try this. get a 5 to 7 kg weight .... and throw it at good speed into your training partners chest. ask how it feels.
Its pretty simple mechanics really IMO ... dont know what the fuss is about. Its simply emparting all the weight of the striking limb into the surface. It is different to some ways of hitting but is found in other arts. Daito Ryu has a way of releasing with gravity thats very similar.
However when you watch Mikhail or Vlad striking they do tend to have something going on in the body too.
With Vlad there is a wave happening in his striking. from 1.45 here. this then gets condensed when he is moving quick. Just from my observations and feeling his strikes. This is becoming less and less apparantly in his later videos and his striking is starting to look more like mikhails ... but its still 'wavey' to my eyes.
With mikhail there is a 'through the back power' happening in the main (which we also see in some xing yi striking) You can also see he is using his body here. Its not happing from just the arm regardless of what is said. If you completely ignor mikhails arm and the guy being hit and just watch the body it is clear, there is a power across his back and a pulse sort of force from his scapular as well as his whole body turning. In some of the strikes its very subtle and short but its always there.
This is entirely from an outside of systema perspective from watching these two guys move and attending a couple of seminar. But i think its pretty clear stuff.
I think once you 'get' how to put your force into the surface this is all familier stuff no matter what art. The idea of just the arm hitting is a little bit of a smoke screen IMO and appears to just be an initial fase of the method. I think systema have a good way of teaching how to give the force of your strike to your opponent using the 'only arm' thing but the general principle is there in other arts. The thing is it is usually attached to other parts of the complete picture of the idividual arts like 6 harmonies etc.
Cheers
Chris