If you're ready to take the regular splits to the next level by trying the splits between two chairs, first you need to be sure you have mastered the standard split. Splits that go beyond a 180-degree angle -- often called the "oversplits" -- will involve a higher degree of strength and flexibility than you'd use for floor splits. To avoid injury performing chair splits, you should spend more time getting ready for the exercise than you will actually performing it.
Warm up your muscles by running, cycling or doing some other type of aerobic exercise for five to 10 minutes or until you've broken a light sweat. Follow that with dynamic stretches, kicking your legs forward and backward and performing high-knee walks. After that, do static stretches that can include stretches for the lower back, hips, buttocks, hamstrings, inner thighs and quadriceps. Move into each stretch slowly; stretching "cold" will set you up for injury.
Arrange two chairs with flat seats about 2 to 3 feet apart, with the edges of the chair seats both facing in one direction. The chairs should be sitting on a surface that will not allow the chairs to slide around.
Place a square sofa pillow on top of each seat, if the chairs do not already have a soft surface.
Ask a spotter to stand near you, in case the chairs start to slide around when you don't want them to do so.
Place one leg along the seat of one chair, either facing toward the chair for the side splits or facing perpendicular to the chairs for the straddle splits. For the side splits, put the back leg on the back chair first. Slide it toward the outside edge of the chair, stopping at the edge of the chair.
Ask your spotter to hold and press against your hands, to help you stay upright as you move your second leg on top of the second chair.
Slide your second leg -- either the "front" leg of the side splits or the second leg of the straddle splits -- toward the second chair's outside edge, allowing the foot to hang off the outside edge of the chair if necessary. Breathe and relax your muscles as much as you can and have the spotter continue to press against your hands as you lower your body down, until your second leg is fully resting along the top of the chair.
Let your spotter know when it's OK to let go of your hands. Hold the position for a few seconds as you tighten your muscles and then let them relax, helping to deepen into the stretch.
Move the chairs 6 inches farther apart and repeat the steps listed above. The farther apart the chairs, the deeper the stretch. If the first round was really difficult, try moving the chairs closer together and working on that level of overstretch before moving the chairs farther apart.