Finally! More Muscle with Lengthened Partials Than Full ROM in Trained Lifters

Chapters:

00:00 Intro

02:08 Study 1: Not just untrained individuals

05:41 Study 2: More growth at long lengths independent of tension?

10:06 Study 3: How long is long enough?

13:35 Practical application

Transcript:

The reputation of long length training and lengthened partials has been a bit like that of Britney Spears. A meteoric rise to popularity followed by a bit of a crash and a burn, but now perhaps a comeback. Up until a few years ago, full range of motion training was the gold standard, something that all evidence based fitness professionals agreed on. However, a few studies then showed that lengthened partials, doing partial repetitions specifically in the part of the movement where the muscle is lengthened, more stretched, actually result in more muscle growth even than full range of motion training. And of course, this got picked up by all the evidence based YouTubers like Jeff Nippard, Mike Israetel, and in particular Milo Wolf leading the charge and going all in on lengthened partials.

The hype train crashed when multiple studies in trained individuals failed to replicate the findings from untrained individuals that lengthened partials beat full range of motion. The main critique, voiced by the likes of Paul Carter and Chris Beardsley was that lengthened partials and long length training are only beneficial to increase muscle length. This works in untrained individuals because they can actually still get longer muscle lengths, and this can result in the illusion, if you will, of larger muscles.

The idea was that long length training results in sarcomerogenesis in series rather than in parallel. Basically, the muscle just gets longer, and since a muscle fascicle can only get so long because it’s bound between two bones, that growth is finite. You can make a muscles total volume larger by lengthening it, but only a little bit. So in untrained individuals this could work. But in trained individuals the idea was, well, they already got those benefits from training with full range of motion, therefore we no longer see the benefits. However, an alternative explanation is simply that trained individuals grow less muscle in any study because in eight weeks, trained individuals are not going to gain a lot of muscle to begin with, so it’s just harder to demonstrate any effect in general in trained individuals versus untrained individuals. So is long length training the muscle messiah, or is it just an overrated fad that we won’t hear from anymore in a couple of years?

I know many of you are sick about hearing about lengthened partials and long length training as you are about AI. However, three new studies fundamentally changed the narrative. The first study, for the first time shows compelling evidence of superior muscle growth with lengthened partials than with full range of motion in resistance trained individuals. The study, still in preprint, had a group of strength trained men complete a lower body training program with either full range of motion or lengthened partials, doing only the bottom part of the movement.

The training program consisted of leg presses, leg extensions and lying leg curls. After eight weeks there were significantly more growth in the semitendinosus of the hamstrings in the group doing lengthened partials, and this was measured using gold standard magnetic resonance imaging, MRI. Total hamstrings growth was also larger in the group doing lengthened partials, but the difference wasn’t, strictly speaking, statistically significant, with a p value just short of the .05 at 0.058. So kudos to the researchers for not doing p hacking there, because I think many researchers would have done that.

This finding is extremely difficult to reconcile with the idea that lengthened partials just cause muscle lengthening. Trained individuals are very unlikely to still experience an increase in hamstrings length from doing lying leg curls. It’s not exactly an exercise that stretches the crap out of the hamstrings. However, the study also doesn’t support going all in on lengthened partials because there were no significant differences in muscle growth for any other muscle group than the hamstrings. For the quadriceps anabolic signaling and biopsy data both also fail to confirm any advantage of lengthened partials over full range of motion training.

You could argue that the hamstrings difference was just a fluke. However, with MRI, in this type of study, I think that’s not particularly likely, and a more likely explanation is that lengthened partials simply have a finite benefit. In the group only doing leg curls, if you’re doing standard lying leg curls, you’re not training the hamstrings at long lengths at all. Lengthened partials essentially are a way to still train hamstrings at somewhat longer muscle lengths. However, for the quads, they were doing leg presses and they were doing very deep leg presses. If you’re already doing very deep leg presses, then doing lengthened partials on top of that is probably not as advantageous. So this would explain why the other muscle groups didn’t benefit from the lengthened partials, or at least didn’t clearly benefit in this particular study, while the hamstrings did.

So what I teach in my online PT course and implement in my App is that you should have at least one good exercise that really targets a muscle well at long muscle lengths. However, you probably don’t need to do long muscle length training for every single exercise with lengthened partials all the time. Moreover, the benefits of lengthened partials and long length training should logically depend on the length-tension relationship of the muscle and the resistance curve of the exercise that you’re doing.

Muscle grows from mechanical tension. Some muscle groups experience more active tension, and in particular also more passive tension at longer muscle lengths, but other muscle groups do not. If you venture into a range where you get clearly more mechanical tension, I think it’s very likely that the longer length training in this particular context leads to more muscle growth. However, when you are venturing to a length where you sacrifice a lot of active muscle tension, then you might not get more muscle growth anymore.

