When you run, you actively contract and relax your muscles. This is controlled by your brain and is one aspect of running. The other aspect is the passive running mechanics. Passive running mechanics aren’t something you can directly control while running, but they can become optimally developed through the right methods of training.

What Are Passive Running Mechanics?

Passive running mechanics can be separated into the following categories:

  • Elastic energy storage
  • Reflexes
  • Passive mechanical principles

This is all linked to how your body, or more specifically your feet and legs interact with the ground when making contact. Every time your foot hits the ground, energy is put into the ground and energy is absorbed from the impact. This energy can be recycled, utilised or wasted.

The structure of the foot, more specifically the arch, means that the body can effectively reuse energy like a spring by compressing, storing energy and releasing it (pushing off the ground).

Improved passive running mechanics leads to a greater elastic energy return and therefore will allow you to run faster with less energy since you are becoming more efficient at utilising energy from the impact. In other words, your running economy improves.

Stretch Reflex

Passive running mechanics can also be seen in the stretch reflex and stretch-shortening cycle. It occurs when a muscle is actively stretched and immediately contracts. The reason for the stretch reflex is due to the muscle spindles in the muscles. These structures detect stretch in a muscle. When too much stretch is detected, they send a signal to the brain telling the antagonist muscle to contract in order to protect the body. During landing, the calf is stretched and quickly contracts to push off the ground.

The amount of elastic energy returned depends on:

  • Length and speed of the stretch
  • Muscle stiffness
  • Time between stretch and contraction

Passive Responses

Certain movements we don’t actively think about. They just ‘happen’. When you run a few steps, you might actively bring your leg forward by contracting your quadriceps, but your body automatically brings your heel and lower leg up to your bum before you actively think about contracting your quadriceps to bring that leg forwards again. This is part of passive running mechanics.

If you push off with a great enough force, the lower leg will be ‘pulled up’ automatically whilst running. The hamstring does not need to do any or much work. If you actively contract the hamstring, then there is a possibility that you’re just wasting energy since this reflex is predominantly passive.

Did you know about passive running mechanics? If not, please spread the word and share with other runners!