I have been following Mike Mentzer's High Intensity Principles, and although I may perhaps be missing details, here is what I understand regarding rest and recovery:
- Exercise is stress. For illustration, assume that Monday is an arm workout. It does not matter whether you just exercise your arms on Monday, because your entire nervous system is employed and taxed to perform the exercise.
Therefore, utilizing Seyle's principles of stress adaptation, one must permit the nervous system adequate time to recover from the stressor before adaptation can occur. Sure your legs are fresh to workout on Tuesday, but your central nervous system probably isn't.
-Regarding the glycogen recovery process, you don't utilize the glycogen stores in your arms only. Your body utilizes gylcogen stores from your entire body to feed our working muscles energy. Therefore, similar to the central nervous system, it needs to be replenished, even though your legs are fresh for Tuesday.
-Before growth can occur, recovery must occur. Muscular glycogen replenishment happens generally within 24 hours, and nervous system recovery within 48 hours. But if you train very intensely (i.e. heavy weights), the body requires more time to fully recover. So, 48 hours, in mine and Mentzer's minds, is the minimum rest interval you should utilize when training with heavy weight lifting/working towards complete exhaustion. Actual growth happens within day 3, 4, 5, etc. Many of Mike's clients noticed hypertrophy even after 1-2 weeks of non-exercise. Now he does not recommend designing your programs with weeks of inactivity; however, to illustrate, the body requires much time to adapt/grow.
Basically, if your body is stressed out about thinking of your next workout, then it probably has not recovered enough.
- Rather than utilize supplementation, FOOD is the best 'supplement'. Ensure that you are eating the appropriate amount of calories and that they are properly distributed among the 3 macro-nutrients (carb, fat, protein) according to your body's metabolic type.
If you are interested in reading material regarding recovery, I suggest:
- High Intensity Training: The Mike Mentzer Way
- any textbook detailing the physiology of stress. Seyle is a good theorist to start with.
I hope this proved useful. Good luck in your jounrney, man!