Do lengthened partials build more muscle than full ROM?

Two recent studies found that training with a partial range of motion is better for muscle hypertrophy than training with a full range of motion. Is training with a full range of motion still the way to go? I recently recorded a lecture for my PT course and I would like to give you a free excerpt of that where I explain exactly what the current deal is with the full range of motion training, stretch-mediated hypertrophy, and lengthened partials.

Transcript

Two recent studies found that training with a partial range of motion is better for muscle hypertrophy than training with a full range of motion. Is training with a full range of motion still the way to go? I recently recorded a lecture for my PT course and I would like to give you a free excerpt of that where I explain exactly what the current deal is with full range of motion training, stretch mediated hypertrophy and lengthened partials. I hope you enjoy it. Principle number three is that you generally want to train with full range of motion, and that’s because of stretch mediated hypertrophy. You specifically want to train with full range of motion when it increases the lengthening of the muscles. Now let’s first get some, some terms straight range of motion is measured in degrees of joint angle. It is not measured in distance. So for example, when you’re doing a Romanian deadlifts, you’re lowering the bar.

Many people think of the ROM as the distance the bar travels. That is not true. The range of motion is measured in the degrees of hip flexion for the hip, you can measure the ROM for other joints as well. So it’s joint specific how much the joint flexes or changes in angle that is the degree of ROM. So for biceps curl here it’s not about how high up the weight goes it’s about the degree of elbow flexion so here you can see in the image exactly what is ROM, you can also see a study where they did partial ROM and they compare that to full ROM. And then they found strong trends for greater muscle growth and strength development with full ROM training. to understand why this is and why there is such a thing as stretch mediated hypertrophy, you need to understand a few concepts of how muscles work, namely the length-tension relation, passive tension and stretch mediated hypertrophy. So the length-tension relationship of muscle is that muscles can generate a different amount of tension at different lengths. There’s a relationship between the muscle’s length and how much tension it can produce. Usually the muscles are strongest in anatomical position, which means when you’re standing upright, just straight up like this, in that position, most muscles are strongest when you shorten them or length of them from that position, they become weaker. You can see that in the left image here. It’s because of the sliding filaments actin-myosin filaments, they basically slide into each other, sliding filament theory, as you learned of how muscles contract. When they do this, they have to be at a certain length of each other, when the muscle is super shorts the actin-myosin filaments are kind of bunched up too much and some muscles can even reach passive or active insufficiency, which means they are so bunched up, they are so short that they cannot effectively perform and form cross bridges anymore.

Similarly, you can have passive insufficiency when the muscle is so lengthened. That they can not reach each other anymore. So you can’t form cross bridges because the actin-myosin filaments. They cannot slide over each other. They can barely reach. you get this optimal overlap when the muscle is near anatomical position for most muscles. In the functional anatomy model, you can see exactly what level is optimal for every muscle and what their exact length to tension relationship is, etc.. Now that’s active mechanical tension. There’s also a thing called passive tension Passive tension is mostly like an elastic bands that are stretched out. It is the more you stretch out a muscle, the more passive tension there is. Just like an elastic band. Muscles are not elastic, they are viscoelastic. which means that if you do the stretch very slowly or you maintain a stretched position, the tension dissipates. But it’s not really relevant to the point here. The passive tension in general, which also you can feel intuitively the more stretched out body part, the tendon, the muscle, everything are, the more passive tension there is on the muscle. Which means that if you look at the image on the right here, you can see that while the active force production is in the normal operating range, which is around anatomical position or resting length, it’s optimal. if you shorten the muscle, you will get a dramatic decrease in active force production as well as in passive force production. So you become a lot weaker, and if you lengthen, you can actually get a little bit stronger. Now some people, this depends on the muscle and the exact situation, but you can become a little bit stronger with some stretching or even with a lot of stretching because you get helped by passive forces, passive tension because the muscle is like what is being stretched out is basically passively helping trying to get back to its shorter position.

