A lot of folks who hear about our idea of an interactive fitness app on a smartphone ask us this question: “You can only track the orientation of either the right or left upper arm, what happens when the exercise is asymmetric (the two arms are not moving the same way at the same time)?”
Our answer is simple: we extrapolate! A basic assumption of the app is that the user is doing the exercise what the trainer shows on the screen. Whenever the arm with the phone doesn’t move (e.g.due to working-out with the other arm), we assume that the user continues with the exercise as she ideally should. A simple analogy could be when you drive into a tunnel on a highway. Although the GPS reception stops, the navigation software keeps on extrapolating your position assuming you’re going straight forward in the tunnel (no turning around please! 🙂 ). With extrapolation we imperceptibly bridge the phases where we the smartphone sensors are blind. Of course in many cases no extrapolation is needed if you have a smart watch on the wrist of your other arm.
Another cool feature is the body posture hold-on timer. Your moves (more precisely the roll, pitch and yaw angles) are compared with the pre-recorded moves of a professional trainer during exercising. In several exercises there are hold-on phases, where you keep the posture and don’t move for a certain amount of time. The algorithm recognizes when you are in one of those phases and automatically shows you a count-back timer how long you need to hold on.
In the attached video you can see both features in a live demo.