You've seen them lying around the gym, but you've never really known what to do with them. At first, you may have thought they looked "girly," but then you probably saw some of the most muscular guys at your gym using them. I'm talking about exercise balls, those big blow-up spheres that can be used to perform an almost endless amount of exercises for every body part. If you've wanted to try them but have never known what to do, here are 10 great exercises to get you started.

Number 10

Trunk extension
What it's for: Lower back

How to do it: Get down on your knees and drape your upper body over the top of the ball, with your arms lightly hugging the back of the ball or with your hands behind your head. Lift your chest off the ball until your spine is straight or slightly extended. Return to starting position.

Number 9

Core crunchers
What it's for: Abs and core muscles

How to do it: Get on your knees, bend at the waist and rest your elbows on the ball. Squeezing your abs, roll the ball forward until your upper body and thighs form a straight line. Roll back to starting position.

Number 8

Basic crunches
What it's for: Abs

How to do it: With your feet flat on the floor, place your lower back on the ball, and your upper body and thighs parallel to the floor. Do crunches as usual, lifting only your shoulders and upper back off the ball, using your abs.

Number 7

Elevated pushups
What it's for: Pecs, shoulders, triceps, and abs

How to do it: Place the front of your knees on the ball and your hands flat on the floor (your whole body should be parallel to the floor). Look down at the floor and lower your face to within a few inches of it, then push back up to the starting position.

Number 6

Bent knee bridge
What it's for: Buttocks and hamstrings

How to do it: Lie on your back with your knees bent and your heels resting on top of the ball. Spread your arms out on either side of you. Lift your butt off the floor while squeezing it, and push your hips toward the ceiling. Pause at the top of the movement, then go back to the starting position.

Number 5

How to do it: Lie on your back with your knees bent and your feet flat on the floor. Place the ball on your thighs, right near your knees, and your hands on top of ball. Lift your shoulder blades off the floor, rolling the ball to the top of your knees, pause, then go back to the starting position.

Number 4

Opposite limb extension
What it's for: Lower back, buttocks and hamstrings

How to do it: Lie with your stomach on the ball and stabilize yourself with your toes and hands. While looking down at the floor, extend your left arm and your right leg simultaneously, hold for 2 seconds, and return to the starting position. Repeat with the opposite arm and leg combination.

Number 3

Balanced pushups
What it's for: Pecs, shoulders, triceps, and abs

How to do it: Place your hands on top of the ball and your body at a 45° angle with the floor, balancing yourself on the tips of your toes. Bend at the elbows and lower your upper body to a few inches from the ball, then push yourself back up to the starting position.

Number 2

Superman
What it's for: Lower, middle and upper back, and buttocks

How to do it: Lie with your stomach on the ball and your body at a 45° angle with the floor, balancing yourself with the tips of your toes. Stretch your arms out in front of you on either side of your head as if you're flying, and maintain the position.

Number 1

Seated wall roll
What it's for: Quadriceps, hamstrings and buttocks

How to do it: Stand with your back to a wall, feet shoulder-width apart, and place the ball between the wall and your lower back. Squat, letting the ball roll along your back, until you are in a "sitting" position with your knees forming a 45° angle. Return to starting position.

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