A system for training proper running of a user, including: at least one inertial sensor for attachment to above a waist of the user and configured to provide sensor data; at least one output interface including a display output interface; memory for storing information for an ideal running gait, the information including animation information and including information for an ideal acceleration over time which correlates to at least a GRF (Ground Reaction Force); and at least one processor in operable communication with the at least one inertial sensor, the output interface, and the memory, for executing instructions stored in the memory which, when executed, cause the at least one processor to: determine the ideal running gait information from the memory, determine the sensor data from the at least one inertial sensor for an actual running gait of the user, perform a comparison determination including: whether a rate of change of the actual acceleration of the user during ground impact is less than a predetermined value, and whether a ground impact period of acceleration is greater than a predetermined value, output to the at least one output interface information based on the comparison determination, and display on the display output interface an animation of the ideal running gait and the actual running gait, both simultaneously with cadence synchronized. at least one inertial sensor for attachment to above a waist of the user and configured to provide sensor data; at least one output interface including a display output interface; memory for storing information for an ideal running gait, the information including animation information and including information for an ideal acceleration over time which correlates to at least a GRF (Ground Reaction Force); and at least one processor in operable communication with the at least one inertial sensor, the output interface, and the memory, for executing instructions stored in the memory which, when executed, cause the at least one processor to: determine the ideal running gait information from the memory, determine the sensor data from the at least one inertial sensor for an actual running gait of the user, perform a comparison determination including: whether a rate of change of the actual acceleration of the user during ground impact is less than a predetermined value, and whether a ground impact period of acceleration is greater than a predetermined value, output to the at least one output interface information based on the comparison determination, and display on the display output interface an animation of the ideal running gait and the actual running gait, both simultaneously with cadence synchronized. determine the ideal running gait information from the memory, determine the sensor data from the at least one inertial sensor for an actual running gait of the user, perform a comparison determination including: whether a rate of change of the actual acceleration of the user during ground impact is less than a predetermined value, and whether a ground impact period of acceleration is greater than a predetermined value, output to the at least one output interface information based on the comparison determination, and display on the display output interface an animation of the ideal running gait and the actual running gait, both simultaneously with cadence synchronized.