I’ve been running the numbers on that idea for a while. The math looks good if you can hit about 30 % efficiency on each heel strike and keep the added mass below 50 grams. The real question is how that extra stiffness and weight alter stride mechanics and whether the power harvested actually offsets the load of any wearable electronics. I’m setting up a bench test with a force plate and a piezo array to measure the net gain, then I’ll tweak the design or scrap it if the data don’t match the theory.