In Finland, a scientist named Heikki Rusko has designed a "high-altitude house." The air inside the house, which is situated at sea level, is at normal pressure but modified to have a low concentration of oxygen, about 15.3% (below the 20.9% at sea level), which is roughly equivalent to the amount of oxygen available at the high altitudes often used for altitude training due to the reduced partial pressure of oxygen at altitude. Athletes live and sleep inside the house, but perform their training outside (at normal oxygen concentrations at 20.9%). Rusko's results show improvements of EPO and red-cell levels.