My Stablecoin Idea - Marathon

My problem with stablecoins is the pegging to a particular asset. i feel a stablecoin would only work if it is pegged to a true constant. Some kind of mathematical constant that considers long time durations passing between the peg and arbitrary assignments of the peg( how would you truly assign a constant value to a unit of gold?).
I was wondering about a unit of value determined by Pure proof of Work - Human Labour
A longtime constant of human effort is the marathon. The marathon is a designated unit of difficulty. For a human to complete a marathon would take a relatively constant effort given many variables. By this I mean if you were a pro athlete or someone in a wheelchair you would burn a fairly similar amount of calories and have to output a similar amount of joules?in effort to complete the task. With extremes considered i feel the average input output ratio would be pretty consistent. My idea is that a mechanism is made where miners anywhere in the world can track their physical energy output. Every marathon completed mints a set amount of tokens. The output would be quite similar 500 years ago or 500 years in the future. Units are sold on the free market with implied value of a hard days labour. Lots of bugs to work out but it was a quick thought i had earlier today during lunch.