Can you pull up your human hard drive (ie. your brain) and remember how good it felt to go to recess as a kid? As a boy, it felt like a tiger being released from a cage to go run...or pummel someone in the face with a dodge ball...or with a wrench? [youtube 0iXP9yoc4VY]
My point is simple, if you want people to work hard you have to have a system that allows people to play hard. Just because we get older doesn't mean that we no longer need or enjoy breaks from what we are working hard on. Opportunities to stop and play. Believe it or not, play can be a critical component of getting work done. Did you know that there are companies out there (Google and 3M) who provide employees with an entire day at work to be creative and play. The rewards from this time are huge! For Google, it lead to Google Maps, Google Voice, Google Calendar, etc... You get the picture.
Don't confuse time off with time of play. I literally mean to take time from working and play together. When was the last time you took your people and went together to do something fun? And this is critical, it has to be something THEY ENJOY. I know a leader who plans to do things only they enjoying doing, not activities their team enjoys. The hard truth is that the team only does it to make the leader happy, so everyone ends up making deposits from their emotional bank accounts because, really, they hate it. LAME. Do something that 80% of the team would enjoy and you'll have a team that works hard together.