19/09/2026
Lots to take in here-I need to properly understand exactly what tolerance means in this context-in my Awareness Through Movement classes it is usually the long-term stretching-folk who take longest to get the idea of staying within their easy range. Regarding my own hypermobility, when I was stretching in dance classes it was my already loose joints that got looser and the areas/directions that are more problematic were very easy to injure.
Part of the challenge I see here is the implied division between the neurological and the structural-we still have a mind-body separation issue, and replacing mind with brain/nervous system is only deferring the need for an updated paradigm.
How does actually make you more flexible? 🤔 I posted about a classic study last week — this is about a new one.
Most people DO get more flexible when they stretch … but how? What specifically changes in the body?
It still surprises many people to learn it’s probably NOT a physical change: you’re not making soft tissue any SOFTER.
It’s also surprising that we still don’t know for sure. New evidence has gotten us closer to a likelier explanation, but it still hasn’t delivered a verdict…
[There are lots of citations and other links in the web version of this post, plus an audio version, a member perk. Links in the comments.]
HOW HAS THE DEBATE EVOLVED SINCE 2010?
Not much! It continues. A big new meta-analysis (Ingram et al. 2025) is a drop-in replacement for Weppler and Magnusson’s 2010 paper, with the benefit of another fourteen years of research: 65 studies now, covering more than 1500 people. They reviewed the evidence for three mechanisms of flexibility:
👉🏻 Stretch tolerance — how much pull you’ll put up with at end range. It rose moderately with weeks of routine stretching.
👉🏻 Fascicle length — whether muscle fibres physically lengthen. The biggest loser: no evidence of change from any kind of stretch.
👉🏻 Stiffness of the muscle-tendon unit — “a small decrease,” and probably not a physical change even then (a 2021 trial found the same easing in the UNSTRETCHED leg too).
Moltubakk et al. did look for the role of texture versus tension more directly in 2021: after six months of daily calf stretching, tendon stiffness and tendon length were unchanged, but subjects could handle more torque at the end of range (tolerance). Curiously, the overall resistance to movement throughout the range eased in BOTH LEGS — the unstretched one too, in sync with reduced muscle activation. That is probably “cross-education,” one leg learning from the other’s training, not a tissue texture thing. So although “stiffness of the muscle-tendon unit” COULD be multiple mechanisms, it probably isn’t a physical change, and this is one of the major sources reporting a clear tolerance signal.
Range-of-motion gains correlated with both increased tolerance and decreased stiffness, so both probably contribute — but tolerance dominates over the long run.
“IT’S MOSTLY ABOUT TOLERANCE” IS THE MAIN FINDING
And yet, many years after Weppler and Magnusson, that finding is still very much UNPROVED. Not only is the evidence still incomplete and of “low or very low” certainty across the board, but the strongest tolerance signals were produced by the weakest trials — exactly the pattern we expect from researchers finding what they want to find.
Tolerance remains a reasonably good bet, but it’s still just a bet, and not even a particularly safe one. We still don’t actually KNOW, which is amazing and disappointing at this point in history. “We can put a man on the moon…” But we can’t figure out exactly how flexibility works? Odd.
The one thing we can safely bet on is that it’s NOT an increase in muscle length. That has been believably ruled out now. So at least we have that.
WE DON’T KNOW HOW STRETCHING INCREASES FLEXIBILITY (OR IF IT EVEN MATTERS)
We’re still scientifically primitive on this topic. Even if we knew that it really is all about tolerance, we’d still need to know how THAT works. Is it a brain thing? A peripheral nerve thing?
Mysteries everywhere!
And always, lurking in the background, is the deeply unpopular idea that flexibility itself is a largely pointless fitness goal, especially without strength to back it up — and building that strength would produce as much flexibility as stretching alone. My huge guide to stretching explores that in detail, and has also been updated with the results of Ingram and Moltubakk (again, links in the comments).
~ Paul Ingraham, PainScience.com publisher
