The splits was a fairly comfortable move for me execute when I first got into circus. It was something I've trained before and decided to progress into those dreamy over splits by stacking yoga blocks and eventually chairs under my front leg.
I've always admired my colleagues and I've always admired them as they've the most beautiful over splits I've ever seen credited to their decades of dance training prior to circus.
Hip soreness, tightness and eventually injuries crept in for those few unlucky few. We were all puzzled and decided to investigate what was going on with our training and that's when we discovered the benefits of squared splits and how much muscular imbalance we've created from constantly practicing our opened splits.
Here, I'll explain what an opened split looks like:
Tilted/rotated hips. Hip bones are pointed diagonal.
Stretch of the adductor of the back leg. (adductor brevis, adductor longus, adductor magnus, gracilis and pectineus)
Stretch along the medial hamstrings (semitendinosus and semimembranosus) of the front leg.
External rotation of the back hip
Shortening of the back leg external rotators & hip flexors
The open split allows a larger range of motion that creates long beautiful lines. Hence, a much favourable options for performers.
A squared split on the other hand looks like:
No rotation of the hips (hip bones pointed forward)
A shortening of the back leg adductors and front leg medial hamstrings
Stretch of the lateral hamstrings of the front leg (biceps femoris)
Stretch of the back leg external rotators and hip flexors.
For those wanting square your splits, I'd suggest looking at yourself in the mirror to ensure both your hip bones are pointed forward, your back knee and ankle are pressed directly into the ground and your shoulders squared forward as well. Feel free to use yoga blocks under your palms to help take some of the loading off so you can concentrate and feel the alignments.
Be patient and good luck!