The authors of this article [Avery et al., 2003: (http://www.fittech.com.au/downloads/bmsdocs/AveryKraemer.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/14636105)] discuss the fact that, as shown by their research and the research of others, 6 or more days are required for a given muscle group to recover from a strength-training workout. Avery et al. (2003) used people who had not been doing weight training, but their statements about the recovery time being 6 days, ideally, are consistent with the anecdotal statements, with regard to recovery time, that people with expertise in sports nutrition and training have been giving for many years. I can't provide any citations to support the statements, but people who have considerable expertise in this area have generally said that a person can wait one week between strength-training/resistance-training workouts of a given muscle group. This article [Tidball, 2005: (http://ajpregu.physiology.org/cgi/content/full/288/2/R345)(http://www.ncbi.nlm.nih.gov/pubmed/15637171)] cites research (reference 23) showing that neutrophil infiltration in exercised muscles may continue for up to 5 days post-exercise. Neutrophil infiltration is not "bad" and can actually help the repair/recovery process, etc. For example, the authors of this article [Lennon et al., 1998: (http://jem.rupress.org/cgi/content/full/188/8/1433)(http://www.ncbi.nlm.nih.gov/pubmed/9782120)] cite research (reference 8 on p. 1439) estimating that 100 billion neutrophils (polymorphonuclear leukocytes are neutrophils and are usually identified by myeloperoxidase expression) migrate from the blood to the extracellular fluid, by the whole rolling/adhesion process (I forget the details), every day in a person in the absence of inflammation, and the neutrophils release adenosine monophosphate that's converted into adenosine and promotes endothelial cell proliferation and barrier function, etc. In any case, one approach would be to allow 5-7 days between workouts of one muscle group and separate the exercises into 3 workouts per week, etc.
It's very important to talk to one's doctor before beginning any exercise program, in part because of the risk of exertional rhabdomyolysis (RBM) (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=exertional+rhabdomyolysis). RBM can be life-threatening and can cause kidney failure and death, as a result of myoglobinuria [myoglobin from lysed (necrotic) muscle cells produces oxidative injury to the kidneys] and disseminated intravascular coagulopathy (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=disseminated+intravascular+coagulation+rhabdomyolysis). If one has any disease or health condition or viral illness or is taking any drug, one should be especially careful to do fewer sets or repetitions than one thinks one can, for the first several workouts, and gradually increase the intensity, etc. It's not muscle soreness or muscle fatigue but is the loss of muscle cells by an undesirable mode of cell death (necrosis) (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=exertional+rhabdomyolysis+necrosis). Necrotic cells dump intracellular antigens (proteins, lipids, etc.) that are usually somewhat shielded from immune recognition, etc. The proteins can also become insoluble as a result of necrotic cell death and cause insoluble immune complexes to form (to precipitate) and cause thromboses (disseminated intravascular coagulation, etc.) (http://scholar.google.com/scholar?num=100&hl=en&lr=&safe=off&q=%22immune+complex%22+insoluble+OR+precipitate). The mechanisms are really complex, but necrotic cell death can, for example, promote dendritic cell maturation and thereby increase the costimulatory capacities of dendritic cells (increasing their antigen-presenting capacities) [Basu et al., 2000: (http://intimm.oxfordjournals.org/cgi/content/full/12/11/1539)(http://www.ncbi.nlm.nih.gov/pubmed/11058573?dopt=Abstract)]. Many IgG antibodies normally bind to intracellular antigens to suppress viral infections, etc., but the loss of skeletal muscle myocytes by necrosis is not desirable.
I don't feel like going into any more detail, but that sort of research and information seems not to be very well-known, still. There's still a widespread belief that resistance exercise is secondary to endurance exercise, in terms of importance and biological effects (on the brain, etc.), but the reverse is actually true, in my opinion. There's no substitute for resistance exercise, as far as many different effects go.
It's always necessary to completely exhaust the muscle group, during a set of repetitions, and the negative (eccentric) contraction should be controlled or be about 2 seconds or even longer. It makes no sense, in my opinion and others' opinions, to try to control one's breathing with each repetition. The muscle group has to be completely exhausted with each set, if one wants to provide a stimulus and produce all of the other biological effects I've discussed in past postings. As far as the repetitions themselves go, people were promoting "slow negatives," which are 4-6 second eccentric contractions (the lowering of the weight in a repetition) for awhile but are not promoting or doing them, to a large extent, anymore. There isn't as much adrenergic activation (and, hence, not as much growth hormone release, etc.) with very slow negatives (eccentric contractions/eccentric work). Some people do some sets with 2-second eccentric contractions and then some with eccentric contractions that are not restricted, in terms of duration, on arm exercises, etc. There aren't that many different ways to do it, and I've never quite understood all of the "programs" and "fad methods." It's my suspicion that the real "secret" behind many "programs" is that the person providing the program is, in fact, taking massive amounts of androgenic steroids, etc. That's just my opinion, though.
Experts generally advise doing no more than 5 sets on a given muscle per workout, but many people do more sets than that. Also, it is not efficient or effective, in my opinion, to wait and do all of the sets sequentially. Many people do one or two sets on a muscle group and then do one or two on an opposing muscle group or other exercise and then return to the first exercise, etc. Up to four minutes are required for 90+ percent recovery of the phosphocreatine (PCr) concentrations (or PCr/Cr ratio, etc.) in a muscle, following a set to exhaustion. Waiting one minute or two minutes between sets means that the muscle is being exercised at 60 percent capacity, essentially. There's no way to avoid that, to some extent, because no one can wait four minutes between every set. But the point is that the muscle is going to be capable of progressively and drastically less work, if one does all sets, on a given exercise, sequentially and waits a minute or two between sets. I can only think of a couple of other things, off the top of my head. The leg-extension machine is an example of a machine that many people would suggest avoiding the use of, given that it can put shear stress on the knee at some points in the range of motion. The behind-the-neck pulldown is also supposed to not be a good exercise, and I forget the reasons for that. The proper way to do that one is to pull the bar down "in front of" the "face." This posting is obviously degenerating rapidly.
In my opinion, these are important considerations, though, if one is trying to actually get something out of exercise, in terms of disease prevention or whatever else. The information on the recovery time is also not intuitive and seems to not be widely known.
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