1. Department of Cardiovascular Medicine, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Kita-15, Nishi-7, Kita-ku, Sapporo, Hokkaido 060-8638, Japan
2. Graduate School of Lifelong Sport, Hokusho University, 23 Bunkyodai, Ebetsu, Hokkaido 069-8511, Japan