The knee (as joint example for Big Rule #2)

Let’s take a look at the knee whilst considering the Second Big Rule of Motion (pp.56 What The Foot?) “Joint’s ACT: Muscle’s REACT” and take a look at the muscle system that is perfectly set up to react to the knee’s in motion movement.

The knee finds itself between the three dimensional ankle and the three dimensional hip. The knee is not technically a 3D joint – more 2D; or as I teach my level 1 students a one dimensional joint for ease of understanding.

That single dominant dimension is the Sagittal plane. The knee flexes and extends. Twice per stride, once in closed chain and once in open chain. Since the dominant motions lie above and below we have to assume optimal movement at both the hip and ankle in order to get what we want at the knee.

A closed chain knee flexion occurs when the foot is flat on the floor with the ankle dorsiflexing.

A standard knee flexion adds tension to the following muscles in the Sagittal plane at the knee:
Primary

  • Distal fibres of rectus femoris
  • Vastus medialis, intermedus and lateralis

Secondary

  • Proximal fibres of biceps femoris; semi-membranous and semi-tendinosus
  • Proximal fibres of adductor Magnus

This of course is providing the standard accompaniment to a closed chain knee flexion are present above and below: ankle dorsiflexion and hip flexion/anterior pelvic tilt.

Tension in the muscle is where my interest lay. You may know it as lengthening or stretching, when in essence it is eccentrically loading (or locked in a long position in cases where the joint position is fixed). In any joint motion there will be excess shortening of some muscle tissue and excess lengthening in others. Excess is simply a way of observing more than is desired. Excess lengthening suggests the muscle accesses a state longer than it’s resting length while excess shortening suggests the muscle accesses a state shorter than it’s resting length. If you stand with a single flexed knee, you are probably aware of this.

The shortening muscles in knee flexion would be:
Primary

  • Distal fibres of biceps femoris; semi-membranous and semi-tendinosus
  • Popliteus

Secondary

  • Proximal fibres of rectus femoris
  • Proximal fibres of gastrocnemius

The difference between a static posture (standing with knee bent) and a dynamic posture is obviously movement. Movement brings a whole new role and some might say complexity to muscles. Muscles that eccentrically load in movement are essentially being used to decelerate joint motion and minimise, yet allow, the body to venture away from balance, neutral or centre and stimulate a stretch reflex contraction in the lengthening muscle.

In motion, muscles lengthen to contract. The lengthening eccentric stimulus of knee flexion generates a subsequent contraction of the knee extensors and hopefully an accompanying eccentric load (lengthening) of the hip flexors and the simultaneous hip extensor activation.

Lots going on.

So in gait at the knee – in the sagittal plane – a simple knee flexion creates all that change in the tissues surrounding the knee. The reaction to a simple knee flexion is for the lengthening tissues to decelerate that motion, or control that motion to minimise over-flexion. The muscles which are lengthening at this point in time are the extensors of the knee – the muscles that will act to extend the knee. They contract concentrially in reaction to the knee flexion (the joint action):

Here we see the following muscles, those that were lengthening, now shortening to extend the knee from it’s flexed position:
Primary

  • Distal fibres of rectus femoris
  • Vastus medialis, intermedus and lateralis

Secondary

  • Proximal fibres of biceps femoris; semi-membranous and semi-tendinosus
  • Proximal fibres of adductor Magnus

and those that were shortening now lengthening:
(Lengthening to decelerate knee extension in gait)
Primary

  • Distal fibres of biceps femoris; semi-membranous and semi-tendinosus
  • Popliteus

Secondary

  • Proximal fibres of rectus femoris
  • Proximal fibres of gastrocnemius

In Anatomy in Motion we see a lot of patients with individual muscle injuries or who are advised to foam roll or localise treatment on individual and specific muscles. Firstly look again at the lists above. It highlights that in the sagittal plane, in a closed chain environment that no biaxial muscles are fully lengthening or fully shortening, but in fact tension is redistributed from the distal portions to the proximal portions of an individual movement to manage the motion of the surrounding joints.

A simple way of reorganising the muscle tensions in all muscles is simply to teach the knee (not forgetting the joints above and below) to simply flex correctly. For the the three structures, foot, knee and hip, to move in such a way that the tension is not excess in any tissues at any point in time during the walking process.

