Hypertrophy: Gaming the System

You stretch after your workout in order to improve your recovery. You may even have dedicated stretching sessions throughout the day to improve range of motion and mobility. But did you know that stretching in between sets could be beneficial for your hypertrophy (muscle growth) as well?!

Wait a second. Why would you stretch in between your sets? What’s the purpose of doing that anyway? Well, in this article, I’ll tell you all about how recent scientific literature has examined this phenomenon and how you could possibly implement this strange but potentially effective method into your training routine.


What Exactly is Inter-Set Stretching?

This type of stretching refers to the utilization of various stretching methods (static, ballistic, dynamic, etc.) between sets of resistance training exercises, which would traditionally be used as a rest period. This is supposedly able to increase and optimize neuromuscular, metabolic, and hypertrophic adaptations [1].

Another added benefit of training with this technique is its efficiency. The time saved by omitting separate stretching routines may help increase adherence to training by limiting exercise time while enhancing both strength and flexibility adaptations, thereby, increasing efficiency [2]. Time-crunched athlete anyone?

Physiological Mechanisms

But HOW exactly does this work in terms of hypertrophy? Well, there are a few mechanisms that researchers believe are responsible for this.

Blood Flow Restriction

According to a study by Kirkebe and colleagues, changes in muscle length decrease both blood and oxygen supply to a stretched muscle [3]. Because of this, it utilizes the same mechanisms that cause growth in a well-known strength training regime known as BFR or Blood Flow Restriction training. This type of training has shown great promise in the scientific literature for increases in muscle strength and hypertrophy.

Although these mechanisms aren’t exactly clear, researchers hypothesize that it has mostly to do with the increase in what’s called metabolic stress. This is what happens when your body runs low on fuel stores during training and accumulates metabolites and waste products, usually during a given set. This often happens during high-repetition sets. The easiest way to practically think about this is the famous “pump.” This is a perfect example of this mechanism in action.

Signaling Pathways

Without getting too complicated into the physiological jargon, there are particular metabolic signaling pathways that tell the body to do certain things. One of these things is to control protein metabolism (protein synthesis and breakdown). One of the most well-known signaling pathways for protein synthesis (favors hypertrophy and tissue regeneration) is called mTOR. Some of the literature has shown that passively stretching the muscle (stretching with assistance, such as having a partner or using the wall to push you into a deeper stretch) leads to increased activation of the mTOR pathway [4].

Time Under Tension (TUT)

An often overlooked part of the equation to hypertrophy is the concept of time under tension. It’s exactly what it sounds like too. It’s simply how much time the target muscle spends under the load you’re putting against it. For example, when you’re performing a barbell bicep curl, there is a certain amount of time you’re performing the actual movement compared to the total duration of the movement. The time you spend bringing the bar up and bringing it back down count towards TUT, but the pause at the top and the time in between reps don’t.

A few studies have actually shown us that since static stretching increases time under tension, it plays a significant role for several muscular adaptations; primarily strength and hypertrophy. [5]. Static stretching is often the most well-known type of stretching. These include stretches such as the standing quad stretch and the cross-body shoulder stretch. These are performed using our own body, without assistance, and in a stationary position… Akin to our favorite ‘Nacho Libre’ stretch.

Decreases Acute Performance

Hold on. Didn’t you just say how it’s supposed to increase the level of my performance? Well, yes AND no. It most certainly isn’t a one-size-fits-all training regime. When we look in the short-term, it has been shown to decrease our performance in terms of how many total repetitions we are able to perform.

In one study, they focused primarily on how stretching between sets affected the number of repetitions the subjects could perform during high-rep exercise [6]. Subjects performed 3 sets of both triceps pushdowns and leg extensions at both 60% and 85% of their 1 rep max (1RM) across 3 different sessions. They also passively stretched the muscle for 30 seconds in between each set.

