Final Exam Flashcards
thermal balance
Core temperature represents a dynamic equilibrium between factors that add and subtract body heat
Integration of mechanisms that alter heat transfer to periphery regulates evaporative cooling and varies heat production to sustain thermal balance
Core temperature rises if heat gain exceeds heat loss (i.e., during vigorous exercise in warm, humid environment)
Core temperature declines in cold when heat loss exceeds heat production
37 degrees Celsius, 98.6 degrees Fahrenheit
how is thermal balance controlled and how can exercise alter you ability to control body heat?
Primarily controlled during exercise through sweat, losing the ability to sweat is losing the ability to control our thermal balance
Trained individual can adapt to heat better due to an increase in plasma volume (allows sweating)
hyperthermia (heat stress)
an increase in deep internal body temperature above normal
heat stress challenges body to dissipate excess heat from working muscles during exercises
75% of energy from food is released as heat
thermoregulation (heat stress)
ability of body to maintain constant internal temperature
human body’s ability to maintain constant body temperature makes us homeotherms - able to perform in extreme environments
how does elevated heat/humidity affect body cooling?
increases challenge by blocking heat dissipation from body
thermoregulation
receptors in periphery & CNS detect temperature changes
periphery
receptors in & under skin, in peritoneal (abdominal) cavity
CNS receptors in:
brain stem
spinal cord
hypothalamus: acts like thermostat
hypothalamic control
hypothalamus contains coordinating center for temperature regulation
cannot turn of heat; initiates responses to protect from buildup or loss of heat
activation of heat-regulating mechanisms:
thermal receptors in skin provide input to central control center
changes in temperature of blood that perfuses hypothalamus directly stimulate this area
circulation
at rest in heat, heart rate and cardiac output increase while superficial arterial and venous blood vessels dilate to divert warm blood to body shell
evaporation
effective thermal defense exists when evaporative cooling combines with large cutaneous blood flow
hormonal adjustments
sweating produces loss of water and electrolytes, initiating hormonal adjustments to conserve salts and fluids (increased aldosterone and anti-diuretic hormone)
fluid loss
Evaporative cooling dissipates heat in exercise, placing a demand on fluid reserves, often producing hypohydration
Excessive sweating leads to serious fluid loss and reduced plasma volume
Competitive cardiovascular demands of exercise in heat:
Muscles require oxygen to sustain energy metabolism
Arterial blood that divert
as we dehydrate…
As we dehydrate, blood thickens.
Heart works harder, blood loses liquid portion and becomes thicker. Cannot deliver the oxygen to skeletal muscle.
Stroke Volume increases
cardiovascular drift
refers to increase in heart rate that occurs during prolonged endurance exercise with little or no change in workload
increase in heart rate due to dehydration without an increase in intensity
consequences of dehydration
Modest fluid loss of 2% body mass adversely affects exercise performance (40-50 minutes in warm environment)
Augmented hyperthermia
Increased cardiovascular strain
Altered metabolic and central nervous system functions
Increased perception of effort
As dehydration progresses and plasma volume decreases, peripheral blood flow and sweating rate diminish, making thermoregulation progressively more difficult
exercise in heat
submaximal exercise produces lower SV, causing higher HR at all submaximal levels
higher HR in maximal exercise does not offset SV decrease, so maximal cardiac output decreases
maintaining cutaneous and muscle blood flow requires other tissues to compromise blood supply
hyperhydration
ingesting “extra” water before exercising in the heat offers thermoregulatory protection
in reality, would have to urinate more often.
