Winter weather can force even the most dedicated outdoor runners onto the treadmill, but that doesn't mean you have to slog out six miles while half-watching the news. Justin Senense, a private trainer at Rich Barretta studios in New York City, showed us four ways to make running in place a little more interesting—and just as effective as a loop in the park.

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The Workout: Interval Sprints

"If you can keep running after your sprint, you're not going hard enough," Senense says of this workout, which gets your heart pumping by alternating 30-second intervals of going all-out with 30 seconds of recovery. It’s a short routine that's especially effective combined with a strength training session or the day after a long run.

Get on it: Set the treadmill to a 2.0 incline; run 30 seconds as fast as you possibly can; walk for 30 seconds. More advanced runners can crank it up to one or two-minute intervals, with a one-minute recovery in between sets. Not sure what your sprint pace should be? Start on the slow side, then up the pace a few notches each interval. You should be running so fast that maintaining that speed for longer than your chosen interval time feels impossible.

The Workout: Squats and Lunges between Intervals

Incorporating squats and lunges into a treadmill routine is one of the best ways to mimic the way your muscles will feel on, say, mile 18 of a marathon, Senense says. "You're getting the lactic acid build-up and learning how to push through that."

Get on it: Senense recommends splitting up a run into two parts (a mile-long hill routine or interval sprints would work well) and doing some lunges and squats when you’re halfway through your workout. The key: Return to the treadmill right away. If your legs are shaky, that means it’s working.

Squats: 3 sets of 10; at the end of each set, hold the pose for 10 seconds
Lunges: 3 sets of 5 on each leg; hold the pose for 10 seconds at the end of each set