Asymmetric interjoint feedback contributes to postural control of redundant multi-link systems

Abstract

Maintaining the postural configuration of a limb such as an arm or leg is a fundamental neural control task that involves the coordination of multiple linked body segments. Biological systems are known to use a complex network of inter-and intra-joint feedback mechanisms arising from muscles, spinal reflexes, and higher neuronal structures to stabilize the limbs. While previous work has shown that a small amount of asymmetric heterogenic feedback contributes to the behavior of these systems, a satisfactory functional explanation for this nonconservative feedback structure has not been put forth. We hypothesized that an asymmetric multi-joint control strategy would confer both an energetic and stability advantage in maintaining endpoint position of a kinematically redundant system. We tested this hypothesis by using optimal control models incorporating symmetric versus asymmetric feedback with the goal of maintaining the endpoint location of a kinematically redundant, planar limb. Asymmetric feedback improved endpoint control performance of the limb by 16%, reduced energetic cost by 21% and increased interjoint coordination by 40% compared to the symmetric feedback system. The overall effect of the asymmetry was that proximal joint motion resulted in greater torque generation at distal joints than vice versa. The asymmetric organization is consistent with heterogenic stretch reflex gains measured experimentally. We conclude that asymmetric feedback has a functionally relevant role in coordinating redundant degrees of freedom to maintain the position of the hand or foot.

Postural Strategies in Diabetes Patients with Peripheral Neuropathy Determined Using Cross-Correlation Functions

“…They demonstrated that, compared with a symmetric feedback, an asymmetric inter-joint feedback strategy has a positive impact on coordination by improving the endpoint control of the limb by 16%, reducing the energy cost by 21%, and increasing inter-joint coordination by 40%. The results obtained in the present study do not fully confirm our hypothesis and the one proposed by Bunderson et al 30 The main limitation of this study is that the angular velocity was collected only in the sagittal plane. In fact, the multi-joint and muscle coordination involved in the equilibrium process does not simply act around the anterior-posterior axes but in every degree of freedom at each joint and for each muscle.…”

“…In fact, as illustrated in Figure 3B, some patients use anti-phase strategies between both ankles under dynamic balance tasks, whereas others do not. In a study conducted by Bunderson et al, 30 the authors simulated asymmetric and symmetric feedback postural control using optimal control models. They demonstrated that, compared with a symmetric feedback, an asymmetric inter-joint feedback strategy has a positive impact on coordination by improving the endpoint control of the limb by 16%, reducing the energy cost by 21%, and increasing inter-joint coordination by 40%.…”

Whole limb kinematics are preferentially conserved over individual joint kinematics after peripheral nerve injury

“…For example, increased force production in the triceps surae muscles related to inadvertent ankle extension would increase inhibition of the quadriceps muscles and result in a compensatory decrease in knee extension. A recent modeling study of the cat hindlimb indicates heterogenic reflexes result in greater stability or maintenance of limb position against perturbations (Bunderson et al, 2007). These and other yet to be identified reflex pathways probably function to regulate automatic joint-level responses to preserve goal-equivalence at the limb level.…”

Bilateral electromyogram response latency following platform perturbation in unilateral transtibial prosthesis users: Influence of weight distribution and limb position

“…Asymmetric feedback is subsequently important in optimizing the control of the intact lower limb [47], and the unilateral lower-limb sensory information received from the sound limb has an influence bilaterally in response to support-surface perturbations [48]. Individuals with a unilateral amputation have the removal of sensory structures in one limb, but postural reorganizations may occur in the prosthetic or intact limbs.…”