Simply Pulling It All Together
We now know from the previous post that "no one runs until they fall," but surely that can't be all there is to it. Well, there is one more thing. Let's pull together the all remaining coaching components attached to running form and find out precisely what it is. Keep in mind that...
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." -- Antoine de Saint-Exupery
Active Knee Drive
Even within the inertia of the conventional wisdom, that is, that running is a result of muscles' efforts, disagreement with regard to knee drive stirs up further confusion. Some describe the swing leg recovery phase as reflexive, which it is. The thigh, when left to its own function, simply rotates around the hip in synch within the runner's stride. Others advocate strong volitional hip flexion, but still argue over whether it's an upward or a forward drive, and what final purpose it's serving. Does it add to stride length, increase horizontal speed, or just result in greater vertical oscillation?
To be sure, some runners flex at the hip quite a bit, some don't. In fact, the previous "World's Fastest Man," Michael Johnson, was known for, among other stride anomalies, low knees -- anathema to sprint culture. Go figure.
So, "active" knee drive is a variable. What's more, because the knee can only trace the arc of a circle, since it hinges at the hip joint, any notion of forward or upward knee drive is imagined.
Paw Back, Foot Drag
Common opinions on the propulsive phase of running include explanations like...
"The extension of the hip is where the power comes from, not from pushing with your toes or other mechanisms which are commonly cited. The hip should be thought to work in a crank like or piston like fashion. This speed and degree of hip extension is what will partially control the speed. A stronger hip extension results in more force application and greater speed, thus how powerfully and rapidly the hip is extended helps control the running speed." -- Steve Magness
And:
"[With paw back, you] help propel your body forward so that your center of gravity is as far forward as possible prior to the push-off." -- Michael Yessis, Ph.D.
And:
"[As per Sir Isaac Newton,] in order to create horizontal propulsion, we must pull straight back against the ground instead of pushing down into the ground ... [which] involves pivoting the leg backward from the hip with the entire leg as a fixed unit." -- Ken Mierke
So, as far as I can tell, the gist here is that the runner should try to pull himself across the ground with great muscular contractions. Problem is, the posterior horizontal ground force always remains below bodyweight, meaning, as per Newton's Third Law -- equal and opposite -- that that sort of horizontal acceleration just doesn't add up. What's more, the proponents of foot drag or paw back seem to turn a blind eye to the reality of the runner's GCM actually bouncing from stride to stride, and swinging around its support on the ground (as described in Pose/Fall). Actions such as paw back and foot drag can certainly be introduced into a running stride, but in general, runners -- including Usain Bolt, and you, too -- can be seen running perfectly well without such variable affectations.
Push-Off
Though it's an illusion, typical pictures of runners sure appear to be powerfully launching themselves forward stride by stride.
An Apparent Push-Off
Here's one explanation...
"The key action that occurs in the push-off is ankle joint extension. Push-off is not, as commonly believed, caused by the glutes and hamstrings being involved in hip joint extension or the quadriceps driving knee joint extension. Observe the ankle joint ... and you can see it goes through a substantial range of motion." -- Michael Yessis, Ph.D.
Now, here's another.
Recall the pie slice range of fall from 12:00 to 12:04 -- any push can only be upward. Further, at the point of greatest apparent push, vertical ground forces have dropped below body weight, and the "pushing" foot is, right then, being pulled from the ground. The biceps femoris is starting to bend the knee, and Achilles tendon activity reflects an elastic component rather than muscle action.
In any event, while some runners do try to push into the ground, and others just leave their foot there for too long, the support leg may indeed straighten at the end of ground contact. This certainly looks powerful and Puritanically significant, effort-wise. But a push only hinders the runner by preventing him from changing support in a timely manner, and burdening his mind and body with misdirected attentions. Since many elite and recreational athletes -- and skilled Pose runners -- release the ground with a bent knee and a neutral ankle joint, the so-called push-off is yet another variable.
The Last Invariable
But we're still stuck to the ground. How do we complete the stride and "Just Let Go and Run"?
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