If you have been in a gym recently and spotted a person walking steadily on the treadmill at a very high incline, they could be following a viral workout trend.

The "12-3-30" workout, the brainchild of social media influencer Lauren Giraldo, involves walking on a treadmill for 30 minutes at a 3 mph pace and on a 12% incline.

Giraldo first shared the low-impact cardio workout on YouTube in 2019 in a video about her wellness routine.

She told " Good Morning America" she figured out the formula through "trial and error" while trying to find a workout that was both motivating and doable.

"I was at a low point and the gym was always an intimidating environment for me. I wanted to find what worked for me and got me excited about remaining consistent," she said. "Through this, I was able to play with the settings on the treadmill and found that the 12-3-30 combination was challenging, but fun."

Giraldo said of her workout philosophy, "I think it’s important that when you’re building out your routine it’s one that makes most sense for you. I don’t believe in strict guides because we’re all different."

Giraldo shared the routine again in 2020, this time on Instagram and TikTok in a video where she credited it with helping her lose 30 pounds. That video received more than 2 million likes on TikTok alone and made her 12-3-30 workout a viral hit.

The hashtag #12330 now has more than 81 million views on TikTok and the workout is tagged in thousands of posts on Instagram.

"We have cultivated a beautiful community of people that feel inspired," said Giraldo. "It’s become more about how it makes us feel, and less the workout itself."

Giraldo added that she believes the simplicity of the workout is what has made it so popular.

"I think we’re always told ‘you need to spend one hour in the gym to see results’ or ‘you need to go X amount of times per week to see results,’ but I think the world is tough enough," she said. "We’re just looking for a moment with ourselves, and for me that was 30 minutes on the treadmill."

Here are five questions answered about Giraldo's "12-3-30" workout.

1. What does 12-3-30 mean on a treadmill?

The workout is an easy-to-follow formula that just involves two settings on a treadmill, done for a time of 30 minutes:

Incline: 12

Speed: 3

Giraldo said in her TikTok video she typically does the workout five days a week.

2. What are the pros of the workout?

The Centers for Disease Control and Prevention (CDC) recommends that adults get at least 150 minutes of moderate-intensity aerobic activity per week, which the "12-3-30" workout can help fulfill.

In addition to being easy to follow, walking on a treadmill for 30 minutes at such a high incline is a solid and efficient workout, according to Dr. Marie Schaefer, a board-certified sports medicine physician at Ohio's Cleveland Clinic.

"It gives you all the basic benefits of cardiovascular exercise. It increases your heart rate. It builds muscle mass," Schaefer told " Good Morning America." "And by putting you on that 12% incline, it's actually going to nearly double your calorie burn and it can increase your heart rate a bit more."

Walking on an incline can also help strengthen a person's glutes and hamstrings, which is particularly beneficial for women, according to Schaefer.

"As people age they, especially women, lose their glute muscles," she said. "This is a good exercise to keep that muscle strong and prevent it from atrophying."

Schaefer noted that both walking and running, as opposed to other cardio exercises like cycling or swimming, are smart ways for women to increase their bone strength overall and lessen the risk of osteoporosis as they age.

"Weight-bearing exercises where you're pounding your legs on the ground are good feedback to your bones to help keep them strong," she said. "Walking on a treadmill is a way to do that, as is walking on the ground and as is running."

3. Are there any cons?

People should check with a healthcare provider before beginning any new exercise routine.

In addition, Schaefer recommends that people know their baseline before starting a new routine.

For instance, before trying the "12-3-30" workout, make sure that you can go on a 30-minute walk on a flat, outdoors surface. Then, make sure you can complete a 30-minute walk on a treadmill.

Then, start adding in the incline and modify as needed, including lowering the incline and using the handrails for safety, according to Schaefer.

"The most biomechanically appropriate way would be to do this without holding on to the rails and having a really good arm swing," she said. "But honestly, it can be too hard for some people to just start out from like walking on a flat ground to going at a 12% grade, which is pretty high."

Schaefer added, "Starting with holding the handrails is OK and then as you feel more comfortable and as you feel more balanced and stronger in your posterior chain muscles, letting go of those handrails as much as you can will give you a better workout with good form."

Schaefer also recommends mixing up the "12-3-30" workout with other physical activity during the week to avoid overuse injuries and to avoid hitting a plateau.

"There will be a time where your muscles kind of equilibrate and get used to this exercise and you do need to change the intensity," she said. "Ideally you would add in strength training with a cardio type of workout so that you're working other muscle groups."

4. Are there ways to modify the workout?

The workout's intensity could be increased by adding hand weights or adding running intervals, according to Schaefer.

Alternatively, the intensity could be lowered by decreasing the incline or speed.

5. What is a similar workout without a treadmill?

If you do not have access to a treadmill, the simplest way to mimic the workout outdoors is to walk for 30 minutes on a hilly route.

Alternatively, bicycling, tennis, swimming and walking or running outdoors will give you a similar, steady cardio workout, according to Schaefer.

Editor's note: This was originally published on Jan. 4, 2023.