Improve Flexibility with Research-Supported Stretching Protocols
Huberman Lab Podcast #76
--
All animals stretch. Flexibility does not receive enough attention as it deserves. Flexibility is fundamental to how we move, and can both prevent and offset injury. Flexibility can improve balance, posture, reduce inflammation around the body and even offset tumour growth. Flexibility is really about maintaining integrity of the neuromuscular system, the connective tissue & the neuromuscular connective network.
Range of Motion
Some of us feel tighter than others. Our body acts to try to restore the body to its original position when stretching. There are two major mechanisms by which neurons communicate with muscles to ensure that your limbs do not stretch too far, or that you do not overload your muscles. We can use these mechanisms to our advantage to improve our range of motion.
- Mechanism 1: Motor neurons & spindle neurons
Lower motor neurons in the spinal cord connect to muscles via neuromuscular junctions. These neurons release acetylcholine (also involved in focus and attention in the brain), which causes muscles to contract by changing the length of the tissue.
Within the muscles themselves, we have neural connections from a different set of neurons in spinal cord, called spindle neurons, which wrap around muscle fibres and are a type of sensory neuron. They sense the stretch of the muscle fibres. Just like neurons in the eye that sense light.
So motor neurons cause the muscles to contract and shorten, and spindle neurons sense what is going on in the muscle.
Spindle neurons send out an electrical signal to the spinal cord if a muscle is stretched too far to tell the motor neurons to contract in order to bring the limb back into a safe range of motion. This process is very fast.
2. Mechanism 2: Golgi Tendon Organs
Golgi Tendon Organs (GTOs) are a safety mechanism that shut down the motor neurons in your muscles by sensing load rather than stretch. These are neurons attached to your tendons. If you try and lift a weight that is too heavy which could rip your tendons the GTOs will sense the excessive load and stop you from performing the movement.
Sensing discomfort
Our flexibility begins to decrease rapidly from age 20 up to 49. After age 49, we have a 10 % decrease every 10 years, or 1 % every year (although this change is not linear). Lifestyle factors such as yoga practice can influence this.
We have the ability to sense the external world, exteroception, and the internal world (e.g. gut pain), interoception.
Insula is a brain area that interpretes what going on within the body. The front of the insula combines external simuli, e.g. smells, with what is going on internally. The back of the insula (posterior) is concerned with your somatic experience (internal experience), e.g. are you feeling good with what your are currently doing.
In the posterior insula, we have a population of large neurons called von Economo neurons (large animals, such as chimps, whales and humans have them). Humans have 80,000 von Economo neurons, whilst other large species have around 1,000–10,000. These neurons have the unique property of integrating our knowledge of body movements and our sense of pain and discomfort. They can also shift our mental state from sympathetic activation (e.g. stress, don’t confuse sympathetic with being calm) to parsympathetic activation (relaxation).
Using this we can override the reflex to contract the muscles via the spindle neurons. The insula and von Economo neurons are part of the upper motor neurons, which can override the lower motor neurons mentioned previously. They are uniquely enriched in humans, unlike other animals.
Stretching Protocol
- Whilst standing try and touch your toes. Preferably with a straight back.
- Contract your quadriceps for 10 to 30 s. Lifting up your toes may help.
- Repeat the stretch.
Most of you will find an immediate increase in flexibility. Contracting the quadriceps relaxes the hamstring. They are antagonists. Stretching the antagonist to the muscle you are focusing on can inhibit the action of the Golgi Tendon Organs in the target muscle, and let you stretch more.
For tight quadriceps you can do the opposite, contract the hamstrings, relax and repeat quadriceps stretch again.
For tight biceps, you do the same thing with the triceps.
Alternating push-pull in the gym with the same rest times, can increase repetitions per set by leveraging the same neural circuits involved in flexibility.
Physiology
Muscles don’t actually get longer. But elements within the muscles change their confirmation, e.g. myofibrils. The sarcomeres in the myofibrils, as well as actin and myosin within the sarcomere, change the way that they slide past each other. We don’t want to think of the muscles as lengthening. Stretching can make both neural and connective changes. There are moments in stretching where we can override our pain and discomfort.
