Many people who engage in sports find it hard to keep track of the way their feet make contact with the ground. If you are a distance runner, this actually matters: heel striking, even with a 2cm foam cushion on your shoes, can result in all sorts of joint damage over the long term. A small change in cadence/grip can have huge effects on results for a sprinter.
Today’s invention is a set of low-height studs embedded in the soles of trail running shoes. These are good for grip in themselves but each stud has a piezoelectric crystal inside which is deformed by the impacts of running (kids shoes sometimes embody a crude version by which a small light illuminates on landing).
As the foot hits the ground, each stud translates the voltage generated in its crystal to an audible beep at a unique frequency. Studs emitting the same frequency are placed in symmetric positions on left and right soles.
During running, a sound pattern occurs which tells the runner whether they are running too much on heels or toes and, more importantly, whether the left foot impact pattern matches that of the right foot.