A system, having: a first sensor module having an inertial measurement unit and configured to be attached to a forearm of a user and to generate first motion data identifying an orientation of the forearm connected between a hand of the user and an upper arm of the user; a second sensor module having an inertial measurement unit and configured to be attached to the hand of the user and to generate second motion data identifying an orientation of the hand; and a computing device communicatively coupled to the first sensor module and the second sensor module through communication links, the computing device configured to calculate, based on the orientation of the forearm, a position of the forearm, and the orientation of the hand, an orientation of the upper arm.