It's always about the execution never about the idea. That is why Silicon Valley has such a track of success. Almost infinite amount of money to exhaust all possible execution paths. Even the worst ideas, will find eventually a success path.
It might seem counter-intuitive as it would narrow the market, but at the same time will provide more value for the potential audience. It will help focus marketing budget also. Like maybe target professional athletes or Pilates fans as an example.
Good luck!