‘Gravity falling’

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By Keith Bateman and Heidi Jones

Some people have been told that they should constantly fall forwards when running and that gravity will provide a proportion of the forwards motion. This advice probably comes from a desire to correct the fact that most people land off-balance and leaning backwards causing unnecessary braking and so tilting more forwards will help to reduce braking. If you have tried this and felt the falling sensation propelling you forward this is merely a false apprehension caused by the fact you are not leaning back and braking as much as you were. Sadly the feeling of propulsion is just an illusion.

The proposition that gravity somehow pulls you forwards contradicts the known physical laws of motion. Gravity acts downwards (or, more correctly, towards the centre of the Earth). This means that, as you fall, your centre of mass will be drawn downwards towards the ground. Not forwards, not backwards, just down.

An orbiting satellite does constantly fall towards the Earth but its momentum means it is also moving away from the earth at the same rate that it is falling which means it never reaches the ground.

So why if gravity is pulling you down can’t it pull you forwards as well? Imagine if you stood vertically on ice skates and fell forwards keeping your body stiff like a plank, the top of your body would fall forwards, but the lower half of your body would slide backwards and “out from under you”. For anyone who hasn’t ice skated you may have experienced the reverse situation. You may have slipped on a wet bathroom floor and your feet shot forwards while your upper body fell backwards and you landed on your behind. Despite the sensation of falling backwards you weren’t propelled backwards, because your feet moved forwards. In other words, your centre of gravity just moved downwards and your body as a whole neither moved forwards or backwards.

If your feet slide then, if the top half of your mass moves forward the lower half of your mass must move backwards to compensate. If you were wearing non-slip shoes instead of ice skates in the example above then your centre of mass would move forwards but in this situation you would be pushing against the ground through your legs and feet. And of course you would not be in a position to continue running!

So while people seem to feel as though they are being propelled forward by gravity when they are running it is just a misleading sensation. The laws of physics dictate that gravity does not move your centre of mass forward, and hence cannot give you any forward propulsion. It just moves you straight down.

If you still feel yourself falling forwards and you are not accelerating, falling over, or running into a strong wind or downhill then it is just your head and torso that are forwards with these being supported or balanced by the lower half of your body.

You must be either:

  • bent over at the waist and supporting your head and torso with an over-stride (foot landing too far in front of you)
  • kicking your feet up behind you in order to act as a counterweight to your too-forward torso.

Neither of these situations represents a good running action.