Stretch-Mediated Hypertrophy Can Triple Muscle Growth
For at least a few decades, bodybuilders have been known for favouring exercises that challenge their muscles at long muscle lengths. “Go deep and feel the stretch.” For instance, bodybuilders used the pullover to stretch out their lats (and triceps) under load, ostensibly to help them build muscle faster. The mechanisms weren’t known, and the results weren’t proven, but it was a popular idea nonetheless: to gain muscle faster, train your muscles at longer muscle lengths.
Now the research is starting to validate what the best bodybuilders have known all along. A systematic review of 26 studies found that isometric lifts that challenge our muscles at longer muscle lengths stimulate nearly three times as much muscle growth. For instance, holding the bottom position of a dumbbell fly (with our chests stretched) stimulates more muscle growth than holding the top position of a cable crossover (with our chests contracted). This is a bit counterintuitive because the cable crossover gives a better pump and burn. But it’s the deep stretch that actually builds more muscle.
So, why is stretch-mediated hypertrophy so powerful? And how can use it to build muscle faster?
- What Did The Study Find?
- Why Do Stretched Muscles Grow Faster?
- Which Lifts Challenge Our Muscles in a Deep Stretch?
- The Problem With Partials
Alright, so, in this article let’s go over a systematic review titled Isometric Training and Long-Term Adaptations: Effects of Muscle Length, Intensity, and Intent: A Systematic Review.
Now, the first thing to note is that this is a review of isometric lifts. An isometric lift has zero range of motion. Think of how a plank trains our abs or how a deadlift trains our spinal erectors. In fact, if you loaded up a deadlift a bit too heavy and weren’t able to pull it off the floor, that’s an example of an isometric deadlift. But most people don’t use isometrics for anything aside from their spinal erectors and abs, and there’s a simple reason for that: they aren’t very good at stimulating muscle growth.
You might wonder, if isometrics aren’t good for building muscle, then why are we looking at research on isometrics? There’s a good reason for that. Isometrics aren’t all that great at stimulating muscle growth, no, but they’re absolutely fantastic for studying muscle growth. With isometrics, there’s quite a bit less skill involved, we can measure exactly how much force someone can exert at any part of a range of motion, and in this case, we can also measure which parts of the range of motion are responsible for stimulating the most muscle growth. So what we can do with this study is look at which isometrics were the best at stimulating muscle growth, determine what made them more effective, and then use those same principles when choosing traditional lifts with a larger range of motion.
Plus, we don’t just need to rely on the results of this systematic review. We have other studies confirming these findings. For instance, this study measured hamstring activation when training at different degrees of stretch. It found that the more we stretch our hamstrings, the more muscle activation we see, and the more strength we gain.
Another study came out a few months later, again comparing seated vs lying hamstring curl research. And similar to the previous study, it found that we can build muscle faster by challenging our muscles in a deeper stretch. What’s neat is that the different areas of our hamstrings are stretched to different degrees when we bend at the hips. The areas that got the greatest stretch saw the greatest growth. The areas that were unaffected didn’t see a difference in muscle growth. And the areas that were shortened by bending at the hips saw less growth. So this most recent study gives us perhaps the strongest indication that challenging our muscles at longer lengths is a way to build muscle significantly faster.
Finally, a 2021 study by Sato et al. found that doing just the bottom half of a preacher curl stimulated around 3x as much muscle growth as as doing just the top half. This is why we recommend lifts like incline curls, preacher curls, and barbell curls, but not spider curls.
Isometrics aren’t nearly as good at stimulating muscle growth as lifting through a full range of motion, but they’re great for studying muscle growth, and we can apply these findings to traditional hypertrophy lifts, especially since they’ve been confirmed with lifts done through a full range of motion.
What Did The Study Find?
