Knee extension strength cutpoints for maintaining mobility - Manini, T M; Visser, M; Won-Park, S; Patel, K V; Strotmeyer, E S; Chen, H; Goodpaster, B; De Rekeneire, N; Newman, A B; Simonsick, E M; Kritchevsky, S B; Ryder, K; Schwartz, A V; Harris, T B (J Am Geriatr Soc, 2007)