Have a ball on leg day with this killer exercise

If your typical leg day consists of just a few general moves spread between the squat rack and leg press machine, youre leaving superhero-sized potential gains out there on the gym floor.

Since they're so essential for explosive, powerful movement, hamstrings are a prime candidate for special attention.

Superhero trainer Don Saladino uses a variety of techniques to help clients like Ryan Reynolds and Sebastian Stan build up their hamstrings, but one of his go-to machine-free moves is the hamstring curl. He's already demonstrated how to use sliders to work the muscles - this week, an exercise ball (also known as a Swiss ball) helps you to get the job done.

"Using the Swiss ball is fantastic because you force the entire body to engage," says Saladino. While the knee is the only joint you'll be moving, Saladino points out that the efforts you'll use to stabilize your hips will also send your core into overdrive, and that you'll get some glute work in to boot.

To perform the move, you'll need an exercise ball. If you don't have one handy, check out this option. Find a spot on the gym floor where you can stretch out, then get ready to curl.

Lay on your back, propping your heels flat on the ball with your legs extended.
Keep your palms flat on the floor to brace and balance yourself.
Hinge at the knees simultaneously to curl your legs in, squeezing your hamstrings to bring the ball toward your butt.
Squeeze your hamstrings and core for a count, then straighten your knees and extend your legs to roll the ball back to the starting position.

Once you get used to the move, you can also get some unilateral work in and ramp up the difficulty by using just one leg at a time.

Add the Swiss ball hamstring curl to your leg day with 4 sets of 8 reps, working up to 12 reps once you find your balance. Cut down the rep count to 5 for the one-legged version to start. For more superhero-body building moves, you can check out all of our Superhero Fit Workouts or Saladino's full program.