Stretching and the nervous system

Today’s post comes from my teacher Carol, who leads the Green Lotus Yoga trainings. She is an absolute wealth of knowledge and explains the link between the stretching  and the nervous system far better than I could. The following is actually a condensed form of Carol’s post; you can find the full thing on her blog here. Even so, this is still a lengthy post, so I’ll keep things brief here. Grab a cuppa and sit down to find out more about how stretching impacts the nervous system. 

Hatha yoga is a practice that aims to balance the nervous system through stretching and breathing. Ha = sun, hot, masculine, fast, activeness, sympathetic nervous system. Tha = moon, cool, feminine, restorative, calming, parasympathetic nervous system. Therefore Hatha = balance of sun & moon, yin & yang, activity & rest, and both nervous systems. So what is the role of stretching in the balancing of the nervous system and how does it work? 

Muscles are in constant communication with the nervous system. Even at rest, skeletal muscles display a small degree of muscular contraction. This small amount of tautness in the muscle is called muscle tone and is brought about by the central nervous system. Muscle tone keeps muscles firm and helps with muscles maintaining posture against gravity. Muscle tone is also very important in smooth muscle tissue, like that found in the arteries and veins and plays a very important part in regulating blood pressure in the body. 

Stretching muscles is also as much about the nervous system as it is about the muscles. The actual length of the muscle doesn’t change that much when stretched (if it did, yogis would be very tall!), however the central nervous system response in relation to that muscle can change considerably. Before we look at that in relation to yoga practices, let’s take a look at the science of stretching: the stretch reflex. 

The stretch reflex

The stretch reflex causes a reflex contraction of a skeletal muscle in response to the same muscle stretching. An example of this is if a yoga student is over-jealously trying to touch their toes in a forward bend and moves too fast too soon. Here, the muscle “spindles” that monitor the speed at which the muscles (in this case hamstrings) are lengthening, will fire causing the same muscles to contract. Thus, muscle stretch is followed by muscle contraction, which relieves the stretching, and possibly prevents injury.

Different types of stretching

There are 3 different types of stretching that are used in yoga classes. Yin yoga and gentle Hatha yoga uses mainly passive stretching. Active stretching is used in Vinyasa classes in conjunction with passive stretching. Finally, PNF stretching is used in strong Hatha classes in conjunction with active and passive stretching. 

Passive stretching

Static stretching is used to stretch muscles while the body is at rest. It is composed of various techniques that gradually lengthen a muscle to an elongated position (to the point of mild discomfort) and hold that position for 30 seconds to 4 minutes. For example, in reclined hand to foot pose (Supta Padangustasana, see image), if a student takes their leg into a belt and just lets the leg hand out with gravity, this is passive stretching. 

Active stretching

This is when the agonist muscle is contracted to inhibit, release or stretch the antagonist muscle. For example, in any hamstring stretch, if you wish to release the hamstrings deeper, you should contract the opposite muscle groups, the quadriceps. As the agonist quads shorten, the hamstrings become inhibited and release; these are therefore called the antagonists in this situation. 

Proprioceptive neuromuscular facilitation (PNF) stretching

This involves a static stretch followed by a strong isometric contraction of the muscle against an immovable force to create resistance.

For example, Cobbler’s Pose offers another great example of PNF:

  • Sit with a straight spine and allow the knees to fall with gravity without pushing or contracting.
  • Place your hands on the inside of the knees.
  • Press the knees up into your hands for 25-50 % of your strength for 10 seconds. 
  • Inhale and on the exhale allow the knees to drop down to their new resting position.
  • From this position, contract the knees up into the hands again. Repeat procedure.
  • Repeat a 3rd or 4th time.

In this form of stretching, when the agonist is contracted for 10 seconds or more, the Golgi Tendons become active, overriding the muscle spindle response (which is to shorten or close the muscle) and the muscle relaxes and opens.

So why stretch?

In today’s world where many people are overstressed, overworked and where the nervous systems are on hyper-alert, relaxation is an art. A healthy nervous system will be able to transition from sympathetic to parasympathetic with ease. Yoga helps us balance the yin and the yang of the nervous system so that we can learn how to open into and enjoy the space between these two extremes. A good level 2 Hatha or Vinyasa class will allow us to feel relaxed and alert (but not hyper-alert) at the same time. It helps us re-set. 

In Yin yoga and gentle Hatha yoga, where passive stretching is used primarily, parasympathetic tone increases in the muscles being used and in the nervous system. So we can use stretching not only to increase mobility in the joints, but also to inhibit the sympathetic nervous systems’ fight or flight response and activate the parasympathetic; in layman terms to relax.

Active stretching has a very different response on the nervous system. It is used primarily in a Vinyasa or strong Hatha class in conjunction with passive stretching. With active stretching, muscle tension can increase when the muscle is actively contracted. In addition, active stretching activates the “reciprocal inhibition” response in the nervous system which inhibits the antagonist muscle. Therefore, this style of yoga will both increase and release tension in the muscles and nervous system depending on the manner of the pose and a good class will combine poses to create balance between sympathetic and parasympathetic activity.