Lengthened Partials: a New Muscle Growth & Mobility Hack?
One of the most important components of “good form” on a strength exercise is the range of motion used. [1]
For instance, a full squat that is performed as deeply as possible will lead to better results that a quarter squat where a person does not squat all the way down.
The reasons a full squat is superior to a quarter squat are:
More overall work is done because the weight travels a farther distance
The working muscles experience a greater stretch, increasing the overall tension they feel.
However, new research is adding an interesting twist to this with the concept of lengthened partials.
So, the aim of this article is to break them down and explain exactly how you can use them to build more muscle and mobility.
What is a lengthened partial?
To illustrate this, let’s use the squat as an example.
A full range of motion squat would involve starting from a standing position and squatting as far down as you are able.
A quarter squat would involve starting from a standing position and squatting a quarter of the way down, until your knees are at about ~90 degrees.
A lengthened partial squat would involve starting from the bottom and squatting up until you reach parallel (thighs parallel with the floor) or until your knees reach ~90 degrees (depth of a quarter squat).
The idea is that you spend the entirety of your reps in the part of the range of motion where your muscle is most lengthened; its most stretched position.
The research has been continually suggesting that training muscles in their more lengthened position is advantageous.
First, it was demonstrated that full ranges of motion are better than partial ranges of motion when the muscle is in a more shortened position, such as a quarter squat. [1].
Then, research showed that selecting exercises that exercises that place a muscle in a more stretched position throughout the entirety of the range of motion are superior. For instance, seated hamstring curls build more muscle than lying hamstring curls for this reason. [2] This has also been shown in the triceps and calves. [3,4]
Lengthened partials are the next step in seeing just how beneficial training muscles at long muscle lengths is.
Benefits of lengthened partials
It’s worth noting that this is an early area of research. It’s possible this won’t be true for every muscle, but it has been true for every muscle it’s been tested in so far, though.
A May 2021 study [5] tested leg extensions done with a full range of motion, final range of motion (straight leg to half way down), and the initial range of motion (completely bent leg to half way up). The initial range of motion is the lengthened partial.
They found that the lengthened partial group built more muscle, but increases in 1 repetition maximum strength were similar.
A February 2023 study [6] had subjects perform bicep curls. One arm did the bicep curls using lengthened partials, while their other arm did bicep curls with the top half of the range of motion.
They found that the lengthened partial group built more muscle overall and had greater increases in 1 repetition maximum strength.
A September 2023 study [7] looked at this in the calves. Some subjects performed full range of motion calf raises, some top half of the range of motion, and others performed the bottom half of the range of motion (the lengthened partial group).
They found that greater muscle growth overall was experienced in the group performing the lengthened partials.
It’s worth noting, though, that there was a degree of regional hypertrophy in each of these studies. In other words, the groups performing the lengthened partials saw greater muscle growth in the more distal part of the muscle; the part of the muscle that’s farther away from the center of your body. For instance, in the leg extension study, the bottom portion of the quadriceps disproportionately grew compared to the top portion of the quadricep.
So, to make the most out of your training, it’s likely worth your time to not do ALL of your sets in a lengthened partial manner. Adding them into 25-50% of your sets, though, will likely bring you bring you great results.
Lengthened partials for mobility improvements
There is no direct research showing that lengthened partial training improves mobility better than normal strength training, however I’d argue it’s fair to think so.
The research shows that when your strength training is done at a full range of motion, it improves mobility just as well as stretching; and in some cases better than stretching. [8]
As a result, I rarely recommend stretching to my clients if they are performing their strength training with full ranges of motion; the strength training is enough to induce mobility gains.
However, given that lengthened partials involve performing your reps in the most stretched part of the range of motion only, it’s likely they can lead to better, faster mobility gains than full range of motion training. It’s more specific to what “mobility” actually is.
How to incorporate lengthened partials into your workouts
The easiest way to capitalize on this form of training would be to turn the last set of each of your exercises into a lengthened partial set.
For instance, say you normally perform 3 sets of goblet squats in a given workout in your week. You could perform the first 2 sets with a full range of motion, and then perform the final set in a lengthened partial manner. This would very likely lead to more muscle and strength built based on the available research.
