Videos, cycling magazines, training books and, of course, the Web offer a wide variety of indoor training workouts. Riding indoors helps you focus on improving aerobic capacity, and weight training benefits cyclist's by increasing their overall power and strength. Squats, leg extensions, leg curls and calf raises are just a few cycling-specific exercises that reap strong benefits. If you don't have a place to work out at home, consider local gyms or colleges. Some gyms offer winter-only memberships.
Swimming is great aerobic exercise and a good way to maintain flexibility.
Use a kickboard to hold you up and kick behind it. Winter riding, whether it is on the roads or on the trails, requires not only more clothing but also a keen awareness of safety issues. Talk to experienced cyclists for tips and advice. Skiing is the perfect winter complement to cycling. Cross-country skiing is a highly aerobic activity that works many of the same muscle groups as cycling.