Abstract: Systems and methods for calculating mobility metrics associated to a plurality of wearable sensors in various arrangements comprising a plurality of communicatively-connected sensors comprising inertial measurement units (IMU) attached to connected bodies of a hinge or ball joint in communication with a computing device. Systems and methods for quaternion calculations comprising a first sensor's quaternion output as estimate into another sensor's quaternion calculation to improve the other sensor's quaternion estimate and vice versa. Systems and methods for data synchronization of a plurality of sensors involving building an external reference time vector and interpolating the sensor's data based on the reference time vector. Systems and methods for calculating a sensor's orientation and position based on the inertial measurements captured by the wearable sensors during hinge or ball joint movements to, at least, calculate a joint angle.