Resist WITH the Stretch, Not Against It
Deep dive into how range-of-motion influences muscle and strength gains
If you’ve been following along with my recent Check-It-Out posts, you’ve seen that I have been diving into research comparing muscle growth and strength outcomes when using different ranges-of-motion (ROM) in resistance training.
And, I recently sat down for the first ever Shortcut U podcast with Milo Wolf P.h.D., an expert in this topic, to discuss this area of research and how it translates to real-world applications in the gym.
Below, I’ll share my takeaways from the research and talking to Dr. Wolf, as well as how I plan to implement it all into my own training.
If you’re interested, you can check out that full conversation here.
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What is ROM?
First, let’s define some terms. Range-of-motion (ROM) is exactly what it sounds like: the spectrum of movement you have available to you at a given joint. For example, when it comes to your elbow, your ROM runs from extending your arm as straight as you can to bending it as much as you can.
What does this have to do with lifting weights? Well, you have the option to use the full ROM with an exercise or a partial ROM.
Going back to our elbow example, if you’re doing a bicep curl, using full ROM means straightening your arm as much as you can at the bottom of the curl and bending it as much as you can at the top of the curl. Partial ROM, on the other hand, looks like cutting out some portion of that full ROM during each repetition (rep).
So, for a partial rep you could only complete the bottom portion of the curl, only complete the top portion of the curl, or complete some combination of the bottom and top portions of the curl while cutting out some of the very bottom or very top.
Lengthened vs. Shortened Partials
These partials are commonly described as lengthened or shortened according to the length of the muscle during the rep.
If you look at your bicep muscle during a curl, you’ll see that it stretches out at one end of the repetition (when your elbow extends straight) and contracts, or shortens, at the other end (when your elbow bends).
For this reason, a partial rep where you only complete the bottom half of the curl (from when your elbow is extended straight to when it is bent at a 90-degree angle) is a lengthened partial. And, a partial where you only complete the top half of the curl (from when your elbow is bent at a 90-degree angle to when it is fully bent) is called a shortened partial.
Here are a few ways to distinguish between lengthened and shortened partials of different exercises:
The lengthened partial involves the first half of the lifting portion of the movement, while the shortened partial involves the second half of the lifting portion of the movement.
There is a great stretch on the muscle at the end of the lengthened portion of the movement, while there is not a stretch on the muscle at the end of the shortened portion of the movement.
The half of the movement where the weight is lower to the ground is the lengthened partial, while the half of the movement where the weight is further from the ground is the shortened partial. (Credit for this description goes to Dr. Wolf)
Importantly, partial reps do not need to be half reps, they can be any fraction of the full ROM (one-third reps, quarter reps, etc.). But, in my experience, they most commonly take the form of half reps and are more easily explained as such.
Who Cares?
Previously, it was generally believed that you build more muscle using full ROM than partial ROM. And, in addition to the hypothetical explanation that greater ROM might lead to greater mechanical tension (force exerted on the muscle) and metabolic stress (the burn in the muscle), there was some research data to support this idea.
Prior to 2023, there were two systematic reviews suggesting that full ROM was superior to partial ROM for muscle hypertrophy. (I, II) The first, by Schoenfeld and Colleagues in 2020, was limited to only 6 studies, 4 of which experimented with lower body muscles. (I) For this reason, along with some conflicting results between studies, their conclusion was only tentatively in favor of full ROM for growing the lower body muscles:
“Current research suggests that performing [resistance training] through a full ROM confers beneficial effects on hypertrophy of the lower body musculature when compared with training with a partial ROM. However, at least for the quadriceps and based on our interpretation of the data, evidence implies that these benefits are apparent only up to a certain ROM threshold, with advantageous effects attenuating beyond the given threshold. Alternatively, research on the effects of ROM for the upper extremities is limited and conflicting, thereby precluding the ability to draw strong practical inferences. No study to date has endeavored to investigate how ROM influences muscle growth of the trunk musculature. At this point, no compelling rationale can be made for employing a given ROM versus another in the upper body muscles. On the whole, some evidence indicates that the response to variations in ROM may be muscle-specific; however, this hypothesis warrants further study.” (I)
In 2021, Pallarés and colleagues published an updated systematic review, including 16 total studies. As far as hypertrophy outcomes go, they looked at the same 6 studies, but, this time, they conducted a meta-analysis (when you combine data points from several studies to quantitatively assess the entire body of evidence for a given intervention). (II)
They found a large effect size of 0.88 for full ROM being superior to partial ROM for building muscle in the legs. (II) In addition, they found statistically significant effect sizes of 0.56 and 1.53 in favor of full ROM for all strength outcomes and lower limb strength outcomes, respectively. (II) And, they found a nearly statistically significant (p = 0.078) effect size of 0.69 for upper limb strength in favor of full ROM. (II)
(Confused about effect sizes? Check out this paper for an explanation.)
