Well, truth, you might not "think" anyone has such control, but the truth is that many of us do.
Allow me to introduce myself..... I am Chief Master D. J. Eisenhart. :mst:
If you would prefer to meet in person, call my school for an appointment.
That is the general idea, Doc. First you learn the power of a kick to break smaller bones, then work your way up to being able to break larger bones. Once you have attained the ability to do certain kicks correctly, there is not any bone, in any human body - - no matter what the condition of the bone or the surrounding muscle, that can not be broken. Excessive fat on a morbidly obese person might make access to some bones difficult, but alternate bones and joints would then be targeted.
The femur is not as difficult to break with a kick as some non-kickers might think. From a medical standpoint, all one needs to do is consult medical journals and records to see how many femurs have been broken over the years in accidents (automobile, mountain climbing, sports: football, soccer, etc.). Don't think for a moment that I can not generate sufficient power to destroy a femur, nor that it would be too difficult to target and break instead of popping the hip or knee (either of which might occur as well). This is exactly what we train to do in Taekwondo, and many of us are quite capable of doing it very well.