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.

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.