It’s the ball. THE ball.

Swiss, exercise, fit, stability — call it what you will. A ball by any other name would give you as excellent a workout.

Forty years after Swiss physical therapists began using them to help patients regain balance and strength, the colorful balls have become fixtures in gyms everywhere. Stability-ball classes are one of the fastest-growing segments of the fitness industry.

This unassuming, inexpensive exercise tool takes you beyond basic weight training by working your 29 core muscles, the body stabilizers that are the starting point for all movement. Strong core muscles improve tone, posture and strength and help protect against injuries.

There probably are a thousand stability-ball exercises, but here are six to get you started, with some variations when you feel confident. Just sitting on it tones the body, which makes it the world’s greatest desk chair — work out while you work!

Be sure to warm up with 5 to 10 minutes of cardio before the workout, then do one to three sets of 10 to 15 repetitions of each exercise. If you find balancing on the ball a challenge, practice the starting position for the easiest variation for each exercise until you feel more confident. Spreading your feet wider will give you more stability, and it’s easier to balance on a softer ball.

No. 1: The crunch

• Muscles worked: Abdominals, obliques
• How to: Sit on the ball and walk your feet out until you’re lying with the ball against your mid and lower back and your feet are shoulder-distance apart. Cross your arms over your chest or put your hands behind your head for support and tuck your chin in a bit toward your chest. Contract your abs and slowly curl up to no more than a 45-degree angle; let your shoulders and upper back lift off the ball. Slowly return to starting position.
• Variation: Lie back with hips supported on the ball and neck, shoulders and upper back off the ball. Your body will form a tabletop, with eyes focused on the ceiling. Curl up from here. To increase difficulty further, move feet and knees closer together.

No. 2: Hip lift

• Muscles worked: Obliques, back, hips, arms
• How to: Lie on the floor with the ball under your knees, hands on the floor or crossed over your chest. Lift your hips until they are fully extended, pressing your arms against the floor to help with balance. Slowly return to start.
• Variation: To make this harder, don’t use your arms to help. Change your starting position by moving the ball under your calves or feet with legs elevated. Move your feet closer together.

Lisa Ryckman stretches over an exercise ball.

No. 3: Reverse curl

• Muscles worked: Abdominals, obliques
• How to: Lie face-up on the floor with arms at your sides. Flex your legs at a 90-degree angle and grip the ball between your thighs and heels. Using your abdominals, lift your hips slightly off the floor. Slowly return to start.
• Variation: For more difficulty, cross your arms over your chest.

No. 4: Arm and leg raise

• Muscles worked: Glutes, hamstrings, deltoids
• How to: Lie over the ball with your body centered, eyes focused down. Extend your right leg, foot on the floor. Extend your left arm, hand on the floor. Simultaneously lift the right leg and left arm, keeping your head still and hips and shoulders square. Slowly lower to start position. Repeat, alternating sides.
• Variation: Lie over the ball with hips supported, both legs extended with toes touching the floor and arms extended with hands apart and on the floor. Lift right leg and left arm as above, and alternate sides. Be sure to keep the head level and still.

No. 5: Push-up

• Muscles worked: Chest, shoulders, triceps
• How to: Lie over the ball, thighs supported, hands on the floor, shoulders directly above wrists. Flex your arms and lower your chest. Pause at the bottom, then press back up.
• Variations: To make this exercise easier, start with the ball under your hips, feet either on the floor or somewhat lifted.