Strengthening your central, upper and lower abdominal muscles can be performed with a variety of exercises. However, to strengthen, tone and reshape your side abdominal muscles, or obliques, you must perform specific exercises. The oblique twist and its variants will help give you a leaner, more muscular mid-section. Perform two to three sets of 10 to 12 repetitions of each exercise. If you’re new to exercise or you have recently experienced a back injury, consult your physician before performing oblique twists or any new exercises.

Alternating Knee Oblique Twist
Step 1
Lie with your back on a yoga mat, bending both legs and keeping your feet flat on the floor.
Step 2
Place your right ankle on your left knee, then cross your arms over your chest or clasp your hands behind your head.
Step 3
Raise your head, shoulders and back off the mat and bring your chest toward your right knee.
Step 4
Twist your torso to the right as your chest approaches your right knee, holding this position for 15-30 seconds and keeping your abdomen tight.
Step 5
Lower your upper body slowly to the original position. Alternate sides between sets.

Double-Knee Medicine Ball Twist
Step 1
Lie on your back on the mat with your knees bent and feet flat on the floor.
Step 2
Hold a medicine ball with both hands and lift your feet 3 to 6 inches off the ground and cross your legs at your ankles if needed.
Step 3
Raise your torso off the ground and twist from the left to the right with the medicine ball, keeping your abdomen tight.
Step 4
Lie back on the mat, returning to the original position, with the medicine ball in both hands.

Inclined Oblique Twists
Step 1
Lower the back of a weight bench to 45 degrees to create more resistance during the exercise.
Step 2
Lie on your back on the bench with your knees bent and feet flat on the bench. For more resistance, hold a dumbbell or plate weight to your chest.
Step 3
Raise your upper body off the bench slightly until you feel your abdomen tightening and twist your torso to the left and right, pausing at the height of each twist.
Step 4
Lower your upper body slowly to the original position.

Things You’ll Need
* Yoga mat
* Dumbbell
* Weight bench
*
Tips
* Complete these exercises along with a full-body strength training session at least two days a week.
Warnings
* Avoid overworking muscles — allow your obliques at least a day of rest between workouts.

Checkout all the video workouts below

Reclined Oblique workout Level 2

Reclined Oblique workout Level 3

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Source: Livestrong