You may be able to get more gas mileage if you run with a forefoot strike because it may allow the elastic structures of the lower leg, namely the Achilles tendon to store more elastic strain energy as compared with heel strike running.
It turns out forefoot striking during running naturally engages the mechanical components for increased elastic power in the Achilles tendon. These mechanical components include increased plantar-flexion, increased knee flexion (knee bending) and heel lowering all of which are shown below:
The prevailing notion is that increased plantar-flexion as well as increased knee flexion (a bent knee) prior to and at touchdown as well as heel dropping shortly after the forefoot strikes the ground slackens the Achilles tendon under low-impact conditions which may load more elastic strain or potential energy through the tendon.
In contrast, prior to and at touchdown in heel strike running the opposite movements of the lower leg occur (shown below) in that the foot is dorsiflexed (forefoot lifted up) with the knee of the landing foot completely unbent which produces high impact conditions and hyper-stretches the Achilles.
This landing configuration may not put to work the elastic properties of the Achilles tendon in the lucrative way forefoot running does. In consequence, landing heel-first with a straightened knee when running may make the Achilles tendon an ineffectual, sloppy spring that could eat into running economy whereas there seems to be more evidence suggesting landing with a forefoot strike during running may maximize the contribution of elastic energy exchange in the Achilles tendon which may cause the muscles to perform less mechanical work and expend less metabolic energy
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BSc Neurobiology; MSc Biomechanics candidate, ultra minimalist runner & founder of RunForefoot. I was a heel striker, always injured. I was inspired by the great Tirunesh Dibaba to try forefoot running. Now, I'm injury free. This is why I launched Run Forefoot, to advocate the health & performance benefits of forefoot running and to raise awareness on the dangers of heel striking, because the world needs to know.