1. Work Environment Research Group National Institute of Occupational Safety and Health, Japan, 6‐21‐1 Nagao, Tama‐ku Kawasaki 214‐8585 Japan
2. Ergonomics Research Group National Institute of Occupational Safety and Health, Japan, 6‐21‐1 Nagao, Tama‐ku Kawasaki 214‐8585 Japan
3. Graduate School of Engineering University of Tokyo, 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐8656 Japan
4. Research Institute National Center for Geriatrics and Gerontology, 7‐430 Morioka ‐cho Obu City Aichi 474‐8511 Japan
5. Graduate School of Dentistry Osaka University, 1‐8 Yamadaoka Suita City Osaka 565‐0871 Japan