The Switching of Trailing Limb Anticipatory Locomotor Adjustments is Uninfluenced by what the Leading Limb Does, but General Time Constraints Remain

Abstract

Research shows a blend of bilateral influence and independence between leading and trailing limbs during obstacle avoidance. Recent research also shows time constraints in switching leading limb strategies. The present study aimed to understand the ability to switch anticipatory locomotor adjustments (ALAs) in the trailing limb. Ten healthy young adults (24 ± 3 years) were immersed in a virtual environment requiring them to plan and step over an obstacle that, for the trailing limb, could change to a platform, requiring a switch in locomotor strategies to become a leading limb to step onto a new surface. Such perturbations were provoked at either late planning or early execution of the initial trailing limb obstacle avoidance. Sagittal plane trailing limb kinematics, joint kinetics and energetics were measured along with electromyographic activity of key lower limb muscles. Repeated measures ANOVAs compared dependent variables across conditions. To adjust to the new environment, knee flexor power around toe-off decreased (p < 0.001) and hip flexor power increased (p < 0.001) for late planning phase perturbations, while there was only an increase in mid-swing hip flexor power (p < 0.05) during perturbations at execution. Findings showed no influence of the leading limb function on the ability to switch trailing limb ALAs during late planning. However, the trailing limb was also constrained for modifying ALAs once execution began, but on-going limb control strategies could be exploited in a reactive mode.

The benefit of knowledge: postural response modulation by foreknowledge of equilibrium perturbation in an upper limb task

“…The goal of the present study was to advance current knowledge on motor preparation by exploring a model in which subjects are suspended upright in the air without foot support, performing a fast voluntary response with one hand (wrist extension, WE) upon a fast mechanical stimulus delivered to one leg (knee flexion, KF), theoretically destabilizing the subject and in some occasions being of startling intensity (fast KF) (Castellote et al 2017 ). We expected a different response when subjects are suspended in the air without leg support, as opposed to known reactions when standing on firm ground (Santos et al 2010a ; MacKinnon et al 2007 ; Fiset and McFadyen 2020 ; Liaw et al 2021 ). The present study complements our previous report of fast hand reactions obtained in a subset of the same subjects (Castellote et al 2017 ) and now focuses on the influence of the subjects’ expectation and preparedness to perform an upper limb motor task on associated motor reactions in the legs.…”

Special Issue: Movement Biomechanics and Motor Control

“…This special issue provides a demonstration of this. The papers collected deal with anticipatory postural adjustments [2] and anticipatory locomotor adjustments [3], strategies to tackle obstacles [2][3][4], the effects of weight unloading on gait [5], posture control in special populations: ataxic children [6] and obese subjects [7], surface perturbation during posture [8], effects of sensory information and feedback on postural control [9,10], elderly behavior during a motor-motor double task [11], upper limb control [12,13], different aspects related to running: ankle joint dynamic stiffness [14] and fatigue [15]. There is also a flash on an ecologic condition where a pedestrian has to program its strategy to cross a road in between two moving vehicles [16], and a study on visual-manual control in monkeys [17].…”