The paper deals with the application of H _∞ -design of a moment controller for the plantarflexor muscle group. This is part of a programme of work in rehabilitation engineering which aims to provide control of unsupported standing in paraplegia. A ver}' popular model of iso-metrically contracting muscle follows the Hammerstein hypothesis. The Hammerstein hypothesis means that the muscle can be modelled by a static nonlinear recruitment curve followed by an LTI-transfer function. But this assumption inadequately reflects the physiological conditions. The first section describes the motivation to apply an H _∞ -design; this is due to the existence of motor units with varying dynamic properties. In the second section the polynomial approach to H _∞ -design is summarized, following the work of Kwakernaak [7, 8, 9]. The third section contains experimental results of a complete laboratory session including muscle identification, controller design and controller tests.