One of the main reasons impact is higher in heel strike running than in forefoot running is that in heel strike running, the knee of the landing foot is hyper-extended and stiff (shown below), which greatly reduces the capacity of the knee-joint to attenuate or deflect impact.
Why Impact is Higher in Heel Strike Running
How you use your knees and feet during running can greatly affect impact production and absorption. For example, landing on the forefoot while the knee of the landing foot is softly bent is an absolute winning combination for optimal impact dissipation that will help you avoid injury. In contrast, you never want to run heel first with a straight knee at touchdown because doing so amplifies impact.
We know that heel strike running initiates more impact than forefoot running, in which the debate becomes meaningless as to which running style is better: forefoot strike vs heel strike. The evidence makes heel strike running the suspect implicated in most running injuries, and here’s why.
Most of the ‘bad’ impact in heel strike running comes from the initial point at which the foot strikes the ground while the knee of the landing foot is straightened out. The initial contact phase in heel strike running is very abusive on the body because it unleashes a tremendous brake force that is implicated in most overuse injuries. This specific brake force unique to heel strike running piles on high shock to the body which goes against the muscles ability to absorb impact, resulting in a greater likelihood of muscle injury. This brake force is significantly lessened in forefoot running, hence why forefoot running is safer on the body.
It has been said that the main reason for the high-impact brake force produced at heel strike is due to the knee of the landing foot being in an unbent, hyperextended, stiff position. When the heel strikes the ground in heel strike running, the knee-joint is less compliant (inflexible), which means that it is too stiff to help absorb impact. This is how the brake force is amplified on the body in heel strike running. Other discoveries have proposed that heel strike running evokes more impact on the lower leg because of the lack of knee compliance or inflexibility of the knee-joint, making it difficult for impact to be absorbed.
Therefore, it makes sense to bend your knee to make it compliant and better able to reduce muscle stress when your foot strikes the ground during running. AND, also make sure to land on the outer edge of your forefoot.
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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.