Challenging Our Muscles While Stretched Stimulates More Muscle Growth
The main finding of the study, as we’ve mentioned above, is that challenging our muscles in a stretched position stimulates nearly three times as much muscle growth as challenging our muscles in a contracted position:
Training Muscles At Longer Lengths Yields More General Strength
Challenging our muscles in a stretched position also resulted in greater improvements in general strength, explosiveness, and athletic performance, which isn’t all that surprising. Bigger muscles are stronger and more powerful, so training in a way that builds more muscle will also yield greater overall improvements in muscle function. But it also seems that developing strength at long muscle lengths transfers better to our strength at shorter muscle lengths, which is neat.
Attempting to Accelerate the Weight Increases Muscle Stimulation
Another interesting finding was that ballistic intent (trying to accelerate the weight) nearly doubled muscle activation. That’s a well-known phenomenon, and it’s why we recommend trying to accelerate our weights through the range of motion before lowering them back down under control. For example, when doing a bench press, we want to lower the weight down slowly and under control until it touches our chests, and then explode the weight back up, trying to accelerate it through that bottom part of the range of motion. If the barbell is heavy, it might not move quickly, but all that matters is that you try to move it quickly.
Moderate-to-Heavy Loads Stimulate More Muscle Growth
There also appeared to be no difference in muscle growth between people training with heavier versus moderate loads. This lines up with previous research on traditional hypertrophy lifts, too, showing that sets of 6–20 reps stimulate similar amounts of muscle growth (study). In fact, according to experts such as Mike Israetel, PhD, the hypertrophy rep range may be as broad as 5–30 reps. Or if you ask Greg Nuckols, MA, perhaps all the way from 4–40 reps. The most important factor seems to be how many challenging sets we do within an effective rep range.
Moderate-to-Heavy Loads Improve Our Tendon Health
Moderate and heavy loads produced better improvements in tendon thickness and strength than lighter loads. This is important because improving the strength of our tendons makes us stronger and tougher, including helping us avoid and recover from tendinopathy—tendonitis and other forms of chronic tendon inflammation. To get those benefits, it seems like we need to lift weights that we can’t lift for more than around twelve reps. If we’re also eager to grow our muscles, that might be a reason to bias our training in favour of, say, 6–12 reps per set, at least on our heavier compound lifts.
Constant Tension Improves Muscle Growth
Finally, uninterrupted time under tension improved muscle growth. This makes sense mechanistically. Keeping the tension on our muscles restricts blood flow, reduces muscle oxygen saturation and increase metabolite concentrations in our muscles, stimulating more hypertrophy. This lines up with previous research done on conventional hypertrophy lifts, too. For example, when doing a bench press, instead of resting the barbell on our chests at the bottom or pausing with our arms fully locked out at the top, it’s better to keep the tension on our muscles throughout the entire set. For a more controversial example, we may also want to keep tension on our muscles when deadlifting, meaning that we want to lower the barbell down slowly and under control instead of dropping it, and we don’t want to release any tension between reps.
To quickly summarize the findings, it’s best to choose lifts that challenge our muscles in a deep stretch at the bottom of the lift, to attempt to accelerate the weight out of the hole, and to keep constant tension on our muscles throughout the range of motion (including lowering the weight down slowly and under control).
Why Do Stretched Muscles Grow Faster?
We now have dozens of studies showing that challenging our muscles in a stretched position yields the greatest amount of muscle growth, but why is that? The main mechanism of muscle growth is something called mechanical tension. The more mechanical tension we put on our muscles per repetition, per set, and per workout, the more muscle growth we can stimulate (up to a point). However, not all parts of the range of motion put equal amounts of mechanical tension on our muscles.
If one part of the range of motion is especially hard, creating a sticking point, then that’s the point where our muscles will contract the hardest, producing more mechanical tension at that point.
On most lifts, the hardest part is when the limb that serves as the lever is horizontal, creating a longer moment arm. For some examples, the hardest part of a barbell curl is when our forearms are horizontal, the hardest part of a bench press is when our upper arms are horizontal, and the hardest part of a squat is when our thighs are horizontal. That’s where the weight is the heaviest on our muscles, where our muscles need to contract the most forcefully, and where mechanical tension is the highest. This is where most of our muscle growth comes from.
