Kinected: About running on hard surfaces

Whether you are a recreational jogger or a marathon runner, we all are concerned with is how do we reduce the chance of injury?

Whether you are a casual, recreational jogger or an experienced marathon runner, one issue we all are concerned with is how do we reduce the chance of injury?

One common question that comes up: does running on hard surfaces cause unnecessary pounding on the legs and will this lead to an injury, or premature wear and tear?

The conventional aphorism is that hard surfaces are hard on the body and will cause injuries to the knees and other structures.

But making this link has been proven tricky, especially considering the growing number of studies since the late 1990s that are showing that there is a complex network of systems in your body which help to mitigate the forces your leg experiences during running.

In both humans and other running animals, the soft-tissues of the leg (muscles, tendons, cartilage) act like a spring to dampen forces, much like the shock-absorbers in your car. By doing this, they reduce the vertical distance that the centre-of-mass travels, giving your body a smoother, more horizontal run.

Add to this fact that, through a complex feedback circuit between your muscles and your central nervous system, your legs adjust the length and frequency of the stride and the degree of bend in the joints at the hip, knee and ankle to dampen forces.

By adjusting these factors, we are able to further adapt to the surface we run on – and this property is commonly called “leg stiffness.”

Researchers have found  that leg stiffness will increase when we are on softer surfaces (bark-mulch trails or rubber track) and it will decrease when we are on harder surfaces.

What happens is that when we run on roads, we naturally and automatically  alter our stride and keep a little extra bend in our joints. We also tend to land more towards the forefoot.

Some people call this running ‘softly.’

When we do this we are transferring the extra force of the running surface to our muscles and soft-tissues.

But when we are running on soft surfaces, joints straighten, and the bones take more of the load.

Since softer surfaces produce a stiffer leg with longer stride lengths and frequencies, they tend to produce faster running times, which is why most racing events are done on tracks that use a rubberized surface.

Note, though, that as the surface continues to get softer (like sand) there is a point of diminishing benefit because the surface is so pliable that more energy is being put in to overcoming the loss of what’s called ‘ground reaction force’ and, thus, speed and running economy suffer.

The interesting thing is that humans and running animals can alter their leg stiffness automatically within one or two strides, as they change surface from hard to soft or vice versa.

The upshot of the topic so far is that hard surfaces don’t automatically cause injuries – we adapt to the type of surface, whether we realize it or not.

To be continued.



Kerry Senchyna holds a bachelor of science degree in kinesiology and is owner of West Coast Kinesiology.


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