2
Topics related to environmental
concerns...
• Science of temperature regulation
• Reducing the risk of heat illness
• Maintaining hydration
3
Heat Illness is Preventable
• Heat illness can significantly reduce level of performance
• Heat stroke: the most severe form of heat illness
4
Heat Illness is Preventable
• Athletic trainers must guard against dehydration & heat illness
• Comprehensive knowledge is critical
5
Science of Temperature Regulation
• Heat regulation
1. Hyperthermia
2. Thermoregulation
3. Hypothalamus
7
Heat Gain/Loss
• Metabolic heat production
• Radiation
• Conduction
• Convection
• Evaporation (sweating)
8
Metabolism
• Energy & material transformations in living cells
• Activity increase
• Heat production
Intensity of activity
Metabolism
Heat production
9
Radiation
• Objects emit heat (infrared radiation)
• Body loses heat to environment
• Body can also gain heat through radiation
– Warm environment
• Sauna
• Hot day
• Effective when skin temp > environment
10
Conduction
• Body can gain or lose heat when it is in contact with an object that is warmer or cooler than itself
• Examples
– Hot pack
– Ice pack
• Heat transfer between solids or solids & liquids
12
Evaporation
• The MOST important mechanism for losing heat
• Most effective means
• Sweating can provide more than 80% of heat loss
• Warmer environment > dependence on evaporative heat loss, thus on sweating
Blood Flow & Heat Exchange
• Proportion of heat lost via radiation, conduction, convection, and evaporation depends on:– Intensity of exercise
– Relative humidity
• Ratio between the amount of water vapor in the air and the actual amount of water the air could potentially hold based on the current temperature
– Ambient temperature
13
14
Evaporation
• Sweating does NOT cause heat loss
• Evaporation must occur
• Role of humidity??
• Limits of efficient evaporation?
Ambient Temperature Influence
• Until 95°F or the relative humidity (RH) reaches 75%, sweating and evaporation account for more of heat loss
• For every 5°F in air temperature, the % that RH raises the risk of heat illness by 10% – Example: 70°F the humidity danger zone = 80% RH– Example: 90°F the humidity danger zone = 50% RH– If RH = 100% and the air and body temp are the same, the
body CANNOT lose heat to the environment
= DANGER ZONE!15
Sweating Mechanism
• Sweating reduces the body’s internal temperature (evaporation)
• Sweat is not pure water; its also electrolytes– Body’s ability to sustain activity is related to
the replacement of water and electrolytes
17
18
Sweat Rates Determined by:
• Athlete’s size
• Acclimitization
• Fitness
• Hydration status
• Environment
• Clothing
• Type of exercise
• Heredity????
Acclimatization
– Physical adaptations that occur in a natural environment
– Gradual exposure to the environmental conditions over several days
19
practice guidelines
• Days 1-5 – One practice/day– Days 1 & 2: helmets only– Days 3 & 4: helmets & shoulder pads– Day 5: full pads
• After day 5: two/day every other day
20
VHSL guidelines
• Days 1- 6: only one full practice /day– No session, should exceed 3 hours – Total time /day = no more than 5 hours
• Equipment restrictions– Day 1-3 helmets only;
– Day 4-5 helmets and shoulder pads;
– Day 6 + full pads.
• Also required recovery periods21
HUMITURE VHSL RECOMMENDATION
22
105º and up: Recommend no outside activities.95º to 104º: Recommend no equipment (helmets, pads, etc) be
used during activity.90º to 94º: Recommend equipment be removed as often as
possible (during rest breaks, on sideline,etc). Careful monitoring of all athletes for signs of heat problems.
Below 89º: Recommend adequate water supply at all practices and competitions with breaks every 20to 30 minutes for rehydration.
24
Sweating: Good & Bad
• Natural response for thermoregulation
• Leads to dehydration
• Dehydration impairs physiological function
• Lean athlete = typically 65% H20
25
Importance of Water
• Helps control temperature of working muscles & vital organs
1. Muscles = 75% H2O
2. Blood = 80% H2O
• Essential for cell functioning
• Medium for nearly all body metabolism
26
Effects of Dehydration
• Performance is reduced
• Prolonged training & competition most adversely affected
• Dehydration + heat intensifies adverse effects
* Warm & humid environment > potential for decreased performance
27
Effects of Dehydration in Sports
• Variable effects on strength & power sports
• Withholding fluids??
28
Physiological Effects of Dehydration
• Decreased cardiac function
• Increased core temperature
• Reduction in ability to sweat
29
Early Warning Signs of Dehydration
• Fatigue
• Loss of appetite
• Nausea
• Poor concentration
• Flushed skin
• Light headedness
• Dark urine
• Muscle cramps
Hydration & Rehydration
• Goal: Match fluids and sodium ingested during activity to fluids and sodium lost during activity.
31
NATA guidelines
1. Establish hydration protocol
2. Fluids should be accessible
3. Begin all exercise well-hydrated
4. Beverage temp: 50° - 59°
32
Each athlete weighs “in” before practice and weighs “out” afterward. In the example, the athlete should have been restricted from practice on day 4 because of a 5 percent loss of body weight.
Weight chartWeight chart
34
Exertional Hyponatremia
• Sodium level drops below 130 – 135 mmol/L• Excessive fluid consumption and inappropriate fluid retention• If untreated can lead to death
– Refer immediately– Do not give fluids
• Signs– Altered mental/cognitive state/headache– Vomiting & nausea– Swelling of the extremities– Seizures– Unconsciousness
Can you drink too much?
35
36
Clothing Choices
• Light colored• Light weight• Porous• Avoid 100% cotton• Avoid ‘wicking’ clothing• Dry shirt slows the
cooling process