Is It Really The Hamstrings?

This post is focused on Acroyoga, but the information is applicable to all movement disciplines!

Quick take aways are at the bottom!

We’ve all seen it – a base with a rolled up yoga mat underneath their sacrum. The cause seems clear: their hamstrings are tight. Hamstrings originate at the ischial tuberosities – your ‘sit’ bones – and go all the way past the back of your knee. To be in an L-basing position this requires the hamstring to be lengthened across two joints – the hips and the knee. So it stands to reason that if a base is having trouble attaining the position it’s probably a muscle-length problem and if you prop up the sacrum you’re effectively un-bending the hips slightly to put the hamstrings on slack. Great! Problem solved. Or is it??

What we think of as a 'normal' stacked 90 deg. hip flexion position for bases in L-basing

The addition of the bolster under the sacrum effectively increases the angle at the hip - or, to put it in terms of hip flexion - there is now LESS hip flexion than before

This line of reasoning makes sense but might be too simplistic. Let’s first explore the issue of length:

Length vs. Range of Motion

Muscles are made up of many contractile protein-machines lined up in series. There are a certain number of these lined up in any given muscle cell and the muscle can’t get longer than the combined full length of all those proteins tied together. In general most of our muscles are long enough for normal ranges of motion (I'm looking at you, contortionists! :) ).

So instead of talking about muscle length what we really need to talk about is ‘range of motion’. This is the amount of motion a joint is capable of achieving. So for bases, instead of looking at ‘hamstring length’ we are looking at ‘hip flexion range of motion’. More specifically we are looking at ‘hip flexion with combined knee extension’ to indicate that the knee is straight while the hip is bending.

At this point many people will say ‘but the hamstrings are the only thing in the back of the leg that can limit hip flexion and knee extension, so it’s the same thing!

I beg to differ.

The back of the leg has many other things that can affect range of motion:

· Nerves such as the sciatic nerve

· Arteries such as the popliteal artery as it passes behind the knee

· Deep fascia of the thigh

And stressing all of these can feel like a 'stretch' that we normally associate with muscles.

The 3 muscles that make up the 'hamstrings': biceps femoris, semimembranosus, and semitendinosus

Nerves, arteries, veins, and lymphatics in the back of the thigh. Notice how many of them follow the same path as the hamstrings!

These structures escape our notice most of the time and it is a burgeoning field of research. The nerves, in particular, are being investigated as a limit to range of motion. Dubbed ‘mechanosensitivity’ this approach looks at not only the length of muscles, but rather length of the nerve and surrounding fascial sheath as a potential limit to range of motion. This gets into a new conversation regarding what ‘pain’ really is. That is beyond the scope of this article, but suffice it to say that pain is something your brain creates when it determines there is a threat to your safety (it’s way more complex than that).

Therefore, if our range of motion is limited for hip flexion we need to investigate what potential causes might be signaling our brain to a threat. There are lots of options, but here are a few:

1) Previous injury has caused scar tissue build up that might tear more muscle if stretched - this scar tissue could be in the muscle or even in the nerve itself. Effectively this scarring can 'anchor' the muscle tissue to surrounding structures, prohibiting normal movement and making it feel like the muscle itself is tight.

2) The brain does not feel 'strong' in this end-range position and thus 'knows' it might fail in a movement causing injury (this is a big one!).

3) Nerves or their fascia are being stretched, triggering some stretch receptors that the brain interprets as a red flag (nerves really don't like being stretched - or, rather, your brain doesn't like it).

4) Reduced abdominal control or strength can result in an 'anterior pelvic tilt' when the legs get loaded - effectively pushing the ischial tuberosities AWAY from the knees, making the hamstrings feel like they're getting stretched more. In order to reduce strain on muscles and other structures the pelvis can have a slight 'tuck' to it, effectively bringing the two ends of all these structures closer together - but this takes coordinated deep abdominal capacity.

This last point deserves a bit of attention. Let's look at an image:

'Tucking' the pelvis brings origin and insertion of muscles that cross the back of the hip closer together while letting the pelvis tilt the other way makes it worse

This graphic shows that a pelvic 'tuck' or what we call a 'posterior pelvic tilt' can reduce strain on structures that cross the hip by effectively bringing the pieces closer together. The structures that connect to the front of the pelvis and can pull 'up' on the pelvis to cause that posterior tilt are your abdominals! This doesn't mean we should all be basing with a full posterior tilt all the time, but knowing how the anterior tilt can mimic a feeling of tight hamstrings is important.

So what is the point of all this discussion?

If you or a base you know has a consistent problem with hamstring length it is important to identify what is really going on. Maybe the hamstrings are truly short - it's certainly possible - but maybe the issue is neural tension or mechanosensitivity or maybe it is a lack of abdominal control - these issues are treated VERY differently.

If you want to explore this with a professional reach out! You can contact me by emailing info@smartmovementpt.com or set up an appointment HERE. If you do not live near me in the Bay Area I do tele-visits utilizing video chat to discuss all of this and provide analysis and coached exercises in addition to in-person visit options.

-Dr. Jaimie Harrow, Physical Therapist