If walking forward on the old treadmill has become a bore, consider walking backwards. Or even sideways. K-Mill allows users to go in multiple directions, which the creator claims builds up more leg strength in multiple areas and also burns 57 percent more calories per minute. But if making exercise more exciting is the aim, consider Virtuix Omni, which adds the elements of virtual reality and gaming to a treadmill workout. As for K-Mill, it’s not entirely clear what the retail price is going to be as of yet.