There is a Kamidana, household Shinto altar in every Do-jo

Every Do-jo has Kamidana, a household Shinto altar.
Every time entering and exiting Do-jo, starting and finishing drill, all member in Do-jo  
We put both fists in the floor of Do-jo and hang down the head facing to Kamidana.
This bobbing a curtsy in sitting is a ceremony.
In my case, these bow to Kamidana makes me concentrated and some gratitude for training.