The etymology of the word 'Anthropos', the Greek word for Human, includes one of the defining characteristics of human beings, which is the ability to stand upright and walk. Locomotion is one of the human's most important functions that serve survival, progress and interaction. The force stimulus generated by the interaction of the foot with the walking surface is a vital part of human gait. Although there have been many studies trying to decipher the load feedback mechanisms of gait, there is a need for the development of a versatile system that can advance research and provide new functionality. Moreover, the role of the load feedback in inter-leg coordination during walking is still not well understood. In this paper, we present a series of studies that attempt to shed light on the role of load feedback on inter-leg coordination using a novel system, called Variable Stiffness Treadmill (VST). The device is capable of controlling load feedback stimulus by regulating the walking surface stiffness in real time. We first present the main functionality of the VST, focusing on the real-time closed-loop control of stiffness. Using perturbations of the treadmill stiffness on one leg of healthy subjects, we investigate the inter-leg coordination mechanisms, in body-weight-supported gait. Results show that ipsilateral stiffness perturbations, affect the contralateral (unperturbed) leg in body-weight-supported gait, while their effect is dependent on the timing of the induced stiffness perturbations. The developed system and experimental protocols are uniquely useful for gait research, can improve our understanding of gait, and create new avenues of research on gait analysis, walking robots and gait rehabilitation.