Here's a quick little video I put together of one of our Coaches, Andy Calvo, putting the guys through a really tough boxing workout.  I can't even explain (or show in a minute long video) how tough these routines are: 90 minutes, very few breaks, high high intensity.  These guys push themselves to the limits and then some.

Besides being physically exhausted, they are really more than anything being mentally exhausted.  I've often repeat the saying "The mind quits 1,000 times before your body does once" and it is so true.  Can you really not do one more pull up?  One more punch?  Or is that just your mind telling you that you can't.