ENVIRONMENTAL INFLUENCES ON PERFORMANCE

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ENVIRONMENTAL INFLUENCES ON PERFORMANCE

• Thermal Regulation And Exercise Mechanisms of
  Body Temperature Regulation
• The heat from deep of body (core) is moved by
  blood to the skin (the shell).
  From there transferred to the
  environment by conduction, convection,
  radiation, evaporation

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• Conduction, convection - heat loss 10 - 20
  percent
• Radiation - 60 percent during rest (infrared,
  electromagnetic waves)
• Evaporation - 80 percent of heat loss during
  exercise
• Heat production at rest - 1,5 kcal of heat/min.
  at exercise - 15 kcal/min.
• Humidity
• high - limits sweat evaporation and heat loss
• low - ideal for sweat evaporation and heat loss.
  

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Control of Heat ExchangeHypothalamus
- Bodys Thermostat

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• Thermoregulatory center - hypothalamus Two sets
  of thermoreceptors central -hypoth. peripheral -
  in skin (temperature around the body) impulses to
  hypoth. and cerebral cortex - consciously
  perceive temperature - voluntary control exposure
  to heat or cold.

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• Effectors Altering Body Temperature
• Sweat glands, smooth muscles around arterioles,
  skeletal muscles, endocrine glands (thyroxin,
  epinephrine)

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Physiologic Responses to
Exercise in the Heat

• Exercise in Hot Enviroment
• Competition between active muscles and skin for
  limited blood supply muscles - blood and oxygen
  for sustain activity,
• skin - blood to facilitate heat loss to keep the
  body cool.

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• Cardiovascular Response
• Adjustement - ? blood volume returning
  to the heart -? end. diastolic volume
  - ?SV - compensation - gradual
  upward drift in HR ? cardiovascular drift.
• Energy Production
• Exercise in hot enviroment - ? O2 uptake, use of
  more glycogen, produce more lactate - earlier
  fatigue and exhaustion

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• Body Fluid Balance - Sweating
• Sweat - filtration of plasma. Reabsorption of Na
  and Cl in passing through the duct.
• Increased sweat rates - quick movement, less time
  for reabsorption - loss of natrium and chloride -
  with training - aldosterone stimulates for more
  reabsorption of Na, Cl . Sweat production in
  hot - 1l/HR/m2 - 2 - 4 percent of
  body weight ? ? blood volume - dehydration.
  Triggering aldosterone, ADH ?? Na excretion in
  kidneys ADH - water reabsorption in kidneys ?
  fluid retention.

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HEALTH RISKS DURING EXERCISE IN THE HEAT

• Heat Stress - reflected not only by air
  temperature, further variables take into account
  humidity, air velocity, amount of radiation.
• Heat-related Disorders
• 1) Heat Cramps
• Involving muscles heavily used during exercise,
  brought on by mineral losses and dehydration
  accompanying high rates of sweating.
• 2) Heat Exhaustion
• Symptoms fatigue, dyspnea, dizzines, vomiting,
  fainting, clammy, or hot dry skin, hypotension,
  weak, rapid pulse - causeCV systems inability
  to adequately meet the bodys needs. Treatment -
  rest in cooler enviroments, feet elevated, salt
  water.

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• 3) Heat Stroke - Life - Threatening Disorder
• CHARACTERISTICS ? internal body temperature ?
  40oC, cessation of sweating, hot, dry skin, rapid
  pulse and respiration, hypertension, confusion,
  unconsciousness.
• CAUSE failure of thermoregulatory mechanism
  Treatment - cooling body in a bath of cold water
  or ice, or wrapping the body in wet sheets and
  fanning.

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• Prevention of Hyperthermia
• Cancel training or competition if the
  environmental heat stress to high, wearing proper
  clothing, being alert to signs of hyperthermia,
  ensuring adequate fluid intake.
• Heat Acclimatization
• Exercise in the heat for up to an hour each day
  for 5 to 10 days. CV changes occur in the first
  3 - 5 days, sweating mechanisms take
  longer, up to 10 days. Heat acclimatization - ?
  the rate of muscles glycogen use, delaing fatigue.

