Ardha Matsyendrasana (Half Lord of the Fishes Pose)

Ardha Matsyendrasana is the seated spinal twist. Ardha means half, and Matsyendra, the lord of the fishes, is a figure in the yoga tradition after whom the full pose, Matsyendrasana, is named. This is the half version, and the half version is what almost everybody practises: the full pose is a considerably more complicated arrangement of the legs and is not on this site's list for a beginners' class.

It is not a pose made with the arms. The hand against the knee and the hand behind the hip are there to hold the position the trunk has already reached, and using them as levers is the mistake that gives twists their bad name. A twist is made by the muscles of the trunk rotating the spine, one segment at a time, from the bottom up.

It is also not the same thing as Matsyasana, the fish pose, despite the shared reference to fishes. Matsyasana is a reclining chest opener with no rotation in it at all. The names are similar and the poses have nothing in common, which is a good reason to learn the Sanskrit properly rather than the translations.

Where it belongs is at the end of the seated group, after the forward bends, and it is often the last pose before the finishing rest. It goes well after Janu Sirsasana and Baddha Konasana, using the same blankets, and it is one of the few poses that is genuinely useful in a chair, which is why it earns a place in the desk sequence.

Every twist worth doing follows the same order, and this pose is where the order is learnt.

Lift. Breathe in and lengthen upwards through the sides of the waist. A spine that is compressed or rounded has very little rotation available, which is why the person who slumps and then wrenches gets almost no turn and a good deal of strain. Sitting on a blanket is part of the lift, not an alternative to it.

Turn from the bottom. Breathe out and rotate, starting at the base of the spine and travelling upwards. The lumbar spine has genuinely limited rotation, by design: most of the turn in a healthy spine comes from the thoracic segments, the part behind the ribs, and that is the part a desk life stiffens. Thinking of the turn as travelling up from the waist rather than starting at the shoulders is what recruits it.

Head last. Turn the head at the end and only as far as it is comfortable. The neck rotates more easily than anything else in the spine, which is exactly why it overturns: it gives you the sensation of a deep twist while the middle of the back has hardly moved. Anyone with cervical spondylosis, and that is a great many adults, should keep the head facing forward and let the turn happen below the shoulders. The same rule runs throughout yoga for neck and shoulder pain.

• Both sitting bones evenly weighted, always.
• Arms hold, never lever.
• Lengthen on each inhalation, turn a little on each exhalation.
• Unwind in reverse order: head, chest, then the base.

Two things are commonly said about this pose, and they deserve different treatment.

The first is that it is good for the back. That is partly true and needs a caveat. Rotation is a movement the spine is built for and rarely gets, and restoring it usually feels excellent. But forceful rotation of a loaded lumbar spine is also one of the positions an irritated disc likes least. The Cochrane review of twenty one trials and 2,223 participants in chronic low back pain found small improvements in back related function from yoga compared with no exercise, and found increased back pain to be the most commonly reported harm, with no serious side effects reported in any trial. So: gentle twists, from a lifted spine, without levering, are worth having. A hard twist on a bad back is not. If pain is present today, use the lying version with the knees on a cushion and read yoga for back pain before anything else.

The second is that twists massage the internal organs and improve digestion. This is said everywhere. What I can tell you honestly is that the pose compresses one side of the abdomen and then releases it, that many students report it settling their stomach, and that I have not found trial evidence that a seated twist changes digestion. I would rather say that plainly than repeat a claim I cannot support. What is measurable is breathing: this pose is part of yoga modules in which lung function improved substantially, as described in the benefits above, and the ribcage movement a twist demands is a reasonable explanation for part of that.

Where the pose does something I can vouch for from four decades of classes is the outer hip and the back of the pelvis. A great many people who arrive complaining of the lower back are stiff there rather than in the spine, and this is the pose that finds it.

Twists are held for a moderate time and repeated, rather than held for minutes on end. The rotation goes as far as it goes within a few breaths.

Daily is fine and the chair version can be done several times a day at a desk without any warming up, since nothing is loaded. Twisting first thing in the morning, before the spine has moved at all, is the one time I would keep it gentle.

Late in a practice, and after the forward bends rather than before them. A useful seated order is Baddha Konasana, then Janu Sirsasana on both sides, then this twist on both sides. All three use the same blankets, so nothing has to be rearranged.

The counter pose is a symmetrical forward bend: Paschimottanasana for a few breaths brings both sides back to the same length, which is what a body wants after being asymmetrical twice. If forward bends are not for you, sitting straight in Dandasana for five breaths does the same job less thoroughly.

Then finish. A few minutes of Savasana after a twisting practice is worth having, and the twist is also a good last pose before sitting for breathing, because it leaves the spine long and the chest open. If you are heading straight into Nadi Shodhana, do the twist first.

The other use is at a desk. The chair twist takes thirty seconds, needs nothing, and is the single most useful thing I can suggest to somebody who sits for nine hours. Twice in a morning and twice in an afternoon, and the difference by Friday is noticeable.

Twists are safe when they are made properly and they are one of the easier poses to make badly, so the modifications matter.

• An active back problem, a disc or sciatica. Do not twist a loaded lumbar spine hard. Use the lying version with the knees resting on a cushion, keep it shallow, and see a doctor before returning to the seated pose.
• Spinal surgery or a fusion. Ask your surgeon. Rotation is the movement most often restricted afterwards.
• Pregnancy. Use the open twist, turning away from the bent knee, keep it shallow, and ask your doctor or midwife.
• Knees and hips. Keep the bottom leg straight rather than tucking the heel in beside the hip. After a hip replacement, ask the surgeon about crossed leg positions.
• Neck. Head facing forward. Cervical spondylosis is common and the neck is where a twist is most easily overdone.
• Over forty and coming back to movement. Chair twists for a month, then the floor version with a straight bottom leg, and read yoga for beginners over 40.

If you want somebody to tell you whether your twist is coming from your spine or from your arms, come to a class and be watched. It is obvious from outside and almost impossible to judge from inside, and a first class is the easy way to find out.