A friend of mine rode his bike the other day for five and a half hours in 16-degree weather. Though his beard had grown longer from icicles by the time he dismounted, he wasn't as cold as he looked. Why? Because he knew how to dress for the weather.
Thermal tights, booties and cycling-specific winter gloves were part of his wardrobe that day. In addition, three pieces of clothing covered his core: a base layer, a long-sleeved jersey and a thermal jacket.
"It's all about layering," noted Jason Wood, category 2 road cyclist.
He's right. According to Stuart Spitalnic, MD, FACEP, emergency physician at Newport Hospital, Newport RI, appropriate weight layered clothing is essential for avoiding hypothermia, a decrease in the body's core temperature.
Dr. Spitalnic spoke with About.com about the threat of cold-weather biking to one's health, recognizing the signs of hypothermia and preventing low core temperature on the bike this winter.
About.com: How can mountain biking in cold weather threaten one’s health?
Dr. Spitalnic: Cold weather training has particular risks. The two most directly related to the low temperature are frostbite (damage to the skin and underlying tissues due to cold exposure) and hypothermia (a potentially dangerous circumstance of low core temperature).
Training in cold temperatures also causes a “cold diuresis,” as blood is shunted away from the skin and moves to the vital organs. The kidneys see more blood flow and make more urine, which can result in dehydration sooner than might be expected for the amount of activity performed.
There is an association between exertion in cold temperatures and heart attacks or cardiac arrest. This is more likely the case in those already at risk for heart disease.
And, don't forget orthopedic injuries. Ice, water from melting snow, and unexpected patches of sand result in plenty of falls with attendant broken bones or head injuries.
About.com: How can mountain bikers avoid hypothermia?
Dr. Spitalnic: Obviously, the most reliable way to avoid hypothermia is to avoid exposure to extreme temperatures in the first place. As more hardcore athletes will not likely take this advice, the next best thing is to respect the outside conditions and dress in appropriate insulating layers with attention to all exposed areas: head, ears, fingers, etc. Keeping a dry outer layer with layers beneath will help maintain some of the heat generated from the activity and decrease the amount of heat lost through evaporation.
Hypothermia in general results from the severity of the exposure to cold, and the time exposed. The worse the conditions outside, the shorter the workout should be.
About.com: What are the symptoms of hypothermia?
Dr. Spitalnic: The early and most obvious signs of hypothermia are feeling cold and shivering. As hypothermia progresses, the victim may begin to exhibit a decreased level of conciousness – appearing drunk almost – with slurred speech, slow response, and as the core temperature heads to the 80s, the victim may become comatose. Heart rhythm disturbances are also seen, and at an extreme low-body temperature cardiac arrest results.
About.com: What are the risk factors for hypothermia?
Dr. Spitalnic: The most important risk factor is the exposure – how cold and for how long. Proper clothing “buys time” for safe exposure. Wind increases the amount of heat loss both by increasing convection away from the body and by increasing evaporation. Cyclists in particular must be more attentive to evaporative loss of heat due to the wind-chill effect. It's no longer just the ambient wind speed, but also the speed they travel on the bike that they are exposed to. There are many medications and medical conditions that make it more difficult regulate body temperature when exposed to cold, and athletes should review their history with their doctors to gauge their potential increased risk.
About.com: How can layered clothing help?
Dr. Spitalnic: The layering allows for an insulating layer of air between layers of cold, which helps keep in some of the heat generated from the activity. A dry outer layer prevents some of the losses through evaporation. I usually recommend three layers: a base layer of a wicking sports fabric, a middle layer (long-sleeve cotton t-shirt is fine here), and an outer wind-breaking layer. And, if that's not enough to keep you safe, consider taking a day off.
About.com: Do you have any parting words of advice for bike riding in cold weather?
Dr. Spitalnic: The best advice for training in cold weather is first to know the forecasts ahead of time and consider scheduling days off or shorter workouts when extreme temperatures are predicted. Cyclists who are “in the zone” should consider a shorter route or a looped route that will keep them from being too far from home in case they start to get into trouble.