By Tawnee Prazak
It was pouring rain when my alarm went off at 4:57 a.m., alerting me it was time for swim class. Not ideal conditions for an outdoor swim, but the pool would be nice and toasty—more desirable inside the water than, say, for my coach standing outside.
Little did I know, though, I was about to get a first-hand account on the physiological effects of training in the cold.
It was still dark, still pouring and about 40 degrees when I learned from my coach that a filter problem messed up the pool's heating, which meant cold water that was getting colder with each rain drop. We were free to leave, but there'd be none of that as far as I was concerned.
If he was willing to coach, I was willing to swim—triathlon season is here and I need all the practice I can get. Following the swim, I got to thinking about the human physiology behind that workout, the extra energy required and such. Triathletes and other sport enthusiasts all over are face cold training sessions beginning in the fall and stretching into early-spring, and it's important to be aware of how the body responds in those situations.
Keep in mind: The degree to which the following bodily responses occur depends heavily on many factors: air temperature, wind chill, weather conditions, body type, clothing worn, sport, intensity, and other minor variables. There's a big difference between 20 degrees and 60 degrees, even if you Californians think 60 feels like 20.
1. Glycogen Stores Are Depleted Quicker
Energy to fuel your muscles for a workout comes from glycogen stores. During exercise in the cold, muscles may require more energy at a faster rate, leaving you vulnerable to fatiguing quicker. This is the case if you start shivering—involuntary muscle contractions—or if you exert yourself harder, perhaps by not resting or taking breaks.
Both are forms of increased metabolic heat production and are meant to offset heat loss by generating heat, and the more muscles recruited the more glycogen stores diminish, all while your workout still requires and uses substantial glycogen stores.
What this means to you: Glycogen stores come primarily from carbohydrate consumption, which means you need ample carbs before, during and after workouts in the cold or fatigue could hit faster than you'd like. If enough energy is exerted, you could be more tired than usual for the rest of the day.
Note: That roughly 30-minute window after training is especially important to refuel muscles, as it aids in a faster recovery. Also important: Don't allow shivering to get out of control. This is a sign of hypothermia setting in, and it's best to stop training and get warm if that's the case.
2. Sweat Happens
Just because it's cold doesn't mean you stop sweating. Exercise = metabolic heat production = perspiration. This is where attire becomes important: If clothing becomes wet or dampened it loses its insulation properties. In cycling, where speeds are generally greater than running and thus a greater wind chill is generated, proper layering is especially important.
However, if workout intensity is high enough, metabolic heat production and other physiological factors should keep your core temperature from dangerously dropping. And don't forget about swimming: Water submersion can cause even more rapid heat loss than land sports via conduction and convection.
What this means to you: It's when you stop working out that's risky—heat production decreases and sweaty clothes can turn into freezing clothes. Therefore, post-workout planning is key.
Some clothing tips: More layers are better for insulation rather than one thick layer, and base layer—material should not act like a sponge. Also, shoot for form-fitting attire to prevent your warm air from escaping and cold air flushing in. In water, a wetsuit is an option. So is a shorter swim.
3. Dehydration Is Possible, so Drink up
Cold weather can depress feelings of thirst, so even though you may not crave a big swig of a sports drink every 20 minutes like you do when it's 85 degrees out your body still needs it. Several factors unique to cold-weather exercise can cause dehydration.
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.
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.
Tawnee Prazak is a freelance journalist, pursuing a master's in kinesiology and is an avid triathlete. Various scientific studies, research and resources, including the ACSM and NSCA, aided in this article. Reach Tawnee at firstname.lastname@example.org or see her blog atwww.tritawn.blogspot.com.