Tech giants and start-ups are vying for the lead in the multibillion-dollar body-monitoring market, but Silicon Valley experts say Apple’s iWatch, rumored to debut in October, could change everything. “If Apple delivers, this could be to health tracking what the iPod was to music,” says Mark Gurman, a senior editor with website 9to5Mac. Though popular, the trackers out now are often inaccurate and don’t give advanced fitness metrics. “Current wearables can’t tell you how fatigued your body is, how your diet affects your health, or what’s happening in your blood,” says Joe Kiani, CEO of Masimo, an Irvine, California–based manufacturer of noninvasive medical devices. Will the iWatch solve those problems? We can take a guess by looking at the biometric-device experts Apple has assembled over the past year or so. In July 2013, the company hired Dr. Michael O’Reilly, the former chief medical officer of Masimo and a part of the company’s research into pulse oximetry, which measures the amount of oxygen in the blood. A device with a pulse-oximetry sensor would allow athletes to track their blood O2 levels while training at elevation and monitor muscle fatigue from a tough workout.