Adam C. Stewart
Many influencers have become enthusiastic about elongated partials and stretch-mediated Hypertrophy. However, the evidence is not as clear as you might think.
If you prefer to listen, we covered a lot of the content of this article in Episode 132 of the Stronger By Science podcast, which you can listen to below. Alternatively, you can also listen on Spotify, Apple Podcasts or YouTube.
Until a few years ago, the full range of motion (ROM) was widely recognized as the best approach for users who wanted to develop their muscles. It was not uncommon for Rome to be treated as an open and closed affair. The only plausible reason to use a partial ROM was to use more weight and stroke your Ego.
However, more recently, the concept of “long partials” or “extended partials” has gained momentum.
In matter you haven’t been following the hype, extended partials are simply partial ROM repetitions performed in the extended or stretched part of the set. Although there are many studies that find better muscle growth in elongated partials than in shortened partials – partial repetitions performed in the shortened part/”maximum pressure” of a movement(1, 2, 3, 4, 5, 6, 7, 8) – There are far fewer studies comparing extended partials to a full ROM(1, 2, 3, 4, 5). The most recent meta-analysis on the theme of Rome was carried out by myself and some colleagues (1). At the time, there were only three studies comparing a full ROM with elongated partial muscles and measuring muscle growth (1, 2, 3). In a subgroup analysis, we only looked at these three studies to determine whether muscle length was important for muscle growth. Here are the results.
As you can see, the extended partials were potentially better for muscle growth compared to a full ROM (6.76% more muscle growth, 95% CI -29.5 – 22.1). However, a significant limitation of the data was the fact that only three studies could be used. Fortunately, there has been other research on the subject since then. First, in a study by Kassiano et al. (1) compared the use of a full ROM with elongated partials (lower half of the repetition) with shortened partials (upper half of the repetition) in the calf lift of the leg press. The authors measured lateral and medial Gastrocnemius hypertrophy. In general, the best hypertrophy results were observed in the elongated subgroup, followed by the complete ROM group, the shortened subgroup being clocked last, as you would expect based on the results of the analysis of the subgroup above. Interestingly, the elongated partial group had about twice as much Hypertrophy at the lateral and medial sites as the complete ROM group (lateral Gastroc: +7.3% versus +14.9%, Medial Gastroc: +6.7% versus +15.2%).
The second study comparing the extended partials to the full ROM was a study by Maeo and his colleagues (1). Unfortunately, this study was only presented at a conference. I contacted the authors to see if they had a complete manuscript in preparation, but they haven’t yet had the opportunity to write the results after the abstract version. Fortunately, the authors are responsible for a large part of the research in this area (1, 2), so I still think that this study deserves to be examined.
Compared the use of a full ROM (90-0 degrees of hip flexion) to a prolonged partial ROM (90-45 degrees of hip flexion) when exercising with several hip machines. For those who don’t know what it is, it is a movement pattern similar to a lapel. However, it should be noted that Maeo et al. asked the participants to minimize the squat and bring the movement closer to a hip joint or a Romanian deadlift movement. They measured the volume of the hamstrings and the gluteal muscle using magnetic resonance imaging (MRI). In short, the elongated partial muscles led to an enlargement of the hip extensors approximately twice as strong as the complete ROM (+6.8% versus +3.1%). More muscle growth was observed in the gluteus maximus, the semimembranous, the semitendinous and the long femoral head of the biceps.
In conclusion, the analysis of the subgroups in Figure 1 has certainly been exploratory and preliminary since more consistent and positive data have been published, increasing our confidence in the recognition that elongated subareas could/are better for muscle growth than a complete ROM. However, these results raise some questions. Why does the muscle length at which resistance training is performed affect the results of Hypertrophy? Why can elongated partial muscles lead to more muscle growth than a full ROM?
Why might extended partials work better?
To find out why prolonged partials lead to more Hypertrophy in these studies, we can examine the subset of ROM and muscle growth studies, which measure the results that can mechanically affect muscle growth. Unfortunately, few studies usually do this, and for good reason: The necessary equipment and facilities (not to mention the investment in additional time) are expensive and rare. However, we have two studies that measured acute mechanistic outcomes from different ROM.
The first study on ROM to measure acute mechanistic data in parallel with Hypertrophy is a study by McMahon et al. (2014). They compared the performance of extended partial to shortened partial in a program consisting of a variety of quadriceps exercises.
The elongated partials were performed from 90 to 40 degrees of knee flexion, while the shortened partials were performed from 50 to 0 degrees. (1) also evaluated the changes in insulin-like growth factor 1 (IGF-1) from before to after The Intervention when IGF-1 was measured at rest. Compared to the Truncated subbody group, the elongated subbody group experienced a greater overall increase in the cross-section of the lateral muscle, especially at the distal site, but also experienced a significantly greater increase in resting IGF-1 levels. Therefore, the authors hypothesized that an increase in IGF-1 could be partly responsible for the Superior Hypertrophy observed in the group of prolonged partials.