Notably, the overall strength outcome refers to both full and partial ROM tests, while the lower and upper limb strength outcomes refer to testing how much subjects can lift with a full ROM. (II)
“The main findings of this study suggest that full ROM resistance training is more effective than partial ROM to maximize muscle strength and lower-limb muscle hypertrophy. Similarly, functional performance appears to be favored by full ROM exercises.” (II)
So, at this point, partial ROM was generally viewed as sub-optimal for building muscle and strength, as compared to full ROM.
Enter Wolf and Colleagues
In 2023, Wolf and Colleagues published a new systematic review and meta-analysis that is distinct from the previous papers in two ways:
They included 23 total studies with 8 looking at muscle hypertrophy outcomes.
They completed several sub-analyses (when you further compare outcomes based on given variables ; for example, comparing outcomes between male and female subjects), including one distinguishing between lengthened and shortened partials.
They found similar results in their main analysis and main sub-analyses to those in Pallarés and Colleagues’ meta-analysis, in that full ROM showed better results than partial ROM for all outcomes. (IV) Though, this time, the effect sizes in favor of full ROM were much smaller. (IV)
Most interestingly, they found a small effect size of 0.28 in favor of lengthened partials as compared to full ROM for muscle hypertrophy and a trivial effect size of 0.08 in favor of full ROM as compared to shortened partials. (IV)
Thus, according to the latest meta-analysis, when distinguishing between lengthened and shortened partials, it appears that there is a dose-response relationship whereby implementing more of the stretched half of movements leads to more muscle growth.
Zooming Into RCTs
Though meta-analyses are useful for combining data points and assessing overarching trends–especially in exercise science research where sample sizes (how many subjects are in each study) tend to be smaller–they often sacrifice some amount of specificity by doing so. This is somewhat inevitable, as restricting your inclusion criteria (the qualifications a study must meet in order to be added to the meta-analysis) too much often means losing out on the size of the meta-analysis–which is sort of the whole point of a meta-analysis.
I discussed this point previously in regards to artificial sweetener research, where one meta-analysis included a study testing stevia pills when assessing the body of evidence on artificial sweeteners and weight management.
Anyways, my point is that, in addition to meta-analyses, looking at individual randomized-controlled trials (RCTs) that are most similar to real-life conditions gives insights into how well interventions work.
In terms of comparing lengthened partials and full ROM, there are two RCT’s that strike me as particularly realistic; interestingly, they both include groups using full ROM, lengthened partials, and shortened partials. (V, VI)
Pedrosa and Colleagues’ RCT experimented with the leg extension exercise in 2021, dividing untrained women aged 18-30 years old into five groups (V):
Lengthened partials (half-reps in the lengthened position)
Shortened partials (half-reps in the shortened position)
Varied (alternating between lengthened and shortened partials each session)
Full ROM
Control (no resistance training)
The subjects completed 3-6 sets of 7 reps (they started at 3 sets and added a set every 3 weeks) three times per week for 12 weeks, using a lifting:lowering cadence of 2:2 seconds for each repetition. (V)
After the 12 weeks, they found the following regarding overall muscle growth (INITIAL = lengthened partials group ; FINAL = shortened partials group ; VAR = varied group ; CON = control) :
“For the [rectus femoris (RF)], INITIALROM and VARROM groups presented a greater change than the other groups, and the FULLROM group presented a greater change than FINALROM and CON groups, which showed similar changes. For the [vastus lateralis(VL)], the INITIALROM, FULLROM, and VARROM groups presented similar responses, which were greater than FINALROM and CON groups; the FINALROM group presented a greater increase than the CON group. Furthermore, INITIALROM and VARROM groups presented a greater increase for the RF than the VL. For the other groups, both muscles presented similar changes.” (V)
Interestingly, they found differences between groups in terms of muscle growth at specific portions of the quads:
“The post hoc test revealed similar changes between the training groups, which were all greater than the CON group at 40% of femur length. INITIALROM and VARROM groups presented similar changes and greater than the other groups at 50%, whereas FULLROM and FINALROM groups presented similar increases, which were greater than the CON group. INITIALROM and VARROM groups presented similar changes and greater than the other groups at 60%, followed by the FULLROM. Moreover, FINALROM and CON groups showed similar responses. INITIALROM group presented greater responses than other groups at 70%. Additionally, FULLROM and VARROM groups showed similar increases and greater than FINALROM and CON groups, which showed similar relative responses. The CSA changes among the 4 muscle regions were similar for the INITIALROM, FULLROM, VARROM and CON groups. However, for the FINALROM group, the CSA changes at 40%, 50% and 60% were greater than at 70%” (V)
So, it appears that training in a more lengthened position led to greater muscle growth at more distal regions of the quads (closer to the knee). (V)
As far as strength outcomes go, Pedrosa and Colleagues generally found that the subjects performed best in the 1-repetition-max (1RM) tests conducted in the ROM they trained in. For example, the lengthened group increased their lengthened partial 1RM more than their full ROM and shortened partial 1RMs. (V)
However, while the lengthened partial and varied groups outperformed the other groups in the lengthened partial 1RM, the lengthened partial and varied groups also achieved similar increases in the shortened 1RM and full ROM 1RM as compared to the other groups.
