Bows are the imagery for structures in the body that can bend to adsorb power and then release it, principally this is loading of tendons, muscles perhaps and the fascia to store and release energy. Leg bows, body bows thumb fore finger bows chest bows etc... are all useful in understanding how to adsorb store and release energy. 

We get some very nice experiences of this from Okajima sensei (see movie), we see it in system and other arts too

Here is a more complete explanation in Mike Sigmans  2nd video