Does Stretching in Between Sets Help Us Grow More Muscle?

Inter-set stretching for more muscle gains?

Inter-set stretching in the context of quadricep training would look like this:

So is it beneficial for our muscle gains?

Well, this study examined static stretching and found that by reducing muscle and tendon stiffness, the static stretching actually reduces muscle power output, force production, and activation. It also affected strength and complete work output during the workout.

And this study found something similar; reduced muscle power output may occur courtesy of stretching. 

Now this is obviously not ideal if maximum muscle growth is the goal: maximum power output is critical for long term muscle growth!

Does inter-set stretching negatively affect muscle power output?

Moreover, in this research, 2 bouts of a 25 second quadriceps stretch as part of a warm-up, significantly cut down the levels of muscle growth during a leg extension program.

Another study examined 12 resistance-trained men who performed leg extensions under three different conditions:

So what did they find?

The inter-set stretching group (group 1) were found to have less quadricep engagement during the leg extensions, which led the authors to report: 

"...inter-set stretching negatively impacts neuromuscular performance and does not increase the metabolic stress compared to passive rest intervals."

So again, inter-set stretching didn't come up favourably. In fact, it was quite the opposite: it allowed for an "increase (in) muscle fatigue, reduced muscle activation, and (muscle) force generation."

Does stretching for long periods work a muscle effectively?

If you've ever really pushed yourself during a stretch, you'll know just how hard it is. It can get very uncomfortable very quickly and we think: "this has to be growing the muscle somehow!"

And some people still claim that stretching can actively "work" the muscle in a way that it might grow.

But this just isn't supported by science. In this study, subjects stretched for as long as 27 minutes, and it didn't result in more muscle growth.

The other theory is that inter-set stretching can affect our hormone levels. Really?

In this study, sixteen males were split into two groups; an inter-set stretching group and a group that just rested in between sets. The men did three training sessions every week for eight weeks in total.

So what did they find?

Both groups improved their strength, but neither saw any changes in their resting growth hormone or cortisol. But the stretching group did see a little improvement in their flexibility.

Scientists are very clear with what causes muscle growth: it's the "recruitment of a higher number of motor units and an increase in firing frequency."

In other words, lifting heavy weight multiple times -- not simply stretching a muscle.

But then came a recent study that turned many heads in the strength training research world: a study that found in untrained subjects, inter-set stretching induced more muscle growth!

But before we get too carried away, the researchers themselves admitted the shortcomings of their findings. They highlighted that although the subjects doing inter-set stretching grew more muscle, "our data are not sufficient enough to conclude that inter-set stretching is superior to traditional strength training for inducing muscle hypertrophic adaptations."

In other words, don't be stretching in between sets just yet, because our data isn't deep enough for a reliable conclusion.

But they can say with confidence that for untrained subjects in the early phase of training (less than eight weeks) this inter-set stretching will be better for muscle growth than ordinary rest in between sets.

But those of you who read this blog enough know that anyone new to resistance training grows muscle quite easily. It stands to reason that NOT stretching is better in the long-term, because of the aforementioned issues with muscle power output. Muscle growth is a long game!

The bottom line is that inter-set stretching does not appear, at this point, to be better for muscle growth.

Scientists confess more research is needed, but no studies suggest a clear benefit. It's recommended that we rest normally between sets and do not perform any form of stretching, to ensure muscle power is not compromised, and we don't negatively affect muscle growth.

This is recommended until further scientific research points to the contrary.