It is always easy to comment on traditions and customs as an outsider to a particular sport. I just assume people know and understand why I shave my legs as a cyclist. But I must admit I am perplexed by one particular running custom – wearing shorts in cold weather. Runners, it would seem, are the only endurance athletes that when it turns cold, insist on wearing the same gear as when it’s 70 degrees and sunny. Is it simply because it’s customary? Does it have to do with ergonomics and not wanting one's legs feeling “restricted?” Is it a toughness thing?
It has been demonstrated numerous times in scientific research that muscle performance decreases in the cold. Power output, force production, and muscle velocity are all diminished when the temperature drops (<50°F). Maximum heart rate is also lower. Granted, for most of us the winter months are about building a base and maintaining our fitness, but why sacrifice the quality of this training by not dressing properly? The better your muscles can function, the better your training becomes.
The reason(s) for running in shorts in the cold is certainly different for every runner, but after reviewing the scientific literature on cold weather and human performance it may be a custom worth rethinking. Since I had so wisely decided to pick up running again right before winter started I for one won't be showing any skin!
There are no hard-and-fast rules about what to wear based on exact temperatures. Over dressing can be just as bad when the weather drops below freezing because being wet with sweat can quickly lead to hypothermia and frostbite. Here is a good review by one winter runner of what to wear.