How much do you know about how your body works? Do you know, for instance, what happens to food after you've put it in your mouth? Do you know how your heart circulates oxygenated and deoxygenated blood? Do you know what gives joints their articulations, or that there are three different types of muscle contractions? If not, why not? It's your body; your life's vehicle, and the only one you get. Your entire physical existence takes place within the parameters of your flesh and bones; aren't you a little curious about how it works? Perhaps the nitty gritty details don't interest you, and that's fine. But if you want your body to work well, wouldn't an understanding of its basic mechanics, functions, and structures seem useful? How do you propose to take good care of something without knowing how it operates?
The human body is complex, sometimes mysterious, endlessly fascinating, and admittedly not an easy subject to study. I have no delusions about all of us being anatomists or kinesiologists; some of us are just naturally more or less scientifically minded than others. But yoga very clearly affects us both anatomically and physiologically, so it's probably worth perusing at even the most elementary level. And that's my way of pep-talking you into indulging me while I share just a little bit about how muscles work!
Muscles exist in order to move joints. Which muscle contracts is what determines which joint moves and how. They, of course, come in different shapes and sizes with some resting very near the surface of the body and others much deeper. Some act as free-movers while others are better at stabilizing. And it's shape, location, and attachments are what dictate how a muscle behaves.
Each muscle attaches to bone in (at least) two places: the more stable, unmoving end of the muscle is called the origin, and the end which is more likely to affect joint movement is called the insertion. For example, the hamstring muscle (which is technically three separate muscles joined by a single tendon and commonly referred to as a single unit) originates on the ischial tuberosities (the sitting bones at the base of your pelvis) and inserts on the tibia/fibula (your lower leg bones). Therefore, the hamstrings are primarily responsible for two movements: (1) posteriorly tilting your pelvis (we often call it "tuck your tail") and (2) flexing (bending) your knee. Stretching a muscle requires the origin and the insertion to move away from each other, while firming and strengthening require the origin and insertion to move toward one another. So in order to stretch the hamstrings, you want to either tilt your pelvis forward or extend (straighten) your knees or both of those things simultaneously. And to stabilize and/or strengthen the hamstrings, you want to tuck your tail or bend our knees or both.
When you bend your knee via hamstring contraction, the hamstrings are acting as the agonist which means they caused the action of that joint. On the other hand, any time a muscle contracts (tones, firms, shortens), some other muscle is relaxing or stretching in opposition, and that muscle is called the antagonist: i.e. when your hamstrings contract and your knee bends, the quadriceps act as the antagonist. If they didn't, their resistance would prevent the hamstrings from doing their job. Furthermore, because muscles do not act in isolation, the movement caused by the agonist muscle is supported by synergists which move in a similar, though typically less efficient, way as the agonist: i.e. the gastrocnemius (the bulky calf muscle) assists the hamstrings in flexing your knee although that is not its primary job.
What does all this mean to your yoga poses? It's simple really: mastery of any given asana comes from successfully utilizing the agonist(s), synergist(s), and antagonist(s) affected by the posture. Of course, you don't have to explicitly understand this in order to have success in your practice. But knowing how the muscles work, even just a little bit, can help you use them much, much more effectively.
Let's stick with the hamstrings as our focal point, but instead of them acting as the agonist for knee flexion, let's look at how we get them to stretch in a pose such as uttanasana (LoY 92). After all, stretching the hamstrings can sometimes seem like all we ever do on the mat, so it's probably advantageous to our practice to know how to do it well!
It's important to remember that muscles are designed to contract; that is, to pull their two opposing ends closer together. Asking a muscle to lengthen instead is counterintuitive which is why it's such a challenging task. And also why it is so important to understand the function of antagonists and synergists.
When you stand in tadasana, the hamstrings are contracting just enough to keep your pelvis in an upright position and thus prevent you from toppling forward. When you start to bend forward toward uttanasana, your pelvis must tilt so that you hinge at your hip joint rather than round in your waist/lower back. But remember the hamstrings are programmed to prevent your pelvis from tilting forward -- it is their job to keep the very action which you are trying to induce from happening! If you want to convince your hamstrings to release into a stretch, a couple of preliminary actions are necessary.
First, the bones need stability. Part of that comes from moving your thigh bones back and apart in order to widen your pelvic floor. When your thigh bones are sitting deeply and widely within the hip socket, the pelvis itself literally has freedom to tilt. Otherwise your thigh bones will act as a kind of clamp compressing the pelvic floor, and, if the pelvis is stuck, then you cannot hinge from your hips. So start by rolling the fronts of your thigh bones in toward one another, then press them straight back, and widen them apart. This action allows the whole pelvic bowl to anteriorly tilt -- your butt sticks out, your pubic bone moves back between your legs, and, if you think about the pelvic bowl as just that, a bowl, then anything contained within it would be spilling out over the top rim as it is now angling forward.
During the first moments of folding into uttanasana, your hamstrings are actually still contracting rather than stretching. Again, remember their primary objective: to tuck the pelvis posteriorly in order to prevent your torso from toppling over (think of the bowl image again, and in tasasana, nothing would be spilling out of the bowl because its top rim is parallel to the floor). As you attempt to fold your torso forward over your legs, your hamstrings intuitively turn on and work hard to control your descent. They don't know that you are folding forward on purpose; they only know very primitively that their job is to keep you from plummeting to the floor. You need to convince them that your hinging forward is deliberate and that it is safe for them to release.