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EXERCISE IN THE COLD

• Cold Stress - environmental condition causing
  loss of body heat threatening
  homeostasis, two major cold stressors air and
  water. Primary means CONSERVING BODY HEAT
  activated by hypothalamus
• SHIVERING - ? 4 - 5 fold increase resting heat
  production
• NONSHIVERING THERMOGENESIS - ? metabolism
  by sympathetic nervous s. - ? internal
  heat production
• PERIPHERAL VASOCONSTRICTION - sympathetic
  stimulation smooth muscles in arterioles - ? heat
  loss metabolism of skin cells - ? less O2
  requirement

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FACTORS AFFECTION BODY HEAT LOSS

• a) Body Size And Composition
• - subcutaneous fat - more fat mass - conservation
  heat more efficiently
• - ratio of body surface area to body mass. ?
  ratio - lower susceptibility to hypothermia
• - gender - defferences minimal
• b) Windchill
• Wind - increase the rate of heat loss via
  convection and conduction

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Heat Loss in Cold Water

• Water - thermal conductivity 26 times greater
  than air. The body loses heat 4 x faster in water
  than in air of the same temperature.
• Internal bodys temperature remain constant at
  temperature down to 32oC. Exposure to water at
  15oC - decrease of rectal t. at 2.1oC/hour, at
  4oC - decrease at 3.2oC/Hr. Heat loss further
  increased - water moving. Survival in cold water
  brief - consciousness lose in minutes. Long -
  distance swimmers - subcutaneous fat important
  role - obese subjects swim for 6 h 50 min. in
  water 11.8oC with no change in rectal temp.
  Swimmers with low body fat - 30 min - discomfort,
  rectal t. drop to 33.7oC.
• FOR COMPETITION, water temp. between 23.9oC -
  27.8oC seem appropriate.

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Physiological Responses to exercise in cold

• When muscle is cooled, it is weakened and fatigue
  occurs more rapidly. Prolonged e.
  in cold, as energy supplies diminish and e.
  intensity declines, susceptibility to hypothermia
  increaes. E. in cold - vasoconstriction ? ?
  circulation to subcutaneous fat - decrease of FFA
  for fuel.

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HEALTH RISKS DURING EXERCISE IN COLD

• Hypothermia
• Decrease of body t. down bellow 34.5oC,
  hypothalamus lose ability to regulate t.
  Completely lost at 29oC - drowsiness and coma.
  Hearts SA-node - drop of HR - ? CO. Breathing
  cold air does not freeze the respiratory passages
  of the lung. Respiratory rate? , MV ?.
• Frost Bite - vasoconstriction to the skin -
  reduced blood flow, skin cooled. Lack of O2 and
  nutrients - skin tissue death.

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• Treatment
• Hypothermia - dry clothing, warm beverages, slow
  rewarming, hospital treatment. Frostbite - left
  untreated until can be thawed, best
  in a hospital.
• Cold Acclimatization
• Chronic daily exposure to cold water increase
  subcutaneous fat. Repeated exposure to cold -
  alter peripheral blood flow and skin temperature
  - greater cold tolerance.

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EXERCISE IN HYPOBARIC, HYPERBARIC AND
MICROGRAVITY ENVIRONMENT

• A Hypobaric environment
• Altitude presents a hypobaric environment.
• The ATMOSPHERIC PRESSURE is reduced, altitudes
  more than 1,500 m notable impact on human body.
  Reduced PO2 - decreased performance at altitude
  (? pressure gradient - hinders oxygen transport
  to tissues).

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• Air Temperature
• Drops as altitude increases, cold air - hold
  little water - dry air - ? susceptibility to cold
  related disorders and dehydration.
• Solar Radiation - more intense (thinner
  atmosphere, drier air)

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• Physiological response to altitude
• ? Pulmonary ventilation both at rest, exercise
  respiratory alkalosis (? CO2 elimination, kidney
  excrete more bicarbonates - more acids in blood -
  compensation for alkalosis) hemoglobin saturation
  drops from 98 percent to 92 percent at height
  2,439 m.
• PO2 gradient arterial blood - tissue drops from
  74 min Hj (94 - 20 ? 74) to 40 min (60 - 20 ?
  40) at 2,439 m height.
• VO2 max decreases as altitude increases.

