What is the benefit of training a muscle at different lengths portions - i.e. selecting an exercise that has higher resistance at a shorten position, other at a mid-range position, and other at a stretched position - and what is the anatomy/bio mechanics theory and/or empirical evidence behind it?
I have an intuitive thought that training a muscle at different lengths can give different stimulus to the muscle, which could lead to greater hypertrophy, or to diferences in regional hypertrophy within the muscle, or at least as a mechanism of getting out of a plateau. But i'm not sure if that's true.
At the same time I feel that matching the resistance profile of an exercise with the force/strength profile of the muscle allow for the higher possible load, thus the higher mechanical tension and thus higher stimulus to hypertrophy. An exercise that has more resistance when the muscle is weaker will limit the amount of load that you can use, and for the portion of the lift when the muscle is strong, wont generate that big of an stimulus, as it could handle more weight*.
The last paragraph described a possible con of training at different lengts, whereas the one before that described a possible pro. If both are true, and if I didn't missed on any other pro/con, which of them outweighs the other?
Even if i don't find the theoretical/empirical reasoning for that, i'm willing to believe the good sources that defend that training a muscle at different lengths is beneficial:
"[People that start to study this subject] think that that's [matching the profiles every time] the most optimal way to train [but ...] there is value to biasing either the shorten position or the lengthen position depending on your goal of that workout is" Cody from N1 Training (https://n1.training/intro-to-resistance-profiles-strength-profiles/)
But i don't know how to use that practically or how my workout goal will influence my use of that information. What i could think was to use an easier-to-overload exercise that matches the force/strength curve of the muscle as a main lift, earlier in the workout, and the versions focused on different lengths as secondaries, placing them after this main lift.
Also, there are evidence that some muscles might have a "preferred length" for training, for example, this research resume by Flow High Performance (https://www.youtube.com/watch?v=sKrLUg_q32E - give him a follow, his channel is amazing) shows that the bicep will increase more in size by training only the start of the range of motion than the end of it. This evidence seems to be another con of training all lengths.
*: One possible solution to that would be to make partial repetitions, only in the portion of the range of motion that you wish to train, but that seems to be against the highly replicated result that larger range of motions seem to result on higher hypertrophy.