Disclosed methods, systems, and storage media may track body movements and movement trajectories using internal measurement units (IMUs), where a first IMU may be attached to a first wrist of a user, a second IMU may be attached to a second wrist of the user, and a third IMU may be attached to a torso of the user. Upper body movements may be derived from sensor data produced by the three IMUs. IMUs are typically not used to detect fine levels of body movements and/or movement trajectory because most IMUs accumulate errors due to large amounts of measurement noise. Embodiments provide arm and torso movement models to which the sensor data is applied in order to derive the body movements and/or movement trajectory. Additionally, estimation errors may be mitigated using a hidden Markov Model (HMM) filter. Other embodiments may be described and/or claimed.