Sentakomono is the most demanding and most risky of the nine Shibari Fumo Ryu suspension positions. It should not be attemted by inexperienced people and requires serious training for the recipient. Even a welltrained recipient will not be able to maintain this for very long. How long? Unfortunately there is no simple rule of thumb, because almost everything depends on bodyweight, physical abilities and muscle strength.     

The reason it is being described here is largely in the need to present a complete documentation and NOT to actually encourage people to try this at home. The risks you run are serious:

While the obvious risk seems to be in the wrist joints and the potential blockage of arteries (which is a risk), the two main risk factors actually are the shoulders and the ribcase. This position locks the rib case and seriously limits the ability to breath. The level of oxygen intake may in fact drop to the point where it becomes life threatening, simply by locking the ribcage. The other main risk is in the shoulders and actually, there are two risks here. Dislocation of the shoulder joints and breaking bones is one of them, but the other is in the fact that a serious segment of the nervous system runs through the shoulders and these may easily be ruptured, which may lead to very nasty consequences such as disability in the arms or hands or lifelong pain or numbness.

A recipient can train for this by simply pulling herself up while hanging on the arms. This is first of all not something everyone can do and it is quite an athletic excersize that needs to be maintained for a longer period of time before attempting this suspension position. And even then the situation will never be entirely safe, due the fact that there are differences in the position of the hands and arms (compared to pulling yourself up).

Besides, even when trained, this position soon becomes exceptionally painful, which is another thing to consider.