Weird Universe tells us that Joseph Pilates (1883-1967), the developer of the popular exercise program that bears his name, invented numerous pieces of exercise equipment. He had a holistic approach to fitness, which prudently included sleep.
In 1930, after immigrating from Germany to the United States, Pilates invented and patented a spring-less bed that has a v-shaped inner frame and mattress. Pilates argued that the human spine tends to curve inward when posture is not deliberately maintained. It is necessary to discipline the spine into proper alignment with a flat, hard bed. The V-shape permits the arms and legs to provide some support and therefore allow the sleeper to relax fully into this cradle.