How Range of Motion Impacts Muscle Growth: New Findings You Need to Know

When it comes to building muscle, the details matter—especially when it comes to how you train. 

Recent research is shedding light on the mechanics of muscle growth, particularly regarding the importance of range of motion (ROM) during exercises. For years, many bodybuilders and fitness experts, including myself, have touted the benefits of full range of motion exercises. But, as with any field in science, things are evolving. 

So, what’s the latest on how the range of motion affects hypertrophy (muscle growth)? Let’s break it down.

Why the Range of Motion Matters

Traditional wisdom has often placed the focus on the "peak contraction" of an exercise. 

This is the point at which the muscle is most shortened, like at the top of a bicep curl. Bodybuilding legend Joe Weider swore by focusing on this part of the movement for maximal muscle growth. And many bodybuilders, including myself, have built their routines around that idea. 

However, new studies are suggesting that the initial half of the range of motion could be more important for muscle growth, especially for beginners. 

In one notable study involving calf raises, researchers found that people who performed calf raises using only the initial half of the range of motion saw muscle growth up to three times greater than those who performed the full range of motion. This was true even compared to those doing only the peak contraction phase.

But that’s not all. Another study on trained individuals showed that performing just the first half of the range of motion for bicep curls worked just as well for hypertrophy as doing the full range of motion. 

This challenges the common belief that the full ROM is always superior for muscle growth. 

Stretching and Hypertrophy: A New Twist

What’s even more intriguing is the role of muscle stretch in hypertrophy. 

We’ve always known that loading a muscle while it’s stretched—such as during the bottom portion of a squat or leg press —can be a potent stimulus for growth. New findings are reinforcing that idea. A study on calf training revealed that simply holding a stretch under load, without even moving the muscle, was enough to stimulate muscle growth. Participants who held a stretch under load for 15-20 minutes saw measurable growth. 

From my personal experience and observations, I’ve also noticed the importance of stretching between sets. Back in the 80s and 90s when I was competing as a bodybuilder, we didn’t just rest between sets—we’d stretch the muscles we were training to keep them under tension and enhance recovery. 

It turns out, that approach may have been more beneficial than we realized, especially for muscles that are more responsive to stretch, like the calves.

How to Apply These Findings to Your Workouts

So, how do you apply this new research to your training? 

I recommend experimenting with partial reps, especially during your strongest phase of an exercise. For instance, when performing a bench press , I’d suggest starting with the bottom half of the movement (where the chest is doing most of the work), rather than pushing through the entire range of motion. By staying within that stretch position, you’re placing more focus on the chest and minimizing involvement from the shoulders and triceps. 

But don’t make the mistake of doing all sets this way. I’d suggest performing your first set of partial reps when you’re the strongest. Then, for the following sets, complete full range of motion reps. 

This ensures that you're not overloading your weaker points and can fully target the muscle for growth.

What About the Full Range of Motion?

Now, don’t get me wrong—full range of motion still has its place, especially when you’re working on exercises that require movement through a large muscle group, like squats and deadlifts . 

These compound movements benefit from a full range because they engage multiple muscles and require functional movement. But if you're looking to maximize muscle size in specific areas, focusing on the initial half or stretch phase can help overload the muscle and trigger new growth, especially for isolation movements.

Time Under Tension: The Missing Ingredient?

The stretch component ties into another critical concept for hypertrophy: time under tension (TUT). 

The longer your muscles are under tension, the more growth you stimulate. This is why partial reps, where you remain in the stretch position longer, can be so effective. For example, on exercises like the bicep curl , I suggest lowering the weight slowly into the stretch position and holding it there briefly before completing the movement. 

This ensures that you’re keeping your muscles under tension throughout the entire movement.

Keep Testing and Refining

While these new studies are fascinating, it’s important to remember that the science of muscle growth is still evolving. 

No single study will provide the definitive answer for every person. What works for one individual may not work for another. That’s why it’s crucial to experiment with your training and find what works best for your body.

As always, I test these techniques on myself and the people I work with—whether they’re athletes, bodybuilders, or everyday gym-goers. The key takeaway here is that muscle growth is a complex, individualized process, and you’ll need to keep adjusting and refining your approach as new research emerges.

Incorporating partial reps, emphasizing the stretch position, and manipulating range of motion are all powerful tools in the pursuit of muscle growth. But as with all aspects of fitness, there’s no one-size-fits-all solution. 

Keep experimenting, stay consistent, and adjust your training based on your results. And remember, while science can offer insights, the best way to discover what truly works is by applying these concepts to your own training.

References

Kassiano, W., et al. Greater gastrocnemius muscle hypertrophy after partial range of motion training performed at long muscle lengths. J Strength Cond Res 37(9):1746 - 1753, 2023.

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