Cyclical locomotion, such as walking, hopping and running, is known to be generated at the spinal cord, guiding human and animal strides over different gaits. Over the last years, many researchers concentrated their study on the origin of such signals, replicating them by either controlling joint angles or torques. In this work, we use a quadruped pneumatic robot to reproduce stable walking on a treadmill through a muscular activation pattern. Unlike previous studies, neither angles or torques are taken into consideration. Similarly to biological morphology, with variating moment arms, muscles contract rhythmically and their inherent compliance adapts to the floor. Proportional feedback upon touching the floor (stretch-reflex) is also tested, and its effects are explained. In the future, this methodology can be used to produce adaptive gait and improve current robotic by exploring interaction between control and soft bodies.