How far can you stretch? The limit isn’t just in your muscles

Two people do the same stretch. One moves into it with relative ease. The other stops well short. The explanation seems obvious: whoever goes farther must have longer muscles, “looser” tendons or tissues that are naturally less stiff.

But flexibility doesn’t work quite that way.

A review published in 2026 in the journal Sports Medicine, written by Dr. Camila D. Lima, a researcher at the Gleb Wataghin Institute of Physics at the Universidade Estadual de Campinas (Unicamp) and a visiting researcher at The University of Queensland, and by Anthony J. Blazevich, brought together evidence on the mechanisms that determine how far we can move a joint and how much the tissues resist during that movement.

The first important conclusion is that these two things are not the same.

In science, one is called maximum range of motion (ROMmax). The other is called stiffness. Understanding the difference helps explain why someone can become more flexible without their muscles and tendons simply becoming less stiff.

So the question changes: when we’re able to go farther in a stretch, what has actually changed?

Flexibility isn’t just one thing

Imagine you try to touch your toes. There’s the farthest point you can reach. But there’s also the resistance that muscles and other structures put up as you move toward it.

These are related but different phenomena.

ROMmax is the maximum range reached by a joint. Stiffness describes the resistance encountered during the movement, which results from the passive properties of the tissues and, depending on the conditions under which it’s measured, from muscle activity as well.

This difference matters because the two variables don’t always change together. It’s possible to increase ROMmax without seeing an equivalent reduction in stiffness.

Put simply: reaching farther does not, on its own, prove that the tissues have become less stiff.

Lima, coauthor of the review, says: “It’s important to point out that a person can become more flexible without this necessarily meaning that their muscle fibers have become permanently longer.”

According to her, the increase in range after a period of training may result from different mechanisms, including peripheral adaptations and changes in stretch tolerance.

Muscle is not a rubber band

When we think about stretching, it’s tempting to picture a muscle as a rubber band: we pull on it repeatedly and, over time, it gets longer.

Muscle is far more complex.

Muscle fibers are organized into bundles called fascicles and wrapped in a network of collagen and other components known as the extracellular matrix. This structure helps transmit forces and contributes to the resistance a muscle offers when it’s stretched.

The review identifies the extracellular matrix as an important source of this passive resistance. Some of the experiments used to understand this mechanism, however, were carried out in animals or in laboratory preparations. That means not every result can be carried over directly to humans.

Lima explains that muscle fascia is part of this matrix and surrounds different levels of the muscle’s organization. With training, changes in the organization and mechanical properties of the extracellular matrix may be one of the peripheral mechanisms involved in increased range of motion. The literature itself, however, still needs to better define how much these adaptations contribute in humans.

Even the arrangement of the fibers can make a difference. During a stretch, fascicles can change orientation, not just length.

What happens inside a muscle, then, is far from a simple process of “stretching out” a tissue.

What tendons reveal

Tendons make this story even more interesting.

Intuitive logic would say that if a person can reach farther, their tendons must have become less stiff.

Not necessarily.

The review brings together studies in which maximum range of motion increased without a corresponding reduction in tendon stiffness. In other words, gains in ROMmax can happen even without the change we would expect to find in the tendon.

That doesn’t mean tendons are irrelevant. It means something more specific: a less stiff tendon doesn’t appear to be a prerequisite for achieving greater range.

And that’s exactly where another part of the story begins.

The body senses the stretch

As we move further into a position, it isn’t only the tissues that are being deformed. The body is also receiving information about what’s happening.

Some receptors detect aspects related to muscle length and changes in that length. Others provide information about position, movement and pressure. There are also nociceptors, which are involved in signaling potentially harmful stimuli.

These signals travel to the nervous system.

The review brings together experiments involving reflexes, vibration and other ways of manipulating this sensory information. The result is a system more complex than the idea of a single mechanism capable of setting the limit of movement: some neural adaptations appear after stretching, but increases in ROMmax have also been found without corresponding changes in certain reflex responses.

Lima notes that adaptations related to the nervous system, including at the spinal cord level, are being investigated, but the literature is still more extensive for muscular and peripheral mechanisms. She considers it possible that training changes the way sensory signals are processed, influencing the response to stretching and tolerance of greater ranges, but stresses that the evidence at the brain level is still more preliminary.

