Effects of short nap and exercise on elderly people having difficulty in sleeping. - Tanaka, Hideki; Taira, Kazuhiko; Arakawa, Masashi; Toguti, Hiroki; Urasaki, Chisae; Yamamoto, Yukari; Uezu, Eiko; Hori, Tadao; Shirakawa, Shuichiro (Psychiatry & Clinical Neurosciences, 2001)