Kent Stephenson lies down during voluntary training while Katelyn Gurley (not seen) tracks his level of muscle activity and force at the Human Locomotion Research Center laboratory, Frazier Rehab Institute, as part of the University of Louisville’s Kentucky Spinal Cord Injury Research Center in Louisville, Kentucky. Photograph: University of Louisville/Handout via Reuters

Four men who had each been paralysed from the chest down for more than two years and had been told their situation was hopeless regained the ab(...)