If you’re looking for a challenging, calorie-burning, engaging workout, should you use a treadmill or a stair climber? Either one is can be a good option, fitness experts say, but they’re not always right for everyone.

There are actually two types of stair climbing machines you might find in a gym, Chris Barucci, a physical therapist and certified strength and condition specialist at the Boston University Physical Therapy Center, tells TODAY.com.

When using the first variation, sometimes called a stepper, your feet stay in place on pedals that go up and down as you step. But when using the second type of machine, colloquially referred to by the brand name StairMaster, your feet leave the machine briefly while climbing a never-ending staircase. This type of machine is also sometimes called a stair mill, Barucci says.

That’s why, while you can get a great workout on either a stair climber or a treadmill, using a stair climber is generally more strenuous, Dr. Jeanne Doperak, a primary care sports medicine physician and associate professor at the University of Pittsburgh School of Medicine, tells TODAY.com. But that also means it can be riskier than using a treadmill — especially for your knees, she says.

Here’s how to choose which machine is best for your goals.

Does a treadmill or stair climber give you a better workout?

Both a treadmill and stair climber can get your heart rate up, burn calories and work your lower body muscles.

But they impact the body a little differently, Barucci says.

When walking on a treadmill, people typically hit the tread in a “heel-to-toe pattern” and work the hamstring muscles on the back of the thigh, he explains. Whereas on a stair climber, “the pressure is mostly on the forefoot and mid-foot, which loads the lower leg, quad and hip muscles more,” Barucci adds.

Plus, the fact that a stair climber requires you to stay upright while stepping adds a balance challenge that engages your core muscles, TODAY.com explained previously.

With both cardio and strengthening components, a stair climber is generally going to be a more intense workout than a treadmill, Doperak says. That’s especially true if you’re comparing a stair climber to walking on a treadmill.

If you have a relatively high fitness level to begin with and are looking for the most efficient workout machine, a stair climber will likely be a better option.

But, the experts say, not everyone needs that. “In the right pace and the right population, (a stair climber) is a great workout,” she says. And the “vast majority of people will find that they can get as good a workout on some of the other apparatuses,” Doperak adds.

You can up the intensity on a treadmill by increasing the incline or speed, for instance, Barucci says. And you can build lower body strength with a dedicated strength-training routine in addition to using a cardio machine, Doperak says.

“Doing a cardiovascular workout and then having a separate strength workout that really is tailored to where you are in your fitness plan probably is the safest (option),” Doperak says.

Does a treadmill or stair climber have more impact on the body?

Climbing stairs is “one of the hardest things that we do on a daily basis as human beings,” Doperak says. When going up and down stairs, you’re putting “anywhere between three to seven times your body weight on your knee,” she adds. And stairs only become more challenging as we age.

For that reason, a stair climber inherently places more impact on the body — especially the knees — than a treadmill.

That also puts you more at risk for an injury to the knee when using a stair climber, Doperak says. “If we load the knee constantly with a motion that’s putting more stress on it, we get more cartilage wear,” she explains. And in the case of stairs, “people will get early wear and tear behind their kneecap,” she says.

To be fair, a treadmill can pose the same risks at a high enough incline. But Doperak is “often hesitant to recommend the stair climber as opposed to other things,” she says, “simply because I do think it puts many people at risk of having these knee issues.”

Should you use a treadmill or stair climber?

A stair climber is a great option for those who want to train for activities like hiking and climbing, Barucci says.

It can also be helpful for those who are just a little bored with their usual cardio workouts in the gym. “Because of the challenge the user faces needing to keep up with the staircase, it’s very difficult to not be focused on the activity while doing it,” Barucci says, “particularly if the speed is relatively fast.”

Additionally, stair climbers are particularly demanding on the quads and calf muscles, Barucci adds, so it can be a good option for people looking to work on those muscles.

But a stair climber isn’t necessarily a good option for beginners. “If the most you’re doing is a walk around the neighborhood, it feels like a big jump to a half an hour on the StairMaster,” Doperak says. She also cautions against using a stair climber if you have certain health concerns, particularly pain in the front of the knee.

A treadmill is ideal for those who want to continue their walking or running indoors, as TODAY.com explained previously. It’s also perfect for folks looking to build up their walking endurance before a big trip, for example.

Of course, there is also value in variety, Doperak says, adding that even stair climber enthusiasts probably shouldn’t use that machine every single day.

Whether you’re using a treadmill or stair climber, Barucci recommends starting with a time, speed and incline or resistance level that leave “plenty of safety margin.” Basically, start with what you feel comfortable with and increase those settings gradually.