Effects of age-related changes in step length and step width on the required coefficient of friction during straight walking

Background: Slipping is one of the leading causes of falls among older adults. Older adults are considered to walk with a small anteroposterior (AP) component and a large mediolateral (ML) component of the required coefficient of friction (RCOF) owing to a short step length and a wide step width, respectively. However, limited information is available. Research question: What are the effects of aging on the resultant RCOF (RCOF _res ) and its ML (RCOF _ML ) and AP (RCOF _AP ) components during straight walking? Methods: We used the kinetic and kinematic data of 188 participants aged 20–77 years from a publicly available database (National Institute of Advanced Industrial Science and Technology Gait Database 2015). The participants were divided into the following three groups: young group (n = 56; age range, 20–34 years), middle-aged group (n = 50; age range, 35–64 years), and old group (n = 82; age range, 65–77 years). Results: The RCOF _res and RCOF _AP were lower in the old group than in the other groups, indicating a lower slip risk in this group. However, the RCOF _ML was higher and the step width was greater in the old group than in the other groups. The higher RCOF _ML and lower RCOF _AP in the old group might be associated with slips in a more lateral direction. Significance: Our findings suggest that older adults have a high risk of slipping in a more lateral direction. Shoes with high-slip resistance in the lateral direction are recommended to prevent hazardous lateral slips among older adults.