I don't believe training all day is required and most probably will lead to injury. Depending on you're fitness level one hour circuit training and a run would be enough... You might also want to add some weights in there. If you can split it into two sessions that would be better as it allows more time for recovery, something like...
AM
weights
PM
hour (or sometimes less) of circuit training followed by tough run.
More can be less. A good circuit may only last 20-30 minuets but by the end you'll be wreaked. Something like Tabata drills (see post just bellow this one.) will only last a few minuets but can have you hanging out.
These kind of thing will be better than hours of endless low intensity exercise. No human can go 100% for 3-4-5 hour straight you're intensity and quality of exercise will soon drop thus making the work out less effective.
my run's are the only things that sometimes last more than a hour. weights and circuit training between 30-60 minuets (occasionally less with really high intensity stuff)
remember to get the correct rest also this is just as important!
make sure there's good verity in you're work outs but don't become obsessed by exercise. Be sure to keep a good active social life as well as training.
I think if you train two sessions a day then any more than 3 hours training (as a hole) should be max and even then you don't need to do that every day. maybe 1-2 times a week a long day like that would be fine the rest of the time 1-2 hours will be more than enough to run you're self into the ground.
Sorry if I haven't been to clear
Hope I’ve helped
Stokey
