Why does vasoconstriction occur when cold

Body temperature is one of the factors controlled by homeostasis. This process is controlled by the thermoregulatory centre, which is contained in the hypothalamus in the brain.

It contains receptors sensitive to the temperature of the blood. The skin also has temperature receptors and sends nervous impulses back to the thermoregulatory centre. When we get too hot, sweat glands in the skin release more sweat.

The sweat evaporates, transferring heat energy from the skin to the environment. Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin and more heat to be lost to the environment. This is called vasodilation. When we get too cold, skeletal muscles contract rapidly and we shiver. These contractions need energy from respiration and some of this is released as heat. Blood vessels , which lead to the skin capillaries, become narrower - they constrict — which allows less blood to flow through the skin and conserve the core body temperature.

This is called vasoconstriction. The hairs on the skin also help to control body temperature. The hairs lie flat when we are warm and rise when we are cold. If we are too cold, nerve impulses are sent to the hair erector muscles which contract. This raises the skin hairs and traps a layer of insulating air next to the skin.

The control of body temperature is an example of a negative feedback mechanism. It regulates the amount of:. The amount of blood flowing through the skin capillaries is altered by vasoconstriction and vasodilation. So drink about five ounces of liquid every 20 minutes. Something with electrolytes is best. If it's cold enough, the body will respond by lessening blood flow to the surface of the skin, especially the hands and feet—known as peripheral vasoconstriction.

This way, less heat is lost to the environment as blood flow remains closer to the core to prevent the core temperature from dropping. More: 4 Tips for Outdoor Winter Runs. The opposite happens in hot conditions with vasodilation—more blood circulates at the surface to dissipate heat, the body's natural cooling system.

Depending on the circumstance, vasodilation can still occur in cold weather because of metabolic heat production. No matter what, however, there's always adequate blood flow to the head; restricted blood flow to the brain would not be good. Therefore, a lot of heat can be lost through the head. What this means to you: Think of keeping your head warm first and foremost. Then consider gloves and a couple of pairs of socks. In the pool or ocean, be extra perceptive to your body and any sort of numbness and paleness.

Don't overdo a workout; listen to your body and get warm if necessary—hypothermia or frostbite aren't worth meeting your mileage for the day. Cold hands, feet and skin, even shivering, could mean less coordination, less feeling and less motor control.

In essence you can become clumsier and accidentally trip or fumble and hurt yourself. There's also a chance of decreased flexibility and strain injuries in the cold. More serious cold injuries include exercise-induced bronchospasm, or exercise-induced asthma , which is not to be ignored—symptoms include labored breathing, excess mucus, coughing and chest tightness.

What this means to you: Performance may not be up to par in the cold if you're shivering and experience depressed motor control. Play it safe. More: Winter Running Tips. Generally, no. It's perfectly fine to carry on with regular training in the cold with no serious consequences, especially if your winter training takes place in mild-winter climates such as Southern California or Arizona. After all, many triathletes have their training schedules planned down to the minute and don't want to stray from that!

However, it's important to be aware of what could happen and to take precaution—gauge the severity of the cold, consume enough carbs, hydrate and wear appropriate clothing. More: Winter Marathon Training Guide. More Health And Triathlon Articles.