(Double post oh no!)
So let's conduct a thought experiment wherein a guy named ilE wanted to do the side splits. What might be the best way of stretching for this? Seated butterflies? Standing with the legs apart? Seated with the legs apart?
Chris has great advice, as always. In addition to hamstring flexibility (which you will need to keep your spine properly aligned in the side splits and the stretches leading up to it, so you can get the most gains), here are a couple of other suggestions that I'm only recommending because you already seem to have good body awareness and a good head on your shoulders with regard to training (i.e. you are not about to go hog wild and hurt yourself with these stretches).
Note to others: these stretches are pretty "advanced" (for lack of a better word). They put quite a strain on your body and I don't recommend them for everyone. If you try these, listen to your body, scale back if you need to, and STOP if anything pulls/hurts.
Make sure you are warm before doing these. I also recommend doing these after you have done some basic hip-opening stretches like butterfly, seated straddle, etc.
1. Supine straddle: lie on your back on a bed that is up against a wall. Scoot your butt up against the wall and put your legs against the wall so your body is making an "L". Relax, breathe deeply, and let your legs slide apart into a V. They will stop when they are at their limit. Breathe, relaxing into the stretch, letting gravity take over and letting your legs give in to gravity as your muscles relax and release.
If you feel any twisting in the knee, or tightness/pain in the hip sockets, either adjust the rotation of the leg, or stop the stretch all together depending on the sensations you feel. Listen to your body.
Hold the stretch for at least a full minute. I had a (hardcore, BAMF-type) dance teacher who had us do this for 30 minutes a day, but I'm not sure that was too wise. Those with more knowledge than I can tell you how long is a good idea to sit in the stretch.
To come out, use your hands to help draw your legs back together. When they are together, bend the knees towards the chest and roll over onto your side.
2. Trestle stretch: get on all fours on the floor. Make sure your thighs are directly under your hips, so your body is at right angles like a table. Spine is neutral, core is engaged to support the torso, spine is long.
Slowly spread your knees apart from one another, letting your pelvis get very heavy, drawing towards the floor. You may have to go down to your elbows to keep your body level.
Your legs will stop spreading when they are at their limit. Breathe, relax, let gravity help you.
3. Frog stretch: From trestle stretch, walk the hands forward until you can comfortably lie down on your belly on the floor with your legs still spread apart. Very carefully, draw your feet together as closely as they will allow, so your legs are making a diamond on the floor. Be very mindful of the knees on this one and adjust as necessary. The goal is to get the legs totally flat on the floor in the diamond shape, with the soles of the feet together.
4. Supine one-legged side stretch: On your back, with spine neutral, core engaged, put your feet on the floor with your knees bent. Bring one knee in to the chest and slowly straighten the leg, as straight as it's willing to go. You may need to use a strap around your heel to hold your leg in place. Let the bent leg drop to the side (as a counterbalance) as the straight leg also opens up to the side. Breathe, relax, stretch. Repeat on the other leg.
5. Wall straddle: Sit in a straddle with your heels against a wall. Scoot forward slightly, just beyond what's comfortable but not to where you're hurting yourself. Breathe, letting the wall help you. Take care to be sure your knees are in line with the center line of the leg, over the middle toes, and there isn't any torquing or twisting. As your muscles relax, continue to scoot towards the wall a bit more, using your hands to push, to try to increase the ROM.
6. Progression to side split: Using a heavy chair or other stable object for support, stand on the floor and slide into a side split (wherever yours happens to be), resting your hands on the chair to help support your weight. You may also want to hang onto an overhead bar instead. The point is to keep a portion of your bodyweight off your legs, but still allowing some weight so that you can increase your stretch. Over time, you want the distance between your legs/pelvis and the floor to decrease until you are in a full side split.
7. Standing side split stretch: Holding on to a countertop or other stable surface for balance, stand with your heels together, legs outwardly rotated from the hip to their natural limit. Be sure you are not twisting your feet beyond the rotation of your thighs/hips. Knees should be directly over middle toes. You should be in ballet first position.
Bend the knees slightly, keeping the torso erect. Lift one leg, maintaining the outward rotation and the bent knee. Reach down and grab the inside of the heel with your hand, and stand up. Lift the knee to the side as high as you can, keeping the working knee bent (standing leg is straight). Use your hand to help pull the foot up and, consequently, the knee.
Be mindful of the rotation of the standing leg. Make sure you are not bending or twisting that leg. Keep the glutes engaged to stabilize the pelvis and protect the knee.
As you gain more flexibility, gradually work towards straightening the leg. You may find it easier to hook the arm under the hamstring of the working leg, pulling the thigh in towards the torso, and the knee towards the armpit, before straightening the leg.
Pelvis should be dropped, lower back long, and lower core very engaged in this stretch to stabilize the pelvis and ensure proper alignment for the stretch, so that you are stretching the right things to get into a split. Otherwise you are working against yourself.
Kind of what these little dudes are doing starting at about 0:30 is the end product you're working for.
http://www.youtube.com/watch?v=w1cqS8W45sYHere is more, to help with general hamstring flexibility and front splits (kind of basic but it's a good starting point). If you can get these, then the side splits are just a matter of hip opening.
http://www.youtube.com/watch?v=h8D7R8QxJL4The biggest key is the alignment of the back and pelvis. The lumbar curve should be preserved. Very often in seated stretches people tuck the pelvis, curving the lumbar out and back. This ends up stretching pretty much nothing; although for most people this is a result of a lack of hamstring flexibility.
I hope that helps you for now. I would love to do a full-on article with pictures and video, because for these stretches the alignment is so important.
All in due time. I need to win the lottery so I can quit my jobs and just train myself and others full-time, and collaborate and write articles!
Good luck! And thanks for your patience.
