Stretching is a common practice among athletes, yogis, and those seeking to improve mobility. But what actually happens in your muscles and nervous system when you stretch to allow for increased flexibility over time? Surprisingly, your brain plays a major role in determining flexibility. Let’s explore the anatomical players involved and how stretching induces neurological adaptations for improved range of motion.
When we think of our own flexibility, we tend to judge it based on how far we can move a joint through its range of motion. For example, when doing a standing hamstring stretch, you hinge forward at the hip until you feel tightness in the hamstrings restricting you from bending further.
The key to improving flexibility is increasing muscle length. Lengthening a muscle enables you to move the associated joint through a greater range. This applies to all muscle groups and their corresponding joints.
For instance, lengthening the calf muscles allows for more ankle dorsiflexion. Stretching hip flexors allows for greater hip extension. The key is targeting the muscles limiting a particular joint’s mobility in order to gain more functional range of motion.
A muscle can only lengthen so far before you feel resistance and tightness. Why is this? The properties of the muscle tissue itself play a role. But your nervous system is also heavily involved in determining flexibility limits.
Embedded throughout your muscles are proprioceptive receptors called muscle spindles. Muscle spindles detect changes in muscle length and relay this info to your brain. They act as a protective mechanism to prevent muscles from over-stretching. Let’s explore muscle spindles further.
Muscle spindles are sensory receptors wrapped in specialized muscle fibers called intrafusal fibers. They are dispersed throughout your skeletal muscles.
When a muscle lengthens or changes length quickly, the intrafusal fibers also elongate. This activates the spindle’s sensory nerve endings. Signals travel to your central nervous system about the rate and degree of muscle length change.
What does your brain and spinal cord do with this length and tension info? Here are the key functions of muscle spindle signaling:
This communication between your muscles and nervous system is key for flexibility. Next let’s follow the pathway of signals from muscle spindles to your brain.
When you stretch a muscle, sensors in the muscle spindles detect the length change. Signals travel up sensory nerve fibers to enter your spinal cord.
From the spinal cord, the signals continue up to your brainstem, cerebellum, and somatosensory cortex. The cerebellum coordinates the signals related to movement.
Your somatosensory cortex creates conscious awareness of body position, joint angles, and muscle tension. This proprioceptive sense gives you spatial orientation.
Without input from muscle spindles, you’d have no idea where your body parts are in space unless you visually looked at them!
Your central nervous system takes the length and tension info from muscle spindles and uses it to determine normal vs worrisome stretching range.
As you lengthen a muscle, eventually your brain says “That’s far enough!” and increases muscle tone to limit flexibility. Think of your nervous system as a puppet master controlling the strings of muscle tension.
If you try to quickly force a stretch past your flexibility limit, your muscle spindle activity sharply increases. Signals race back to your spinal cord to trigger a stretch reflex – involuntary contraction of the over-stretched muscle to protect it from tearing.
For example, when your doctor taps your patellar tendon with a reflex hammer, it swiftly lengthens your quadriceps muscles. Sensory signals bypass your brain and directly stimulate a reflexive knee extension to resist the quick stretch.
So your nervous system acts as a gatekeeper for your range of motion by modulating muscle spindle sensitivity and reflex activation. Let’s see how this allows your flexibility to improve over time.
With consistent stretching, your nervous system adapts to allow greater muscle length before triggering reflexive tightness. Here’s how:
Instead of muscle tension increasing at the usual 30° hip flexion in your hamstring stretch, your “tightness checkpoint” may shift to 45° after a month of stretching training.
Rather than a mechanical change in muscle itself, your brain permits greater length by reducing reactivity of the muscle spindle reflex. This demonstrates the huge neurological component in increased flexibility from regular stretching!
There are many types of stretching – static, dynamic, PNF, ballistic etc. For sustainable flexibility gains, most experts recommend:
This provides the nervous system consistent data that the new muscle lengths are safe. Static holds allow muscle spindle signaling to diminish so muscles relax into stretches.
Maintaining a balance of mobility, stability, and strength is ideal. Flexibility for over-mobile joints needs to be paired with targeted strength training.
Your nervous system won’t allow your joints to move through expanded ranges of motion if the surrounding muscles lack the capacity to stabilize them. Stretching and strengthening go hand and hand.
The interplay between the nervous system and the musculoskeletal system is fascinating. Understanding these mechanisms provides key insights into building mobility and resilience effectively.
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