This would explain, for example, why one of our own earlier studies found that hip thrusts and squats result in equal muscle growth in the glutes. Hip thrusts should generate a lot more active tension, but squats have the advantage of training at longer muscle lengths and more passive tension.

Presumably somewhere there there is a level of equivalence where you can get the same muscle growth either with more active tension or with more passive tension. And this is also what the researchers concluded in the second new study, although the way I read the results it actually makes a more compelling case for lengthened partials than the researchers say.

The researchers had a group of non strength trained individuals complete a lower body training program in one of three ways. All of the groups did 3 to 4 sets at 8 to 10 repetitions. The full range of motion group did 0 to 90 degrees of knee flexion at 80% of 1RM at that range of motion, so the 1RM was tailored to the specific motion that they were doing, which is good because some studies they forget to do this, the shortened partials group, they did 0 to 50 degrees, so shortened partials, about half the range of motion, only the contracted part of the movement, also at an 80% intensity, think partial squats the way many people do them, and then the lengthened partials group did a 40 to 90 degrees, so basically like the bottom half of the movement, although this isn’t technically real super long length training still, but they did it at a 55% intensity. So that’s partial reps in a stretched position, but with substantially less weight.

The substantially lower weight was chosen to equate the total amount of mechanical tension. So you have with a heavyweight full range of motion or shortened partials, or a lighter weight lengthened partials. The idea being that at this lighter weight the total amount of tension in the quads was going to be equivalent in the shortened partials and the lengthened partials group. In the full range of motion group it should still be higher, more mechanical tension. So this study essentially answers the question do lengthen partials still beat a shortened partials when we equate for total mechanical tension?

One previous study on this found that the difference disappears when we equate for total tension, as you would expect. Tension is the main mechanism of muscle growth, so the benefits of lengtened partials should be mediated by mechanical tension. This is however, not what they found. After eight weeks, the lengthened partials resulted in significantly more growth than the shortened partials, even with the lower weights, and this was significant at two out of three of the locations they measured. Moreover, the lengthened partials, despite being at a lower weight and having a lower estimated total amount of mechanical tension on the quads, rivaled full range of motion training. They had similar muscle growth.

The researchers concluded that since active forces were equated between the lengthened and shortened partials group, the extra muscle growth must have come from passive mechanical tension. However, this is not in line with how they measured total tension because the researchers measured total quadriceps tendon force. Total force logically includes both active and passive force, which means that all forms of mechanical tension contribute in the measurement.

Technically, they measured quadriceps torque corrected for hamstrings coactivation divided by the patellar tendon moment arm. So it’s basically an estimate of total forces, not just active forces.

If we take these results at face value, it would mean that there is an additional mechanism beyond mechanical tension that drives the benefits of long length training. This would be an absolute game changer, not just for long length training and lengthened partials, but for our entire understanding of how muscle grows. Because we don’t have any established mechanism other than mechanical tension as to what drives muscle growth. Such a complete paradigm shift generally shouldn’t happen based on just one study, and there are indeed three big caveats to keep in mind here.

The first major caveat is that total tendon force is not an unreasonable measurement for total muscle force, but it is not the same as specifically the amount of tension that’s going on in the vastus lateralis, where muscle growth was actually measured. Moreover, these are estimates, and during a dynamic contraction where pennation angle changes and the muscle changes shape, these estimates are known to be somewhat inaccurate.

Related to this, it’s unknown how close to failure exactly the groups trained. They did a given number of reps with a given weight, and the idea was that this equatee tension, but they did note that some of the subjects in the lengthened partials group noted that the movement was harder than expected, so maybe they were actually simply training harder than estimated, and tension was actually higher in this group.

And third, if we go back to the original critique that most of the muscle grow from lengthened partials might just be lengthening of the muscle rather than thickening, which is very finite in duration, these were untrained individuals, and the researchers measured that muscle fascicle length actually increased. So in this case, it could be the case that much of the additional growth was indeed just lengthening. And it might not apply to trained individuals like in the previous studies.

The final and strongest argument against long length maxing is that most research doesn’t support that longer lengths are always better. Which brings us to the third new study I have for you today on how to optimize your biceps curls. Bicep curls are an exercise where research has looked a lot into different muscle lengths, and generally it finds that longer lengths indeed have a benefit compared to shorter lengths. But there is a clear limit.

The researchers had a group of untrained individuals train their biceps with Bayesian curls – cable curls looking away from the cable tower. One group did them the way I originally coined the exercise, which is with the elbow at the site. The other group let their elbow get dragged all the way back to get even longer muscle lengths.

