Achilles Stretch

The evidence I've reviewed to assess Huntington's claims have not backed them up:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5950739/#:~:text=Achilles%20tendon%20stiffness%20was%20not,shorter%20GCT%20during%20drop%20jumps

.

"Achilles tendon stiffness was not significantly correlated with squat jump and counter movement jump height, respectively. According to the results, we can confirm the main hypothesis that a stiff Achilles tendon tends to result in a shorter GCT during drop jumps."

https://www.uab.edu/news/research/item/1489-longer-tendons-make-faster-runners-suggests-uab-research

"The runner with the longer Achilles tendon gets more of that needed force from the tendon’s elastic recoil, requiring the muscle to generate less force and use less energy while running at that speed. Theoretically, a shorter tendon doesn’t have as much potential to stretch and thus supply additional force"