Muscle contraction – which muscles are active and which ones are not – is one of the hardest things to understand in yoga. But if you want to be a good yoga teacher who can help his / her students to enhance their practice you do want to know how the human body works and how muscles work.
Their are a few basic things you have to know about muscles to understand how they work.
- A muscle can only pull (contract). It can’t push
- A muscle crosses at least one joint. When the muscle contracts the bones that form the joint moves towards each other.
- A muscle can only work in its line of fiber. For example the erector spinae This muscle and it’s fibers run along the back from the pelvis to the back of the head. It brings the body in an upright position when we are in a forward bend. If we are in a lateral bend (see the blog about anatomical language) the muscle won’t bring us up right, because this isn’t the way the line of the fibers run.
- Muscles work in pairs. If we can flex and extend at a joint we need a muscle on both sides of the joint. If the muscle on one side contracts, the muscle on the other side has to lengthen.
The roll of gravity
Before we look at the different types of muscle contraction there is one thing that is a puzzle for a lot of people. When do we actually contract or engage which muscle? Often the idea is that when we go in a forward bend, we are contracting our abdominal muscles to go down. Simply because our abdominal muscles are on the front. This is only partly true. What we have to keep in mind is the roll gravity plays.
Lets take a look at a ball. If I keep it in my hand, while standing, the ball will in in the air. On top of my hand. If I take my hand away the ball will fall down, because gravity is pulling on it. Now lets attach two elastic strings on the ball: one on top, one underneath. If I hold the ball in the air again and I hold on to both strings, nothing is going to happen. If I hold on tight to the top string and I pull on the bottom string still nothing is going to happen. Only when I let go of the top string the ball will fall down.
If I want to lower the ball slowly to the floor instead of letting it falling down, I can lengthen the top string bit by bit and the ball will go centimeter by centimeter towards the floor. With muscles it works the same. If I’m standing and I want to bend forwards it is not my abdominal muscles that do the work, but my back muscles. They slowly lengthen and let me bend down.
When I’m folded forward all the way and I want to deepen, I can engage my abdominal muscles to pull me deeper in the pose.
There is one more misunderstanding we have to get out of the way. Often we think of muscles to be either relaxed or contracted. His black and white idea doesn’t work. Lets look at our forward fold one more time. For example Prasarita Padottanasana C (wide legged forward fold). To bend forward my back muscles have to lengthen. But if they directly totally relax I will just fall forward. To go down slowly the muscles are actually engaging and then bit by bit relaxing so we go down slowly.
Two types of muscle contraction
We use some technical terms to describe these actions.
- Isometric contraction: static contraction. The muscle contracts, but there is no movement involved; no change of length. We use this to stabilize our body.
- Isotonic contraction: The muscle contracts and the length of the muscle changes. There are two types of Isotonic contraction:
- Isotonic eccentric: the muscle contracts and lengthens. The distance between the two ends of the muscle gets longer. This is what is happening in our back muscles when we bend forward.
- Isotonic concentric: the muscle contracts and shortens. The distance between the two ends of the muscle gets shorter. This is what happens when we are in our forward bend and we come up again. Our back muscles contract (and become shorter) to lift our torso up.
Translating all this to yoga
Students get stuck into a yoga asana or transition, because they don’t know which muscles they have to engage and which muscles they should relax. Knowing these basics can help you as a yoga teacher to guide your students deeper into poses or help them flow through transitions. I will write more about how you can do that in one of my next blogs.
To lift a flyer up in High Star we have to contract our quadriceps. From bend legs to straight legs is isotonic concentric contraction. As soon as the flyer is in the air we are stabilizing our legs. This is isometric contraction. Photo Jared van Earle