Unfortunately, they saw that the stretching group performed significantly fewer reps than the group who did not stretch at all. The researchers were not sure of the reasoning behind this, given the preceding success that was already current in the research. This could have to do with the particular sample that they chose and that some individuals respond to training much differently than others do. This could potentially be a positive for the time-crunched athlete however, especially considering you can achieve greater hypertrophy with less time.

Chronic Effects of Inter-Set Stretching

However, we see a completely different side of the spectrum here when we look at stretching and its effects on muscle over a longer period of time.

One study looked at the effects of inter-set stretching on flexibility, strength, and hormonal adaptations over a period of 8 weeks [1]. There was a control group (no stretching), static, and passive stretching group. Each group had a rest interval of 2 minutes between sets, with 30 seconds of it consisting of stretching.

What the researchers found out was that after 8 weeks of strength training, although there was no difference in hormonal adaptations, there were significantly greater gains in both strength and flexibility in both of the stretching groups, but not in the control group.

Practical Application

So, although this type of training is still relatively new in the world of strength training, I still would suggest implementing into your routine. It has its limitations but shows great promise in particular areas as well.

So what we discovered today was that inter-set stretching:

  • Acutely decreases high-repetition performance.
  • Increases flexibility over the long term.
  • Great potential for an increase in hypertrophy, but more research is needed.
  • Saves people a lot of time as it creates greater exercise efficiency.

So try throwing in 30 seconds of static or passive stretching in between your sets of strength training. It may or may not work for you. However, the only way to find out is for you to TRY IT. Until further research is released, trial-and-error is the only way to be sure if this type of training works for you or not. Let us know how it works out for you!

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References

  1. Souza, A. C., Bentes, C. M., Salles, B. F., Reis, V. M., Alves, J. V., Miranda, H., & Novaes, J. D. (2013). Influence of Inter-Set Stretching on Strength, Flexibility and Hormonal Adaptations. Journal of Human Kinetics, 36(1). doi:10.2478/hukin-2013-0013

  2. Simão, R., Lemos, A., Salles, B., Leite, T., Oliveira, É, Rhea, M., & Reis, V. M. (2011). The Influence of Strength, Flexibility, and Simultaneous Training on Flexibility and Strength Gains. Journal of Strength and Conditioning Research, 25(5), 1333-1338. doi:10.1519/jsc.0b013e3181da85bf

  3. Kirkebø, A., & Wisnes, A. (1982). Regional tissue fluid pressure in rat calf muscle during sustained contraction or stretch. Acta Physiologica Scandinavica, 114,(4), 551-556.

  4. Sakamoto, K., Aschenbach, W. G., Hirshman, M. F., & Goodyear, L. J. (2003). Akt signaling in skeletal muscle: regulation by exercise and passive stretch. American Journal of Physiology-Endocrinology and Metabolism, 285(5), E1081-E1088
  1. Mohamad, N. I., Nosaka, K., & Cronin, J. (2011). Maximizing Hypertrophy: Possible Contribution of Stretching in the Interset Rest Period. Strength and Conditioning Journal, 33(1), 81-87. doi:10.1519/ssc.0b013e3181fe7164

  2. Aydin, E. M., Ucan, Y., Yarar, H. (2017). The acute effect of static stretching between sets on the number of repetitions performance in resistance training. International Journal of Human Sciences, 14(4), 3913-3922.

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Shayne Gaffney

About the Author Shayne Gaffney

Shayne holds a bachelors degree in Health Science in Professional Development and Advanced Patient Care, is a licensed physical therapy assistant in Massachusetts, a USA Cycling Level 1 (expert level) certified Coach, a USA Cycling Power Based Training certified Coach, Precision Nutrition Level 1 certified Coach, a US Military Endurance Sports (USMES) affiliated Coach, and USA Olympic Committee Safe Sport certified. He is the owner and head Coach of GC Coaching, Workout Content Editor at Zwift, the creator of P2 Coached Computraining, and the creator of Zwift’s “Build Me Up” Flexible Training Plan. He has been published in Bicycling Magazine, the TrainingPeaks blog, and Zwift Insider. He can be contacted directly via info@gaffneycyclingcoaching.com

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