An action state
estimation apparatus is provided that includes a sampling portion, a statistic calculation portion, an action
state model storage, and an
estimation calculation portion. The sampling portion samples a displacement measurement
signal within a predetermined time and generates displacement measurement data. The statistic calculation portion calculates a statistic of the displacement measurement data. The action
state model storage stores an action
state model modeled by associating the statistic with a loaded state of a
muscle of the
test subject. The
estimation calculation portion estimates the loaded state by setting the statistic as an input vector and using the action state model.