It may not look like it quite yet, but there's a storm brewing. The wearable fitness market is exploding right about now, and while Fitbit ( FIT ) is currently the undisputed market leader with 85% market share, Apple ( AAPL -0.38% ) hopes to change that in the coming years with Apple Watch. On one hand, it's possible that there's limited overlap between the two companies' target markets, but inevitably the pair will have to compete.