A recent media report in NY Times indicates that running backward improves fitness. According to a 2011 study, when runners stride ahead, they typically strike the ground near the back of the foot and roll onto the front, coiling muscles, and tendons and, in the process, creating pent-up energy in the tissues that is forcefully released as the foot pushes off. Backward runners do not generate the same kind of pent-up energy, the study found. Instead, to complete each stride, they use more leg muscles than in forward motion and burn about 30 percent more energy to go at the same pace as when running forward.
Because it is relatively strenuous, backward running can be effective in building fitness. Backward running also results in less pounding of the knees, studies show, so it is sometimes used to help runners rehabilitate from injuries to that joint. But there is a literal downside. People often trip, stumble or slam into objects and other people while running backward.