Improve Flexibility with Research-Supported Stretching Protocols

High-Level Overview

In this solo episode, Andrew Huberman makes the case that flexibility and stretching deserve far more attention than they get. He argues they are built into our basic body plan and matter not just for yoga or injury prevention, but for how we move, learn new movements, recover from injury, manage inflammation, and even tolerate physical and emotional pain. He starts with the biology: the nerves, muscles and connective tissue that set our range of motion, the reflexes that protect us from overstretching or overloading, and a little-known class of brain cells that helps us decide whether to relax into discomfort or back away from it.

With that foundation, Huberman walks through the research on which kinds of stretching work best, how long to hold a stretch, how many sets to do and how often, how hard to push, and when to stretch relative to exercise. He closes with two surprising studies: one in mice linking daily stretching to slower tumor growth, and one showing that yoga practitioners have far higher pain tolerance and a larger insula. The tone is professorial but practical, moving from neuroanatomy to at-home experiments to specific, study-backed protocols.

The Discussion Explores:

• The three systems behind flexibility: neural, muscular and connective tissue, and how they keep limbs in a safe range.
• Two built-in safety reflexes: muscle spindles that sense stretch and Golgi tendon organs that sense load.
• Von Economo neurons and the insula: brain cells that help us decide whether to push through discomfort or relax into it.
• A quick flexibility trick: contracting the opposing muscle to instantly increase range of motion, and using the same idea to interleave push and pull sets in the gym.
• The four types of stretching: dynamic, ballistic, static and PNF, and why static stretching wins for long-term gains.
• The protocol numbers: 30-second holds, at least five minutes per muscle group per week, spread over at least five days.
• Low-intensity "microstretching": why stretching at 30 to 40% of the pain point beat stretching at 80%.
• Beyond flexibility: stretching, relaxation and tumor growth in mice, and yoga's effect on pain tolerance and the insula.

Deep Dive into Main Ideas

The Biology of Flexibility: Nerves, Muscles and Connective Tissue

Huberman begins by noting how much flexibility varies between people, from those who feel tight to a relative of his who can bend her fingers back to touch her wrist without pain. He then points out the flexibility we all have: if you move your arm behind your torso and let go, it returns to your side. That happens because the nervous system, skeleton, muscles and connective tissue (including fascia, which he says deserves its own episode) work together to keep limbs in a particular position relative to one another. These are the same processes we tap into when we try to become more flexible.

The key players are the lower motor neurons in the spinal cord, which send wires to muscles and release acetylcholine at the neuromuscular junction to make them contract. Nerve controls muscle contraction. Alongside them are sensory neurons, and in particular the muscle spindles, which wrap around muscle fibers like a corkscrew and sense how much the muscle is being stretched. When a muscle stretches too far, the spindles fire, signal the spinal cord, and trigger the motor neurons to contract the muscle and pull the limb back into a safe range. This loop is very fast and protects us from injuring muscles and connective tissue.

The second safety mechanism is the Golgi tendon organ (GTO), sensory neurons near the tendons that sense load rather than stretch. If you try to lift something so heavy that it could tear a muscle or tendon from the bone, the GTOs fire and shut down the motor neurons, making it impossible to keep contracting. Huberman stresses that both reflexes are protective, but both can be used in a logical and safe way to increase range of motion, sometimes within seconds.

Why Flexibility Matters With Age

Huberman notes that there are now dozens, if not hundreds, of studies showing that a dedicated stretching practice improves range of motion. Just as important, we all lose range of motion unless we do something about it. Pooling the studies, flexibility declines from about age 20 to about age 49 and beyond, at roughly 10% every 10 years. That averages about 1% a year, but it isn't necessarily linear: someone might feel fine through their twenties and then lose 5% by 32.

Lifestyle matters a great deal. Yoga, a dedicated stretching practice, and even resistance training can help offset the decline. Maintaining and even improving range of motion is, in his words, of immense benefit for preventing injury, provided it isn't pushed too far, since people who push range of motion to extremes can suffer both acute and chronic injuries. Later in the episode he adds that good range of motion supports posture, walking, balance and physical performance, and is linked in the literature to pain management, including headaches, making it a real, if underappreciated, part of longevity.

Von Economo Neurons, the Insula and "Relaxing Into" a Stretch

The brain also shapes flexibility. Huberman introduces interoception, our sense of what is happening inside the body, and the brain region most associated with it, the insula. The back of the insula, the posterior insula, integrates how we feel internally with the movements we are making, sorting experiences into what he calls yum, yuck and meh: keep going, get out, or neutral. Within the posterior insula sit unusually large neurons called von Economo neurons, named after Constantin von Economo, who described them around the turn of the 20th century. They are found in whales, elephants and chimpanzees, but humans have upwards of 80,000 of them, compared with roughly 1,000 to 10,000 in those species.