After ten weeks, there was no meaningful difference in muscle growth between the arms. It was 6 to 9% in both of the arms, as measured by ultrasound in the top and bottom parts of the elbow flexors. Bayesian analysis further supported that there was indeed no difference. This finding makes sense in light of the length-tension relationship of the biceps.

I originally recommended Bayesian curls over dumbbell or barbell curls because with a dumbbell or a barbell there is no resistance in the bottom part of the movement. Gravity is only pulling straight down, so it’s only as you start flexing the arm that you actually get some resistance. This is very detrimental for the biceps in particular, because the biceps actually produces the most active and passive force when the elbow is at your side, roughly in anatomical position.

When you stretch the biceps beyond this point and get the elbow behind the body, you actually decrease the amount of active tension. And this is probably not entirely offset by the increase in passive tension. It’s not just a case of getting the muscle to a longer length and thereby getting more growth. You also need to get high tension at that long muscle length. Often, when you let your arm get dragged back during a Bayesian curl, you lose some of the tension at longer lengths.

All these limitations and talk of potential mechanisms aside, the strongest argument I think right now for actual long length maxing is that in basically every single study we see benefits or neutral effects. There is no evidence of harm. However, I’m still not a proponent of actually just doing all exercises at long lengths and always doing lengthened partials for two main reasons. The first reason is that injury risk and fatigue both are known to be correlated to the joint angles that you train in. Fatigue is joint angle specific, and injury risk and damage are also highly specific to movements and joint angles. So if you load all of your training on one muscle length, so the longer muscle lengths and you do partial range of motion all the time, then you’re loading all of that volume on one vector, and I think your total volume tolerance might be a lot lower.

The second reason not to go all in on lengthened partials is that tracking your progress becomes very difficult. I think tracking your progress is extremely underrated, because if you don’t know if your program is working, you don’t know how to update it. There’s so much talk about program optimization, and very few people talk about how to sustain progress on a program. If you don’t know if you’re progressing and with lengthened partials, you often won’t, you don’t know how to update your program because it’s super difficult to know with a lengthened partial if you’re just sacrificing range of motion, or if you actually got stronger.

With a leg extension, a decent rule of thumb is that if you are leg gets horizontal, you can see that pretty well, and you have an idea of how you’re progressing. This is even more easily the case with a chin up or a bench press, or a squat, where you get the weight up or you don’t. With a lengthened partial, however, if you’re getting the weight halfway up, how do you know if this time you weren’t just short cutting the range of motion just a little bit to get that one extra rep. Your progress becomes a slippery slope.

In my online PT course, I evaluated all the practical and theoretical evidence, and I came to the following guidelines, which are also largely what I implement in my App. First, it’s almost certainly a good idea to have at least one exercise for every muscle group that trains that muscle at a long muscle lengths. Most people don’t do this. Many people in the gym, they train with partial range of motion. They don’t even use full range of motion, let alone lengthened partials, and they don’t have exercises that train a lot of muscle groups at long muscle lengths, so they’re probably leaving significant gains on the table.

Big, big picture. One of the main findings of the whole lengthened partials and long length training movement is that we know why full range of motion training is beneficial over shortened range of motion training. The reason is that it’s the longer muscle lengths that are driving the benefit, not so much the extra range of motion per se. It’s about reaching longer muscle lengths, not about just maximizing joint range of motion.

Second, I like doing lengthened partials in the last set of an exercise or the last sets of an exercise, and then leaving the first set with full range of motion so that you can still accurately benchmark your progression. And finally training at longer muscle lengths is most likely specifically beneficial when it actually increases total muscle forces, thereby mechanical tension. This includes active and passive tension.

As a practical rule of thumb, exercises where you can do significantly more reps when you shortcut the range of motion benefit the most from lengthened partials. Think, for example, leg extensions, lying leg curls, or calf raises. And these are indeed exactly the muscle groups and the exercises for which we have compelling evidence that they do get more from lengthened partials than even full range of motion training. The fact that you can use substantially more weight or do substantially more reps with lengthened partials for these exercises, is basically an indication that you are leaving tension on the table.

Exercises like calf raises benefit from lengthened partials, because the bottom part of the range of motion has a much higher active and passive forces. If you force yourself to go all the way up to lockout, while good for progress tracking, you do limit yourself in terms of the total mechanical tension that can be produced because you’re limited by the very top part of the movement. While there’s a large bottom part of the movement that could do a lot more.

I hope this video helps you design more effective training programs and get more out of your training. If you like this type of evidence based fitness content, you’ll probably also like this video and you’ll probably love my online PT course. It is the most comprehensive course on the market by far that teaches you how to take your physique to the next level. Check it out!