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Thermoregulation

February 24, 2014

It is important to have proper hydration and thermoregulation during exercise and activity! It is hot, hot, hot, outside! 

 

As we are approaching summer more people are being active outdoors. This can create a health hazard if appropriate precautions aren’t followed, but it also provides an opportunity to change up your exercise and activity routines. Before you lace up your shoes and take a run in the sun, there some important facts that may change the way you approach exercising outside.

 

Now you may be asking yourself, what on earth is thermoregulation? Simply stated, thermoregulation relates to the way that your body regulates core temperature. There are multiple ways that the body can dissipate excess heat, but most body heat is lost through evaporation. When the temperature around the body (also known as ambient temperature) is hot, there isn’t a large gradient that favors the body to lose heat.

 

As we begin to sweat heavily, the fluid we lose typically comes from blood plasma, which is comprised of mostly water and contains proteins and sugars. As the plasma is depleted, the blood becomes thicker. This increase in blood viscosity requires more effort of the heart (in speed and strength of contraction) in order continue physical activity or exercise. The increase in sweating allows the body to cool while the moisture is being evaporated.

 

Typically, fatigue is associated with increased ambient temperature because the body is working so hard to provide energy for multiple cooling mechanisms. The blood in the digestive organs is redirected towards the skin because there is a better gradient for cooling, this occurs very quickly in response to added heat stress. As blood concentration increases due to loss of plasma volume, blood is directed away from the kidneys and towards the skin for cooling, this signals a need for a cascade of molecular pathways to begin to increase water and sodium reabsorption.

 

The Center for Disease Control has listed cardiovascular disease as the leading cause of death in both males and females. As you can imagine, when the heart is already vulnerable, adding extra stress by having a lower plasma volume can create a host of issues, including a myocardial infraction (known as a heart attack). The combination of dehydration and increased ambient temperature can be deadly.

 

Exercise should be fun and if you are following good hydration and thermoregulation practices, being active outdoors can be a wonderful way to keep your body in motion!

 

Research has repeatedly demonstrated a decrease in physical performance with dehydration. At high exercise intensities there is a competition for blood flow between the working skeletal muscle and the skin to be used for cooling.

 

As exercise intensity increases the working skeletal muscle will always win the competition and therefore blood flow will be redirected from the skin to the skeletal muscle. The ability of the body to provide adequate blood flow to the skeletal muscle allows the body to maintain blood pressure (which is a primary priority during rest and exercise alike).

 

When the skin loses blood flow to the skeletal muscle, the ability to dissipate heat is compromised, which leads to a higher risk for developing a heat injury. Heat injury has many factors including humidity, ambient temperature, clothing choices, fitness level, hydration status, metabolic rate, wind, and other factors. There are stages of heat injury: heat cramps, heat exhaustion, and heat stroke.

Signs and Symptoms
There are multiple phases of dehydration and heat stress. Dehydration is often hard to recognize because the symptoms can be very mild. Urine color is frequently used to detect dehydration outside of a lab, but urine color can be easily altered with food, medication, or vitamins.

 

Thirst is not the best indicator of hydration status, thirst is often a late stage indicator of dehydration. For proper hydration, it is a good rule of thumb to take your body weight and divide it in half, to get the amount of water you should consume daily, in ounces. For example a 160 lb person should consume a minimum of 80 ounces per day of water.

 

Heat Cramps
Heat cramps are often associated with cramping in the back side of the leg, such as the hamstrings or calves, and also the abdomen. Heat cramps typically feel like a muscle spasm and can be very painful. If you are experiencing heat cramps, it is important to rest, rehydrate, and mild stretching can often alleviate pain.
 

Heat Exhaustion

Heat exhaustion is typically associated with multiple symptoms including an increase in heart rate, heavy sweating, fainting, nausea, headaches, confusion, and others. During heat exhaustion the body is struggling to maintain homeostasis and therefore can exhibit many abnormal reactions. Remove any restrictive clothing, rest, rehydrate, apply cold to the body through ice packs or cold showers.
 

Heat Stroke
Heat stroke is a medical emergency. Heat stroke can be fatal and is associated with very high body temperature (which can be as high as 104°F) disorientation, absence of sweating, difficulty communicating or breathing, seizures, a coma, yet many people show a variety of symptoms. It is vital to seek medical assistance immediately if you believe someone is experiencing symptoms of a heat stroke. Often the line between heat cramps, heat exhaustion, and heat stoke is not clearly separated. Many symptoms can be experienced in all stages of heat illness, or an individual may not experience typical symptoms in any stage of heat illness.
 

Recommendations
(Adapted from the American Orthopaedic Society for Sports Medicine)

  • Allow frequent periods of rest and hydration during activity outdoors and indoors. Fluid replacement is essential to preventing heat injury.
     

  • Make sure you are well hydrated before, during, and after exercise.
     

  • During exercise, consume 8 ounces of water every 20 minutes. If exercising more than 60 minutes, consider including electrolytes through a sports-drink.
     

  • Monitor the color of your urine. The darker your urine, the less hydrated you are and the greater your risk for heat injury.
     

  • Weigh yourself before and after activity to monitor water loss. Make sure you have replaced fluids before your next exercise session. Gradually increase activity in the heat over a period of 7-10 days to allow adequate acclimatization.
     

  • Wear light-weight and light-colored clothing during exercise or physical activity.
     

  • Schedule outdoor exercise at the coolest time of day, either early morning or after sunset. Strongly consider postponing or cancelling your activity when there are extreme heat and humidity conditions.
     

  • Pay close attention to temperature and humidity. Swimming and being active in the water is a great way to keep your core temperature cool while increasing your fitness level, but remember to hydrate throughout your exercise session.

 

 

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