The middle splits will be unique to every individual, as every individual’s hip geometry will be subtly different, this means that you have to experiment with various amounts of hip tilt/lower back arch as well as femur external/internal rotation. If at any point you feel any pinching or a hard stop deep in the hips, there is a chance you’re hitting a bony limit, which is a sign that you need to reassess what your hips/femur are doing.
The first exercise I use for establishing the level of hip tilt and external rotation needed for the side split is the horse stance:
The horse stance techniques vary wildly depending on the purpose it’s being used for. For the purpose of learning the middle splits it’s important to keep the chest up, lower back arched and knees pulled out. Once your hips are below your knees you can start bringing the feet wider.
Similar to the long lunge, the horse stance can be progressively widened to the point of being a horse stance, explored in two more of my horse stance videos:
Weighted Horse Stance Squats
The key with the weighted horse stance squats is not to progress it as you would a typical weighted exercise by increasing the weight over time, but instead you want to reduce the amount of weight used, while still producing increases in range.
3-5 sets 10 reps, 2320 tempo, hold last rep deep for 10s seconds. 2-3 times a week
A Method to Speed Up Your Horse Stance
This is a genius exercise from Thomas Kurz, the grandfather of advanced stretching methods.
What it is, is a Horse Stance Squat Press, alternating sides. You must make sure that the kettlebell (or any weight really) returns back to your shoulders as you return to the bottom of the horse stance.
3 – 5 sets 10 reps (5 reps a side). 2 – 3 times a week.
For further information on the Horse Stance, I helped with a Horse Stance Motivational Month on reddit /r/flexibility forum, which can be found here.
Quick and Dirty Side Splits Routine
This routine is a general case application of some of the Methods and Principles of the Modern Methods of Mobility syllabus. This would be aimed at people who want to make very quick progress on the side splits and reduce the volume on other lower body flexibility volume.
As everyone’s hip geometry is different so you have to really find your own here. Also be careful of keeping the feet flat and forward Chinese martial arts style as a lot of you haven’t got the required ankle mobility to uncouple the external rotation of the femur from the ankle position and will just kill progress by not getting any external rotation.
Every 5 days perform the following:
A: Tailors pose  3-5 sets of 10-15 reps + 20 – 30s hold on the last reps
B: Horse stance squats  3-5 sets of 10-15 reps + 20-30s hold on the last reps
C: Isometric side split holds, 3 – 5 sets of 45s – 60s
Notes: For A and B add 1 set each repeat til you reach 5 sets, then deload back to 3. For the holds on A and B do not relax fully but maintain a 50% contraction. For C slide out into your current middle split do a couple of quick 2-3 second contractions slide further. Then start the isometric. If you can’t hold steady unwavering tension then more your feet in a couple of cm on the next set.
Kung Fu Twins Side Splits
This is a routine that was done by a pair of twins that I came across at a juggling convention many years ago. I’ve forgotten their names but to this day they had the best side splits I’ve ever seen, which was made even crazier by their complete lack of flexibility in other positions.
Seems to draw influence from chinese kung fu/wushu, so uses a lot of pulsing to develop range. My only prerequisite is that you can sit on the floor in a pancake.
1 – 5 reps each side, alternating sides
2 – 5 reps hinging forward while trying to open out the hips forward by engaging the glutes
3- Then lift your hips and widen your legs
When talking to the twins, they recommended between 200 – 400 reps a day in each direction, with a noticeable difference between the two, as one did 200 and the other 400. Start with 50 – 100 reps daily in each direction to start, as 1 continuous set and progress from there.