- The 20 degree rule. A good approximation is to dress for temperatures that are 20 degrees Fahrenheit warmer than the actual temperature. So if it's 20 degrees out, dress for walking in 40 degrees.
- Dress in layers. Layers will keep you warmer than a single layer, and allow for flexibility of removing some of your insulation.
- Shed after warm-up. If practical, you can overdress for the first mile or so, until you warm up. This requires you having somewhere to discard the extra clothes, or a way of carrying them.
- If your hands are cold, wear a hat. This is an old boy scout saying, but it works. If you core temperature starts to drop, your body will protect your vital functions by sacrificing your extremities, such as hands and feet.
- Don't sweat through. If you wear too many clothes and sweat too much, you will sweat through your clothes. Once your clothes are soaked, you will become suddenly chilled. This means you will probably have to dress to be slightly cold, rather than toasty warm.
- Windproof layers are a mixed blessing. A windproof layer will boost the insulation value of the underlying layers, which can really help keep you warm. Unfortunately a windproof layer also stops sweat evaporating, which regulates your temperature. This makes it much more likely that you will sweat though and become cold. I use a windproof layer, but open it up as soon as I warm up, then try to stay slightly cool. A windproof layer is very useful as an extra layer, as it can be wrapped around your waist easily. I will wear it until I warm up, then carry it in case I need some extra warmth later in the run.
- Hydrate. Just because it's cold doesn't mean you don't need to drink. Use your thirst as a guide - for more on hydration see http://fellrnr.blogspot.com/2009/09/running-tip-14-practical-hydration.html and http://fellrnr.blogspot.com/2009/09/running-tip-15-hydration-101.html
- Try to stay dry. Rain can chill you very quickly, so in cooler conditions, you need some rain protection. More on this in the next post.
- Your lungs are fine. Your lungs will not freeze, not even at -40 degrees. Your lungs may get irritated by the low humidity, but they will get used to that. It is possible to get exercised induced asthma, which is a narrowing of the airways when exercising. If you suspect you have this condition, seek medical advice.
- No cotton. This is true for any conditions, but worth restating here. Wear clothes made from synthetic, wicking fibers, such as CoolMax.
- Watch for frostbite. Your extremities may go numb early in your run, but they should warm up. Anything that stays numb needs to be checked.
- Watch for ice. Slipping on ice can pull muscles or cause falls. You can get traction aids to attach to your shoes if ice is a significant problem – look for Yaktrax or similar.
- Hat and gloves. These are important to keep you warm, but they can also be taken off and tucked in a waist band easily. This allows you to adjust your insulation for the conditions. I like gloves that convert into mittens (more on these in a future blog)
- Vaseline. If you are still having problems with your hands and feet, spreading Vaseline over them before putting on your socks or gloves will dramatically improve the insulation. It’s a bit strange the first time you do it, but it works very well.
Hypothermia is often thought about in connection with very cold temperatures, but mild temperatures (50s) and rain are common causes of hypothermia.
If you are shivering, but can stop if you make an effort, you are suffering from mild hypothermia (core 96-98f). This will reduce your coordination, which could be a problem on technical trails. The biggest problem is that mild hypothermia will make you mildly stupid, and less lightly to make good decisions. It is important at this stage to correct the problem as soon as possible.
If you are shivering and cannot stop even if you try, you have moderate hypothermia (core 91 - 95). This is a dangerous condition; You need to get warm and dry urgently.
“The first casualty of hypothermia is good judgment.” If you are hypothermic your decision making is likely to be impaired. If in doubt, seek shelter, get warm and dry. If you are with someone who appears to be hypothermic, you may have to look after them more than normal.