Why can’t we all do the box splits?

In class we will be exploring the balance between flexibility and strength, and why it is that both of these elements need to be present in our practice to maintain good health. Rather than bamboozle you with lots of technical jargon in class (though I will be touching on some of this stuff so read on if you want to get a gold star),  here is an overview of what science can teach us about stretching. Strangely all of these techniques get utilised in yoga though the anatomy that underpins these techniques would not have been understood at the time that the yoga asanas were created. As a pragmatic Taurean science orientated kind of a gal, it gratifies me when science explains and concurs with the teachings of yoga.

So, here goes, why do we need to stretch and how, and can science illuminate this aspect of our yoga practice?

Now most of us cannot do the box splits, correct? And yet if we were unconscious there is a chance that our body could actually be arranged into that position quite easily. (Please do not try this at home…….oh dear God!) In my murky past when I worked as  a nurse and spent some time in the operating theatre, I often saw the surgeons have to manipulate people’s bodies into some pretty intense positions, especially during orthopaedic surgery, positions that I was fairly sure those people would not be able to do when they were awake. It also explained why people were often very sore after a surgery, especially such things as hip replacement: patients would often say they felt like they had been in a boxing match or been hit by a car once they woke up and the initial pain killers had worn off……having watched the operation I could see why!

As we age on the whole we become stiffer, and usually when we start yoga (with the exception of those of us who have hyper mobility issues) we are alarmed at how inflexible our bodies have become. Students are often quite mournful and annoyed with themselves at the state they feel they have ‘let their body get into’. I do find it quite alarming though that these days I am seeing children as young as seven or eight who have lost the joyful exuberant natural flexibility of their childhood already, partly due to the fact that we start training them for life at an office desk as early as three now when they start pre-school and have to sit on a chair. Don’t get me started on why chairs are bad for us all, I digress….

…so why as adults are we not so bendy? Think of the soft velvety hide of a newborn calf…..now think of an old leather shoe cracked and stiff……a large part of this process is ageing and dehydration. As we age, even if we stay pretty active our  muscle fibres begin to adhere to each other, and slowly get bound up with connective tissue (in this case fascia) and become more and more unyielding. Stretching can slow this process of dehydration by stimulating the production of tissue lubricants, and helping to break the muscle fibres free of any fascial restrictions by not only stretching the muscle fibres but also the fascia that tightens around them. And here is a big clue as to what is possibly restricting out ability to stretch.

Muscle fibres can be stretched to approximately 150 percent of their resting length before they tear. This should enable muscles to move through a wide range of motion, sufficient for most stretches—even the most difficult yoga asanas. But most of us, me included, do not have that range of movement.

One major school of scientific thought on what actually most limits flexibility  focuses not on stretching the muscle fibres themselves but on increasing the elasticity of connective tissues, the cells that bind muscle fibres together, encapsulate them, and network them with other organs; our ‘internal knitting’ if you will. If  you have ever prepared meat and pulled an animals carcass apart (sorry fellow vegetarians but it is a good way of seeing fascia in action, as is watching human dissection if you have the stomach for it)) you will have seen the almost transparent very thin layers of material (fascia) between and around the flesh (muscles).

So lets look at this connective tissue stretch idea…

Tendons don’t stretch, ligaments only a little but fascia can and will stretch. Muscle fascia is the third connective tissue that affects flexibility, and by far the most important. Fascia makes up as much as 30 percent of a muscle’s total mass, and it accounts for approximately 41 percent of a muscle’s total resistance to movement. Fascia is the stuff that separates individual muscle fibres and bundles them into working units, providing structure and transmitting force. Interestingly, fascia stiffens when you are shocked, either physically or psycho-emotionally, which  is why we shake after a shock to re-loosen our fascia (so sedatives given to stop shaking prevent the fascia from softening…)

Many of the benefits derived from stretching—joint lubrication, improved healing, better circulation, and enhanced mobility—are related to the healthy stimulation of fascia. Of all the structural components of your body which limit your flexibility, it is the only one that you can stretch safely. Long holds in poses where you are neither forcing pushing or bouncing give the fascia time to stretch. If you hold poses for shorter periods, you get a nice sense of release, but you aren’t necessarily going to get the structural changes that add up to a permanent increase in flexibility unless you hold a stretch for between 30 seconds and a minute. (I must add an aside here, if you get any sensations such as tingling, pins and needles, ‘electric’ jolt type pain, any weird sensations such as crawling or sensation radiating into places far away from where you are stretching you need to back off, as these are signs that the nerves are being stretched and if they sustain more than an 11% increase in length they lose their oxygen supply and could be permanently damaged, in short nerves do not like being over-stretched!)

So you can see why the longer held poses that we do in class can be beneficial, because they give the fascia time to stretch and release, and this in turn will free up the movement of your muscle fibres giving you increased range of movement as well as the other benefits of stretching already described.

The second scientific school of thought addresses how the  autonomic (involuntary) nervous system halts our flexibility.

So how could our nervous system be limiting our flexibility? There are three main ways in which it can: the stretch reflex, proprioceptive neuromuscular facilitation (PNF for short and if you manage to come out with that phrase in class this week I will give you a lollipop) and reciprocal inhibition.

