GRAVITY ROLE IN RUNNING

People have been thinking about the role of gravity in movement throughout the entire time of recorded history. Some of these thoughts were very insightful, as those of Leonardo da Vinci, for example, who considered the body weight to be the major cause of human (and animal) movement.

Newtonian mechanics allowed us to see gravity as the main component of interaction between physical bodies and calculate different parameters of this interaction. Modern times mechanics applied to human movement, called biomechanics, got developed to a very sophisticated level and helped us to understand human movement better and successfully apply this knowledge to our everyday practice.

Nevertheless there are some questions here which are still unsolved and became topics of heated discussions. One of them is the question of gravity's role in running. According to classical mechanics and modern biomechanics, gravity is neutral in horizontal direction of movement in running, and this postulate was never challenged until now. But today this paradigm doesn't fit with many facts emerging both from everyday practice and science research.

The predominant explanation of horizontal propulsion in running is the one attributing it to the work performed by muscles and tendons. This seems to be an obvious assumption from available science data and just from common sense. But knowing that gravity is the most powerful mechanical force on Earth, it is difficult to avoid thinking of its influence on everything, including any moving or running body as well. It can't be absolutely neutral, there should be some ways to tap into this powerful source of energy and use it to our advantage and maybe incorporate it into running mechanics as a propulsive force as well.

The confirmation for this was found in space travel, during exploration of the Moon. Scientist, Rodolfo Margaria, described the astronauts' experience of walking and running on the Moon as surprising because they couldn't use their usual form of these movements as on Earth and had to change it to skipping and hopping. They still had the same muscle force as on Earth and the same support on the ground, but they couldn't run and walk in the same bipedal manner. It means that they couldn't make a push off. The Moon's gravity force is only 1/6 of the Earth's gravitational force, which seemingly immediately "eliminated" forward propulsion from muscle work. Here the question arises, why couldn't the muscles perform their task? Isn't it easier to do it in reduced gravity?

There is another question to be considered here which arises from a fact from running biomechanics known as "extensor's paradox". The essence of this "paradox" is that any electrical activity (EMG) of powerful front thigh muscles ceases during support time from the midstance to toe off. So, what we thought was the powerhorse of running - propulsive efforts of the push off, doesn't exist in reality, and is basically a myth, which we worship and try to "confirm" by our wrong perception.

It is easy to check it through a simple experiment. Try to move forward from the Pose stance and you'll see that it's only possible when the body leans forward. To continue this discussion, we'll present some science data confirming the discussed logic of the role of gravity in running.

DrRomanov