Create Value by Walking - A Blockchain Idea

So I was walking around my hometown the other day when a idea occurred to me. What if we could create a cryptocurrency based on exercise? I am a millenial with a very, very limited basic understanding of the blockchain. This is what I was thinking . . . Each person installs a app that contains a pedometer/fitness tracker. Each step - or predetermined number of steps processes transactions on the "Runcoin" (placeholder name) network and over time (spent walking) creates a block. The walker gets some coins from the process. Over time it will take more and more steps to create a block, thus creating more incentive for exercising. Hopefully, over time, the value of the coin would rise with demand. More and more people would begin walking, hoping to create blocks and and gain "Runcoins." The question i am musing over is how to prevent a eventual cap on Runcoins due to the amount of effort needed to create a block? What if the day comes where it takes 40 miles of walking to merely make a few coins? Maybe that wouldn't be a bad thing if the coin had enough value to warrant the effort. Anyways, what do y'all think about the idea?