convection (mechanisms of heat loss)
air blows over surface of skin (or running water as with swimming)
fluid medium to cool
conduction (mechanisms of heat loss)
physical contact between 2 surfaces, such as sitting in a cold-water bath to treat heat stroke
gaining heat (or cool) from hot (or cool) surface
radiation
molecules in motion emit electromagnetic waves such as the sun
worse at altitude
only 4% of heat loss from radiation in hot environments (vs. 67% at normal temp)
evaporation
sweat on skin vaporizes, taking heat with it. Risk of dehydration
convection and evaporation work together
Three factors influence total amount of sweat vaporized from skin and/or pulmonary surfaces:
Surface exposed to environment
Temperature and relative humidity of ambient air
Convective air currents about the body
Relative Humidity…
most important factor determining effectiveness of evaporative heat loss
ratio of water in ambient air to total quantity of moisture that air could contain
in humid environment, less convection and evaporation
countermeasures (clothing)
Physiologic adaptations can only protect an individual to a certain degree
Designed to protect against environmental stressors
Technological advances for both cooling and keeping you warm in microclimates
circulatory and metabolic responses to heat stress
Heat increases heart rate & cardiac output (sub-maximal activity, decreased at maximal exercise)
Redirects circulatory flow to periphery to:
Dissipate heat
Cool blood
Reddens skin
Flushes complexion
body composition (influence of body composition and physical fitness level)
Larger body mass = greater heat production
Ratio of body volume (generate heat): body surface area (dissipate heat) less favourable in some NFL players
Body fat insulates, makes heat loss more difficult
Adipose tissue decreases ability to dissipate heat
fitness level (influence of body composition and physical fitness level)
Hot environments require redistribution of blood from core and muscle to periphery to dissipate heat
Greater fitness = greater cardiac output
Greater cardiac output = improved ability to redistribute blood from muscle and dissipate heat
Age:
More body fat
Decreased ability to tolerate and dissipate heat
korey stringer
core temp reached 108 degrees
died from heat stroke
brain turned to “mush”
heat cramps
muscle cramps that occur when one is exposed to heat
triggered by intense exercise
characterized by painful, involuntary muscle contractions
heat cramps result from
dehydration - lose plasma volume & sodium
electrolyte imbalance, specifically whole-body sodium deficit
neuromuscular fatigue
syncope
fainting or “passing out”
often occurs when sitting or standing or after an activity in heat, dizziness or lightheadedness may occur beforehand
more common when individuals have not be acclimated or acclimatized
need adequate cool down
syncope is caused by:
Excessive peripheral dilation
Pooling of blood in legs, reducing venous return
Dehydration
Reduction in cardiac output
Brain ischemia
heat exhaustion
typically occurs in hot & humid environments
confused with exertional heat stroke
fluid loss decreases SV, decreasing cardiac output
heat exhaustion is caused by:
heavy sweating
dehydration
sodium loss
energy depletion
exertional heat stroke (EHS)
medical emergency: can lead to death if not treated quickly (temp above 109)
body loses its ability to cool itself
failure to dissipate heat after intense exercise
termoregulatory center is overwhelmed, leading to stroke
core temp above 104 degrees
exertional heat stroke treatment
rapid cooling of body
ice bath, cold compress
cool blood where major arteries are (head, neck, armpits, groin area, back of knees)
complications of exertional heat stroke
Lactic acidosis
Acute renal failure
Rhabdomyolysis (destruction of muscle tissue releasing proteins into blood)
Bleeding disorders
Death
Treatment: immediate, rapid cooling preferably in ice water bath; monitor temperature with rectal thermometer
fitness level (factors affecting heat illness)
Greater fitness = less susceptibility to heat illness
Carefully consider fitness before engaging in activity in heat
Cardiovascular fitness should be primary focus of conditioning
age (factors affecting heat illness)
Cardiovascular function declines with age
Decline in cardiac output with age reduces tolerance to heat
Heat acclimatization is possible
endurance performance in the heat
as heat increases, performance declines
measures to ensure optimal performance
Prior acclimatization (go to where you’re going to be competing) or acclimation (use to environment you’ll be competing in through artificial means)
Proper hydration
Physical conditioning (actual temperature, relative humidity, cloud coverage, and non/prevelance of wind)
wet-bulb globe temperature (WGBT)
a composite temperature used to estimate the effect of temperature, humidity, and solar radiation on humans
depends on duration of event & duration of heat exposure (anaerobic & strength performance in the heat)
Limited exposure in shorter activities may not affect performance at all (100-m track)
Longer events are more likely to affect performance (1500-m track) and predispose to heat illness
Hypohydration does reduce strength, power, and muscular endurance
anaerobic & strength performance in the heat improved by:
cooling methods
hydration
limiting of exposure to heat
acclimation
physiological adaptation to an artificial environment
acclimatization
physiological adaptation to a natural environment
takes bout 2 wks to adapt to altitudes up to 2300 m (7500 ft); after, each 610-m increase requires 1 extra wk
adaptions dissipate within 2-3 wks after returning to sea level
time course of adaptations: cardiovascular system
1-5 days (plasma volume, reduced heart rate at workload, improved blood flow)
