This winter season it's more important than ever (it always is) to stay healthy. It's far too easy to make excuses revolving around shorter days or colder temperatures justifying a lack of physical activity. Often, the lack of activity and a diet consisting of starchier foods will tend to make you more disposed to inactivity, furthering the cycle.

You must break the cycle

The way I like to stay in great shape is by hitting the slopes all winter season. I get the benefit of a great aerobic exercise at elevations up to 12,500' in addition to amazing scenery. There is nothing like a crisp winter morning by yourself ripping through the trees. Skiing is a great all-body exercise that works not just your leg muscles, but your core and balance, as well.

Often the day after skiing I take a yoga class. Skiing is fast and intense and taking yoga the next day provides a nice balance with its structured breathing, slow movements, and contemplative poses. I find that that the two sports complement each other quite nicely.

Exercise promotes further exercise

There are two ways to spend your winter. 1) Staying indoors cooking food and being sedentary, unmotivated to go play because you are out of shape or 2) constantly reinventing yourself, pushing the limits, enjoying everything that the world has to offer. When you have fun outside you become preoccupied with having more fun outside. Staying sedentary promotes feelings of inactivity.

I'd suggest the second route as you'll have more fun and your body will last a lot longer. I've personally regretted periods of my life where I was inactive but never once have I thought that a ski trip or a bike ride was just a frivolous waste of time.