It Pays to Have a Spring in Your Step

It Pays to Have a Spring in Your Step

I recently came across a research study that stopped me in my tracks. “It Pays to Have Spring in Your Step” demonstrates that it’s not just muscles that power our movement, but also the elastic rebound of our fascial system that contributes to our locomotive efficiency. This is a theme I have written about before here (link go further… blog)

This matters because all biological systems are traininable – including our fascial system. If we can improve the elastic rebound property of our fascial system – we go further with less energy.

Use the Force

When we look at the training philosophies and strategies of top level runners we find a mountain of protocols designed to improve aerobic metabolism, but almost none designed at enhancing the bounce in our step. That’s because western training methods are almost entirely focused on the metabolic and muscular system.

A more comprehensive study of human biology reveals that our fascial system (that wraps all of our muscles and tendons) can produce a rebound force, without taxing our energy system.

“Ultrasound imaging has allowed for quantitative assessment of the mechanisms for elastic energy storage and return at the ankle joint in vivo during human walking. Essentially, the plantar flexor muscles and their long compliant tendon act like a catapult. The Achilles tendon slowly stores elastic energy during the majority of stance, releasing it…to produce a rapid recoil with very high pushoff peak power output (9,15). One important feature of the ankle ‘catapult mechanism’ is that the stretch and recoil of Achilles tendon allows muscle fibers to remain nearly isometric producing high forces with very little mechanical work (Figure 2).”

It Pays to Have a Spring in Your Step

The Catapult Mechanism

The ‘Catapult Mechanism’ was a feature first discovered in the Red Kangaroo, a remarkable animal known for its incredible jumping prowess. Owing to its ability to cover huge distances in a single bound, and do so seemingly efficiently – researchers went to work understanding the mechanics of the kangaroo jump. What they discovered was that they possess unique architecture that allows them to take advantage of a long and elastic achilles tendon. 

The characteristics that contribute to the Kangaroo’s  jumping ability have come to be known as the “Catapult Mechanism” and notably, are present in humans as well.

The Ankle as a Special Joint

Humans are bipedal – we walk on our hind legs! As a result our anatomy has specially developed characteristics in our feet and ankles to maximise the efficiency of that movement. The design of the ankle is unique, and as such delivers exceptional efficiency compared to other joints.

“The ankle joint apparent efficiency we found using our robotic exoskeleton (61%) was 2.4 to 6 times greater than the numbers suggested by previous studies. These findings strongly suggest that the ‘catapult mechanism’ substantially enhances the efficiency of ankle joint mechanical work and reduces the metabolic energy consumed during walking.”

It Pays to Have a Spring in Your Step

That’s the line that really stops me in my tracks! Not only does the ankle display incredible mechanical efficiency, but that efficiency is largely due to the tendon, not the muscles. When tendons lengthen and shorten (store and release kinetic energy) they do so at no metabolic cost. Muscles also shorten and lengthen but require fuel to do so. Where both contribute to our movement only one does so for ‘free.’

Collagen is a protein composed of chains of amino acids, it is not serviced by the vascular system, and doesn’t not recycle ATP to power itself. In western thinking muscles are the engines of our movement, and collagen merely transfers to the force to our ‘wheels’ or joints. That is true, but it is only half the picture. Collagen which is the structural material of our fascial network is also responsible for producing force via rebound.

Studies that examine the role of muscles and collagen fibers in the action of walking have discovered that the muscle acts isometrically (neither lengthening or shortening). 

“In summary, fascicle [muscle fiber] behaviour during a counter-movement plantar flexion revealed almost isometric, not lengthening, action of the gastrocnemius [calf muscle] muscle fibres in the ‘eccentric’ phase of the joint.”

In vivo muscle fibre behaviour during counter-movement exercise in humans reveals a significant role for tendon elasticity

The Diagram below shows how the test was performed, with the subject laying on his/her back with force applied through the foot to a plate

From:  In vivo muscle fibre behaviour during counter-movement exercise in humans reveals a significant role for tendon elasticity

As a result of the remarkable efficiency of the ankle joint, researchers concluded:

“Because of the contrasting joint efficiencies, reliance on hip work to compensate for decreased ankle work can substantially increase the metabolic cost of locomotion.”

It Pays to Have a Spring in Your Step

Traditional strength training interventions have focused heavily on the contribution of the muscles of the upper leg and glutes – but our conclusions are that improved human mechanics need to be reverse engineered from the foot up. 


It is the unique architecture of the foot, and ankle that make human movement so remarkably efficient – and in order to enhance it we must reinforce the natural mechanics of a bare foot, focusing on the properties of the fascial system – whose improved characteristics will not be accompanied by an energetic cost, or an increase in weight.