As mentioned, you still sweat, and some of that may evaporate in cold air leaving you unaware of the extent of perspiration. In addition, fluid is lost through humidified breath in cold weather, and the body may also produce increased amounts of urine in the cold—eventually leading to dehydration. Even overdressing can factor into dehydration if heavy attire causes you to sweat more.
What this means to you: If dehydration sets in, performance can be impaired, as well as your body's ability to retain heat. Headaches, cramps and elevated heart rate are all symptoms of dehydration. So drink about five ounces of liquid every 20 minutes. Something with electrolytes is best.
4. Less Blood Flow to the Skin's Surface
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.
(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.
5. Cold-Induced Injuries
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
So, is exercising in the cold risky?
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.event to add to your calendar.