A modular artificial skeletal muscle (MASM) actuator having a plurality of dielectric elastomer units assembled in series or in parallel. A proximal anchoring member is connected to a proximal end of at least one proximal dielectric elastomer unit and is configured for attachment to a proximal anchor point relative to a user. A tension member has a proximal end attached to a distal end of at least one distal dielectric elastomer unit and a distal end configured for attachment to a distal anchor point relative to the user. A controller is configured to cause simultaneous contraction or expansion of plurality of dielectric elastomer units, which contraction or expansion causes displacement of the tension member. A plurality of MASM actuators may be attached to an exoskeleton attached about an ankle of a user and controlled for therapeutic purposes, such as for assisting pediatric patients with cerebral palsy.