These neurons integrate information about body movement, pain and discomfort, and can drive the motivation to lean into discomfort when we decide it serves a goal. They also connect to brain areas that shift us from sympathetic (alert, stressed) to parasympathetic (relaxed) states. That, Huberman says, is what "relaxing into the stretch" really means: using these circuits and the upper motor neurons in the brain to gently override the spindle reflex. He compares it to the reflex that pulls your foot away from a sharp object, which needs no thought and even works without a cerebral cortex, yet which you could consciously override if your life depended on walking across hot stones. Every stretching session involves a similar fork in the road: relax into the stretch, push through a bit of discomfort, or let the reflexes stop you.

A Quick Experiment: Using Opposing Muscles to Stretch Further

Huberman offers an at-home demonstration. Stand with straight legs and see how far you can reach toward your toes. Then stand up and contract your quadriceps as hard as you can for about 10 seconds (kicking the foot out and pointing the toes back toward the shin helps), release, and try again. Most people find an immediate increase in hamstring range of motion. If you don't, he suggests contracting harder and longer, perhaps 20 or 30 seconds. The reason is that the quadriceps and hamstrings are antagonistic muscles: contracting one relieves some of the spindle-driven tension in the other. The same trick works for other pairs, such as flexing the biceps during an overhead triceps stretch, or contracting the hamstrings before a quadriceps stretch.

He explains that these quick gains don't come from muscles getting longer. Over weeks of consistent stretching, work he attributes mainly to researchers at McGill University suggests the arrangement and spacing of structures inside the muscle change, such as the sarcomeres and the interlocking myosin and actin filaments. So the resting state of a regularly stretched muscle differs, but muscle belly length and where muscles insert are genetically set. He later adds that part of PNF's effect comes from GTO activation in one muscle inhibiting the spindles of its antagonist, which he refers to as autogenic inhibition.

The same principle carries into the gym. With straight sets of a pushing exercise and two minutes' rest, someone might manage 10, then 8, then 6 reps. Interleaving pushing and pulling sets of antagonistic muscles, while keeping the same rest for each muscle group, often lets people hold performance closer to 10, 9, 8. The catch, he jokes, is that you may become the person who occupies several machines at once.

The Four Types of Stretching and Why Static Wins

Huberman groups stretching into four categories. Dynamic and ballistic stretching both move a limb through its range of motion, with ballistic using more momentum and swinging, especially at the end range. Static stretching holds the end range of motion with as little momentum as possible, and can be active (applying force to extend the range) or passive (relaxing into it). PNF, or proprioceptive neuromuscular facilitation, deliberately uses the spindle and GTO reflexes, for example lying on your back and pulling a leg overhead with a strap, sometimes with a partner, loads or machines.

Across at least four studies, the answer is the same: for long-term gains in range of motion, static stretching, including PNF, beats dynamic and ballistic stretching. That doesn't make dynamic and ballistic stretching useless. Huberman says physiologists he has spoken with, including Dr. Andy Galpin and Dr. Kelly Starrett, point out that safe dynamic and ballistic stretching before resistance or cardio training can prime the neural circuits and joints you're about to use. But for becoming lastingly more flexible, rather than temporarily looser, static stretching is the route to take.

The Numbers: How Long, How Many Sets and How Often

Huberman first describes a study by Bandy and colleagues on the effect of time and frequency of static stretching on hamstring flexibility. It involved 93 people (61 men and 32 women aged 21 to 39) with limited hamstring flexibility, split into four stretching groups that stretched five days a week for six weeks, plus a control group. The authors found that "the change in flexibility appeared to be dependent on the duration and frequency of stretching," and that "a 30 second duration is an effective amount of time to sustain a hamstring muscle stretch in order to increase range of motion." Going from 30 to 60 seconds, or from one to three sessions a day, added nothing.

He then turns to a 2018 review by Thomas and colleagues on stretching typology and duration, which narrowed the literature to 23 eligible articles. It found that "all stretching typologies showed range of motion improvements over a long term period," but static protocols produced significantly greater gains: on average about 20.9%, versus about 11.65% for ballistic stretching and about 15% for PNF. Crucially, what mattered was total time per week, at least five minutes per muscle group, and frequency, at least five days a week. Time within a single session didn't seem to matter much. The first three weeks of gains come largely from neural changes and improved stretch tolerance.

Putting it together, Huberman's example protocol for the hamstrings is three sets of 30-second static holds, repeated five or even six days a week, with other muscle groups in the same session. He couldn't find research on the ideal rest between sets, so he suggests that roughly double the hold time seems reasonable, and invites viewers with evidence to share it. For those who can't commit to five days, there is some evidence that 60-second holds done every other day can work, though this hasn't been studied systematically. He also suggests using the rest between sets to stretch or load the opposing muscle group, for efficiency.

