Boosting Hypertrophy By Simply STRETCHING??

For this week’s tip, I’d like to introduce you to a recent discovery in the exercise science world. It appears that simply passively stretching a muscle (i.e. without any contractive force generated by that muscle) may be able to induce muscular hypertrophy / growth all by itself!! This is a complex topic with many important implications, so I’ll be doing a comprehensive YouTube video on it in the future with more details… but for now, here’s a brief overview for you:

There are two general use-cases for stretch-induced hypertrophy that are being studied:

1) Stretching without any resistance training involved

2) Inter-set (aka between-set) stretching during a resistance training workout.

This is the most compelling study I’ve come across for the first use-case. In it, researchers discovered that stretching the gastrocnemius (the largest calf muscle) for just 15 minutes, 5 days a week significantly increased muscle fiber size after just 2 weeks!! However, the big caveat is that the study was done on mice. It appears harder to achieve the same results with humans… however, these researchers found that stretching the calves for an hour each day for 6 weeks resulted in an average of 15% growth (interestingly more in the lateral gastroc head than in the medial head) in humans.

Despite that, the more promising use-case so far has been inter-set stretching. For example, in this study, researchers set up an upper & lower-body training regimen that had half of the participants include a 30 second stretch within the standard 90 second rest time between sets. After 8 weeks, the stretch group had achieved significantly more hypertrophy in both the upper and lower limbs compared to the non-stretch group! And this effect has been replicated in other studies.

However, the results are far from conclusive at this point, since other studies have failed to show any hypertrophic or strength advantage to inter-set stretching. More research is necessary. But with that said, there does appear to be valid physiological basis behind why stretching could induce muscular hypertrophy. One example is that stretching has been shown to activate mTOR-related signaling receptors involved in the hypertrophy pathway (see diagram below), which are not activated by loaded contractions of any type (concentric, eccentric, etc.). 

Finally, I have to advise you to be extremely careful if you want to try implementing inter-set stretching, because numerous studies have shown that static stretching BEFORE weight lifting significantly increases the risk of injury. So you must be fully warmed up and into your actual workout before starting to add in any between-set stretching!!

APPLICATION: Be sure to consistently stretch! On top of all the well-known benefits of flexibility, it will likely boost your gains as well!

Relevant Research Article(s):
  1) Influence of Long-Lasting Static Stretching on Maximal Strength, Muscle Thickness and Flexibility
  2) Inter-set Stretching vs. Traditional Strength Training: Effects on Muscle Strength and Size in Untrained Individuals

Related Dr. Gains YouTube Video(s):   
      1) The Soleus Secret (The Anatomy behind Calf Definition and Volume)