Earthy scored a first senior goal in the final day win against Luton.
"You know the level you have to be at, and you see it around in all the players," he told whufc.com.
"That's why the off season is so important, to build yourself back up for the pre-season at such a high level. It's amazing to see all the testing and all that that goes on at pre-season now, but yes, it's very high level, so have to try and maintain that.
"You have to sort of look after yourself - and that means a couple of weeks of just planning and working hard just to kind of get yourself back up to that level before you even come back. So, yeah, buzzing to be back here now."
Earthy added: "It's been good to meet all of the coaches. It's good to see (Julen Lopetegui) around the building and see them on the training pitch - how they work differently to other managers.
"It's really exciting times at West Ham to work with the new manager, the new staff, meet them all, see how they work and what we can do differently as a team."