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.
More: Cold-Weather Training and Your Body
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.
More: Fueling for Cold-Weather Exercise
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.
More: How to Stay Motivated When the Temp Drops