Locomotor adaptations: paradigms, principles and perspectives

The term ‘locomotor adaptations’ (LMA) indicates the alteration in motor commands that is automatically or volitionally generated in response to a perturbation continuously altering the task demands of locomotion. LMAs have been widely studied, using a variety of experimental paradigms and analysis techniques. The perturbation can be expected or unexpected and constituted by a change in the movement environment, by forces actively pushing the person’s body segments, by a modification in the sensory feedback associated with the task or by explicit task instructions. The study of LMAs has been key in widening our understanding of the principles regulating bipedal locomotion, from the overall strategies driving the short-term adjustments of motor commands, down to the different neural circuits involved in the different aspects of locomotion. In this paper we will provide an in-depth review of the research field of LMAs. We will start with an analysis of the principles driving the evolution of bipedal locomotion in humans. Then we will review the different experimental paradigms that have been used to trigger LMAs. We will analyze the evidence on the neurophysiological correlates of adaptation and the behavioral reasons behind it. We will then discuss the characteristics of LMA such as transfer, generalization, and savings. This will be followed by a critical analysis of how different studies point to different task-goal related drivers of adaptation. Finally, we will conclude with a perspective on the research field of LMAs and on its ramifications in neuroscience and rehabilitation.