So that’s passive force. Passive force is greater when you stretch the muscle more, and it’s the sum of the active and the passive force together that determine most likely how much total tension there is and how much the muscle will grow and adapt. this passive force seems to be responsible, at least in part for a phenomenon called stretch mediated hypertrophy. We see research that stretching the muscle alone not in term of yoga or anything like that, but in terms of heavy weighted, long, very arduous, hardcore, painful, static stretching. That type of stretching can actually induce a lot of muscle growth and in extremes can even induce as much muscle growth as traditional training. There have been studies, for example, that found that stretching the calf for an hour every day with an orthosis, the device that basically pulls the calves into as much stretch
as possible, which is very painful. You have to do that for an hour a day. Then the calves can actually grow as much, at least in untrained individuals. But also even in some trained individuals in research, they can grow as much as from doing 15 sets of calf raises per week. So it’s equivalent to a serious strength training program. Of course, it’s not very practical, but it illustrates that purely passive tension, no active force contribution required can already stimulate a lot of muscle hypertrophy and that’s stretch mediated hypertrophy. Similarly, we see that at longer lengths muscles grow more when they are trained at longer lengths versus shorter lengths. There are multiple studies now showing that muscles grow more, which we call stretch mediated hypertrophy, and this is likely in large part mediated by passive mechanical tension. And this passive tension can be sensed by titin.

Like I said, it’s spring loaded during eccentric contractions that lengthen it to, the muscle to a large degree. And titin is also a mechano sensor, so it also registers the amount of mechanical tension and signals to the muscle to stimulate muscle proteins to grow and to get bigger. So in the end, we don’t care about the range of motion itself, but we care about the functional excursion, which is the muscle lengthening. Functional excursion refers to the total amount of lengthening that can take place. And it’s like the percentage of functional excursion that is really relevant for muscle hypertrophy. The range of motion itself, again, it’s not distance, it’s not the degrees of joint angles, but it’s technically the amount of muscle lengthening that takes place and that governs primarily how much muscle you gain due to stretch mediated hypertrophy, this also explains why seated leg curls result is significantly more muscle growth than lying leg curls.

Even though both are a leg curl, the machine is roughly equivalent. During a seated leg curl, you are stretching the hamstrings at the hip because the hamstrings are bi-articulate. Remember, they are not just active at the knee but also at the hip. So when are stretching them at the hip, they’re at longer lengths and then when you do a leg curl they grow more because on average you are at far longer lengths. You also reach a length closer to a maximum in fact, in the seated leg curl machine. What you can do is you can kind of lean forward to really emphasize the stretch, especially if you don’t get full range of motion when you just sit in it, some machines, they don’t let your legs go all the way up. The plates will cling on to each other. Right. And cannot get your legs fully straight, what you could do then is you can lean forward to lengthen the hamstrings even further and therefore still allow you to get full range of motion, still get high tension in the fully stretched position and it will probably enhance stretch mediated hypertrophy. It’s currently not clear yet how much we really need to emphasize the stretch if it’s necessary to go like all in. It probably isn’t, as we’ll go into in in a minute, but it does seem beneficial to get high muscle lengths and especially for muscles like the hamstrings probably that can reach very long lengths compared to their resting length.

And to further illustrate how important it is to lengthen the muscles, the extra muscle growth that occurred during the seated leg curls was specifically in the heads that are bi-articulate and that stretch more at the hip so it didn’t occur in the short head of the biceps femoris because that head is not stretched at the hip and therefore it doesn’t experience the stretch mediated hypertrophy. We also have a study from the same research team which found that overhead triceps extensions stimulates significantly more growth than pushdowns They are much more effective for longer the long head. Interestingly, in this study they were also more effective for the other heads. That might be because in the case of a push down in the stretched position, there is very little tension.

So yes, you are getting full ROM, but you’re not getting all the tension in the lengthened position. For one, the long head isn’t lengthened much at all. And even the other heads that don’t have a lot of tension when they are lengthened. In the case of overhead triceps extension In this position there is very high tension because if you use a dumbbell this is basically a position of maximum tension, right? And with a cable you still get high tension throughout the entire ROM. with the pushdown fully lengthened position, which is the top here. If the cable is in line with the forearm, there’s actually no tension at all in that position. And even when you’re leaning a bit more forwards, which is generally good to do during a pushdown, you want to lean forward to get the elbows forward. It’s still not great. The sticking point is very clearly in full contraction and you want the sticking point to be more in the middle or near the stretch, which is true for most exercises because you want to stimulate the stretch mediated hypertrophy. for some exercises it actually appears that stretch mediated hypertrophy is so much more important than full ROM per se that doing short range partials is more effective than training in the full ROM. This has only been found in untrained individual so far, And that’s because some exercises are just very poor at stimulating the muscle in lengthened position. This goes for leg extensions and calf raises, for example, for those exercises, it might actually be better not to do full ROM.

