Body pressure that is being applied to the body, from the mattress, is a new area of research. Researchers and physicians have long recognized the association between pressure on the skin and bed sores. Most healthy people will move often enough at night, due to sleep stage changes, that development of bed sores are not a concern. However, if high pressure develops over the large bony joints, it can cause long term problems. When sleeping in the side laying position the highest pressures can develop over the shoulder, hip and ankle. Over time, this excessive pressure can cause pain on the joint affected. It has been shown that people who sleep on hard bedding will move more often due to the excessive pressure. These excessive movements will fragment sleep and cause daytime sleepiness.