Someone made a comment on my discussion board and it brought up a few practical points that I think probably should be included here for completeness. Here's a quote from the thread...
...keep in mind that the body adapts very specifically. If you usually do 16-20 sets your muscles will have the energy systems developed for that volume (i.e. substrates to replenish ATP, glycogen, etc), whereas on a full-body routine the energy systems for each muscle only have to 'answer the call' for 4-10 total sets per body part - completely different demands and the body will react completely differently to it. I would expect more sarcoplasmic hypertrophy on a split.
The weekly workload is a different story. If you were to do 4-10 sets per body part per day on full-body, you'd rack up 12-30 total sets in a week, but at each session less localized muscular endurance would be needed. The muscles would lose their ability to sustain output over higher volumes, but sarcomeric hypertrophy would be stimulated three times per week.
In other words, train long enough on full-body routines and you'll get better at developing power for limited bursts, and train long-term on a high-volume split and the muscles will adapt to produce force for longer periods. Of course, this is a function of daily body part volume and training frequency, not the fact that you're training your full-body at one time.
You can see the same sorth of thing with whatever volume you use for each exercise now. For instance, take an exercise that you've done say 3 sets on for years and suddenly add a fourth set. You'll do the first 3 sets as always, but probably suddenly and unexpectedly 'die' a few reps into the fourth set (unless you take long rests between sets and/or use very low reps). It will take a few weeks, at least, for the body to increase the capacity of the energy systems required to get through that fourth set (increase enzymes and substrates involved primarily in the anaerobic glycolysis and oxidative phosphorylation systems).
Full-body and 'strength' and 'power' training go hand and glove in an energy substrate sense, but frying the nervous system and overloading the joints have to be guarded against. There's a little different mentality involved. You have to start focusing on every rep rather than the overall workout for any particular body part. You can't think of saving yourself for the rest of the workout, you have to build up to having the full-body endurance to hit everything at once and not back-off on anything just so you can get through. That ability comes with time.
The liver also has to increase it's glycogen storage and glucose production capacities to get you through very demanding full-body workouts - which is a large part of the reason you must eat well after a hard full-body workout. Liver glycogen content is an indicator of the body's overall state --> depleted liver glycogen = body catabolic, full liver glycogen = body anabolic (in a broad sense). So, good nutrition is crucial to getting full-body to work - you must replenish that liver glycogen afterwards. Until your body begins upregulating the enzymes and substrates involved you probably won't feel 'right' doing full-body. After you've adapted to it you'll be surprised just how much you can do (take ) in one workout.
So, it's important not to jump into full-body training headlong, especially if you haven't trained that way in awhile. Like anything else it's an adaptation process and that has to run it's course before you can go all-out. Not giving themselves proper time to adapt is why a lot of people training on split routines feel like they couldn't possibly train their full bodies in one session. From the other perspective, once you get used to training your full body hard in one session, training just a few body parts on a split feels like the lightest of 'light' days.
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Last edited by BendtheBar; 11-30-2009 at 10:48 AM.