The 20 pairs of walking shoes put through their paces at CR’s laboratories had to endure more than a pounding on the pavement. They also were subjected to a machine designed to check on the flexibility of their soles. The device, shown at right, measures the amount of force it takes to bend the shoe at the ball of the foot, as a walker would do out on the roads. Other tests measured shock absorption at the heel of each shoe, where the impact is greatest.