What's stretch-mediated hypertrophy and how's it help grow muscle?

Stretch-mediated hypertrophy for muscle growth

Stretch-mediated hypertrophy is triggered when sarcomeres are stretched beyond a certain point.

A sarcomere is the basic contractile unit of muscle fiber.

And stretch-mediated hypertrophy is achieved basically when muscles are trained at a longer length.

For example, holding the stretch at the bottom of a dumbbell fly as opposed to holding the contraction at the top of the fly movement with our chests contracted.

Recent research found isometric exercises (static contraction) that force our muscles to work at longer muscle lengths translate to nearly three times as much muscle growth.

Put simply, a muscle worked at a deep stretch allows for better muscle growth results.

However, before you go out and try any exercise that gives you a muscle stretch, keep in mind that just because your muscles are stretched, it doesn't always mean your sarcomeres are.

I'll provide some exercise examples of what we're looking for later in this article, so you can take advantage of stretch-mediated hypertrophy!

What exercises for stretch-mediated hypertrophy?

Isometric studies aside, this study in 2021 discovered when subjects did just the bottom half of a preacher curl, it elicited about three times as much muscle growth as just the top half movement.

It's all about that stretch!

Another study into hamstring training found that the more the hamstrings were stretched, the more they were activated, and the more strength is gained.

Another piece of research into hamstring training confirmed the same thing; more of a stretch meant more muscle gains.

The study compared lying hamstring curls versus seated hamstring curls, and found seated hamstring curls were better due to a deeper stretch when we bend at the hips (ie, when we are seated).

And here's a common problem in the fitness game: the average gym-goer confuses range of motion (ROM) for thinking it's, for example, bench pressing with the bar down to your chest and back up.

But that doesn't work your chest completely at all. 

Range of motion isn't defined by exercise, but rather by joint.

Back to our aforementioned hamstring study; you can perform what you think to be a "full range of motion" by doing a lying hamstring curl. 

But really, a "full range of motion" lift with your hamstrings would be on the seated hamstring curl, whereby your hamstrings are actually activated in a full range of motion; defined by joint and not exercise. 

So, when you hear people talking about range of motion, what they're really getting at (whether they know it or not) is muscle length.

We've spoken about the three principles of muscle growth here frequently:

1. Mechanical Tension

2. Metabolic Stress

3. Muscle Damage

The first one here, mechanical tension, is the amount of weight a muscle is lifting and thus the force it is generating. And the amount of tension a muscle can produce is variable across its length.

Scientists call this the length-tension relationship.

And the reason we favor exercises (like the seated hamstring curl) is that the length you can train a muscle determines how much tension you can put it under.

You simply put your hamstrings under more tension during a seated hamstring curl because it works at a greater length.

When you perform a bench press movement, your pecs shorten during the contraction. This is what scientists call excursion; the distance a muscle can shorten.

So "range of motion" as it's generally defined isn't what's going to help your muscle growth; it's actually muscle excursion that will deliver the gains you want!

Best muscle excursion and stretch-mediated hypertrophy exercises for growth

So, now we have some context around what we should be aiming for, here are some exercises that will allow for better muscle growth under the principles we've just outlined:

Chest: Push-ups with your hands elevated (on handles or weight plates), dumbbell or cable flyes, holding the stretch at the bottom of the movement.

Hamstrings: Seated leg curls.

Biceps: Curls or preacher curls (with a real focus on the bottom part of the movement)

Triceps: Skull-overs (the normal skull crushers just don't cut the mustard!)

Back: Chin-ups, allowing for a stretched position at the bottom of the movement. Lat prayers as detailed in this Bulk Nutrients blog: The best exercises for lats and muscle growth.

Quads: Leg extensions (Focusing on the bottom of the movement, aka the initial movement)

Glutes: Squats or hip extension exercises (hip thrusts don't allow for a great level of stretch-mediated hypertrophy!). 

Shoulders: Try working your side deltoids by performing your lateral raises on a bench, leaning on the side, for a bigger stretch.

The bottom line is that range of motion is misunderstood in the general fitness community. Stretch-mediated hypertrophy is what most people are getting at when discussing muscle growth from a full range of motion. Optimal mechanical tension, one of the three principles of muscle growth, is achieved best when muscles are trained at a longer length. The distance a muscle can shorten during a movement is called its excursion; the bigger the better! 

A great example of a good muscle excursion is seated hamstring curls or cable flys with a solid stretch at the bottom of the movement. We should prioritise high excursion exercises for stretch-mediated hypertrophy for maximal muscle growth.