075: Stretching Can Increase Muscle Size But It Takes Time

muscle growth strength stretching Apr 11, 2023

Several days ago, I shared a post on social media that received a near-equal measure of criticism and praise. The post - accessible to you by clicking here - appraised a recently published paper wherein the authors documented similar enhancements in muscle strength and thickness caused by stretching and hypertrophy-focused resistance training. This paper represents one example of an expanding pattern that reveals augmented muscular force and hypertrophy after static passive stretching. It is worth reiterating that for years, the consensus of the general health and fitness industry was that stretching solely modified pain sensitivity, not tissue structure.

The headline of my post, "Static stretching increases strength and muscle thickness to levels similar to resistance training," was not disingenuous. The authors did, in fact, ascertain that stretching yielded similar changes as hypertrophy-focused resistance training. Nonetheless, a few individuals commented and sent messages, suggesting that the post necessitated greater precision because the stretching and resistance training loads were not evenly matched. As an educator for more than 25 years, I am always amenable to the prospect that any misunderstanding may stem from my own communication. Consequently, I believed that this blog entry might prove useful for disambiguating the post.

The training loads between the two groups were not volume equated. Volume - the amount of work undertaken during a particular training interval, such as a week - is crucial in instigating flexibility and hypertrophic adaptations. "Volume equated" denotes that the amount of work carried out in two programmes is analogous. The training volumes in the paper that I assessed in my post were distinctly dissimilar. In the stretching group, the subjects stretched for one hour daily at an intensity of 7-8/10. The participants in the resistance training group performed 5 sets of 10-12 repetitions to failure, which they repeated thrice weekly (taking approximately 45 minutes per week). It is evident that these loads are different.

However, a salient point to consider here is that the authors did not intend to equalise the training volume between the two groups. Previous studies demonstrated that undertaking the same amount of stretching load mentioned above (7 hours per week x 6 weeks) produced muscle strength and thickness enhancements. The latest study aimed to determine how such changes brought about by stretching compared to a conventional hypertrophy-focused resistance training program. As per the authors' report, there was no difference in results between stretching and resistance training. Nevertheless, the stretching volume was substantially higher - to such an extent that the authors concluded that stretching, with the primary objective of promoting muscle growth, is not feasible.

But why did the researchers use such a high volume of 7 hours per week instead of something more manageable, like three sets of 30 seconds per day? We already know from prior research that such brief durations seldom stimulate morphological modifications in the muscle's composition. The prevailing notion was that a substantial duration and/or intensity was necessary to encourage structural adaptations, which was later substantiated in several human trials. It is also well-established that intense stretching for one hour daily is adequate for producing significant muscle strength and size changes. Nevertheless, this approach is unlikely to be optimal. The aim of research moving forward should be to work backwards, with shorter stretching durations and fewer applications per week, until we can pinpoint the minimum effective dose for eliciting similar gains.

Except in rare cases (such as during injury rehabilitation), we should not rely on stretching as the primary approach for augmenting muscle strength and size. Despite my admiration for flexibility training, I can think of numerous other activities I would prefer to engage in for 7 hours per week rather than contorting my body into a stretch. However, we must view these findings as proof that stretching adaptations surpass mere sensory modifications. This is particularly noteworthy since the sensory hypothesis is frequently touted as a rationale for why stretching is "worthless," which is a preposterous claim.