  In this study, we developed a method to estimate the relationship between
stimulation current and volatility during isometric contraction. In functional
electrical stimulation (FES), joints are driven by applying voltage to muscles.
This technology has been used for a long time in the field of rehabilitation,
and recently application oriented research has been reported. However,
estimation of the relationship between stimulus value and exercise capacity has
not been discussed to a great extent. Therefore, in this study, a human muscle
model was estimated using the transfer function estimation method with fast
Fourier transform. It was found that the relationship between stimulation
current and force exerted could be expressed by a first-order lag system. In
verification of the force estimate, the ability of the proposed model to
estimate the exerted force under steady state response was found to be good.
