To pit the two approaches head to head, researchers recruited 32 participants -- who ran regularly but didn't do speed work -- and divided them into three groups. One group continued its regular training routine, while the other two did two steady runs plus two interval workouts per week.
(For more must-have tips from the pros, read these 13 Things Serious Runners Wish You Knew.)
Those running hills turned their treadmill incline up to 10 percent and did 10 to 14 30-second sprints. The others followed an approach used in previous studies and training plans, running intervals on a treadmill set to a 1-percent incline at a speed and distance determined by a test of their fitness. That way, the intensity level of their intervals matched those running on the incline.
After six weeks, researchers found that people who ran hill and level-ground intervals improved by several measures, including top speed and the amount of time they could sustain it. Meanwhile, runners who stuck to their regular schedule (sans intervals) saw no gains, despite spending more than twice as much time exercising.
(Want top training advice for your first big race? Check out The 101 Best Running Tips Ever.)
Interestingly, those running flat intervals improved slightly more than those huffing and puffing at an incline -- but that difference may not mean much, says study author Derek Ferley, Ph.D., C.S.C.S. Why? The way his formulas worked out, flat runners ended up running fast about twice as long each week as those running hills.
The bottom line: While any speed work will help your performance, hill training gives you a great workout in a relatively short period of time, Ferley says. The incline instantly turns up the intensity, and you don't have to run as fast to net similar gains. Even more: Hills likely strengthen muscles and improve running economy -- your ability to use oxygen more efficiently while running, says Ferley.
If you've reached a plateau, consider swapping an easy run for a hill routine. Warm up with a jog, then find a grassy hill or crank up the treadmill to an incline between 5 and 10 percent. Sprint at the fastest speed you can sustain for 30 seconds (but not longer), then rest until your heart slows down again. Start with six repetitions and build up to 12. Or do this: The Best Interval Workout You’ve Never Tried.
Whatever your goal, find your perfect training plan at the Men’s Health Running Center.