PUBLISHED 12/06/2005
I've finished winter races where the condensation of my breath had frozen on my mustache and beard, making me look like a demented goat, and my hands were so numb that someone else had to unlace my shoes. But not all winter races are so unpleasant. In fact, anytime I stood on the starting line of a marathon feeling slightly chilly, I knew it was going to be a good day. When race-day temperatures sink into the 30s and below, however, it puts extra demands on your body.
Running at a submaximal pace in the moderate cold--temperatures in the 40s--doesn't affect your VO2 max or the amount of energy your body needs to sustain the workload. But when temperatures drop lower, it can take 15 to 20 percent more oxygen to maintain that same pace. Part of this increased energy cost is due to shivering. The energy we use to shiver comes mostly from blood glucose and muscle glycogen, thus compromising performance by reducing the fuel available to your muscles.
Your heart, that all-important working muscle, is also affected during cold-weather racing. Low temperatures can diminish cardiac output. That means there's less blood reaching your working muscles. And when your blood temperature goes below 98.6 degrees, the hemoglobin binds oxygen molecules more tightly than usual, causing the blood to release less oxygen even when it is delivered to your muscles as you run.
