An analysis of sit-to-stand movements.

We analyzed the movements involved in rising from a knee-high chair in 12 healthy men weighing within +/- 10% of standard body weight. A regular series of transition points was observed in the angles of the hip, knee, and ankle joints throughout the sit-to-stand movement, which was classified into six stages. As the duration of sit-to-stand movements increased, the duration of Stage 2 decreased, whereas Stage 3 grew longer. The durations of stages 4 and 5 remained constant. We also calculated the minimum unilateral hip and knee extension torque per weight in kilograms required for natural sit-to-stand movements, or N-Stand (1.7-2.3 seconds), and found that minimum hip extension torque was 0.7Nm and minimum knee extension torque was 0.9Nm. The minimum hip and knee extension torque required for N-Stand corresponds to a mean 27% and 30%, respectively, of the actual maximum hip and knee extension torque.