how people respond to stressors
-depends on

bodies may show no strain, illness, or injury
depends on
-level of tolerance developed
-immune system competence
-level of fitness
-number/intensity/type of previous exposures to an environmental stressor


what are excessive physiological stressors exaggerated by

other diseases and disorders (heart problems, arthritis, renal function)



many adaptive responses to different environments affect thermoregulation
hypothalamus plays a large part
heat transfer mechanism


hypothalamus functions

acts as a central monitoring system, but receives feedback from the peripheral system
sensitive to temperature changes in the blood
attempts to maintain a core temp. of 37C (98.6F "normothermic)
-too hot: hyperthermic
-too cold: hypothermic
initiates efferent feedback via the SNS to dissipate or conserve heat


heat transfer mechanisms

radiation: direct transfer of heat
convection: fluid (air/water) movement over skin
conduction: contact with skin
evaporation: sweat vaporization


exercise in the heat acute responses: how do you keep cool?

increases blood flow to skin via vasodilation of cutaneous arterioles conducts heat away from core to environment
sweating releases fluid to skin for evaporation
blood plasma volume typically decreases
retain H2O and NaCl via kidneys to offset fluid losses
hormones typically do not play a role in cooling


results of exercise in the heat

core temperature increases


what happens when humidity rises above 50-70%

effectiveness of evaporation decreases and skin stays hot (and flushed)


exercise in the heat exercise/performance implications

as core temp increases, performance typically decreases (CV function, muscular endurance, metabolic function, CNS drive, etc.)
-maximal strength appears to be unaffected
other negative effects include dehydration, heat exhaustion, cramps, and syncope


heat acclimation

sweating response improves: more sweat, faster onset, occurs at lower temperatures, more dilute to spare electrolytes
blood volume increases to lower exercise HR while maximizing skin blood flow
decreased core temperature (hopefully)
improved exercise tolerance (but dehydration is still a major hurdle)


acute responses to exercise in the cold: how do you keep warm?

SNS initiates skeletal muscle tremors (shivering) and thyroxin released from thyroid to increase basal metabloic rate (BMR) and core temp.
increased blood flow to core via vasoconstriction of cutaneous arterioles concentrates and conserves heat around vital organs
decreased max HR and Q
decreased dissociation of O2 from Hb
skin and hair trap air and warm it to create a boundary layer of insulation
decreased blood plasma volume due to some evaporative cooling
retain H2O and Na+ via kidneys to offset dehydration


cold exercise/performance implications

weight and awkwardness of clothes may conserve heat, but increase exertion
shivering increases VO2 at submax intensities and decreases motor coordination
decreased Q and O2 delivery with increased muscular demand increases reliance on anaerobic energy production, which shortens time to fatigue
increased risk of hypothermia and frostbite
increased risk of dehydration


cool acclimatization

more efficient thermoregulation capabilities
greater reliance on FFA due to Epi and Norepi release from SNS
reduced skin blood flow increases venous return, which increases SV
lower lactate production due to glycogen sparing effect of FFA use
cold may actually ease exercise effort


acute responses to exercise in thin air

O2 and CO2 relative proportions (%) do not change at higher altitudes, but air densities (quantity) (PO2, PCO2) decrease
resting and submax VE increase to maintain adequate Hb O2 saturation, which increases PAO2 and PaO2, decreases PvCO2 and PaCO2
decreases blood plasma volume and lower SV due to renal diuresis, increased VE, and increased evaporative cooling
increased resting and submaximal HR in order to increase Q and O2 transport to working muscles
reduced VO2max due to the aforementioned increases and greater reliance on glycolytic system


altitude exercise/performance implications

VO2max begins to decline around 1500m with additional 3% losses every additional 300m in altitude, but O2 cost of exercise remains the same as sea level
-short duration (<2 min), high intensity exercise appears to be unaffected at reasonable altitudes
if altitude becomes too high, too little work is accomplished during exercise to be useful
decreased total body water increased the risk of dehydration
risk of AMS, HACE, HAPE at altitudes above 2400m


altitude acclimatization

increased RBC density due to increased erythropoietin (EPO), which ultimately results in greater Hb levels of O2 loading and transport
increased 2,3-BPG: oxyhemoglobin curve shifts right (like the Bohr effect) to improve O2 unloading at muscles
decreased resting and submaximal HR
competition at altitude appears to be best improved
enough anecdotal and research evidence to back up the live high, train low philosophy
moderate elevations (1500-2200m) appear to be best for exercise performance and acclimatization