incognito42,
football-type training and optimal strength training are very different (since the two endeavours of mass gain and athletic perfomance are counter-productive). athlethics-oriented routines account for endurance work as well hence the increased number of days.
however for optimal strength and size gains you have to carefully moderate volume and intensity on anything other than a simple 3-day split. yes muscles can potentially recover in 24-48 hours (note: that's how long they need to recover, NOT rebuild themselves stronger and bigger to handle heavier weights, it takes longer than that) but this doesn't tell the whole story:
consider a guy repping in the high 400's for deadlifts and doing singles, triples or something similar on this exercise. then take another guy doing half that weight for 3 x 5. given all else is equal, can you really say that the first guy's back would be recovered in two days time to be trained again?
I know a lot of people on 5-day splits, and none of them squat, deadlift or row. Yeah there's a few military presses thrown in here and there but they're avoiding the big compounds because, quite rightly, these lifts will destroy you and make it impossible to train them more frequently than once a week or thereabouts.
they make good initial gains on these 5-day routines but burn out quickly thanks to overtraining and CNS fatigue. the central nervous system does NOT recover as quickly as the body does, so even if your muscles are primed to work out but your CNS is not, then you're not in a fit state to train optimally. now these guys are volume junkies and live in the gym so they won't take a day off and continue pounding themselves into the ground, their weights remaining stagnant and their bodies never changing (except some of 'em who actually LOSE muscle thanks to overtraining).
heavy training will kill the CNS if volume, recovery measures (stretching, supplementation, cardio, diet) and intensity aren't checked, and that's the reason why I don't think anyone on this forum (myself included) has any place doing a 5-day split unless they're an advanced bodybuilder (6-7 PRODUCTIVE years of training, not a 21 year old who started lifting at 14 and is still the same size today) possibly on drugs as well.
(also note that such a bodybuilder will have a great strength base so that his higher volume, lower intensity (for him) approach will be productive, and by this strength base I'm talking deadlifting and squatting in the 400's, rowing and benching in the 300's, curling and military pressing in the 150's, dips and chins with 50lbs chained to them etc. that's what really everyone should be worrying about if they want to look like they work out, getting those strength gains as fast as possible.)
it's simply too much work for the average guy to handle physiologically (I'm not doubting anyone's heart or determination here) and it's definitely overkill for you guys who just want a reasonably fit, toned body. you'll do yourselves a favour and cut your volume down if you want to succeed.
yes, I know that you can train a bodypart more than once a week but not optimally, something along the lines of twice in ten days (a la DC) is doable but it'd still require a fairly low volume approach which a lot of people are put off by simply because "it doesn't seem enough work" .. I'm talking 8-10 sets PER WORKOUT here, not per bodypart - and even that's pushing it. and if you are gonna train more frequently than that then you'd better have everything recovery-wise working in your favour: diet, cardio, supplements, stretching, stress, sleep.. because it's walking the line of overtraining anyway.