It's easy to slack off on workouts during the coldest times of year, but you'll regret it once bikini season comes around in a few months. Stay on top of your fitness by choosing to work out outside at least one day a week. Revolutionary materials, like moisture-wicking fabrics, make it easy to stay warm and comfortable when you layer them. Bring something warm to sip that'll also keep you hydrated along the way - green tea offers flavor and a boost of energy if you choose to go caffeinated. A workout buddy can be essential to motivation at this time of year - when you're held accountable, it's harder to make excuses not to work out. Begin your workout inside by stretching your muscles.