Just to promote knee flexion, with ankle dorsiflexion and hip flexion in a sagittal plane environment will bring all of the above mentioned muscles into line. This is why we follow the Second Big Rule of Motion “Joints ACT: Muscles REACT”.

Concentric stimulus

I’ve said many times that in motion there should be no primary concentric stimulus. Concentric actions are “effortful” and – when in motion – present as a result of failed eccentric load or joint positioning.

Look back at the muscles that are loaded (lengthened) in knee flexion. Muscles which attach directly onto the front of the knee load in flexion, their concentric partners will be shortening but should not be over working to do so.

A concentric muscle action has a simple goal. To kick start the muscle journey back towards centre from it’s lengthened position. The actual concentric contraction seems to last for a moment with the eccentric contraction lasting way longer as the momentum of the mass requires urgent deceleration and control. Once the concentric contraction fulfills it’s goal of bringing the joint back towards it’s midline, momentum takes over and the body lurches forwards – awaiting muscle’s on the oppsoite side to pick up the deceleration role again. The more time we spend in a concentric action, the more effort there is in our movement and the less energy we have to spend on our eccentric activity which allows us our freedom of movement.

Frontal and transverse plane at the knee

In a good healthy knee, there should be no frontal plane motion available. Observers of the frontal plane may beg to differ but once again it is the hip and ankle in the transverse plane that give the appearance of a knee that passes inside the midline. An internal rotation of an ankle coupled with a sagittal plane flexion of the knee will give any frontal plane observer a sense of a knee that has crossed the midline of the body in the frontal plane. AND it does; so it pays us to understand the muscles that are set up around the knee to help control this movement inwards to a position where it appears to have no support beneathe it.

As the leg rotates internally and is flexed towards the midline, it’s worth taking a look at the muscle’s and structures which are set up to manage it. Tension is added to the following muscles in the frontal / rotatonal planes at the knee during the closed chain gait cycle when the foot is flat on the floor:

Primary

  • Distal fibres of rectus femoris
  • Vastus medialis, intermedus and lateralis
  • Iliotibial band and TFL (hip)
  • Distal fibres of sartorius

Secondary

  • Proximal fibres of biceps femoris; semi-membranous and semi-tendinosus

The knee is truly compromised as it journeys inwards. When it stands in centre, it has the luxury of a strong pillar beneathe it (the tibia) upon which to stabilise, as it ventures towards the midline it has less and less of that luxury and must begin to rely on the muscle and ligment system strapped to it. It seems, to me anyway, that one look at these muscles and you can see that pretty much all of them must act to control any dangerous venture of the knee away from it’s midline, even the ITB and lateral quad and hamstring muscles – I know people don’t think the ITB does much, but I have to say, that in movement a) you can feel it and b) those with problems in the ITB always have issues with speed of ankle pronation and knee passing toward the midline! So again, less cadaver based science and more ‘feeling while doing’ please! Even the lateral tissues appear to have to control an inward motion of the knee. It’s that much of a responsibility.

Before anyone points out that I’m the first to say that the “Knee over Toe” discussion is moot. I’d like to agree and stress that this is another movement that we must explore and yet not access in excess. To get the knee to comfortably pass inside, the tissues mentioned above MUST be in a position to allow this movement whilst preventing an excess of it. Again, the motion of this joint in these planes means that the reactive concentric action will be one that extends the hip and knee from their flexed positions (as seen above) whilst also abducting the hip from it’s adducted position, externally rotating the hip from an internally rotated position,  and also resupinating the foot from it’s pronated position – which drove the knee inwards in the first place!

It seems there are a whole bunch of muscles set up to control these wayward movements of the body and yet the wayward movements of the body are designed to wind up the muscles for an optimal contraction. This is the deep irony as to why we focus fully on stability in a fully three dimensional and mobile structure.

Once again, working with the structures of the foot, knee and hip to promote good clean healthy movement accessing all available ranges in all three dimensions in the skeleton is your single solitary ticket to bringing all responsible muscles into line. Trust me: They WILL always react to the quality of joint motion in the joint in question. Saves chasing after the one and means you can target the many muscles involved and dynamically stabilising your system – not omitting the quality of muscles in far flung outreaches elsewhere in the body 🙂

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