Flexibility – The Stretch Reflex
My Daughter working on her Static Active flexibility.
Flexibility training is one of those things that comes up a lot, so I thought I’d put out a quick post on it.
Bare with me on this, being a bit technical.
The stretch reflex (myotatic reflex) is designed to protect us. It is a monosynaptic reflex which provides for the regulation of our skeletal muscle length. When a muscle is lengthened, the muscle spindle is stretched which in turn increases alpha motor neuron activity. This causes the muscle to contract and thus resist the stretch.
There is a secondary set of neurons that causes the antagonist muscles to relax. This phenomenon is known as reciprocal inhibition. Gamma motoneurons regulate the sensitivity of the stretch reflex by either tightening or relaxing the fibers within the spindle.
The Golgi Tendon Organ (GTO) records the change in tension, and the rate of change of the tension, and sends signals to the spine. When the tension exceeds a certain threshold, it triggers the lengthening reaction and inhibits the muscles from contracting by inhibiting the alpha motor neurons. This causes the agonist muscle (stretched muscles) to relax. The lengthening reaction is possible only because the signaling of the GTO to the spinal cord is strong enough to overcome the signaling of the muscle spindle.
How can we use this information?
One of the ways I have found useful for gaining Static Passive flexibility is the use of combining Isometrics with static passive stretches. This is done by stretching the given muscle or muscles to the first point of tension and pausing there for roughly 10 seconds. During the 10 seconds I will coordinate deep breaths with focus on intentionally relaxing the stretched agonist muscle.
This takes practice but once mastered it will help.
Once the range of tension is relaxed, come out of the stretch slightly; contract the given area either by isometric hold or slow isotonic contraction to increase blood flow. Then move slightly past the previous point and statically stretch for around 30 seconds, again focusing on intentionally relaxing the muscle and coordinating the breath. Rise & repeat a few times. This will help achieve autogenic inhibition, a reflex relaxation that occurs in the same muscle where the GTO is stimulated, increasing the Range of Motion (ROM) before invoking the muscle spindles.
Similarly you can contract the opposing muscle group which will help you achieve reciprocal inhibition, a reflex muscular relaxation that occurs in the muscle that is ‘opposite’ (antagonist) the muscle being contracted (agonist). This is the primary method used when seeking to increase Static Active flexibility. Static active flexibility is basically the holding of a position utilizing the strength of the agonist muscles only.
Many times muscle strains and tears occur due to the process of invoking the muscle spindles, causing the muscle to contract when it should be relaxed and thus a tear occurs. This can cause a misfiring of both the agonsit and antagonist muscles, leading them to fire at the same time. Usually the weaker muscle will lose and a tear will occur in that muscle.
While flexibility in motion is known as Dynamic flexibility and statically holding a position via the opposing muscle group is known as Static Active flexibility, having a good base in static passive flexibility is important, think of it as your foundational ROM.
When we exceed our normal ROM through the use of momentum then we are moving into a form of movement known as Ballistic. You can relate ballistic movements to something similar to plyometric movements where you are relaying on the stretch reflex action of a muscle and trying to increase ROM by taking the amortization phase (brief transition period from stretching to contracting) beyond your static passive range via a dynamic movement.
Out of all the types of flexibility the hardest to increase is static active and the most dangerous method of stretching is in the use of Ballistic movements. Including Self-Myofascial Release (SMR) and Neurofascial Release (NFR) techniques are also helpful in increasing your flexibility and prevention of injuries.
Generally speaking I use dynamic stretching as part of my warm-ups and use static passive as the primary means of increasing or maintaining overall ROM of a joint. I generally perform static passive after hitting each muscle group being targeted with Self-Myofascial Release (SMR). This helps release any trigger points or knots and makes the stretching more effective. I use a variety of tools such as tennis balls, medicine balls, golf balls, 3″ & 4″ PVC pipe. I give myself at least 48 hours between Isometric/Static Active stretching sessions on the same muscle groups. And I often perform dynamic flexibility exercises early in the morning which help to increase my dynamic ROM range throughout the day.
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