The next thing to consider is that our muscles are able to produce the most contractile force at their resting length—the length of our muscles when we’re standing in a relaxed position. So if the sticking point of the lift is around that point, we’re stronger, able to lift more weight, and able to generate more mechanical tension. That’s great for building muscle.
If we consider a lift like the bench press, the sticking point is when our upper arms are horizontal, which puts our chests at resting length, which is where it’s able to generate the most contractile force. That’s great. That’s a great strength curve for building muscle.
But there’s another key factor at play here, too. As we’ve just covered, the main way that we produce force with our muscles is by actively contracting them, producing active tension. But our muscles also behave somewhat like elastics. When we stretch them, they pull themselves back towards their resting length. This extra tension is called passive tension, and it means that we’re also quite strong when our muscles are stretched. Perhaps more importantly, when we combine active tension with passive tension, then we have more overall mechanical tension on our muscles, stimulating more muscle growth.
Greg Nuckols, MA, did a good job of explaining the mechanistic evidence in Monthly Applications in Strength Sport: “While active contractile tension of a muscle tends to be highest at around resting length, passive tension from non-contractile elements (the tendons and muscle fascia) increases as muscle length increases, such that total muscular tension is generally highest when muscles are in a stretched position. Tension primarily seems to matter for hypertrophy because tension is sensed at costameres (where muscles attach to the surrounding fascia), which activate a protein called focal adhesion kinase (FAK), which then triggers the mTOR pathway, which is primarily responsible for exercise-induced hypertrophic signaling. In exquisitely controlled rodent research (study), it’s been shown that tension itself, not just active tension generated by muscle contraction, is what kicks off this pathway. Thus, even though active tension drops off, the disproportionate increase in passive tension, which leads to more total tension, should also lead to more hypertrophic signaling.”
So mechanical tension is the main driver of muscle growth, and mechanical tension is highest if we have overlapping passive and active tension. That overlapping tension happens when we challenge our muscles in a stretched position. For example, if we fully stretch our chests out at the bottom of a dumbbell chest fly (maximum passive tension) and that also happens to be our sticking point (maximum active tension), then we have a maximum amount of overall mechanical tension on our chests.
However, to take advantage of this added passive tension, it needs to be helping us overcome the sticking point of the lift. Otherwise, the active and passive tension won’t be overlapping. They won’t be adding to one another. Overall mechanical tension won’t be higher.
For example, if we’re doing resistance-band squats, say, then the load is light when our quads are stretched at the bottom, and hard when our quads are contracted at the top. We’re getting a full stretch, but the stretch doesn’t overlap with the sticking point. This is why we specify that we need to challenge our muscles in a stretched position. And this is why challenging our muscles in a contracted position doesn’t stimulate as much muscle growth. (And why free weights and bodyweight exercises tend to be better than resistance bands for building muscle.)
This may also explain why accommodating resistance doesn’t seem to stimulate much (if any) extra muscle growth. Accommodating resistance is where resistance bands or chains are added to barbell lifts to make them more challenging at the top of the range of motion. The bands and chains don’t make the bottom harder, just the top. Since most of our muscle growth comes from challenging our muscles at the bottom, it makes sense that making the top harder wouldn’t help very much (if at all).
To summarize, when we challenge our muscles under stretch, there’s a combination of both passive and active tension, raising overall mechanical tension. Since mechanical tension is the main driver of muscle hypertrophy, when we have overlapping active and passive tension, we stimulate more muscle growth. This is why the strength curves of our lifts matter. If we can find lifts that challenge our muscles at longer muscle lengths, we can build muscle much more quickly.
Which Lifts Challenge Our Muscles in a Deep Stretch?
