That's because when you're always running at the same pace, your body gets a little lazy. Take things up a notcheven for just a few minutesand you leave that comfort zone, which translates into greater fitness gains. The big one: calorie burn. You can torch about 20 percent more calories simply by running an eight-minute versus a 10-minute mile. And when you do repeated speed intervals, you're creating a bigger "afterburn," with oxygen consumption (and therefore caloric expenditure) staying high as your body works to return to its pre-exercise state. You'll also better engage your glutes and calves, which will help power you forward, adds Siik, while your abs work extra hard to help counter some of the torque that occurs at higher speeds.
You don't have to be an elite athlete to reap the benefits. "Just doing one speed day a week where you up the pace for 8 to 10 minutes can make a difference," notes Chris Heuisler, a certified running coach in Boston and the RunWestin concierge. Be sure to build up gradually, he warns: Too much of the fast stuff can lead to injuries like Achilles tendinitis, plantar fasciitis and shin splints, since the lower legs tend to bear much of the added impact that comes with speedwork. (Do speed workouts no more than twice a week.)
Finally, remember that you don't need to run so hard that you feel like you're going to lose your lunch all over your Nikes. "The key is to move away from that easy-run pace into an area where saying more than a couple of words at a time is difficult," says Heuisler. And don't worry: Like anything else, the more you do it, the better you'll feel. Our handy guide will help you navigate the speedways.
More: 5 Fat-Burning Plyometric Exercises
The Run-Faster Warmup
You're asking a lot of your body when you increase the intensity, so it's crucial to warm up properly. Add these four moves before going faster, advises Eric Barron, coach of Track Club LA and cross-country coach at Santa Monica College. Oh, and always begin your runs with a few minutes at an easy pace.
Strides: Start to run at your regular pace, then take a few longer and slightly quicker steps. Do about four to six strides on each leg for about 250 feet (or about 25 seconds).
Leg swings: Stand with feet hip-width apart. Swing left leg forward and back 8 to 10 times, moving through the full range of motion. Switch legs and repeat. Then swing each leg side to side 8 to 10 times.
Carioca: Think of this like the grapevine move from aerobics. Stand with feet hip-width apart, knees soft. Push off with left foot, crossing it behind right foot, then step to the right with right foot. Then cross your left foot in front of you and step to the right again with right foot. Keep moving to the right for 8 to 10 reps, then repeat, switching directions.
Skips: Skip forward, bringing front foot high above knee and using arms for momentum. Continue for about 100 feet (or about 10 seconds). Then repeat, this time bringing front foot to about midcalf height. Finish series by lifting front leg just above ankle.
More: 7 Moves for a Better Butt
3 Get-Faster Workouts
By manipulating the machine's speed and incline, you get a tough workout you can easily adjust to suit your pace, says creator David Siik.
How it works: After a three- to five-minute easy warm-up, run fast for 30 seconds and recover with a slow jog for one minute. Repeat six times, building each segment by 0.2 mph. Next, run at your last speed, adding a 1 percent incline to each 30-second interval. (Rest for one minute between each.) Repeat six times, finishing at a 5 percent grade. Last, run at your fastest speed on a 5 percent incline. Begin with a 30-second interval, recover, then add 10 seconds to each interval until you're at 60 seconds. End with a few minutes of easy jogging. For more, go to health.com/treadmill-run.
Strength and speed go hand in hand, which is why hill work is so essential to runners. For this workout, find a steep hill that takes about 20 seconds to run up. Core stability is crucial to good running form, says Heuisler; adding planks to your warm-up will help you build strength in that area. Finish with a few minutes of easy jogging.
How it works: Warm up with 10 minutes of easy jogging, followed by two one-minute planks (forearms on floor, legs extended behind you, body forming a line from head to toe). Sprint up the hill at close-to-maximum effort for 10 to 20 seconds. Walk slowly back down to recover. Repeat four to five times, building up to 10 to 12 reps.
No traffic lights and a forgiving surface make tracks ideal for speedwork. And the distance is a cinch to measuretypically about a quarter mile around. Plus, "it's easy to stay consistent, even during your speed intervals," notes Barron. These repeats help you build both strength and stamina, challenging you to work harder with each sprint session.
How it works: Warm up with 10 minutes of easy jogging. Then do the dynamic stretches (see Getting Warmer, previous page). Run once around the track at a hard effort, then jog slowly to recover. Repeat for a total of four to six intervals. Finish with 5 to 10 minutes of easy jogging. Each week, add another interval until you get to a total of eight.
How to Build a Better Running Playlist
One simple way to get swift: Turn up the tunes. Research shows that it can be a great motivator. To build a better playlist, download these music apps.
PaceDJ: Have a favorite running tune, but its tempo doesn't fit your workout? No problem. This app will speed up or slow down the song to match your target pace. ($3; pacedj.com)
TempoRun: Once you select your pace (speedy or snail), the app analyzes the songs in your library, then categorizes them by beats per minute. ($3; temporunapp.com)
FitRadio: Choose a genre plus your target pace (for speedwork, that's between 120 and 140 beats per minute), and this app will formulate a playlist to match your taste and preferred tempo. (Free; fitradio.com)