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• Plasma Volume decrease - ? red blood cells
  concentration - more O2 transport
• COINCREASE by increase of HR.
• During maximal work - SV, HR decrease
• CO DECREASE - ? O2 delivery and uptake.
• Oxidative capacity decreased, anaerobic energy
  production increase - ? blood lactate level.
  Hypoxic vasoconstriction in pulmonary arteries ?
  PULMONARY HYPERTENSION
• ENDURANCE ACTIVITY - most limited - oxidative
  energy production decreased.
• Anaerobic SPRINT ACTIVITIES ? 1 MIN - not
  limited.
• Thinner air - less resistance to movement (long
  jump record 1968 at Olympic games in Mexico city)

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Altitude Training

• Hypoxic conditions - ? release of erythropoetin -
  INCREASED RED BLOOD CELL PRODUCTION - increase
  blood oxygen - carrying capacity. Advantage
  during first few days after returning
  to sea level.
• Athletes who must perform at altitude - train at
  altitude of 1,500 - 3,000 m
• FOR AT LEAST 2 WEEKS prior to performing
  (adaptations to hypoxic and other environmental
  conditions at altitude).

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CLINICAL PROBLEMS OF ACUTE EXPOSURE TO ALTITUDE

• Altitude (Mountain) Sickness
• Symptoms headache , nausea, vomiting, dyspnea,
  insomnia
• Appear - 6 - 96 HR after arrival
• Cause - probably accumulation of CO2 in tissues
• Prevention - gradual ascent, no more than 300 m
  per day above 3,000 m
• Treatment - acetazol amide, dexamethazone,
  retreat to lower altitude

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• High Altitude Pulmonary Edema (HAPE)
• Symptoms dyspnea
• Treatment Retreat, oxygen
• High Altitude Cerebral Edema (HACE)
• Mental confusion, coma, death.

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B) HYPERBARIC CONDITIONS - EXERCISING UNDERWATER

• Submersion in Water
• Exposal to hyperbaric conditions -volume
  decreases when pressure increases.

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• More molecules of gas are forced into solution,
  with rapid ascent, they come out of solution and
  can form bubbles - emboli develop, block major
  vessels, extensive tissue damage.
• Resting HEART RATE DECREASES by 5 - 8 beats per
  minute (facilitation blood return to the heart)
  diving in cold water - greater bradycardia,
  higher incidence of arrhythmias

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• BRETH-HOLD DIVING. Hyper ventilation used
• (? PaCO2), dangerous (? PaO2 - lose conscious
  ness under water). Volume of air can be reduced
  to RV, but no smaller.
• TLV/RV - limit the possible diving depth large
  TLV/RV - deeper diving
• SCUBA DIVING - inhaled gas pressurized, equal to
  that of water. Deeper dives ? greater air flows,
  less time to exhaustion of the tank exhaustion.

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Health Risks of Hyperbaric Conditions

• 1) Oxygen Poisoning
• Visual distortion, rapid, shallow breathing -
  convulsion. PO2 ? 318 mm Hg - constriction of
  cerebral vessels.
• 2) Decompression Sickness
• Nitrogen bubbles in circulation and tissues -
  attempt to rapid ascent. Symptoms pain in
  elbows, shoulders, knees. Treatment - placing in
  RECOMPRESSION CHAMBER

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• 3) Nitrogen Narcosis
• Symptoms - impaired judgement, similar to
  alcohol intoxication (for every 15 m increase in
  depth ? 1 Martini on an empty stomach).
• 4) Spontaneous Pneumothorax
• Expansion of air in lungs during ascent, over
  distension - rupture of aveoli.
• 5) Ruptured Eardrum
• Inability to equalize the pressure in the middle
  ear - force against eardrum - pain, rupture

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C) MICROGRAVITY ENVIRONMENTS, EXERCISE IN SPACE

• Physiological changes during extended periods
  exposure to microgravity similar to those with
  detraining in athletes and in aging population.
  Weight bearing bones, antigravitational muscles
  are unloaded - reduced ability to function -
  similar effects in CV system. Strength and
  cross-sectional area of SA AND FA FIBERS
  DECREASE. BONE MINERAL DENSITY DECREASES
  approximately 4 from the weight bearing bones.

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• Microgravity results in bodys dumping
  a large percentage of plasma volume -
  ORTHOSTATIC HYPOTENSION ON RETURN to earths
  atmosphere. Exercise - most effective counter -
  measure during space flight for successful
  adaptation on return to earth.