If your fitness regimen is a little less, well, regimented, in the winter, join the club. It's our mammalian nature to slack off a bit during the cold season. In fact, experts say that taking two weeks off of a training schedule or dramatically cutting back on the amount and intensity of it for two to four weeks after competition is important—especially if there's nothing on the race schedule for three to four months.

But now that spring is merely weeks away, it's a good time to start thinking about your re-entry plan. Fortunately, there are a few simple ways you can tweak your fitness program to get back in race shape. If you maintain a good aerobic base—meaning you exercise for at least 30 minutes, three times a week—you can easily modify your program so you're ready to compete at the drop of a hat. Whether you want to run, bike, swim or skate your way to glory (or at least to the finish line), here's how Rob Sleamaker, M.S., sports physiologist and author of Serious Training for Endurance Athletes, suggests you train year round to maintain top form:

Train long once a week. In addition to your three standard aerobic workouts, add one "extended duration" workout to your weekly routine. How long should it last? Generally speaking, about twice as long as your event. For instance, if you run a 10K in 45 minutes, aim to spend about 90 minutes on one aerobic workout each week, working at the low end of your training zone. On your long day, you can do whatever aerobic activity, or combination of activities, you want. It's a great cross-training opportunity.

Train hard once a week. Make one of your weekly workouts a high-intensity interval workout. Ideally, you should do this throughout the year, but at the very least, add an interval workout to your program four weeks before the competition date. "You want to simulate the heart rate you're going to experience during the event," says Sleamaker. Here's how: Start with a 10-minute warmup. Then do a one-minute interval of all-out effort (whether it's running, swimming, biking, etc.) followed by three minutes of recovery. Alternate between the two intensities for about 30 minutes, gradually increasing the duration of the high-intensity effort until you can work at your maximum intensity for three minutes, followed by a three-minute recovery for a total of 36 minutes. Finish with a five- to 10-minute cool-down.

Bonus Tip: "Try to do your interval workout on the same day of the week that your event will take place," recommends Sleamaker. "That way, physically and mentally you're prepared for race day." Your body settles into a rhythm, he explains, and if you're used to working hard on, say, Sunday, then come race-Sunday, you're ready.