Get in shape this summer: Teens work out for free at Planet Fitness

School's out, the gym is in.

Starting May 15, high school teens, ages 15 to 18, can exercise for free at Planet Fitness gyms across the country all summer long.

Planet Fitness, a sponsor of "Good Morning America," is committed to helping teens kick start their summer fitness regimen with the Teen Summer Challenge.

"We did an internal survey and almost half of the students say they don't stay physically active when school ends and summer starts and 90% of students wanted to stay active," Chris Rondeau, Planet Fitness CEO, told "Good Morning America." "And almost more intriguing than that was that more students wanted to stay active, not be on social media, not watch TV and not play video games, so Planet Fitness is here to give access."

Rondeau said he hopes teens are able to make fitness and wellness part of their lifestyle from the program and also develop self-esteem and a more positive body image.

"With bullying that you see in the news today, I think it's really good to help build some of that self-esteem along the way," Rondeau said. "Personally, I started working out when I was 16 right after I got my license. For me, I think it builds regimen and discipline and I think it can be used in a lot of facets of your life, whether it's career or personal life."

The challenge gives teens the opportunity to achieve the recommended level of at least 60 minutes of moderate-to-vigorous daily physical activity set by the U.S. Department of Health & Human Services.

Plus, to jump start for the future, all participating teens will be entered into Planet Fitness' Scholarship Sweepstakes where 51 lucky teens will receive a scholarship for college, including a $5,000 grand prize. Learn more about the challenge here.

Brian Zehetner, the director of health and fitness for Planet Fitness, shared a teen-friendly workout with "GMA" that combines cardio, strength training and exercises that enhance flexibility.

Scroll down to get his recommended strength-focused moves to start your summer fitness routine out on the right foot and feel your best.

4 strength exercises to know about

Perform the each exercise for 30 seconds and then rest for 30 seconds as you transition to the next station. Follow this pattern until you have completed all four movements.

Dumbbell Chest Press: First, select two dumbbells that are a comfortable weight for doing chest presses. Next, lie on a flat bench with a dumbbell in each hand and lift the dumbbells in succession, keeping them above your chest simultaneously. Keep your core engaged and your head, shoulders, and back flat against the pad. Avoid locking out your elbows at the top. Your arms should stay at roughly 90-degree angles at the bottom.

Lat Pulls: Using a pulldown machine, first select a comfortable weight to get started. Then, pull the bar down in one complete motion, bringing the bar to the top of your chest. Keep your core engaged and your back flat throughout the movement. Avoid locking out your elbows.

Smith Machine Squats: First, select an appropriate weight. Then, proceed with successive squats using the Smith Machine, keeping your chest up, back flat and core engaged as you lower your body. Shift your hips back so that your knees don't go past your toes. Push through your heels to return to the top and avoid locking out your elbows.

Rope Crunches: Using the rope attachment on a cable system, first select a comfortable weight, then kneel in front of the machine so that the rope hangs just in front of your head. Grasp the rope with both hands and pull down; keep your arms in a consistent position throughout the movement and avoid using momentum.