You do the splits by extending one leg forward, while extending the other leg backward and lowering your pelvis to the floor. The splits require flexibility in the quads and hamstrings as well as the hip flexors and buttocks. If you have issues with flexibility, you may not be able to do splits from a standing position, or be able to touch the pelvis to the floor without hurting yourself. You can still do a full split by starting on the floor and using props to help your body ease into the position.
Warm up with at least 5 minutes of aerobic exercise before doing the splits. Alternatively, do your splits at the end of your workout, when your muscles are completely warmed up.
Kneel on the floor with your buttocks on your heels. This will be the start position for your box split.
Lean to the left and pull your right foot forward. Rest your right shin on the floor with your heel in front of your left knee and your right knee pointing to the right. Relax into this position for 10 seconds. You should feel a slight stretch on the outside of your right leg.
Lean forward and put your hands on the floor for support, if necessary. Extend your left leg behind you until your leg is straight and the top of your foot rests on the floor. Keep your right leg bent. Relax into this pose for 10 seconds. You should feel a stretch on the outside of your right leg and along the front of your left thigh and hip. Put a yoga block or large book under your right hip, if necessary, to support your body weight.
Extend your right foot forward until your right leg is straight and your right heel rests on the floor. If necessary, put one or two yoga blocks, or books, under your right hip to support your weight. Relax into this position for 10 seconds. You should feel a stretch along the back of your right thigh and buttock and the front of your left leg and hip.
Remove one block to get closer to the floor, if your flexibility will allow. If not, stay in the high split. Over time, your muscles and tendons will become more flexible and you will be able to remove the supports.
Bend your right leg, lean on your right hip and swing your left leg forward to come out of the split. Shake your legs, then rest in a comfortable seated position for 30 seconds. Repeat the split with the opposite leg.
As you become more flexible, you will eventually be able to do the split from a standing position by sliding your front foot forward and your rear foot back.
Do not attempt to go into a full split from standing if you have never done it before -- you may pull, tear or strain your muscles. Stop immediately if you feel pain in your thighs or hips, or if you feel or hear a pop.