Your speed and cadence won't be detected with a non-ANT speed and cadence sensor. You could still use it for heart rate based workouts, assuming you have an ANT heart rate strap.
Check out our VirtualPower page, though. It's the reason you might consider dropping $40 on an ANT+ sensor like the Wahoo Speed/Cadence sensor. If you have a trainer we support TrainerRoad converts speed to power in real time allowing you to do power based workouts indoors. A head unit like the Garmin Edge isn't required since the TrainerRoad app displays your data while your riding and saves it in the cloud when you are done.