Prentice Ch. 6 - Environmental Considerations Flashcards
Hyperthermia
elevated body temperature
metabolic heat production
the higher the metabolic rate, the more heat produced
heat can be gained or lost though:
- metabolic heat production
- conductive heat exchange
- convective heat exchange
- radiant heat exchange
- evaporative heat loss
Conductive Heat exchange
physical contact with other objects can result in either a heat loss or a heat gain
ex. standing on turf
Convective heat exchange
occurs when a mass of either air or water moves around an individual, body heat is either lost or gained
ex. cool wind
Radiant Heat Exchange
radiant heat from sunshine causes an increase in body temperature
- during exercise the body attempts to dissipate heat produced by metabolism by dilating superficial arterial and venous vessels thus channeling blood to the superficial capillaries in the skin.
Evaporative Heat Loss
sweat glands in the skin allow water to be transported to the surface, where it evaporates, taking large quantities of heat with it.
Rate of sweat
- normal person can sweat off about 1 quart of water per hour for about 2 hours.
- however, certain individuals can lose as much as 2 quarts of water (4 lbs) per hour
- sweat must evaporate for heat to be dissipated
Impairing heat loss
it is impaired when relative humidity reaches 65% and virtually stops when the humidity reaches 75%
Prevention of hyperthermia
- appropriate hydration
- unrestricted fluid and electrolyte replacement
- gradual acclimatization
- identification of susceptible individuals
- appropriate uniforms
- weight records
- monitoring of the heat index
Hydration
- ingesting sufficient fluids in the 24 hrs before exercise
Mild Dehydration
- loss of less than 2% of body weight
- rehydrate with sports drink/water
- fluid intake should = fluid loss
sweat loss/fluid replacement
- normal sweat loss for a person doing an hour of exercise ranges between 0.8 and 3L with an avg. of 1.5L/hr
- once body weight drops to 1-2% the individual becomes thirsty
- by the time thirst develops the body is already slightly dehydrated
- most people replace only 50% of the water they lose
Electrolyte replacement
- well formulated sports drink is more effective than using water alone
Why is water a bad rehydrator
- water is a good thirst quencher but it is not a good rehydrator because it turns off thirst before the body is completely rehydrated
sports drinks best formulation
14g per 8oz of water of carbohydrate (6% carbohydrate) produces the quickest fluid absorption
Gradual Acclimatization
- a good preseason conditioning program started well before the advent of the competitive season and carefully grades as to intensity is recommended
Gradual Acclimatization timeline
- 7-10 days
- the first 5-6 days an 80% acclimatization can be achieved by 2 hr practice period in the morning & in the afternoon
practice breakdown
20 mins of work with 20 mins of rest in the shade
Identifying susceptible individuals
- overweight/large muscle mass
Selecting appropriate uniforms
- should be selected on basis of temperature and humidity
- initial practices should be in t-shirts shorts and socks
- move gradually into short-sleeved net jerseys & lightweight pants
Maintaining weight records
- weights should be measured both before and after practice for at least the first 2 weeks of practice or as long as hot, humid conditions persist
- a loss of greater than 2% of body weight indicates that the athlete is severely dehydrated and should be held out of practice until normal body weight has returned
WGBT
- wet bulb globe temperature
- provides the ATC with an objective means for determining necessary precautions for practice and competition in hot weather
Dry bulb temperature (DBT)
- recorded from a standard mercury thermometer
Wet bulb temperature (WBT)
- recorded from a wet wick or piece of gauze wrapped around the end of a thermometer that is swung around in the air
Globe Temperature (GT)
measures the suns radiation and has a black metal casing around the end of the thermometer
WGBT equation
WBGT = 0.1 x DBT + 0.7 x WBT + GT x 0.2
Equation for only WBT & DBT
WBGT = 0.3 x DBT + 0.7 x WBT
Psychrometer
- two identical thermometers - when cloth is soaked the thermometers are properly ventilated
- the wet bulb temp will be lower than the dry club because of the cooling due to the evaporation of the water from the cloth
- takes around 90 seconds
- old sling psychrometer may have the greatest accuracy
Heat Rash
- also called prickly heat
- benign condition
- sensations of prickling and tingling during sweating
- usually occurs when the skin is continuously wet with unevaporated sweat
- localize to areas covered with clothing
- continually toweling the body can help prevent the rash from developing
Heat Syncope
- also called heat collapse
- rapid physical fatigue during overexposure to heat
- occurs from by standing in heat for long periods or by not being accustomed fro exercising in the heat
Heat Syncope cause
- caused by vasodilation of superficial vessels, hypotension or a pooling of blood in the extremities which results in dizziness, fainting and nausea
Heat Syncope relief
- laying athlete down in a cool environment, elevating the lower extremities and replacing fluids