A New Mexico-based company which produces "pain relief" running shoes with a spring in the heel to people aged 50 and over has revealed it has almost tripled its sales in the past 12 months. Z-Coil Shoes, of Albuquerque, said it is shipping around 5,000 pairs of shoes a month as older consumers with foot and leg pains rush to snap up the design that boasts a plastic brace like that seen in an orthopaedic shoe.