There is More to Training for Hypertrophy Than Long Muscle Lengths

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TRAINING TAKEAWAY: To maximize hypertrophy on a per set basis, select exercises that not only expose the target muscle to a long length but also provide a decent amount of difficulty in its lengthened position.

Background

Until the last year or so, discussions surrounding range of motion lacked nuance. Previously, meta-analytic data simply allowed us to conclude that longer ranges of motion are likely superior to partial ranges of motion. However, attention has recently been brought to the importance of training through a long muscle length, with an analysis of the available data in a recent pre-print by Wolf and colleagues.

This is an exciting time for this area of research, and it’s important to emphasize that we have a lot to learn (luckily, I’m aware of multiple ongoing studies in the area). In the meantime, the goal of this article is to highlight a less-talked-about consideration when selecting exercises. Specifically, we’ll discuss whether a muscle simply needs to be exposed to a lengthened position or if this lengthened position should be the most difficult portion of the exercise. Let’s dive in, starting with a quick overview of recent research.

Overview of Recent Evidence

The below table summarizes some recent evidence in the area. This table is not comprehensive; I selected studies to highlight concepts we’ll be discussing in this article.

To make sure we’re on the same page, let’s define our terms:

Longest Muscle Length: The longest muscle length that occurs in the range of motion.
Muscle Length at Point of Peak Difficulty: The length of the muscle at the most difficult portion of the range of motion.
Total Range of Motion: The distance traveled from the start to the end of each repetition.

In the above table, we see a few patterns:

Total range of motion does not appear to drive hypertrophy.
In studies that feature a group training through a longer muscle length, that group generally grows more.
In studies that feature a group training at a longer muscle length at the point of peak difficulty, that group generally grows more.

Things get interesting when we consider the interplay between #2 and #3. Many of the study designs comparing longer and shorter muscle lengths lead to the muscle length at the point of peak difficulty also being at a longer length. However, there are some exceptions.

Muscle Length at the Point of Peak Difficulty

For a while, the Nunes study was the only to isolate the muscle length at the point of peak difficulty in their design. Specifically, Nunes compared hypertrophy from cable preacher curls (which is most difficult at a shorter muscle length*) to barbell preacher curls (which is most difficult at a longer muscle length) and did not report a difference in hypertrophy (+7% vs. +8%).

In 2022, a pre-print from Zabaleta-Corta became available, which allows us to look at a similar concept. Zabaleta-Corta compared hypertrophy from dumbbell incline curls (which is most difficult at a shorter muscle length) to dumbbell preacher curls (which is most difficult at a longer muscle length) and reported nominally (but non-significant) differences in hypertrophy in favor of the preacher curl group (average growth of +8.0% vs. +3.2%). However, this study differs from the Nunes study in that the group with peak difficulty at a shorter muscle length (incline curl group) was exposed to a longer muscle length than the other group. As a result, this study allows us to compare the benefits of exposure to the longest possible muscle length and peak tension at a long (but not longest) muscle length. In this study, the latter came out on top.

I don’t want to overstate the results from the Zabaleta-Corta study for two reasons. First, it’s just a pre-print as of writing this, and I suspect the statistical approach will change when it’s published. Second, I did the statistical analysis the best I could from the pre-print data, and the between-group differences were not quite statistically significant. With that said, we can triangulate the mentioned data with the study from Pedrosa for additional insight.

The Pedrosa study compared quadriceps hypertrophy in a group training full range of motion (30° knee flexion → 100° knee flexion; 70° total) leg extensions to a group training only the bottom 35° of the movement. So, both of these groups had the same longest muscle lengths. Importantly, training loads were normalized to the range of motion trained. Since a leg extension is hardest at the top, the group training the bottom portion of the range of motion used heavier loads and thus had a longer muscle length at the point of peak difficulty. Hypertrophy results generally favored the group training only the bottom portion of the movement (growth averaged across 8 sites of +21.3% vs. +14.6%). Put simply, this study supports the notion that placing peak tension at a longer muscle length leads to greater muscle growth.

These three studies provide the best insight on the influence of the muscle length at the point of peak difficulty for hypertrophy. I’ve summarized the findings in the below table.**

Regional Hypertrophy

In the above table, the Nunes study is the only one without a meaningful difference between groups. To potentially explain this, let’s consider how hypertrophy is measured in research.

A common hypertrophy measurement is muscle thickness or cross-sectional area via ultrasound. In short, a site on the muscle is located (e.g., 50% of the way down the upper leg), an ultrasound probe is placed there, and an image is captured. Thus, the conclusions of a given study are limited to the site measured.

The importance of this concept is displayed in studies where multiple muscle sites are measured. In these studies, it’s quite common for there to be a significant between-group difference at one site but not at another site (example). If these studies instead only measured one site, one may incorrectly conclude that muscle growth was similar when in fact it was different at an unmeasured site. This concept may explain the lack of a difference reported in the Nunes study, as seen in the above table. Only the middle portion of the biceps was measured, so we can’t necessarily assume there wasn’t a difference at the more distal sites. Indeed, we generally see a larger difference in hypertrophy in more distal sites with a greater longest muscle length. This can be seen in the study from Sato, which is outlined in the initial table.

It’s reasonable to assume that this pattern would also emerge when looking at the muscle length at the point of peak difficulty. The lack of a distal measurement site in the Nunes study may explain why this concept was overlooked for a while. Ultimately, with the research we do have, it seems that placing peak tension at a moderate-long muscle length is our best bet.

What Does This Mean for Training?

By providing a few examples, hopefully you can see how this concept may apply in the gym:

A cable curl facing away from the weight stack in which you step far enough away so the cable pulls you back at the bottom, creating resistance in the lengthened position. Based on the research, I’d hypothesize this will lead to more muscle growth than a dumbbell curl on an incline bench.
A cable lateral raise in which the cable is set around shin height, making the most difficult portion of the range of motion near the bottom. Based on the research, I’d hypothesize this will lead to more muscle growth than a dumbbell lateral raise.
A leg extension with a cable that pulls you straight back at the bottom. Based on the research, I’d hypothesize this will lead to more muscle growth than a plate-loaded leg extension.
A leg curl that is most difficult in a relatively lengthened position. Based on the research, I’d hypothesize this will lead to more muscle growth than a leg curl that simply exposes the muscle to a long length but is most difficult in a shortened position.

As I mentioned at the start of this article, there’s a lot to learn. For example, we may learn that these concepts are not applicable to all muscles. Further, this article has considered hypertrophy per set; it very well may be that exercises that are most difficult in the lengthened position are more fatiguing, limiting the number of sets that can be productively performed. Lastly, I’d like to emphasize that shortened-biased exercises are not bad, they just don’t seem to lead to quite as much hypertrophy in the research; a sound training program may purposefully include some shortened-biased exercises to “cover your bases” given the uncertainty in the research.

In the meantime, ensuring a good amount of your training consists of exercises that are most difficult in an at least somewhat lengthened position is probably a good idea.

Footnotes

* In a bicep curl, the point of peak difficulty will generally be when the moment arm on the elbow joint is greatest. In practice, this will generally be when the resistance is perpendicular to the forearm.

** The Pedrosa study only reported percentage changes for each group, so I was unable to calculate between-group effect sizes of the nature I’d like. So, I chose to simply report average percentage changes from each study for easy comparisons.