What I like to do often with clients is to do the first set, or all sets except the last one with full ROM, because it allows you to track your progression. We’ll go into that all in more detail later, but you won’t progress overload, you need to be able to track your progression. If you don’t know if you’re progressing or not, you don’t know if your program is working. Therefore we don’t know if you need to adapt it and how to adapt it. Monitoring your progression Is crucial to be able to effectively update your program in response to your progression. So and that’s a big problem with training lengthened partials, like half leg extension. What is it, what is half? You know, it’s very hard to measure your performance that way, measuring until your leg is straight or horizontal. It’s a much more clear end point, much more easy benchmark to use to track your progression. So for these exercises, research found that at least in untrained individuals doing lengthened partials leg extensions and calf raises is better because you’re still not overloading the lengthened position.

Most leg extension machines at the top position, they’re by far the hardest and in the bottom position you’re just not overloading the muscle. So you can forgo the top part and you can use more weights, which is also the case which both of these studies found crucially, crucially important point. They could lift more weight with the partials for the same number of repetitions. Therefore, you get a higher overload of the stretched position where you’re only doing the bottom part. So only doing this part instead of the whole movement, you’re doing the bottom part with more weights, you’re overloading the bottom part more. So for these exercises that don’t stimulate the muscle while in the lengthened position, it might actually be better to do lengthened partials. A compromise that is often practical is to do lengthened partials for all sets other than the first set, or just do them for the last set, depending on if it’s safe. And the exercise lends itself well to lengthened partials. You also have to think of practical limitations here, of course Now, stretch mediated hypertrophy isn’t the end all be all. It’s very important, it can stimulate significantly more muscle growth and traditionally programs have very much lacked emphasis on stretch mediated hypertrophy. It is truly a revolution of the last years of exercise science.

However, we also have studies showing that active tension is probably just as important. For example, we actually did a study ourselves where hip thrusts and squats turned out to be equally effective for the glutes. Now, hip thrusts shine for active tension, but they don’t stimulate a lot of stretch mediated hypertrophy. Probably they don’t put a lot of tension at long lengths because they don’t even lengthen the glutes that much. Squats are much better at lengthening the glutes and therefore probably stimulate more stretch mediated hypertrophy. We have research showing that the glutes grow more at longer vs shorter lengths, just like most other muscles. If fact all tested muscles so why then are hip thrusts equally effective? Well, it’s likely because they generate more active tension. The glutes are strongest. Probably, actually for the glutes is not completely clear, but based on the research we have, the glutes are strongest in anatomical position, which means that they can produce the most active force there, which is the top position of a thrust. So a sticking point corresponds with the point where the muscle can produce the most force, which is great. You get a match between the resistance curve and your strength curve essentially, and therefore it seems that active mechanical tension can compensate for lack of stretch to the perch feet. We also have a study on the hamstrings, which is a kind of an artificial design.

Where they equated the total torque and they trained them at longer vs shorter lengths. And they found that the growth was the same when the total torque was equated, which meant that basically the seated leg curl were more lengthened. Seated leg curl group in this case was not producing as much active force, therefore suggesting that active and passive tension are both equally important for muscle growth. Now the exact mechanisms of stretch mediated hypertrophy have not be fully elucidated, but I think this is currently the best working theory that corresponds well with all the exercise comparisons that we have We also know that there’s probably a limit to how much stretch mediated hypertrophy really helps. Like it doesn’t help to stretch the muscle beyond a certain point. Probably. We have, for example, a study showing that the preacher girls so when you have to the elbow a little bit forward on a preacher-curl bench they do put a lot of tension when the muscle is relatively lengthened in the bottom position, but the muscle is not fully lengthened and they compare that with incline dumbbell curls, which is when you’re sitting, you’re leaning back or bench and your elbow is all the way back.

So the biceps gets a great stretch. But in the bottom position, because you’re using a dumbbell, gravity pulls straight down, there’s actually no tension on biceps. And they showed that the preacher curls seem to be slightly more effective for bicep growth, illustrating that for when the biceps gets the most active tension in the bottom position. But also there’s probably a limit to just lengthening the muscle. How much that really helps. You, for one, need tension. you don’t need to just lengthen the muscle, but you also need to lengthen it under high tension. And even then, there’s probably a limit because we have another study that compared preacher curls with the barbell, which really hammer the bottom position versus a cable whic is more of an equal resistance curve throughout the entire range of motion. They were equally effective for muscle growth.

So you don’t always have to go all in on stretch mediated hypertrophy. It’s also important to get high active tension and even if there is stretch mediated hypertrophy at play, there’s probably a limit to how much it will grow and how much further emphasizing the stretched position and resistance in long muscle lengths, how much that will further benefit muscle growth. If you appreciate this type of evidence based fitness content, I’d be honored if you like and subscribe.