Hideki Tanaka, Kazuhiko Taira, Masashi Arakawa, Hiroki Toguti, Chisae Urasaki, Yukari Yamamoto, Eiko Uezu, Tadao Hori, and Shuichiro Shirakawa, «Effects of Short Nap and Exercise on Elderly People Having Difficulty in Sleeping,» Psychiatry and Clinical Neurosciences 55 (2001): 173–74.