Biomechanical Properties of Shoes and Risk of Falls in Older Adults Allan F. Tencer, PhD, à wz Thomas D. Koepsell, MD, MPH, à §k z Marsha E. Wolf, PhD, à Cara L. Frankenfeld, MS, à § David M. Buchner, MD, MPH, # Walter A. Kukull, PhD, à § Andrea Z. LaCroix, PhD, Ãà Eric B. Larson, MD, MPH, zÃà and Milda Tautvydas, MFA à § OBJECTIVES: To determine the relationships between the biomechanical properties of shoes worn in a cohort of healthy older adults and the risk of falling. DESIGN: Nested case-control study, comparing biome- chanical measurements of shoes worn by those who reported a fall with measurements of shoes worn by age- and sex-matched nonfallers engaged in broadly sim- ilar activities. SETTING: On-site measurements where falls occurred. PARTICIPANTS: A cohort of 1,371 older adults, of whom 327 reported a fall and 327 served as age- and sex-matched controls. MEASUREMENTS: Shoe measurements related to lateral stability (heel height and width, critical tipping angle), foot position sense (heel-collar height, sole thickness, and sole flexibility), and the shoe/surface interface (foresole materi- al, shoe-to-ground coefficient of friction, sole contact area). RESULTS: Greater heel height was associated with in- creased risk of a fall (P for trend 5 .03), whereas greater sole contact area was associated with reduced risk (P for trend 5 .005). Shoe characteristics related to foot position sense bore little apparent relation to fall risk. Coefficients of friction of 0.5 or greater were observed in 93% of shoes measured, indicating that very few were excessively slippery. CONCLUSION: Certain measurable properties of shoes were found to be significantly related to risk of falls in older adults. Wearing shoes with low heels and large contact area may help older adults reduce the risk of a fall in everyday set- tings and activities. J Am Geriatr Soc 52:1840–1846, 2004. Key words: biomechanics; falls; elderly; shoes I n the United States, about one of every three people aged 65 and older fall each year. 1–3 Several studies of falls in the elderly have suggested that shoes may be a significant contributing factor. One study 4 conducted examinations of the environmental and behavioral circumstances associated with falls in the elderly and identified seven factors, includ- ing frictional variations between shoes and floor coverings. Another study 5 reported that poorly fitting shoes were thought to have played a role in 51% of fall cases in a hospital survey, whereas another study 6 reported that, of 274 patients in a geriatric unit, only 53% were wearing adequate footwear. One investigator 7 compared communi- ty-based fall-prevention interventions, such as removal of environmental hazards in the home and promotion of the use of safe footwear. These interventions resulted in signif- icantly lower fall fracture rates outdoors and in private homes in the intervention municipality than in a reference city in which no actions were taken. Nevertheless, there has been little empirical research aimed at what specific features of shoe design identify a relatively safe shoe in terms of fall risk in older adults. Heel height has been the subject of a number of inves- tigations, particularly in relation to women’s shoes. Heel height significantly changes gait, decreasing step and stride length 8,9 and increasing vertical forces 10,11 and pressure under the forefoot. 12 Heel height may also contribute to fall risk by increasing a shoe’s potential to tip sideways on an uneven surface (lateral stability). A second mechanism may involve how shoe character- istics affect foot position sense in relation to the walking surface. One study found that foot position awareness was positively correlated to stability 13 and that foot positional error increased with advancing age. 14 They reported that thin, hard-soled shoes provided better foot positional awareness and stability for men than did shoes with thick Supported by Grants AG13793 from the National Institute on Aging and CCR002570 from the National Center for Injury Prevention and Control, Centers for Disease Control and Prevention. Address correspondence to Allan F. Tencer, PhD, Department of Orthopedics and Sports Medicine, Orthopedic Sciences Laboratory, Harborview Medical Center, MS 359798, 325 Ninth Ave, Seattle, WA 98104. E-mail: atencer@u.washington.edu From the à Harborview Injury Prevention and Research Center, and Departments of w Orthopedics and Sports Medicine, z Mechanical Engineering, § Epidemiology, k Health Services, and z Medicine, University of Washington, Seattle, Washington; # Physical Activity Branch, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia; and Ãà Center for Health Studies, Group Health Cooperative of Puget Sound, Seattle, Washington. JAGS 52:1840–1846, 2004 r 2004 by the American Geriatrics Society 0002-8614/04/$15.00