There is therefore no evidence of a single “flexibility sensor” or a physiological switch that, on its own, determines how far we can go.

Why do we stop?

Think again about that reach toward your toes.

At some point, you stop.

But why?

Has the muscle reached its physical limit? Did tension appear? Pressure? Discomfort? Pain?

This is where one of the review’s central concepts comes in: stretch tolerance.

The point at which a person voluntarily stops a stretch doesn’t have to represent an absolute mechanical barrier. The sensations that appear as the movement progresses can also help define that limit.

Dr. Lewis Ingram, a researcher at Adelaide University and lead author of a systematic review and meta-analysis on the mechanisms behind range-of-motion gains after static stretching, was interviewed as an independent expert. He adds a distinction based on time:

“In short, the immediate (i.e., acute) improvements in range of motion we see after stretching are largely due to decreased stiffness, whereas the long-term (i.e., chronic) improvements are mainly due to a greater tolerance of the discomfort we perceive when stretching a muscle to longer lengths.”

This distinction doesn’t mean there is a single mechanism for all types of training, joints or individuals. Prof. Dr. Christian Emmanuel Torres Cabido, a professor at the Universidade Federal do Maranhão (UFMA), interviewed as an independent expert on the mechanical, sensory and neural mechanisms related to flexibility, reinforces this caution:

“Sensory and mechanical mechanisms can act together, with different weights depending on the dose and the method.” The same observable result — reaching a greater range — can therefore have different explanations depending on the time frame and the context.

But there’s another important distinction: stretch tolerance doesn’t simply mean pain tolerance.

The review discusses studies linking pain tolerance and ROMmax, but it also shows that there are still open questions about the interaction among pain, muscle activity and resistance to movement.

So understanding that perception plays a role in movement doesn’t mean concluding that someone should learn to endure more pain to become more flexible. Pain should not be deliberately ignored or pushed through during exercise on the basis of these findings.

What about the brain?

If the information produced during stretching reaches the nervous system, a question inevitably arises: could brain processes also play a role in this limit?

The answer calls for caution.

Lima and Blazevich propose that proprioceptive, nociceptive and mechanoreceptive information is processed at higher levels of the nervous system. This processing may contribute to stretch tolerance and, potentially, influence the decision to continue or stop the movement.

That adds an interesting dimension to the problem: ROMmax may not depend solely on the physical properties of the tissues.

But there’s an important difference between a physiologically plausible explanation and a directly demonstrated mechanism.

The authors themselves acknowledge the need to directly investigate the specific influence of cortical processing, psychological state and decision-making on ROMmax. Lima reinforces this caution by saying that, at the brain level, the evidence is still more preliminary. Cabido adds that studies in humans support neural modulation during stretching, including temporary changes in spinal reflexes, but this does not show that such modulation is solely responsible for the increase in range.

The boundary becomes clearer when it comes to cognitive processes. Cabido considers the role of perception and neural modulation to be supported, but believes the specific causal influence of attention, motivation, confidence or conscious decision-making remains hypothetical. Ingram, consulted as an independent expert, also avoided extrapolating and described cortical processing and psychological state as topics outside his scope.

We know that the nervous system receives and processes information during movement. Determining how much higher cognitive processes explain the point at which a person decides to stop is a different question.

And that answer has not yet been established.

That’s why it would be wrong to conclude that “flexibility is in the brain,” that the brain directly determines the limit of flexibility or that the mind is more important than muscles, tendons and joints.

What really changes when we become more flexible?

At this point, it would be convenient to have a simple answer.

We don’t.

Depending on the type, duration, dose and method of training, there may be mechanical adaptations, changes related to the sensations experienced during stretching, or a combination of these mechanisms.

Ingram’s contribution helps make this difference concrete for static stretching: immediately after a session, reduced stiffness appears to carry more weight; after weeks of training, greater stretch tolerance becomes more important.

Some explanations that seem intuitive also still lack sufficient demonstration in humans.

The review points out, for example, that the relationship between the number of sarcomeres — the microscopic units that make up muscle fibers — and ROMmax has not yet been directly investigated in people. Components that matter at the microscopic scale also don’t necessarily, on their own, explain the behavior of the whole muscle.

