Distribution of Short Physical Performance Battery (SPPB) scores of patients enrolled in the Frequent Hemodialysis Network trial. Lower-extremity function was measured empirically using the SPPB, which measured: (1) gait speed for a 4-m walk, (2) chair stand with a goal of standing unassisted without use of arms 5 times within 60 seconds, and (3) balance score, which measures the capacity to stand with feet together for 10 seconds. Each exercise was scored from 0-4, with higher scores representing fewer limitations. SPPB score was the sum of these component scores. For composing this figure, scores were grouped by 2.