Running outside can be a great way to enjoy some chilly winter air, but there’s a line between pleasantly crisp and holy-hell-it’s-cold-outside. That’s where these treadmill workouts, developed for SELF by Shred415 founders Tracy Roemer and Bonnie Micheli, come in. These four routines will test your endurance, challenge you with hills, and spike your heart rate with intervals—and the only time you need to spend outside is the walk from your car and the gym.

The workouts use intervals and hills to deliver the intensity of an outdoor run. And you can modify the routines to match your current fitness level, Roemer and Micheli explain. Here’s how: All of the treadmill workouts below are based on a 5.0 MPH (miles per hour) starting point for beginners. For an intermediate workout, start at 6.0 instead (and add 1.0 MPH to each speed noted below). And if you’re really looking for a challenge, start at 7.0 (and add 2.0 MPH to each speed). And don’t forget to save these pins for easy reference next time the temperature dips to, well, there’s no way degrees.

1. Try this straightforward hill workout if you’ve only got 10 minutes to get it done.

Graphic by Valerie Fischel

“Slow and steady wins the race—keep your pace fairly consistent as you slowly climb to the top of a moderate hill,” Micheli and Roemer explain. “As you work your way down the other side, steadily increase your pace and end with a fast, flat one-minute run.”

2. Try to keep your speed consistent during each two-minute interval block.

Graphic by Valerie Fischel

You only need to change your speed every two minutes in this workout, so your mind can focus on crushing every stride.

3. This interval workout plays with both speed and incline.

Graphic by Valerie Fischel

This routine will keep your body guessing (and your heart rate climbing).

4. This killer rolling hill workout simulates a tough outdoor run.

Graphic by Valerie Fischel

“Your incline will vary from a flat road to a nine percent during this challenging 20-minute workout,” according to Micheli and Roemer. “Raise your heart rate as you push through the tough hills, and drop it back down during your active recovery on the lower inclines.”