The present invention provides a system for determining power output and propulsion efficiency of a user's limb during limbed propulsion； the system comprising: (a) at least two or more accelerometers to measure the acceleration of the limb in at least two substantially orthogonal planes, (b) a processor means to calculate the power output generated by the limb to derive a limb propulsion efficiency measure, and (c) a transmission means to send the limb power output and limb propulsion efficiency metrics to a receiving device； and wherein the system is wearable on the user's limb.