“The post hoc test revealed that in 1RM testing performed at the initial ROM, INITIALROM and VARROM groups showed greater changes than the other groups, and FINALROM and FULLROM groups showed similar changes, which were greater than CON group. For the 1RM test performed at the final ROM, the training groups showed similar increases, all of which were greater than the CON group. In the 1RM test performed at the full ROM, INITIALROM, FULLROM, and VARROM groups presented similar relative increases, which were greater than FINALROM and CON groups; FINALROM showed greater changes than CON group. Additionally, INITIALROM and FINALROM groups presented a greater increase in the 1RM test at the respective ROM trained, and the other groups did not show differences between the tests.” (V)
In 2023, Kassiano and Colleagues’ also tested full ROM, lengthened partials (half reps), and shortened partials (half reps), this time using the calf raise exercise on a leg press machine. (VI) The subjects–women aged 18-35 years old who hadn’t resistance trained for at least 6 months–completed 3 sets of 15-20 reps three times per week, using a lifting:lowering cadence of 1:2 seconds (particularly realistic when it comes to hypertrophy training). (VI)
At the conclusion of the 8 weeks, the full ROM, lengthened partials, and shortened partials groups averaged 6.7%, 15.2%, and 3.4% increases in medial gastrocnemius (inner calf) muscle thickness and 7.3%, 14.9%, and 6.2% increases in lateral gastrocnemius (outer calf) muscle thickness. (VI)
The differences were statistically significant in favor of lengthened partials for the medial gastrocnemius compared to both full ROM and shortened partials. For the lateral gastrocnemius, they were statistically significant in favor of lengthened partials as compared to shortened partials and nearly statistically significant (p=0.06) as compared to full ROM. (VI)
So, what are some takeaways from these fairly realistic RCTs?
First, lengthened partials seem to be much better than shortened partials for building muscle. In the Pedrosa study, lengthened partials produced ~1.3-3X more relative growth (measured by cross-sectional area) than shortened partials at 50% and 60% femur length and led to 18-32% growth at 70% femur length, while the shortened group showed a similar response to the control group at this region. (V) And, in the Kassiano study, the lengthened partials group gained ~4X and ~2X more muscle (measured by muscle thickness) on average in the medial and lateral gastrocnemius, respectively, compared to the shortened partials group.(VI)
Second, lengthened partials seem to be better than full ROM for building muscle. In the Pedrosa study, lengthened partials produced ~1.14-2X more relative growth than full ROM at 50%, 60%, and 70% femur length (differences varied within this range depending on the region and muscle, the rectus femoris or vastus lateralis). (V) Further, in the Kassiano study, the lengthened partial group achieved ~2X more relative growth in both the medial and lateral gastrocnemius, though the result for the lateral gastrocnemius was just shy of statistical significance (p=0.06). (VI)
Third, lengthened partials seem to significantly increase full ROM 1RM. In the Pedrosa study, the lengthened partial group increased their full ROM 1RM by ~20%, which was a statistically similar increase to that shown by the full ROM group. (V)
Limitations
To be fair, as with all research, there are some limitations to the meta-analyses and RCTs mentioned above.
First, most of the research I’ve seen on this topic involves untrained subjects, so it is unclear exactly how much, if at all, the results carry over to more experienced lifters. Also, in regards to the Pedrosa and Kassiano et al. RCTs, both studies only looked at female subjects, so it is unclear how much, if at all, those results carry over to males.
Second, most of the research in this area involves muscle groups of the upper and lower limbs, leaving the question as to whether the results will be similar for all muscle groups across the body.
Third, the longest study design I’ve seen using lengthened partials is 12 weeks long. For this reason, it’s unclear whether the superior gains from lengthened partials last indefinitely or taper off over time (i.e. are the differences simply due to exposing the muscles to an unfamiliar stimulus?).
Conclusions
With all of that said, as you may have guessed, I am fairly bullish on lengthened partials and the stretched position in general.
In particular, I agree with Dr. Milo Wolf’s position that, at the very least, you aren’t losing any gains by using lengthened partials as (to my knowledge) there is no data showing that full ROM leads to better outcomes than lengthened partials.
And, I am especially convinced that, whether it be with full ROM or lengthened partials, it is significantly better to utilize the stretched portion of the movement, rather than complete shortened partials where you don’t go all the way down. Not only do I think this is better for muscle and strength gains, but I think it is (maybe most) beneficial from a flexibility standpoint.
As I’ve covered previously, a meta-analysis showed that resistance training leads to similar improvements in flexibility as stretching or stretching plus resistance training. (VII) And, it seems plausible that it’s including the stretched portion of the movement in resistance training that leads to these flexibility improvements–something Dr. Wolf suggested in our conversation.
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