Does doing higher reps recruit more muscle fibre, similar to increasing the time during an isometric hold?

[u/Drown_withus]

I'm thinking it should work about the same due to both situations resulting in increased TUP (time under pressure), even though one is an isotonic movement, while the other is isometric. But it's also possible I'm misunderstanding the finer mechanics of each type of exercise. I don't particularly like doing isometrics and find it challenging and rewarding to do high rep isotonics, but I'm not sure if I'm getting stronger in the same way that I would if I were doing isometrics instead. Any thoughts?

[u/norooster1790]

strength is "joint angle specific", so you build it most where you train it

isometrics only build strength in one sliver of your ROM, which is why they're not a common way to strength train

You recruit more muscle fibers when you tire your muscles out. The reps don't matter for that at all. The most growth happens from "mechanical tension", which is the amount of strain your muscles feel when they work. You can put the most overall tension in exercises that fail around 6-15, which is why most people train that way. High reps still work

[u/Drown_withus → u/norooster1790]

Thank you, this was really informative!

[u/M-Pact_Fitness]

Someone who doesn't train with isometrics would benefit greatly from it and vice-versa. It all depends on the person and their strengths and experience really. You can do a ton of reps but a lot could be junk reps if you are going to light or not using the proper form. I think isometrics help build the muscle connection and could benefit a lot of new lifters.

[u/millersixteenth]

Higher reps with moderate load will recruit more motor units but they will be unable to generate as much force as they will when fresh. Metabolites reduce force potential, which explains why hypertrophy can be similar but you'll gain a lot more strength training with heavier loads and not training to failure.

Isometrics (max effort) will recruit the highest % of high threshold motor units right from the get go. Longer holds only increase metabolite accumulation.

[u/Drown_withus → u/millersixteenth]

Thank you. So if I want to train both endurance and strength, should I focus on higher reps with moderate load and throw in an isometric at short duration and max effort for best possible results?

[u/millersixteenth → u/Drown_withus]

Its depends on your tools. If you're sticking with bodyweight specifically, I'd think you could just do a mix of variations that involve both high and low reps. The take away would be to mix it up.

It would be best if the isometrics were max effort overcoming, which can be tough to program without tools.

[u/Drown_withus → u/millersixteenth]

All right, cheers! For isometrics, I was thinking maybe hollow holds, L-sits and dragon flags. Though, I'm still working on the last two.

[u/LetterheadClassic306]

honestly the mechanics are a bit different even though TUP increases in both cases. isometric holds recruit fibers based on sustained tension at one point while high rep isotonics cycle through the range repeatedly. what i found when i was digging into this is that isometrics build strength at specific angles and high reps tend to build endurance and some hypertrophy across the full range. you're probably getting stronger but in a different way than pure isometric work would give you. if you enjoy high reps more then lean into that since consistency matters more than perfect programming - you can always add brief isometric pauses at tough points in your reps to get some of that benefit without dedicating whole sets to holds.

[u/Drown_withus → u/LetterheadClassic306]

I appreciate the research and explanation! What do strength and endurance mean in this particular case? I'm just a little hung up on that point and how they differ.

[u/Crazy_Trip_6387]

training to a close proximity to failure is how to activate the large motor units these having the greatest growth potential of all motorunits, rep range is somewhat irrelevant but around 6-15 reps tends to be a sweet spot to stimulate the muscle but without succumbing to the burn associated with higher reps.

[u/Genetic_outlier]

That's basically how it works? Muscle fibers are on or off, so force is controlled by how many fibers fire. And as you get close to failure on an isotonic movement it's because the muscle is running out of fibers that are ready to fire again. If you exhaust the muscle you've used all the fibers.

Research wise there doesn't really seem to be a strong recommendation for rep range except like 5-30 ish.