Knees: The Hinge that Twists, Causing Cringes and Torque
Our knees. One of the joints in our body that we see as most resembling a door hinge; seeing it as a joint that bends forward and backward -straight plane, sagittal movement of flexion and extension.
YET, that sneaky hinge allows for a fair amount of lateral movement and rotational movement.
Remember, all motions of our body are tri-planar — combined motion in all three planes of movement.
The knee is designed to move three dimensionally, and needs to for good arthrokinematics — optimal movement. The knee allows for more lateral and rotational movement than some deem appropriate or safe. But more on that in a minute.
The knee, through the work of the quadriceps (front thigh muscle) and hamstrings (back of the thigh muscle (and contributions of the work of every muscle below the knee and even up at the thigh), can act as a spring to load and bend, to then release the tension, aiding in the stepping and forward propulsion. Contributing to the good cause — not the primary power source.
That concept is seemingly accepted and on many levels, easy to understand.
But what else does the knee do for us?
What does the knee do for us in the swing phase of gait? When the leg is in the air?
The knee bend allows for us to recoil and retract our leg so we can advance/swing our leg more efficiently. But shortening up the lever arm/length of our limb, it is much easier for our hip and torso to advance the leg when it is bent — a simple case of physics, lowering the amount of torque needed.
With that knee bending during swing, the length/tension relationship between our hamstrings, quads, and hip flexors combine their forces to drive that knee forward.
The bending of our knee as we lift our foot of the ground combines with the hip transfer cases and torso, converting the twist of our trunk into forward drive of that leg.
But wait. There’s more.
Think of a 100m sprinter and their running form. Now think of a football player running with with ball. Their forms look different.
The sprinter has a fairly erect, upright posture (hopefully not compromising the natural thoracic kyphosis), and running in a straight predictable line.
The football player is much more crouched down. The athlete has to run fast, and at the same time, change directions, zig or zag, to avoid being tackled.
What’s going on here?
The sprinter can take advantage of the predictability of running in a straight line to capitalize on the spring loading of the muscle at the knee complex in the stance phase and recoil and forward drive of the knee in swing phase. She doesn’t have to worry about changing directions — and thusly can run uprightly.
The football player has to be really good at going fast, but must be better at shifting and twisting to change directions to keep running. A posture of increased forward hunch, a lower center of gravity, and more knee bend afford the athlete to do so.
Torque capital. Torque economy. With the increased knee bend and forward bend in the trunk, the hips and trunk are offered more degrees of freedom to move laterally and rotationally with greater leverage and power.
With more of a knee bend, more twisting and side bending can occur at the knee, but more importantly at the hips (and trunk) for power.
No, I am not expecting anyone to train like a running back necessarily. But understanding the concept of hip power and the freedom of the knee joint to laterally bend and twist is key for efficiency and resiliency.
You may notice a difference comparing a run on pavement to a run on snow, to a run on a trail.
On a single-track, undulating, climby trail, weaving in and out, up and around, the path is convoluted and uneven. The constant change of direction and shape of the ground requires our running to look a bit more like a football player than a sprinter.
A bit more of a ‘squat’ in our posture/stride affords not only a lower center of gravity for better overall balance, but also more knee bend (flexion) to increase the degrees of freedom for our hips (and foot/ankle) and trunk to move in the lateral and rotational planes:
To meet the demands and need to produce more power and torque the trail demands,
And also to actually move in the lateral and rotational planes to shift and run in the ever-changing direction of the trail — something a sprinter or pavement running does not require.
Because of the pavement’s decreased demand for balance, challenge of uneven/ever-changing ground, or continual changing of directions (bending, shifting, twisting), or running form doesn’t have to be as ‘on point.’
It isn’t right to call our running form ‘lazy’ or ‘lackadaisical,’ but that refined acuity of our stride can be decreased and somewhat lost on predictable pavement.
Pavement running introduces the ‘freedom’ of our spines and knees to run in a ‘straighter,’ more extended fashion, without the immediate, noticeable consequences if we were to run that upright (like a sprinter not a football player) on a single-track trail. On the trail, we would bounce around, lose our balance, throw off muscle timing, and increase our joint compression. On pavement, though our balance is not super-challenged, our timing is thrown off (though less severe), and joint compression is still increased (though less severe).
Notice the difference when running on dry vs wet/snowy/icy pavement. Our centers of gravity are higher up, we run ‘taller,’ and slip around more when we don’t account for the inclement surface conditions.
With each step, our knees grant freedom for our hips (and foot/ankle) and torsos to navigate the lateral and rotational planes for increased balance, muscle timing, torque and power output each step.
Our knee drive in the swing phase of running translates rotational and lateral forces of our hips and torso into forward propulsion.
But why do some people that run have huge quads? Does that mean they are less efficient in the lateral/rotational power planes and use a compensatory strategy that works but isn’t necessarily the way it is designed?
Could that be likened to drag-racing a station wagon?
In a way, yes.
What about calf muscles?
What about them?
© Dr Adam Fujita