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I have spent a lot of time searching on pubmed for the effects of on the viscoelastic properties of the Achilles tendon in runners who habitually forefoot strike versus those who habitually rearfoot strike. My understanding is that a forefoot strike would allow the gastrosoleol complex to undergo eccentric activity, which would increase the elasticity of the Achilles tendon allowing it to have more energy storing potential. Rearfoot strikers would thus have a more stiff Achilles tendon since it only undergoes concentric activity.

I also have read an article about downhill running which talked about how the quad muscles are used more as shock absorbing and the calves are used more as propulsion, but I wasn't able to find any information on the actions of the gastroc vs soleus in forefoot and rearfoot strike running. Here is what I have been pondering about and would like to find more information on:

With the calf muscles' different points of origin but same insertion site, I'm imagining that the soleus is better suited for eccentric activity to decelerate a forefoot strike landing. From midstance to propulsion, the soleus is holding its contraction, keeping the Achilles tendon tensed. Approaching propulsion, the knee is extending, which places the fast-firing gastroc muscles in a tensed state, and with the Achilles tendon already tensed from the soleus, when the gastroc fires, it adds an extra boost of energy to be stored into the Achilles tendon. Without having habitually using eccentric activity to improve the elastic property of the Achilles tendon, this energy storage capability is diminished making it more difficult to adopt the forefoot running style immediately for habitually rearfoot runners.

 

Not a direct answer to your question, but see this thread:
Impact frequency data suggest unique risks for forefoot strikers