If you’ve ever run up a steep hill, attempted to run a longer distance than you’ve trained for, or done a handful of 200-meter repeats, you know that running can feel like a leg workout just as much as it is a cardiovascular exercise.

But does going for a run “count” as leg day? Before you’re tempted to skip your squats and lunges in favor of a few miles, it’s worth knowing how running actually stacks up against strength training. Here’s what fitness experts have to say about whether running can make your legs stronger.

Which muscles does running work?

Running is truly a full-body exercise, with even the core and arms getting in on the action to help stabilize us and propel us forward. But “the greatest contributors to running are the muscles of the lower leg and ankle—the calves, soleus, hamstrings, glutes, and quads,” says Kate Baird, ACSM-CEP, CSCS, an exercise physiologist at the Hospital for Special Surgery in New York.

However, there are some muscle groups in the lower body that’ll mostly be neglected if all you’re doing is running, like certain muscles in your hips (external rotators, abductors, and adductors), says McKenna Coughlin, CSCS, ACSM-CPT, a personal trainer and certified running coach. (Trail running is a different story, since it often involves more side-to-side motion, she says.)

Plus, everyone’s body and running form is different. “Depending on where your frame is strong or not strong, you may prioritize one muscle group over another,” says Baird. “Plenty of people run with no hip extension, which tells me their glutes and hamstrings aren’t doing as much as they could to contribute to their running. So, doing exercises that focus on the glutes is important.”

“Strength training has benefits to all athletes.” —Asher Kyger Henry, DPT, CSCS

How does running compare to resistance training?

Both running and resistance training can make your legs stronger, but typically they’re building two different types of strength. When you’re running, you’re relying a lot on your type one muscle fibers, also known as “slow-twitch” or endurance muscle fibers, that are harder to fatigue and use fat as fuel, Baird says.

Resistance training, on the other hand, is usually building type two or “fast-twitch” muscle fibers (though running at very fast speeds—think sprints up to around 800 meters—also activates those type two fibers because it requires faster, more forceful contractions), Baird says.

And unlike in the gym, where hopefully you’re gradually increasing your weight or your reps, “we don’t get a muscular progressive overload with running,” says Asher Kyger Henry, DPT, CSCS, a physical therapist and running coach. “It’s important to maintaining our longevity to do isolated exercises that have progressive overload, and without that increasing stimulus, you’re not going to get the gains muscularly.”

Will running alone strengthen your legs?

In theory, running alone can strengthen your legs, but unless you’re doing dedicated workouts to build power—like hill sprints or strides—you’ll mostly be developing those endurance-focused, type one muscle fibers.

“Running is primarily a cardiorespiratory activity, so outside of developing your muscular endurance, you’re not really building actual muscle,” says Henry. “When we’re running, we’re utilizing the strength and muscular build that we’re getting in the gym to help maintain mechanics and forward propulsion.”

Whether you’re actually building that muscular endurance or just maintaining the muscular endurance you already have will depend on whether or not you’re progressing in your running, says Baird. For instance, if you run the same mileage at the same intensity every week, you’re probably just maintaining, whereas someone who is new to running or is adding speed or mileage will increase their muscular endurance.

Plus, “if all you do is run, you’re probably going to skew your body to some sort of imbalance of tightness and weakness,” Baird says. “That can make you a less economical runner and make you more prone to injury.”

The bottom line: Does running count as leg day?

Going for a run has very different benefits for your legs than hitting the gym. So can it count as leg day? Not really—but maybe in some specific circumstances.

Coughlin puts it this way: “If you’re a runner and you think, ‘I do leg day every day,’ think about leg day in the gym. If you were to do leg day every day, you wouldn’t be a very happy person,” she says. “If you’re a runner and you’re counting running as your leg day, you could see huge improvements if you were to implement just one dedicated gym leg day a week.”

That said, “if you’re more of a gym person and you want to mix it up a bit, I think there’s a time and a place where running could supplement a leg day,” Coughlin says. “But I don’t think it can completely replace it.”

That doesn’t mean you should overlook the impact running can have on your legs, especially if you’re doing hard workouts or high mileage. “There’s definitely times when I’m going to do less strength training for my lower body because I’m running a lot, and I’m doing sprints and tempo runs and I don’t want to overdo it,” says Baird. “And then there are other times when I’m running less and I’ll do a lot more strength training to balance out my frame again, so I can be healthy when I go back to running more.”

A helpful way to know just how much running is challenging your legs: How you feel the next day. “If you go on a run and you wake up the next day and your legs are tired, you did leg day,” Baird says. “But if you wake up and you’re like, I’m gonna go take a Barry’s class, your run probably falls more into strict aerobic training without much contribution to the strength of your legs, and you still need leg day.”

Ultimately, logging lots of miles is not a get-out-of-leg-day-free card. “Strength training has benefits to all athletes,” says Henry. “Don’t try to wiggle out of it. It only takes 10 or 15 minutes, and it has a very big effect on your performance level and your muscular development.”