Wow you people aren't familiar with Sports Acrobatics. I instruct it. This is a typical classic pose in the trio division of Sports Acrobatics. It's practically compulsory. The pic is definitely real. None of them are under any particular strain since they're completely conditioned and trained in the art and practice daily for an average of 2-4 hours per session often more than one session per day. The bottom girl assumes her position, the middle girl gets on top of the bottom girl and assumes her position and the top girl steps onto the bottom girl and then onto middle girl's upper back and, in this case her right buttock, takes hold of the middle girls top foot with both hands, does a muscle-up style pull-up to a support position as one would be in at the end of a typical ordinary parallel bar dip but with the hands together and then lifts her legs into the straddle L support you see her finishing with. From here she'll press into a handstand and do variations of handstands some on one arm and with contortions such as splits, side planches etc.
@kryten8, That's a function of both strength and flexibility. No matter how strong the muscles involved may be and there are many many muscle groups involved biomechanically, if they aren't well balanced in both strength and flexibility to extreme degrees there will be not only strain but actual injury. It's also knowing how to utilize the flexibility and strength to achieve a balance point where to the onlooker it seems there can't possibly be one. The science of acrobatics. Hence knowing how to condition the body for this and how to apply the correct techniques are what make it appear to be more difficult for the performers than it actually is.
Wow!