Abstract: A portable data processing system includes a memory system, a processing system and a reception system for receiving data from acceleration sensors indicating test subject's acceleration in three orthogonal directions plus orientation of the acceleration sensors. The memory system includes routines for 1) determining instantaneous vertical, longitudinal and lateral accelerations from the received acceleration sensor data; 2) identifying periodicity in one of the instantaneous accelerations and using the periodicity with the instantaneous accelerations to determine dynamic movement parameters related to movement over ground, separately for both legs; 3) using a vertical energy loss and brake energy loss to determine a combined energy loss; and 4) outputting an indication of the combined energy loss and/or correction instructions.