The Big Three Lifts
Okay, so now that we’ve covered that challenging our muscles in a stretched position produces more muscle growth and why that’s the case, we can talk about choosing lifts where our muscles are challenged in a stretched position. Fortunately, that’s not all that difficult:
- The squat challenges our quads in a stretched position, especially if we “sit down” instead of “sitting back” into our squats. This benefit is even more exaggerated if we do front-loaded squats with a lot of bend at the knees, such as deep front squats.
- The bench press challenges our chests and shoulders in a stretched position, especially if we bench deep (without an excessive arch). If we bench with a wide grip, the load is greatest on our chest. If we bench with a close grip, the load is greatest on our shoulders.
- The deadlift challenges our hips, hamstrings, and traps in a stretched position. The Romanian deadlift does an even better job of specifically loading the hamstrings in a stretched position.
So what we’re seeing is that the “Big Three” barbell lifts that are so popular in strength training, powerlifting, and bodybuilding are also great for challenging our muscles in stretched positions. We can emphasize the stretch a bit better than powerlifters would by squatting with more knee bend and benching with less of an arch, but the Big Three lifts all have great strength curves for building muscle.
The Big Five Lifts
The Big Three are well and good for powerlifting, but we generally recommend the “Big Five Hypertrophy Lifts when training for muscle size, general strength, and aesthetics. By switching from a back squat to a front squat, and then adding in the chin-up and the overhead press as main lifts, we gain much more upper-body size and strength.
By adding in chin-ups as a foundational lift, we now have a main lift for our upper backs and biceps. By adding in the overhead press, we have a lift dedicated to building bigger, stronger, and broader shoulders. By giving them equal priority to the squat, bench press, and deadlift, we have a good base for a hypertrophy routine.
So let’s talk about the chin-up and overhead press, too.
The chin-up has a reasonable strength curve. Any lift that challenges our lats while our arms are in front of our bodies is challenging them in a stretched position, and the chin-up does that. It’s hardest on our lats in the middle of the range of motion, when our upper arms are still quite far in front of our upper bodies.
If we compare that against the barbell row, which is most challenging at the very top, we see why chin-ups tend to be a better bulking lift than rows. However, if we wanted to really train our lats under a heavy stretch, we could follow our chin-ups up with some pullovers.
But when we’re doing chin-ups, we aren’t just trying to stimulate our lats and upper backs, we also want to stimulate our biceps. And that’s where things get tricky. The long heads of our biceps connect at our shoulder joints, and so when we raise our arms above our heads, they become shorter. As we pull ourselves up, we bend at the elbow joint, cancelling out the lengthening at the shoulder joint. That means that the chin-up is perfectly fine for the short head of our biceps, but we aren’t doing the best job of stimulating the long heads.
That’s not a huge problem. The chin-up is an extremely heavy lift, putting a fair amount of mechanical tension on our biceps all through the lift, and so it will still stimulate quite a lot of biceps growth—especially in the short heads. But if you want to fully maximize your biceps growth, I’d recommend including some biceps curls in your routine as well. Speaking of which…
The Biceps Curl
For biceps growth, we have a study directly comparing muscle growth from doing cable curls, which are harder in a contracted position, with preacher curls, which are harder in a somewhat stretched position (study). The study found no significant differences, although it’s worth noting that the group doing preacher curls did indeed see more muscle growth, just not to a statistically significant degree. I take a few things from this:
- The most important thing is training hard and challenging our target muscles. So any lift that does a good job of stressing our biceps will be able to cause a good amount of growth.
- It does seem that challenging our biceps at somewhat longer muscle lengths stimulates either equal or slightly more biceps growth.
- The preacher curl may not be the absolute best exercise for getting an edge on your biceps training, since our biceps aren’t actually in a stretched position, even at the bottom of the movement.
That final point is the tricky one. Our biceps are a bit hard to train in a stretch position. If we let our arms hang naturally at our sides, that’s the natural resting length of our biceps. That’s a rather long resting length, and it just so happens to line up with the bottom of a barbell curl. That means that the barbell curl starts at resting length. There’s no stretch.