Types of stretching
Dynamic & Ballistic: Involve momentum. Force to generate movement, involving momentum. Ballistic involves more swinging, and consciously moving the body beyond the end range. They have a certain amount of risk due to the use of momentum. Doing dynamic stretching prior to resistance training is useful. It increases core temperature and also familiarises the body with neural circuits required for motion.
Static: For example, bending at the toes and then holding at the bottom. Two types: active and passive. Active has a dedicated effort on the part of the stretcher. Whereas passive involves relaxing into the stretch.
PNF (Proprioceptive muscular facilitation): PNF involves both stretching and contracting (activation) of the muscle group being targeted.
Improving flexibility
Static type (including PNF) more effective at increasing flexibility than dynamic stretching. Static may actually be more superior to PNF protocols.
Stretching across various studies:
Static: +20.9 % flexibility improvement
PNF: +15 % flexibility improvement
Ballistic: 11.65 % flexibility improvement
How long ? 30 s most effective stretching time to increase flexibility. No increase from 30 s to 60 s, or when stretching is performed 1–3 times per day.
How often ? Dose dependent. The amount of stretching scales with the increase in flexibility. Previously, in terms of hypertrophy training, 6–10 sets per week per muscle group was found to be optimal. Let’s now see the optimal stretching frequency below.
Stretching time in a single session is not important, but cumulative time per week (at least 5 mins/week on a single stretch). These stretches need to be performed on at least 5 days/week, so you cannot do it all in one day, but need to distribute it.
Rest times? No data available on optimal rest times between sets, e.g. 1:1, 1:2 ratio etc.
Warm up? Even static stretching requires a warm up. Although, this does not need to be extensive. Performing static stretching after cardiovascular or resistance training is particularly useful as your body is already warm, so no warm up is required.
Static stretching before resistance training or cardiovascular training can limit performance. This is controversial, but static stretching after exercise or a brief warm up seems like the best way to go. Certain situations may require some static stretching prior to exercise, for example if people are coming back from injury or need to increase their end range of motion, even if it may decrease their final load.
Hack ? Most of us to not have the time to perform stretching 5 times a week. Especially if we are working on multiple muscle groups. Longer hold times up to 60 seconds, may allow us to do less stretching sessions per week.
All this shows that stretching requires dedication, which is probably why most of us do not do it, as it takes regularity to see benefits.
Combining different types of stretching is a potential stretching protocol.
Effectiveness
We should not base our flexibility based on where we managed to reach the other day, e.g. toes. Our flexibility has a high level of variability, for example based on room temperature, stress etc. We need to let our ego aside and define end range of motion as where we feel the stress in our muscle groups. We need to pay attention to the feel of the stretch and the muscles involved. Don’t get attached to what you could achieve in the last session.
Low intensity stretching may be more effective at increasing range of motion. Effort that do not feel painful or feel easy, may be more effective at increasing flexibility. 30–40 % of pain tolerance is most effective based on one study, than feeling a maximal pain threshold of 100 %. So performing relaxing ;low intensity stretching may be more effective, e.g. in Yoga, with lower injury risk due to pushing into the pain zone.
Stretching to avoid cancer
Recent studies have shown that daily stretching of 10 minutes can reduce local connective tissue inflammation and fibrosis. Stretching reduced tumour growth in mice in a mouse breast cancer model from 2018. Yes, you can get mice to stretch through the manipulation of their tail. Mice with induced tumours were stretched for 10 mins every day for four weeks. Tumour volume at the end was 52 % smaller in the stretch group compared to the non-stretch group, in the absence of any other treatments. Stretching because of its impact on the fascia may create more micro-environment that are more permissive to tumour growth in certain instances. If you can periodically relax the nervous system through stretching, this can affect certain pathways that would allow the immune system to combat the tumour growth.
