Muscles Work In Yoga?
What muscles work in yoga? What muscles work in trikonasana/triangle pose? What poses can I do to work my biceps? Questions like this are common, and to answer them you must first understand how muscles "work". The term "work" is rather vague when describing muscle activity. Understanding some key anatomy terms about muscles will allow you to gain a more thorough understanding of what different muscles are doing during different yoga poses.
To start the difference between stretching a muscle and strengthening a muscle must be distinguished. Stretching is an important part of all exercise and obviously a key component of one's yoga practice. Simply put, for a muscle to get stretched or become more flexible, the muscle must be lengthened. For example, as you maintain a forward fold and reach your head towards your toes, you feel a stretch in the hamstrings (the muscles that run down the back of your thighs). In this case, each end of the hamstring muscles is being stretched away from each other. One end of the muscles is in the back of the hips and is known as the origin of the hamstrings. The other end of the muscles is in the back of the knees and is known as the insertion of the hamstrings. While in the forward fold, the backs of your hips lift up, away from the back of the knees. In other words, the origin and the insertion move away from each other. But this action does not come from any "work" of the hamstrings. The hamstrings are passive in this move. In other, perhaps more familiar words, the hamstrings are "opening up". What you feel is the elongation of the muscle. It is stretching and is should feel good!
Now focus on the strengthening component of muscles. After you have done 20 sun salutations or held Warrior II for ten breaths, you might start to feel your muscles "working". What you are feeling is the fatigue in your muscles as they are contracting. It is through repeated muscle contraction (against some level of resistance) that the muscles get stronger.
Muscles contract in different ways: concentric contractions, eccentric contractions, and isometric contractions. All three of these types of contractions are used throughout your yoga practice.
When a muscle performs a concentric contraction (see image A), the muscle actively gets shorter. Each end of the muscle is attached to a different bone. As the muscle shortens, it pulls on the bone that the muscle is inserted on. The bone that has the muscles insertion, generally moves towards the bone which the muscle originates on. The muscle works against some level of resistancs to bring the tow bones closer together. In the case of a concentric contraction, the. Consider the biceps as shown in the image. The origin of the biceps is at the shoulder and the insertion is just below the elbow. As the muscle shortens, it pulls the arm bone just below the elbow up towards the shoulder, causing elbow flexion (elbow bending).
A muscle's concentric contraction is what is often first understood. When someone is proud of how large their biceps are and wants to "show off their guns", they shorten the muscle via a concentric contraction in order to create a bulging muscle. Even if you are not looking to show off your bulging biceps, you use concentric contractions of the biceps in your yoga practice. For example, as you bend both of your elbows to bring your hands together in prayer position, you biceps contract concentrically.
Now consider how your biceps will create an eccentric contraction. During an eccentric contraction, the muscle lengthens (see image B). In this case, the insertion of the muscle (which for the biceps is just below the elbow) moves away from the origin (which is at the shoulder) toward the floor. That is, the muscle must control its action against the pull of gravity. Eccentric contractions are used quite frequently in yoga. As you unfold your hands from prayer, you use an eccentric contraction of the biceps. You may be thinking this looks like the muscle is stretching. But there is a significant difference: the biceps muscle is active here. The primary purpose of the eccentric contraction is to provide controlled movement of the bones when moving with resistance. During the concentric contraction of the biceps, the muscle has to overcome resistance of gravity (and the hand weight). However, during the eccentric contraction, the biceps must control elbow extension (elbow straightening) so that gravity does not just pull the lower arm down to the ground.
Finally, explore isometric contractions. When a muscle is isometrically contracted the length of the muscle does not change, and therefore no movement occurs at the joint. The insertion moves neither towards or away from the origin, but rather remains stationary. Isometric contractions are very common in yoga, particularly when poses are held for several breaths. As you move in and out of a pose, you are likely using concentric and eccentric contractions. Though when you hold the pose, the contractions are likely isometric.
Try this simple activity to make sense of the various types of muscle contractions. Sit comfortably and bring your hands to prayer at your heart center. You just performed a concentric contraction of the biceps in order to bend your elbows and bring your hands up. Your biceps got shorter. Now hold your hands in prayer position. Your biceps work isometrically to maintain that position. There is no change in the length of the muscle. They stay in the shortened position you previously put them in. Now slowly hands from prayer position and lower them to your side for mountain pose. The biceps work eccentrically. That is, if you do not want to flop your arms down by your side in a careless manner. To carefully place your arms by your sides, you must use an eccentric contraction. Remember, with eccentric contractions, the muscle lengthens but through an active contraction. You will primarily gain strength (not flexibility) with repeated eccentric contraction.
A variety of concentric and eccentric contractions are used until your body has reached a desired shape. Once you are ready to hold that shape, the muscles must maintain the shape via isometric contractions. The longer you hold a pose, the longer the muscle must maintain the isometric contraction and it will eventually start to fatigue. That may be when you feel like getting out of the pose. Stay in the pose and let the isometric contraction get you stronger.
Understanding the terms described above will help you understand what muscles work in yoga. Subscribe by Email to New Angle Yoga's Blog in order to learn more about anatomy for yoga. In addition to introducing key concepts of functional anatomy and clarifying commonly misunderstood ideas, specific muscles (and how they "work") in yoga will be explored regularly. Thanks for reading and please leave comments or ask questions!
Trish Corley is a Baptiste certified yoga teacher and a licensed doctor of physical therapy.