Learning how to walk is difficult for toddlers to master; it’s even harder for adults who are recovering from a stroke, traumatic brain injury, or other condition, requiring months of intensive, often frustrating physical therapy. With the recent boom of the robotic exoskeleton industry, more and more patients are being strapped into machines that apply forces to their legs as they walk, gently prodding them to modify their movements by lengthening their strides, straightening their hips, and bending their knees. But, are all patients benefiting from this kind of treatment? A group of scientists led by Paolo Bonato, Ph.D., Associate Faculty member at the Wyss Institute for Biologically Inspired Engineering at Harvard University and Director of the Motion Analysis Laboratory at Spaulding Rehabilitation Hospital, has discovered a crucial caveat for rehabilitative exoskeletons: humans whose lower limbs are fastened to a typical clinical robot only modify their gait if the forces the robot applies threaten their walking stability.