Warming Up and When to Stretch

To avoid injury, Huberman recommends raising core body temperature before stretching, even for static stretches. If you're already warm from running or lifting, you can go straight into stretching afterward. Otherwise, five to seven, or up to 10, minutes of easy cardio or calisthenics is enough. Doing static stretching after resistance or cardiovascular training seems most beneficial, and he notes a number of papers suggesting that static stretching beforehand may limit running and lifting performance, though he acknowledges the literature is split and runners argue about it endlessly.

Borrowing what he jokingly calls "Galpinian logic," he says the right choice depends on the goal of the session. If tightness prevents good form or stability, static stretching before lifting can be worth a small loss in the load you can lift. The same applies when returning from injury, surgery or a layoff. Dynamic and even ballistic stretching before skill work, cardio or weight training can warm up the relevant circuits, joints and tissues and improve accuracy, stability and confidence.

Low-Intensity "Microstretching" and the Anderson Approach

How hard should you push? Huberman highlights a principle from the long-established Anderson method: stretch to the end of your range, but define that end by where you feel the stretch in the target muscle that day, not by where you think your range should be. Range varies with stress, room temperature and other factors. His summary: "feel the muscles as you stretch them. Don't just go through the motions." He compares this to hypertrophy training, where the goal is to challenge the muscle rather than just move weight.

That fits a six-week study of recreational dancers comparing low-intensity "microstretching with moderate-intensity static stretching. Both groups stretched daily and held each set for 60 seconds, but one group stretched at 30 to 40% intensity, where 100% is the point of pain, while the other stretched at 80%. The low-intensity group saw greater improvements in lower-limb range of motion, and the authors wrote that the most interesting aspect of the study was the greater increase in active range of motion compared to passive range of motion by the micro stretching group." Huberman finds this a relief: you don't need to push to the point of pain, and doing so may be both less effective and riskier. He is skeptical of the authors' explanations about sympathetic and parasympathetic activation, but finds the core result sound.

Stretching, Relaxation and Tumor Growth in Mice

Huberman then turns to stretching's effects beyond flexibility. He describes the work of Dr. Helene Langevin, a medical doctor who has studied the mechanisms behind practices like acupuncture and is a director at the National Institutes of Health's center for complementary and integrative health. Her work has shown that a brief whole-body stretch shifts the nervous system toward parasympathetic relaxation, and that gentle daily stretching for 10 minutes can reduce local connective tissue inflammation and fibrosis.

In a 2018 study in Scientific Reports, mice with induced breast tumors were gently stretched for 10 minutes once a day for four weeks, or not stretched. The tumor volume at the endpoint was 52% smaller in the stretch group compared to the no stretch group, with no other treatment. Huberman is careful to note the limits: this is an animal study, and the authors don't think stretching shrinks tumors directly. They even raise the possibility that stretching could make fascia environments more permissive to tumors in some cases. The more likely explanation, he says, is that periodic relaxation influences inflammation and immune pathways that help the immune system fight tumor growth.

Yoga, Pain Tolerance and a Bigger Insula

Finally, Huberman returns to the insula with a 2014 study in Cerebral Cortex titled "insular cortex mediates increased pain tolerance in yoga practitioners." Practitioners of several yoga styles, compared with non-practitioners, showed pain tolerance double or more that of controls, for both heat and cold pain, and not only among hot-yoga practitioners. They also had greater gray matter volume in the insula, which scaled almost linearly with years of practice; people with 15 or 16 years of yoga had a much larger left insula.

He also highlights the mental strategies each group used during a cold pain task. Non-practitioners tended to distract themselves, ignore the pain, or engage negative emotions. Yoga practitioners tended to use positive imagery, relaxation, acceptance, observing themselves, and above all a focus on breathing. Huberman, who says he doesn't practice yoga regularly, admits the study has him considering taking it up, because it seems to train circuits that extend into managing stress and challenges in everyday life, not just flexibility.

Conclusion

Huberman's message is that flexibility is a trainable, science-backed pillar of health rather than an afterthought. Our range of motion is set by protective reflexes and by brain circuits that decide whether to relax into discomfort, and we can work with both, from contracting an opposing muscle to calmly relaxing into a hold. His distilled protocol is simple: warm up or stretch after training, favor static stretching, hold for about 30 seconds, get at least five minutes per muscle group each week spread over five or more days, and stay gentle, around 30 to 40% of the point of pain. Keep dynamic and ballistic stretching for warm-ups before activity. Beyond range of motion, the relaxation that stretching brings and practices like yoga may shape inflammation, immunity, pain tolerance and stress resilience, making this an episode well worth hearing in full for anyone who wants to move better as they age.

This is a summary of "Improve Flexibility with Research-Supported Stretching Protocols" from Huberman Lab, giving you the GIST so you can decide if you want the REST. Listen to the full episode.