Therefore, the next step is to stabilize the upper body. This part is fairly simple: press your hands on to something solid. If you cannot reach the floor, then use blocks or a low stool or a chair seat or a counter top. But do not do not do not allow your arms to dangle. As long as your torso is unsupported, your hamstrings will contract which will tuck your tailbone which means you are rounding at the waist/lower back. So put your hands or fingertips on the floor or blocks or whatever else you can reach. But don't just touch down with your weight still leaning back into your heels/legs; you have to actually bear a moderate amount of weight into your arms. Once your body is supported, your hamstrings no longer need to contract and they will slowly relax. Relaxation becomes stretching, and to do more of that you need to employ the antagonists.
In order to actually improve flexibility, you need to coax the hamstrings to lengthen beyond their original capacity. So far all we've really done is maximized their current state by moving their origin and insertion as far away from each other as possible but without much (or any) intentional stretch. The quadriceps on the fronts of the thighs will play a big role here.
Muscle tissue is very elastic. It is made up of teeny tiny strings of cells all braided together. Like a rubber band, it stretches out easily, and as soon as you release that tension, it retracts. When a muscle is in a resting or contracting state, all the cells are knitted tightly like when you interlace your fingers and press your palms together. If you were to then open your palms apart but keep your fingers tightly interlaced, it would be like what we just created in our first stage of uttanasana: length but not necessarily stretch in the strong sense. However, if you slowly pull your fingers apart, you'll start to create open space between them, and that's actual stretching. Muscle tissue works similarly: as you pull on it, the braids separate slightly which creates space in between them. And the good news is that the body pretty immediately (within just a few hours) responds to these open spaces by generating new tissue. So, whereas when you release the tension of a rubber band, it retracts back to its original length, a muscle only retracts a little bit because your body fills in the open spaces. Little by little this creates flexibility.
Back to the quadriceps. Like all muscles, the quads act to pull their origin (basically the anterior inferior pelvis and anterior femur) toward their insertion (on and just beneath the knee cap). When your quads contract, your pelvis will flex (anteriorly tilt) or your knees will extend (straighten) or both. This is of course the opposite (or antagonistic) action of the hamstrings. And it also happens to be exactly what we need in order to maximally stretch the hamstrings -- straight legged forward folding action, right? By contracting your quads, you will (1) send a signal through your nervous system to your hamstrings telling them to release, and (2) intentionally increase the distance between your hamstring's origin and insertion. Think about the hands interlaced again. Without the contraction of the quads, all you can do is create the stage at which your palms are opened wide but your fingers are still tightly interlaced. When you engage your quads, you create the leverage necessary to pull the fingers apart and keep them apart long enough for the body to start the process of filling in those empty spaces with new tissue. You must challenge the muscle into a new state of length as well as allow the nervous system time to understand that that action is deliberate and safe; otherwise nothing new will happen.
How do you know if you're engaging your quads? One really easy way of finding out is by trying to wiggle your knee cap. Sit on the floor with your legs straight out in front of you (dandasana), and gently pinch your knee cap between your thumb and fingers. If you can wiggle it slightly side to side, then your quads are relaxed. Now tone the fronts of your thighs and try again -- your knee cap is locked in place. If you want to stretch your hamstrings, your quads need to be contracted.
And don't forget about the synergists. Remember synergists are muscles which assist the agonists but in a less direct way. The gastrocnemius helps the hamstrings by bending the knee even though its primary job is to bend the ankle. If your calf muscle is tight, you will struggle to straighten your knee, and, if you cannot straighten your knee, you cannot effectively stretch the hamstrings. Flexible calf muscles mean more stable lower legs, and in turn greater likelihood of affecting positive change upon the hamstrings. For uttanasana, utilizing the synergists means keeping the hips stacked directly over the ankles rather than allowing the hips to lean back over the heels. It is really the combination of the antagonists (quadriceps) contracting and the synergists (gastrocnemius) lengthening which induces the most stretch upon the agonist (hamstrings).
So to recap, stretching your hamstrings requires that your thigh bones are set back and wide in order to hinge the pelvis forward, your torso is supported in order to relax the hamstrings, and your quadriceps are contracted in order to create actual stretch. Or to apply this more generally to the body as a whole, the primary joint being affected needs range of motion, the secondary joints need stability, and the synergists and the antagonists need to cooperate to cue the agonist into relaxation. All of this can be refined with even more intelligent alignment (for instance, we can focus on one side at a time by working asymmetrical poses which are often more accessible, and we can also fine-tune the actions of the upper body in order to minimize eccentric contractions), but this is a good foundation. The take away is: contract the opposing muscle(s) to induce the greatest amount of change upon the target muscle(s). Another (although very simplistic) way to think about it is that forward bends stretch the back body while contracting the front body, and back bends stretch the front body while contracting the back body. It is not enough to simply fold forward or bend back; it is necessary to utilize the body's structures and mechanics.
Our sequence now includes a few simple seated forward folds as well as a few belly-down back bends. These poses are not "easy", but they are fundamental, and are a great way to introduce the basic, gross workings of our flesh and bones. As you practice the new poses, think about what needs to stretch (open, loosen), and how you can utilize the contraction (firming, shortening) of its opposites to enhance the form of the posture.
"Lock your attention within the body. You can hold your concentration on breathing, on tissues that are being stretched, on joints that are being stressed, on the speed of your movements, or on the relationships between breathing and stretching. You can also concentrate on your options as you move in and out of postures. Practicing with total attention within the body is advanced yoga, no matter how easy the posture; practicing with your attention scattered is the practice of a beginner, no matter how difficult the posture...[Y]oga trains the mind as well as the body, so focus your attention without lapse."
(H. David Coulter, Anatomy of Hatha Yoga, 17)