The Stretch Reflex

OK back to the box splits theme, if you are walking along an icy pavement, and you slip and one leg goes one way and the other leg the other way very very quickly, how come we never end up in the box splits?  Because, as soon as your feet start to splay apart at high velocity your muscles are fired into action by the nervous system, and by tensing quickly they draw your legs back together and regain control. What just happened in your nerves and muscles?

Every muscle fibre has a network of sensors called muscle spindles. They run perpendicular to the muscle fibres, sensing how far and fast the fibres are elongating. As muscle fibres extend, stress on these muscle spindles increases.

When this stress comes too fast, or goes too far, muscle spindles fire an urgent neurological “SOS,” activating a reflex loop that triggers an immediate, protective contraction. And that’s why most experts caution against bouncing while stretching. Bouncing in and out of a stretch causes the rapid stimulation of muscle spindles that triggers reflexive tightening, and can increase your chances of injury. (Again an aside: there is a place for very gentle oscillating in stretches for those people with nerve damage, but that is another topic entirely)

Slow, static stretching also triggers the stretch reflex, but not as abruptly. That’s why improving flexibility through static stretching takes a long time. The improvement comes through slow conditioning of your muscle spindles, training them to tolerate more tension before they apply your ‘neuro-brakes’. So we can see why going into poses very slowly and smoothly, and perhaps not working immediately to the edge of your stretch but easing in slowly and waiting for the feeling of release before inching a little deeper into the pose would overcome some of this largely protective stretch reflex. And be careful coming out of poses too, this is when people tend to be less careful and you are vulnerable as you release your stretch.

Proprioceptive Neuromuscular Facilitation

This technique came about as a physical therapy I believe in the 1940’s as part of a programme to help people suffering from some kinds of paralysis. The PNF method manipulates the stretch reflex by having you contract a muscle while it’s at near-maximum length. In a seeming paradox, contracting the muscle and then relaxing it again actually allows it to lengthen.  If you engage and then release your muscle fibres in this way, you will probably discover more comfort in a stretch that was near your maximum just seconds before. Now you’re ready to open a little more, taking advantage of a momentary lull in neural activity, deepening the stretch. Your nervous system adjusts, affording you greater range of motion. You could use this technique in something like single simple leg raise (supta padangustasana). If you can find a doorway in your home (or office go on I dare you) where you can lie on the floor with one leg through the doorway on the ground and the other leg up the wall, that would be ideal (check that there is another doorway that allows you to work on the other leg!) and have a belt around your lifted leg. So your working leg, the one up the wall is being stretched, so sit with this for a while (the leg may not be straight and that is OK) then you press your heel into the wall quite hard for a count of 20 seconds, then release the contraction take hold of the belt and see if the leg will give a little more into the stretch. This is PNF in action.

Reciprocal Inhibition (R.I)

R.I is a built-in feature of the autonomic nervous system that allow our muscles to release and extend. In essence this is what it means:  whenever one set of muscles contracts,  R.I  causes the opposing muscles  to release. Try it. Stand in front of a hard surface like a desk or counter top, make and  gently press the edge of your hand, karate-chop style, onto the surface. If you touch the back of your upper arm—your triceps muscle—you’ll notice that it’s firmly engaged. If you touch the opposing muscles, the biceps (the big muscles on the front of your upper arm), they should feel relaxed. The best type of flexibility combines improved range of motion with improved strength. Let’s call this ‘intelligent’ flexibility. If you only increase your ‘mindless’ flexibility (what I call flopping into poses) without developing the strength to control it, you make yourself more vulnerable to a serious joint injury. This is why it is important to engage muscles as you stretch and to work with microbends in the joints if you are hyper mobile.  It is extremely important to develop strength in the muscles you are stretching. So an example here would be in a a pose such as an asymmetric forward fold (parsvottanasana: legs on train tracks one leg forward one leg back hinge over at hips, stretches back of thigh in front leg)) in which I ask that you maintain some contraction in the front of the thigh (quads) of the front leg not only to protect the ligaments in the knee from being potentially put in harms way, but to activate R.I for, if the quads are contracting, the hamstrings will release more improving flexibility. (Another aside: this is an actively debated issue in the yoga world and other schools of thought in yoga absolutely disagree and think that is OK to relax into these stretches, I guess we all have to gauge for ourselves what makes sense to us within the exciting laboratory of our own human body)

So there you have it, a very long answer to the question why do we need to stretch and how, and can science illuminate this aspect of our yoga practice?

Don’t worry there won’t be a test in class…or will there!?




What Science Can Teach Us About Flexibility by Fernando Pagés Ruiz

The Anatomy of Hatha Yoga by David Coulter

Playing it Loose by Hillari Dowdle


  1. I am havung trouble understanding the doorway stretch. Do you have a photo, diagram or video so that I can see what you mean? You clesrly have lots of knowledge to pass on I would be very grateful.

    Thank you,


    1. Hi Imogen,
      so here we go. Find a wall beside an open doorway. Lie yourself down on the floor so lets say your left leg is up the wall as straight as you can manage, and your right leg is on the floor and through the doorway.
      You have a belt or strap around your left foot held with your hands, and you press your left heel into the wall strongly for about 20-30 seconds. Then relax and pull on the strap to stretch the back of the left leg a little more, and hold for 20-30 seconds…does that help at all? Then find a different doorway so your right leg can be up the wall and your left leg on the floor and through the doorway and do it all again!

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