time course of adaptations: temperature regulation
5-8 days (sweat rate, sweat at lower temperatures, sweat gland adaptations)
time course of adaptations: conservation of sodium chloride
3-9 days (losses from urine and sweat decrease)
time course of adaptations: all adaptations
up to 14 days (increased heat loss, decreased core & skin temp, decrease VO2 at workload, improved exercise economy)
Adaptations lost after 2.5 to 5 weeks out of heat
cold receptors in body
Monitor change & rate of decrease in temperature
Signal many different actions to occur
Are fewer in number than heat receptors
Are found in the skin, abdominal viscera, & spinal cord
bodys defense against cold
Vasoconstriction of blood vessels in skin
Decrease sweating
Release thyroid hormones to increase metabolism and heat production
Shivering of skeletal muscle
Epinephrine: increase metabolism; norepinephrine: increase vasoconstriction
Hair stands up to increase insulation (less effective in humans)
Decreased blood flow to skeletal muscle (unless physical activity increases)
Curling up to preserve core heat, seeking shelter, finding heat sources, eating, putting on additional clothing
hypothermia
decrease in bodys temperature to a point that normal physiological function is impaired
hypothermia stage 1
body temp 1 to 2°C below normal
Loss in ability to perform complex motor tasks
Breathing becomes rapid & shallow
hypothermia stage 2
body temp 2 to 4°C below normal
Neuromuscular function is affected
hypothermia stage 3
body temp below 32°C
Body systems shut down, organs fail, brain dies
afterdrop
the continued fall of deep body temperatures during rewarming after hypothermia
performance responses to cold
Reductions in neuromuscular activity
Reduction in nerve conduction velocity, or rate that neural impulses travel to muscle fiber
Reduction in force production (except possibly eccentric actions, but only with mild cooling)
Diminished power output
Decreased heart rate at given workload
Decreased time to peak power
physiological adaptations of acclimatization/acclimation
vasodilation in response to high altitude cold exposure
higher basal metabolic rates (Eskimos)
barometric pressure (Pb)
760 mmHg at sea level
partial pressure of oxygen (PO2)
portion of Pb exerted by oxygen
0.2093 x Pb ~ 159 mmHg at sea level
reduced PO2 at altitude limits exercise performance
hypobaria
reduced Pb seen at altitude
results in hypoxia (partial pressure of O2 is reduced)
stress of altitude
Altitude’s physiologic challenge comes directly
from decreased ambient Po2
O2 transport cascade refers to progressive changes in environment’s O2 pressure and bo
other challenges with altitude
Increased cold with increased altitude
Dehydration induced by cold (which has lower water vapor than warm air, increases loss of water - particularly when paired with physical exertion)
Increased solar radiation (decreased distance and thinner atmosphere above individual) – vitamin D production, sunburn, DNA damage, skin cancer
cardiopulmonary responses
Hyperventilation from reduced arterial Po2 reflects the most important and clear-cut immediate response of native low-landers to altitude exposure
Resting blood pressure increases in early stages of altitude adaptation
Increases in H.R. and Q
fluid loss
Ambient air in mountainous regions remains cool and dry, allowing body water to evaporate as inspired air becomes warmed and moistened in respiratory passages
Respiratory water loss, urine production (Lose up to 25% plasma volume)
Fluid loss becomes pronounced for physically active people because of large daily total sweat loss and exercise pulmonary ventilation
catecholaimne response
Sympathoadrenal activity progressively increases over time during rest and exercise with altitude
increased BP & HR at altitude relate to steady rise in plasma levels and excretion rates of epi
increased sympathoadrenal activity contributes to regulation of BP, vascular resistance, & substrate mixture during short & long-term hypobaric exposures
hematologic alterations
Increase in blood’s oxygen-carrying capacity provides important longer-term adjustment to altitude exposure
two factors account for hematologic alterations
initial decrease in plasma volume
increase in erythrocytes and hemoglobin synthesis
cellular adaptations
Remodeling of capillary diameter and length with formation of new capillaries
Improved microcirculation to reduce oxygen diffusion distance between blood and tissue
Increased myoglobin (augments O2 storage)
Small increase in mitochondrial number and concentration
Slight right shift of oxy-hemoglobin dissociation curve (more unloading)
Increased 2,3-DPG concentration
Increased EPO
body mass & composition
Basal metabolic rate
Increased Thyroxine secretion
Increased Catecholamine secretion
Must increase food intake to maintain body mass
More reliance on glucose versus fat
Anaerobic metabolism= increased lactic acid
Lactic acid production decreases over time
No explanation for lactate paradox
sport performance
Aerobic exercise performance affected most by hypoxic conditions at altitude
VO2max decreases as a percent of sea level VO2max
Given task still has same absolute O2 requirement
Higher sea-level VO2max —> easier perceived effort
lower sea-level VO2max —> harder perceived effort
live low, train high (LLTH)
has little to no enhancing benefit
Wilbur 2007 - small # of significant improvement in blood parameters, aerobic capacity, or work performance
blood doping
Increasing the number of red blood cells either by transfusion or by the use of erythropoietin (EPO) to boost the production of red blood cells; typically not permitted and of unknown efficacy
450-1800 ml of blood taken usually 12-16 weeks prior to event
Re-infused about a week before event
