Pushing yourself to your physical limits is fun sometimes. Take, for instance, sprinting as fast and as far as you can to increase your strength and endurance. Or using the heaviest dumbbells you’ve ever used before in a workout. Or, if it’s a lower body day, sweating through the hardest resistance band leg workouts that exist.

It’s especially key to strengthen your lower body muscles because your lower half is responsible for taking you wherever you go. “Leg exercises are crucial because they are the foundation for your functional strength and for having balance,” says Ridge Davis, a celebrity trainer and Puma athlete. If something is off or imbalanced in your leg muscles, it can throw the rest of your body out of whack. “Many upper body posture issues stem from weak or tight lower body muscles,” he says, pointing to lower cross syndrome and sway back, which happen when the glutes and hamstrings are weak and the quads and hip flexors are tight.

“I always preach that glutes are everything,” says Davis. “We use them in all movements—even abs and upper body ones.” To hit your glutes, quads, hammies, and calves—and hit them hard—he’s revealing his go-to leg exercises that will have your legs quaking, but all the more powerful once you’re done. Keep scrolling to start sweating.

4 of the 4 Hardest Leg Exercises That Boost Your Lower Body Strength you can do

1. Weighted plyo switch lunges

This exceptionally challenging lunge variation not only hits all of your leg muscles, but it works as cardio, too (thanks to the plyometric movement). Start at the bottom of a lunge with your front knee over your front ankle, dumbbells in each arm at your side. Jump straight up by pressing the floor away hard with the front foot, then land softly into the starting position. Keep your chest lifted, and try to land softly. Switch legs.

2. Bulgarian split squat

Challenge your balance and your glutes, hamstrings, quads, and calves with the Bulgarian split squat. Begin with both calves touching a bench or box behind you. Hold a dumbbell one to two inches in front of your chest. Take a medium step forward with one foot, and raise the rear foot to the bench or box with your toes down. From here, lower your rear knee to the floor, maintaining even pressure through your foot, then press the floor away to stand up. Make sure the front knee is pressing outwards, and that all of your weight in the front foot is in your heel and outer foot. Switch legs.

3. Stability ball leg curl

Your stability will be tested with this exercise, which will strengthen your lower body—especially your glutes and hamstrings—along with your core muscles. Begin on the floor lying on your back with your feet on top of a stability ball. Make sure that when your legs are extended, your ankles are on top of the ball—this is your starting position. Raise your hips off of the ground, keeping your weight on your shoulder blades and your feet. Flex your knees, pulling the ball as close to you as you can as you contract your hamstrings. After a brief pause, return to the starting position. Keep your hips lifted the entire time and your belly button pressed towards your spine.

4. Wall sits

The exercise you used to do in P.E. is actually really challenging, and Davis likes to up the ante with weights. Sit with your shoulders and lower back pressed against a wall, and bend your knees at 90-degrees. Hold. To try it with weights, hold a pair of dumbbells at your shoulders or pressed overhead. Remember to breathe.