The Knee is responsible for the majority of energy absorption during the running cycle, while the hip is responsible for the greatest energy generation. Basically, this tells us that strong hips (specifically hip extensors, gluteals) will increase the ability to run fast. It also tells us that knee injuries from repetitive loading are likely to be the greatest cause of exercise cessation for runners.
With running having the highest injury rate of any sport, minimising these running related injuries makes sense.
So how can we minimise the force absorbed at the knee, while not losing any of the force generated by the hip?
Firstly, what is force absorption? Try this. Stamp your foot on the ground. The force between the ground and the sole of your foot is called a ‘ground reaction force’. There is also a force that is transmitted through your leg to your ankle, knee and hip. These are called ‘joint reaction forces’. If we can minimise these joint reaction forces, we can minimise running related joint injuries.
Think of it like a car’s shock absorbers. The springs ‘dampen’ any bumps in the road to increase the smoothness of the ride. Running is the same. The shock absorbers in this case however, are the muscles and how they act over the joints.
The human foot (with a lot of help from Natural Selection) has evolved two arches – bone supported by ligament:
- A transverse arch runs from one side of the foot to the other.
- A longitudonal arch runs the length of the foot.
It is this longitudonal arch that plays such a wonderfully effective roll as a shock absorber. In fact, this analogy is apt, because just like a shock absorber, the longitudonal arch of the foot has two roles:
- It absorbs shock to reduce impact when the foot contacts the ground (also called ground reaction force or GRF).
- It stores this energy to then increase the body’s ability to generate power – like hitting your teacher with a rubber band from across the classroom.
So the foot is beautifully evolved to do what it is that it does. Minimise injury and increase performance. The naked human foot is really really good at… well… being a foot!
Modern running shoes have lessened this shock absorbing effect by making it ok to run on your heels.
By changing our running technique, we are effectively ‘changing the shock absorbers’ and dissipating the joint reaction forces before they get to the knee. Your ride becomes smooth.
Effective running involves running with a forefoot or midfoot strike, rather than a heel strike. There’s more to it, but that’s a good start. So even if you change nothing else, try running on the balls of your feet.
