It’s natural to have some asymmetry between left and right sides as well as between opposing muscle groups (e.g. triceps/biceps). I’m even unsure how to quantitate the extent of imbalance in opposing muscle groups; are there commonly accepted ideal ratios between opposing groups?
Some activities (pitching, tennis) contribute to lateralization of muscle development and others (rock climbing) to increased development of one of an opposing pair of muscles (biceps over triceps, IMHO, in climbing)
The question is how far can asymmetry go? Has anyone pushed the limits? What if I work out on a machine designed to completely isolate my biceps (it somehow takes the wrist flexors and triceps out of the exercise), how asymmetric would I become? Are there limits? Do the signals for muscle enlargement act only in the group being used or are there (possibly) broader signals that allow for some development of unused adjacent or even distant muscle groups? Are there human or animal experiments that shed light on this question?
i believe there are both systemic and local mechanisms. but systemic ones probably mostly insignificant. even if we think growth hormone release which is systemic, then we still have to take into account that upregulation of receptors for IGF ( IGF is released by GH ) is local.
people who tear a muscle and thus can’t work it, lose the size on that muscle pretty fast and there ain’t much left of it afterwards even if the other muscles are big.
A typical knee problem is the result of muscel disbalance. If one of the quadriceps muscels is weaker than it’s antagonist (typically the vastus medialis), this may lead to a distorted patella. It is simply pulled to much to one side. Results may be luxation and cartilage damage.
So there is always a natural equilibrium and if it’s out of balance it’s usually bad for you.
No cite, but I recall reading that the medieval long bow was so difficult to use that the musculature on the “pulling side” became so developed that it affect the curvature of the spine. Supposedly, human remains of long bowmen could be identified by this characteristic curvature.