Now, is challenging our muscles at their resting length a problem? Not really. It’s not quite as good as challenging them in a stretched position, but it’s still much better than emphasizing the contraction. But the barbell curl has another problem: it’s relatively easy at the start of the range of motion. The sticking point is in the middle, when our forearms are horizontal. We’re challenging our biceps in a contracted position.
As a result, there are two lifts that are often used to challenge the biceps at longer muscle lengths: the preacher curl and the incline curl. The preacher curl puts our arms in front of our bodies, which gives us less of a stretch at the bottom of the biceps curl. However, the preacher curl does do a good job of making the bottom portion of the curl harder.
So that gives us the incline dumbbell curl, which is done by sitting on an incline bench and letting our upper arms hang down behind our torsos. By bringing our arms behind our bodies, we succeed at stretching our biceps, which is perfect. However, there are two slight issues: 1) the short heads aren’t stimulated very well, and 2) you need an incline bench and dumbbells.
That gives us a fourth variation of biceps curl that we can use: the sissy curl. The sissy curl is a strange barbell curl variation that I’ve invented. It works like this: when we lean back, we increase the moment arm on our biceps at the beginning of the lift, making the barbell curl more challenging at the beginning of the range of motion. Since our arms are still in line with our torsos, both our short and long heads are at a relatively long length. Furthermore, because the long head attaches at the shoulder joint, the long head needs to work extra hard to keep our upper arms from falling backwards.
So to summarize, if you have an incline bench and dumbbells, you could combine the chin-up and incline curl to get fairly balanced overall biceps growth. Or, if you have just a barbell, combining the chin-up with the sissy curl should help you accomplish more or less the same thing.
The Overhead Press
The overhead press is a great lift in the sense that we need to transfer strength from our toes all the way to our finger tips. Like the deadlift, it’s a true compound lift, building strength all through our bodies. However, it’s a shoulder lift, and our shoulders are notoriously hard to stimulate in a stretched position.
One trick to getting more muscle growth out of the overhead press is to explode out of the bottom. That way we’re working our shoulders as hard as possible right from the get-go. But it’s not a perfect solution. We still aren’t training our shoulders in a stretched position.
As I’ve tried to mention at every opportunity, that’s not the end of the world. It’s a big heavy compound lift that will stimulate a ton of overall muscle growth. Plus, we’re also doing the bench press as one of our main lifts. If we bench with a moderate or close grip, we’ll be working the fronts of our shoulders hard in a stretched position. And for the backs of our shoulders, we’re saved by the chin-up. The chin-up workouts our rear delts in a stretched position quite well.
But that doesn’t help our side delts, and it’s our side delts that give us broader shoulders. For our side delts, we turn to the lateral raise.
The Lateral Raise
So we’re trying to challenge our side delts in a stretched position, and neither the bench press nor the overhead press is very good for that. But we have lateral raises for that, right?
Not quite. The lateral raise starts at resting length and only gets challenging in a fully contracted position. That may explain why your side delts never get sore and grow rather slowly.
I need to do more testing on this, but one solution I’ve found is to do lateral shoulder raises while lying on a bench. That way I can bring my arms across my body at the bottom of the lift, putting them into a stretched position. Perhaps more importantly, the sticking point of the lift is when the upper arms are horizontal, which is right at their resting length. If we lift explosively out of the bottom of the lift, that gives us a near-perfect strength curve for building muscle.
I didn’t expect these to work very well, but no other lift has worked my side delts as hard or made them as sore afterwards. Those aren’t perfect proxies of muscle growth, but they’re good signs.
The Triceps Extension
The bench press is an amazing lift for stimulating growth in our chests and shoulders. It loads them extremely heavy in a stretched position where they also have great leverage to press from. No wonder it’s such a popular lift.
