Intersegment Dynamics In Multi-joint Control Of The Lower Limb During Walking

Abstract

PURPOSE: To fully understand the control and regulation of multi-joint movements, the biomechanical properties of the moving subject, specifically intersegment dynamics, must be considered in the motor control research. This study was to understand the multi-joint control of the lower limbs during walking, by studying the intersegment dynamics of the hip, knee and ankle. METHODS: Subjects (n=16, male) performed over-ground walking at 2 different speeds (1.5m/s, 2m/s). Three-dimensional kinematic data were collected via 16 high-resolution cameras (200 Hz). The Ground reaction forces were collected by 2 recessed forceplates (1000 Hz). Data from the right lower extremity in the sagittal plane were used for the intersegmental dynamics analysis. Torques at each joint were separated into five categories: net torque (NET), gravitational torque (GRA), interactive torque (INT), external contact torque (EXT), and muscle torque (MUS). NET is the sum of the other four components. An impulse analysis was used to evaluate the contribution of each component to the NET. All the torques were normalized by the product of body weight (N) and height (m). RESULTS: During the stance phase, the dominant joint torques which provided the positive contribution to the joint movement were all MUS at the hip, knee and ankle (e.g. 2.0m/s, 2.0±0.5, 1.2±0.6, 2.5±0.4). However, during the swing phase of walking, the dominant joint torques which provided the positive contribution to the joint movement were GRA at the hip (e.g. 0.4±0.1); GRA at the knee during 1.5m/s walking (0.4±0.01), MUS at the knee during 2.0 m/s walking (0.6±0.02); INT at the ankle (0.02±0.01). Speed was significantly associated with the impulse of each torque, especially INT (e.g. INT at knee in swing phase: 0.5±0.01 vs 0.7±0.01, p<.01). CONCLUSIONS: During the stance phase of walking, the joint motion was mainly generated by the muscle strength at each joint. However, during the swing phase, interactive forces and the gravity were exploited to generate the joint motion. The control strategy also changed as the movement speed increased. The central nervous system not only exploits the muscle strength, but the passive torques to perform effective and economical limb movement.