I think that everyone knows the Greek mythological hero Achilles. His body was invulnerable besides one little part: the heel. And exactly his heel was his doom and so he died in the Trojan War. To avoid problems with the Achilles tendon during sports I do the following very easy exercise that increases also the bounce.
I stand on my toes on a step and lift the heels up first, hold the position and lower the heels back down under the horizontal level of the step.
Have a nice day!