Modularity in Motor Control: Similarities in Kinematic Synergies Across Varying Locomotion Tasks

Abstract

Kinematic synergies (kSYN) provide an approach to quantify the covariation of joint motions and to explain the mechanisms underlying human motor behavior. A low-dimensional control strategy by means of the activation of a moderate number of kSYN would simplify the performance of complex motor tasks. The purpose of this study was to examine similarities between the kSYN of varying locomotion tasks: straight-line walking, walking a 90° spin turn and walking upstairs. Task-specific kSYN were extracted from full body kinematic recordings of 13 participants by principal component analysis. The first five kSYN accounting for most of the variance within each task were selected for further analysis following previous studies. The similarities between the kSYN of the three different locomotion tasks were quantified by calculating cosine similarities (SIM), as a vector-based similarity measure ranging from 0 (no similarity) to 1 (high similarity), between absolute principal component loading vectors. A SIM between two kSYN > 0.8 was interpreted as highly similar. Two to three highly similar kSYN were identified when comparing two individual tasks with each other. One kSYN, primarily characterized by anteversion and retroversion of the arms and legs, were found to be similar in all three tasks. Additional kSYN that occurred between individual tasks reflected mainly an upwards/downwards movement of the body or a countercyclical knee flexion/extension. The results demonstrate that the three investigated locomotion tasks are characterized by kSYN and that certain kSYN repeatedly occur across the three locomotion tasks. PCA yields kSYN which are in descent order according to their amount of total variance accounted for. Referring to the placing of a kSYN within the order as priorization, we found a change in priorization of repeatedly occurring kSYN across the individual tasks. The findings support the idea that movements can be efficiently performed through a flexible combination of a lower number of control-relevant variables.

Effects of Hip Bracing on Gait Biomechanics, Pain and Function in Subjects With Mild to Moderate Hip Osteoarthritis

“…Therefore, future research should include analyses of the contralateral limb, adjacent joints or even whole body movement. Thereby the application of pattern recognition methods such as a principal component analysis or cluster analysis on whole body kinematics as proposed by Meyer et al (2015) , Stetter et al (2020) and van Drongelen et al (2021) might allow us to gain additional insights into HOA and brace effects in other joints or the entire body.…”

Influence of Controlled Stomatognathic Motor Activity on Sway, Control and Stability of the Center of Mass During Dynamic Steady-State Balance—An Uncontrolled Manifold Analysis

“…When controlling the body during balance tasks, the CNS has to coordinate a redundant musculoskeletal system (Bernstein, 1967) possessing more degrees of freedom than necessary to achieve the given task (Latash et al, 2002). Different approaches have been suggested to analyze how the CNS treats this redundancy, such as motor programs (Schmidt et al, 2018), optimal control (Todorov and Jordan, 2002) or synergies (d 'Avella et al, 2003;Latash et al, 2007;Stetter et al, 2020). Latash et al (2007) define "synergy" as a neural organization consisting of a multi-element system that organizes sharing of a task among a set of elemental variables (EVs), and ensures the stabilization of a performance variable (PV) through the covariation of EVs.…”

Actuation Strategies for a Wearable Cable-Driven Exosuit Based on Synergies in Younger and Older Adults

“…Some previous studies have ascertained that human gait can be explained by muscular synergies by analyzing the electromyography signal during walking [ 22 , 23 , 24 ]. Studies based on multi-segmental kinematic signals have also been carried out on human gait [ 22 ] and in varying locomotion tasks [ 25 ]. However, examining such kinetic variables as the force or net joint torque would provide a fuller comprehension of how the different motor behaviors develop under distinct constraints [ 26 ].…”