Lima draws attention to another misconception: treating flexibility as a fixed trait or one determined exclusively by muscles and tendons. It can be modified by training even after maturity, and gains in range can combine peripheral and neural adaptations, along with changes in stretch tolerance.

That rules out easy answers.

There is no evidence to say that a certain percentage of flexibility lies in the tissues and another in the brain. Nor can we conclude that increasing ROMmax simply means permanently “lengthening” a muscle.

What we can say with greater confidence is more precise: the maximum range we’re able to reach doesn’t function as a direct readout of how stiff our tissues are.

Does this change how we train?

For now, less than you might think.

The review helps better explain the mechanisms involved in flexibility, but it doesn’t establish a new training strategy based on cognitive processes. Cabido also notes that measuring ROMmax alone doesn’t allow us to conclude that the tissues now offer less resistance: the torque–angle relationship and the torque tolerated at the end of the range can help distinguish mechanical from sensory changes.

Ingram considers static stretching an effective way to improve ROM and a reasonable starting point for many people. For higher flexibility demands, he cites methods such as PNF, ballistic stretching, loaded stretching, isometrics and eccentric exercises as additional options. His practical conclusion, however, is less prescriptive: the choice depends on the individual and their specific goals.

Lima also sees promise in investigating strategies that take neural mechanisms into account, but stresses that this area still needs more study. Cabido arrives at a more conservative application: the data support progressive, tolerable protocols tailored to the goal, without turning intense pain, attention, motivation or decision-making into proven techniques.

This is especially important for proposals involving music, neuromodulation or other interventions aimed at neural processing. The review treats interventions targeting perception and decision-making as an avenue for future research, not as an established recommendation.

The study does not show that mindfulness, music, relaxation or neuromodulation can increase ROMmax in a clinically meaningful way. Nor does it support the idea that deliberately increasing pain tolerance is a strategy for gaining range.

For now, its main contribution lies in better understanding what happens when we become more flexible, not in offering a new universal recipe for getting there.

A limit between body and perception

The review by Lima and Blazevich is a narrative review. The researchers gathered different types of studies to build an interpretation of the mechanisms involved, rather than conducting a meta-analysis capable of estimating the effect size of each component.

This makes it possible to bring microscopic muscle structures, tendon and joint properties, sensory receptors and nervous system processing into the same discussion. But it also imposes an important limitation: we don’t know how much each of these components weighs in a person’s final range of motion.

Perhaps that is precisely the most interesting point of the review.

When someone manages to go a few centimeters farther in a stretch, we can’t look only at the muscle and conclude that it got longer. But neither can we look at the brain and conclude that the limit was there alone.

Between the two lies an entire organism: tissues that offer resistance, receptors that detect what’s happening and a nervous system that receives and processes that information.

There is already good evidence that maximum range of motion and stiffness are not the same thing. The contributions of Lima, Ingram and Cabido reinforce that gaining range can involve distinct mechanisms — mechanical and sensory — and that their importance can vary with training, dose, method and time.

Figuring out exactly how much each mechanism — mechanical, sensory and, possibly, cognitive — determines how far we can go remains an open question for science.

About the study

Article: Mechanisms Influencing Maximum Joint Range of Motion and Stiffness: A Narrative Review

Authors: Camila D. Lima and Anthony J. Blazevich

Journal: Sports Medicine

Year: 2026

DOI: 10.1007/s40279-026-02491-8

Type: narrative review

The authors report that there was no funding related to the review and declare no financial conflicts related to the content of the article.

Key references

Lima CD, Blazevich AJ. Mechanisms Influencing Maximum Joint Range of Motion and Stiffness: A Narrative Review. Sports Medicine. 2026. DOI: 10.1007/s40279-026-02491-8.

Ingram LA et al. Mechanisms Underlying Range of Motion Improvements Following Acute and Chronic Static Stretching: a systematic review, meta-analysis and multivariate meta-regression. Sports Medicine. 2025;55(6):1449–1466.

Cabido CET et al. Acute effect of constant torque and angle stretching on range of motion, muscle passive properties, and stretch discomfort perception. Journal of Strength and Conditioning Research. 2014;28(4):1050–1057. DOI: 10.1519/JSC.0000000000000241.