However, the bench press is also notoriously poor for bulking up our triceps. That’s not necessarily a stretch issue. Our triceps are somewhat stretched during the bench press. Rather, it’s because the long heads of our triceps connect at our shoulder joints, so as we press upwards, the shoulder joint lengthens the triceps. This gives them poor leverage for pressing.
Fortunately, that’s where the triceps extension comes in. When we move our arms in front of our bodies, we place our triceps in an even greater position of stretch. This means that skull crushers challenge our triceps in a greater position of stretch than the bench press. And because there’s no movement in the shoulder joint, our triceps grow just fine.
We can exaggerate the stretch even more with overhead triceps extensions. Not everyone can do these comfortably. But if you can, they’re a great way to build bigger triceps in a hurry.
The Deficit Push-Up
Even regular push-ups are great for stimulating chest and shoulder growth, stimulating about the same amount of muscle growth as the bench press. But we can make them even better.
If we raise our hands up on handles, weight plates, or speculative fiction novels, we can increase the depth by a few inches, giving our chests and shoulders a maximal stretch at the bottom of the range of motion.
The Dumbbell Fly
The dumbbell fly is another great lift for challenging our chests while maximally stretched. It often gets criticized for not being challenging enough at the top of the range of motion, but that’s not much of a criticism.
The dumbbell fly is hard at the part that stimulates the most growth (the stretch), easy at the part that stimulates the least growth (the contraction). That’s the same “problem” that the squat, bench press, and deadlift have. It’s not much of a problem.
With that said, although the dumbbell fly is a great chest builder, it’s also kind of redundant. If you’re already doing the bench press, and especially if you’re also doing deficit push-ups (or dips), then your chest is already being challenged in a stretched position by several different lifts (study).
If we look at muscle growth from doing just the bench press, we see that it’s the triceps that lag behind, not the chest. Unless your chest is stubborn or lagging behind, it’s probably better to choose triceps isolation exercises over chest isolation exercises.
The Problem With Partials
As you might be able to guess, if we don’t sink deep into our lifts, we won’t stimulate as much muscle growth. If we don’t squat deep, our quads won’t be as stretched. If we don’t bring the barbell down to our chests when bench pressing, or if we use too big of an arch, then we won’t get a good stretch on our chests and shoulders. If we do above-the-knee rack pulls instead of deadlifts, we won’t stretch our hamstrings or glutes.
If we cut the top part of the range of motion off, though, there’s no problem. In fact, if we don’t fully lock out our squats or bench presses, we can keep constant tension on our muscles throughout the entire range of motion, which may even increase muscle growth. The same is true with biceps curls, triceps extensions, and dumbbell flyes.
So the trick with using partials is to emphasize the deep part of the range of motion, not the lockout:
- Wide-grip deadlifts instead of rack pulls
- Front squats instead of half squats
- Deficit push-ups instead of diamond push-ups
- Incline curls instead of spider curls
When we challenge our muscles under stretch, there’s a combination of both passive and active tension, raising overall mechanical tension. Since mechanical tension is the main driver of muscle growth, challenging our muscles in a stretched position stimulates quite a bit more muscle growth—up to three times as much. As a result, when possible, we should choose lifts that allow us to challenge our muscles in a deep stretch.
Fortunately, many of the most popular lifts are already fairly good at working our muscles hard under stretch, including deep squats, the bench press, the deadlift, the chin-up, the pullover, the skull crusher, and the overhead triceps extension.
Other lifts emphasize the contracted part of the lift and thus tend to be less good for building muscle. Examples include spider curls, hip thrusts, glute bridges, half squats, rack pulls, and resistance-band exercises.
Finally, we should be able to improve the growth stimulus of some lifts by making them more challenging at the bottom of the range of motion, such as doing deficit push-ups instead of regular push-ups.
If you want a customizable workout program (and full guide) that builds these principles in, check out our Outlift Intermediate Bulking Program. Or, if you’re still skinny, try our Bony to Beastly (men’s) program or Bony to Bombshell (women’s) program. If you liked this article, I think you’d love our full programs.