Bhujangasana (Cobra Pose)

Bhujangasana takes its name from bhujanga, a serpent, and the image is exact: a cobra raising its hood while the rest of the body stays flat on the ground. That second half of the image is the part people forget. From the hips down, the pose is entirely on the floor and pressing into it. Only the chest rises.

It is one of the twelve positions of Surya Namaskar, arriving seventh, on an inhalation, immediately after the eight limbed salutation. It is also one of the most commonly practised poses in India outside of any class at all, which means most people arrive already doing a version of it, usually with straight arms and a compressed lower back.

What it is not is a test of how far back you can bend. The photographs that circulate, with the arms locked straight and the head thrown back, show a pose that is being performed by the arms and felt in about two vertebrae. A cobra done well is much lower, spreads the extension along the whole spine, and is felt as work in the back rather than as a stretch in the front.

The honest answer is: as high as your back muscles can lift you, plus a very little more from the hands.

Here is the test I use, and it settles the question in one attempt. Set up properly, lift to your usual height, and then take both hands off the floor for one second. Most people drop several inches. That drop is the amount of the pose that was being done by your arms.

Practise at the height you can hold with the hands hovering. Keep the palms lightly on the floor for balance if you like, but do not push. Over a few months that height rises on its own, because the muscles doing the lifting are actually being trained instead of being bypassed.

• Week one to four: sphinx, or baby cobra at whatever height the hands off test gives you.
• Month two: the same, held for thirty seconds, three repetitions.
• Month three onwards: allow a little arm pressure, keeping the elbows soft and never locking them.

A cobra with straight locked arms, in which the pubic bone leaves the floor, is a different pose called Urdhva Mukha Svanasana, upward facing dog, and it belongs to a stronger practice.

This pose has a reputation for helping back pain, and in my experience it earns it, with two important conditions attached.

The first condition is that the pose must be low and anchored. The hips, the thighs and the tops of the feet stay pressed into the floor throughout. If the pelvis lifts and the legs go soft, all the extension collects into two or three joints in the lower back and the pose stops being a lengthening and becomes a compression. That is when people report that cobra hurt them.

The second condition is that not all back pain is the same. Backs that feel worse for sitting and better for walking and standing usually respond well to gentle extension, and cobra suits them. Backs that hurt more with any arching, or that have a diagnosis of spondylolisthesis, stenosis or an irritated facet joint, may be aggravated by exactly this movement. Pain that shoots down a leg needs assessment, not a pose.

What I do in class is simple: I teach the sphinx first, for two or three minutes of quiet breathing, and I ask afterwards whether the back feels better, the same, or worse. That one question sorts most people correctly. The full picture of which movements suit which backs is on the yoga for back pain page.

In Surya Namaskar this is position seven, and it lasts one inhalation. You arrive from Ashtanga Namaskara, the eight limbed salutation, and you leave into Adho Mukha Svanasana, downward dog.

The single instruction that decides whether this is a good cobra or a sore back is the direction of travel. Slide the chest forward along the floor first, then lift. Coming from the eight point position the chest is already low and slightly behind the hands, so the natural but wrong movement is to push up and back. That shortens the lower back before you even begin.

Forward, then up. It takes about a quarter of a second longer and it changes the pose entirely.

Two other practical points. Keep the lift low in the sequence, lower than you would in a held practice, because you have only one breath and no time to set up carefully. And keep the legs pressing down, because in a flowing round the legs are the first thing to go slack.

Consider what most adults do with their shoulders for fourteen hours a day: forward. Typing, driving, cooking, holding a phone, carrying a bag. The muscles across the front of the chest shorten, the upper back lengthens and weakens, and the head drifts in front of the shoulders to compensate.

Bhujangasana reverses every part of that, provided you do the shoulder work rather than only the spine work. Before you lift at all, draw the shoulder blades down the back and broaden the collarbones. As you rise, keep drawing them down. If the shoulders end up near the ears, the chest has not opened at all and you have simply arched the lower back.

Students who add three short repetitions of the sphinx at the end of a working day often notice the change first in their breathing rather than their back, because a chest that is not collapsed has more room to expand. That is also why it works well as a preparation for sitting down to Anulom Vilom or any other breathing practice.

Fifteen to thirty seconds, three repetitions, with three easy breaths lying flat between them. That is the standard practice and it suits almost everybody.

The sphinx version is the exception: because it is so gentle, it can be held for two or three minutes, and held that long it becomes a quieting practice as much as a strengthening one.

Time of day matters more with this pose than most. Practised first thing in the morning the spine is stiffer and, in the hours after waking, the discs hold more fluid, so I keep the morning version low and short. In the evening the same pose feels twice as available. If you have a sore back and only one slot in the day, take the evening.

Empty stomach, as with everything face down. Three hours after a full meal, one hour after something light. Lying on your front on a full stomach is uncomfortable in a way that teaches you the rule faster than I can.

Three short lifts beat one long one, and that is true for years rather than weeks. Height is not on this table on purpose.

The forearms down version is not a beginner's compromise. I still use it myself, and most sore backs should stay with it permanently.

The cobra is a gentle extension, and gentle extension is the direct answer to a life spent bent forwards. That is why it appears on seven of the nine condition pages here, and why the caution attached to it is always about how high rather than whether.

• Yoga for neck and shoulder pain uses the low version, forearms down, with the eyes on the floor rather than the ceiling.
• Yoga for beginners over 40 keeps it at three breaths, three times, instead of one long hold.
• Yoga for weight loss and yoga for diabetes include it because it is a repeatable pose that opens the front of the body without a floor to ceiling demand on the spine.
• Yoga for PCOS and yoga for thyroid use it as the accessible chest opening in place of the shoulderstand, and yoga for high blood pressure does the same for the same reason.

It appears in the ten minute morning routine and in the seven day beginner plan, and a standing version against a wall is how it is done in the desk sequence, where nobody is going to lie on an office floor.