TO PUSH OR NOT TO PUSH?

"To be or not to be? This is the question" This is how the push off problem looks for many people participating in this thread on the Pose Tech running forum. This reminds me of the Russian revolution, where everything was divided into two extremes: either you are with us or against us. Fortunately the world doesn't exist in this polarized reality, but on the opposite, it exists as a cooperative, integrated system, where everything can have its own place. One of the best examples is the third law of Newton: every force has an equal and opposite force, both existing at the same time.

So what is there about the push off that we couldn't accept or we should accept? Does it exist, or it doesn't exist? Neither is right, but neither is wrong, too! How could it be, you would ask? Yes, sometimes it is difficult to accept this kind of reality, but whether we want it or not, the reality still exists, and the main thing is to understand this, then it is easier to accept it.

What should we understand there? Basically, a very simple thing that push and pull coexist in the same system of movement, sometimes simultaneously, sometimes separated by a fraction of a second. All our movements contain both pull and push and it is very difficult to see whether we are pushing or pulling and for what purpose. In running push-pull relations are hidden, camouflaged by a seemingly obvious presence of push off, so obvious that there is almost no reason to question it.

But questions are there: do we have a push off and do we need to do push off? The answer to the first question is positive. We have a push off, and the sport science received a tremendous number of force platform data confirming that there is a vertical and horizontal components of the ground reaction force. But does it mean that we got the answer? This movement is not as simple as it seems. There are two kinds of movements, which are happening here and only one of them have to be produced by our voluntary muscle contractions, by our muscle efforts. The other is not. The question is which one? What are we supposed to do and what not?

The answer seems to be very obvious: we have to push off our body vertically and horizontally, as well, up and forward, in order to run. The force platform data seems to confirm it. But what they confirm is the third law of Newton and our desire to move forward. At this point we have to use our logic and understand what we are doing and what is actually happening. What we are doing is of primary importance and what is happening is secondary. So which is what? We have several movements to look at: the body's GCM vertical and horizontal displacement and the foot leaving from the ground after the body left the state of balance or support.

From this short list we have to choose what we'll be doing, where our focus will be. Vertical displacement in running happens by utilizing muscle/tendon elastic property, which lifts the body just 4-6 centimeters above the ground, just enough to shift the body weight from one support to the other. This data was found in all ranges of speed and distances of elite runners. Any efforts over this need would mean rising the GCM against gravity and wasting energy. R.Margaria (1976) found that the GCM vertical displacement in running doesn't go higher than an erect standing position of the body, which could be interpreted as the best position of the body to fall forward and down, get muscles/tendons loaded and stretched, then return this energy for moving body up to the same height.

We don't need to do it by voluntary muscle efforts, all we need to do is to release the elastic property to do the work. While this happens the body is moving (rotating) forward by gravity force. We just need to keep the body geometry (Pose) right to allow gravity lead this movement. What we are still missing is where do our muscular voluntary efforts come in? We need them to keep the body geometry and pull the foot from the ground up, because it is the only part of the body left on the ground and therefore needs to be moved by our own efforts in order to keep up with the running away body.

This happens in the fast and slow run and in moving from the starting blocks in sprinting. It's all the same. Our muscles/ tendons are loading in the faster run more, because of the quicker change in both vertical and horizontal directions. Then our muscles are responding (reacting) to these requests. The primary request is falling forward, but then the change of support comes into play, so we need to remove the body weight from support and after that the foot from the ground. This is the running cycle.

So to sum it all up, there is push off in running, but it happens by itself. Muscular elasticity does it for us and we actually use our voluntary muscular efforts just to hold the body right. That's it.

Dr.Romanov