Maintaining muscle strength in older age, especially for women, is critical for an independent life with minimal assistance by others. In a cross-sectional and 4-year longitudinal cohort study, we aimed to clarify how various lifestyle-related variables affect knee extension strength, which is a representative index of lower limb function, in elderly Japanese women. Participants were community-dwelling women living in the Itabashi Ward of Tokyo, Japan, aged 75-85 years at baseline (in 2008), who returned for a follow-up examination 4 years later (in 2012). Maximum isometric knee extension strength in the dominant leg was measured during comprehensive medical check-ups at baseline and at follow-up. Interviews with participants included questions on their history of 11 diseases, and lifestyle-related factors such as physical activity, as well as dietary, smoking, and drinking habits. Cross-sectional and longitudinal analyses yielded inconsistent results regarding the associations between lifestyle-related factors and knee extension strength. While going out more frequently and regular physical exercise positively affected baseline knee extension strength, they did not affect knee extension strength in the longitudinal analysis. The longitudinal analysis revealed that more frequent intake of soy products or green and yellow vegetables at baseline decreased age-related knee extension strength decline. Thus, recommending higher intake of soy products, and green and yellow vegetables for the elderly might help maintain their muscle health.

References
1. Kojima N, Kim H, Saito K, et al. Association of knee-extension strength with instrumental activities of daily living in community-dwelling older adults. Geriatr Gerontol Int. 2014;14: 674-680.
2. Kojima N, Kim M, Saito K, et al. Lifestyle-Related Factors Contributing to Decline in Knee Extension Strength among Elderly Women: A Cross-Sectional and Longitudinal Cohort Study. PLoS One. 2015;10: e0132523.