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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.

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There's good evidence that training throughout a full ROM leads to greater hypertrophy than training only at short muscle lengths,1 However some recent studies2,3 have also shown that training through a partial range of motion at long muscle lengths produces as much, or possibly even greater hypertrophy than training through a full range of motion, and with that hypertrophy being particularly concentrated in the more distal parts of the muscle.

Note that study 3 linked above is the one that the Flow High Performance video is describing. This study (and the video) did not report that biceps have a "preferred length" or that training at all lengths is suboptimal. All it did was compare training short ROM at short muscle length to short ROM at long muscle length and found that the latter as superior. They didn't compare to full ROM or to a combination of different ROMs. Study 2 linked above did compare full ROM and alternating long or short muscle length partial ROM from workout to workout, and found that both these options gave better hypertrophy than training only at short muscle lengths.

In summary, we know that training only at short muscle lengths is suboptimal, but probably don't have enough evidence yet to say for sure whether training specifically at long muscle lengths is better than training through a full ROM. Practical considerations tend to make full ROM training easier, since partial ROM training requires you to come up with a way of ensuring your ROM is consistent from workout to workout, mixing sets of different ROMs does that as well as making it more difficult to track weights used between workouts, since your one exercise, e.g. bicep curls, has now become three or more exercises: bicep curls at short muscle length, medium muscle length, and long muscle length.

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  • Thank you for the help! The "preferred length" part was indeed poorly phrased. Those articles are helpful, but my question was more about, within a full ROM exercise, if there are benefits of varying the portion where the exercise has the most resistance. There might be an extrapolation to be done about "is better to train only the lengthen part of the ROM" -> "is better to train full ROM exercises overloaded in the lengthen part", but other than that, it doesn't seem to be much literature on this specific topic. Jan 19 at 22:35
  • From that extrapolation, my intuitive "pro" of "different stimulus" might be wrong as focusing on the shorten position is sub optimal, and i'd be inclined to give preference to exercises that are overloaded in the middle/lengthen portions. But this is all extrapolation so i'll keep on looking. Jan 19 at 22:35
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    The Pedrosa et al. (2021) study found that alternating (session to session) between doing partial reps at short muscle length and at long muscle lengths gave at least as much hypertrophy as doing a full range of motion, and possible even more. So you could do that, at the cost of complicating your workouts by needing to track different weights to use with different ROMs. But otherwise, yes, giving preference to exercises that are overloaded in the middle/lengthen portions is definitely a good way to go. Jan 22 at 10:39

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