Multi-joint Control Strategy Of The Lower Limb During Walking And Running

Purpose:Unraveling the principle used by the brain to organize human movements is one of the primary goals of motor control research. The underlying mechanisms of the neural control of movement have long been explored, with a focus primarily on central control aspects and often overlooking the intrinsic mechanical properties of the motor system. To fully understand the control and regulation of multi-joint movements, the biomechanical properties of the moving subject, specifically interactive torques, must be considered in the design, evaluation, and interpretation of empirical data. A series of research results of upper-limb movement using intersegment dynamic approach have shown that the joints of a multi-articular limb play different roles in movement production according to their mechanical subordination in the joint linkage. A Leading Joint Hypothesis has been proposed as an alternative interpretation of control of human movements. However, limited attempts have been made to reveal the underlying mechanism of multi-joint control of lower limbs. This study was aimed at understanding the multi-joint control strategy of the lower limbs during walking and running, by studying the intersegment dynamics of the hip, knee and ankle joint. On the basis of the current literature, we hypothesized that these three joints play different roles in lower-limb control during locomotion.Methods:16 male students of Shanghai University of Sport participated in this study. They were asked to perform 6 different movements: walking(1.5m/s, 2m/s) and running(2m/s, 3m/s, 4m/s, 5m/s). Three-dimensional kinematic data were collected at a sampling rate of 200 Hz via 16 high resolution cameras. The Ground reaction forces(GRFs) were collected with 2 recessed forceplates. From the collected three-dimensional data, twodimensional sagittal plane coordinates were extracted. Data from the right lower extremity were used for the following analyses. The intersegmental dynamics analysis was conducted with a customized program. The lower limb was modeled as a linked-segment system(thigh, shank, foot) with frictionless joints at the hip, knee, and ankle. One of the trails containing valid force plate contacts was analyzed for each movement of the subjects.Results: During the stance phase of running, the dominant joint torques which provided the positive contribution to the joint movement were the external contact torque(EXT) at the hip and the muscle torques(MUS) at the knee and the ankle, respectively. During the swing phase of running, the dominant joint torques which provided the positive contribution to the joint movement were MUS at the hip and the interactive torques at the knee and the ankle. During the stance phase of walking, the dominant joint torques which provided the positive contribution to the joint movement were all MUS at the hip, knee and ankle. But during the swing phase of walking, the dominant joint torques which provided the positive contribution to the joint movement were the gravitational torque(GRA) at the hip; GRA at the knee during 1.5m/s walking, MUS at the knee during 2.0 m/s walking; INT at the ankle. The torque components varied among different running speed and different gait pattern.Conclusion: During the stance phase of running, the knee and ankle were the leading joints according to the Leading Joint Hypothesis(LJH). The hip was the subordinate joint. During the swing phase of running, the hip became the leading joint which accelerate or decelerate the whole limb, and the knee and ankle were the subordinate joints. The movement of these two joint were conducted by the INT. During the stance phase of walking, the limb movement was similar to the sum of three single-joint motion. During the swing phase of walking, the hip or knee joint would become the leading joint and the ankle was the subordinate. The central nervous system(CNS) exploits the gravity of the limbs, the external contact force and the inertia force for movement organization, to perform effective and “economical” limb movement. The control strategy varies with different movement speed and gait types.