Balance control and adaptation of kinematic synergy in aging adults during forward trunk bending

Assessing multiple muscle activation during squat movements with different loading conditions - an EMG study

Surface electromyography (EMG) is a valuable tool in clinical diagnostics and research related to human neuromotor control. Non-linear analysis of EMG data can help with detection of subtle changes of control due to changes of external or internal constraints during motor tasks. However, non-linear analysis is complex and results may be difficult to interpret, particularly in clinical environments. We developed a non-linear analysis tool (SYNERGOS) that evaluates multiple muscle activation (MMA) features and provides a single value for description of activation characteristics. To investigate the responsiveness of SYNERGOS to kinetic changes during cyclic movements, 13 healthy young adults performed squat movements under different loading conditions (100%-120% of body weight). We processed EMG data to generate SYNERGOS indices and used two-way repeated measures ANOVA to determine changes of MMA in response to loading conditions during movement. SYNERGOS values were significantly different for each loading condition. We concluded that the algorithm is sensitive to kinetic changes during cyclic movements, which may have implications for applications in a variety of experimental and diagnostic settings.

Shape-based coordination in locomotion control

Highly articulated systems are capable of executing a variety of behaviors by coordinating their many internal degrees of freedom to help them move more effectively in complex terrains. However, this inherent variety poses significant challenges that have been the subject of a great deal of previous work: What are the most effective or most efficient methods for achieving the intrinsic coordination necessary to produce desired global objectives? This work takes these questions one step further, asking how different levels of coordination, which we quantify in terms of kinematic coupling, affect articulated locomotion in environments with different degrees of underlying structure. We introduce shape functions as the analytical basis for specifying kinematic coupling relationships that constrain the relative motion among the internal degrees of freedom for a given system during its nominal locomotion. Furthermore, we show how shape functions are used to derive shape-based controllers (SBCs) that manage the compliant interaction between articulated bodies and the environment while explicitly preserving the inter-joint coupling defined by shape functions. Initial experimental evidence provides a comparison of the benefits of different levels of coordination for two separate platforms in environments with different degrees of inherent structure. The experimental results show that decentralized implementations, where there is relatively little inter-joint coupling, perform well across a spectrum of different terrains but that there are potential benefits to higher degrees of coupling in structured terrains. We discuss how this observation has implications related to future planning and control approaches that actively “tune” their underlying structure by dynamically varying the assumed level of coupling as a function of task specification and local environmental conditions.

INTERSEGMENTAL COORDINATION IN LOWER EXTREMITIES AND MULTI-SEGMENTAL SPINE DURING DIFFERENT ACTIVITIES OF DAILY LIVING

Background: Human movement consists of numerous degrees of freedom (DOF). How the nervous system (NS) computes the appropriate command to coordinate these DOFs to finish specific tasks is still hotly debated. One common way to simplify the redundant DOFs is to coordinate multiple DOFs by combining them into units or synergies. The present study aimed to investigate the kinematic complexity of five activities of daily living (ADLs) and to detect the amount of kinematic synergy during every ADL and the relationship of the motion pattern between these ADLs. Method: Twenty-six able-bodied male individuals performed level walking, stair climbing, trunk bending, ipsilateral pick-up and contralateral pick-up in sequence. The segmental excursion of the thorax, upper lumbar, lower lumbar, pelvis, thigh and shank was calculated. Principal component analysis (PCA) was applied to determine the motion pattern of every ADL. Result: In the sagittal plane, trunk bending, ipsilateral pick-up and contralateral pick-up could be simplified by using one principal component (PC) with more than 95% variance accounted for (VAF). In addition, the motion pattern of every PC was similar among the three ADLs. Moreover, the angles between the vectors representing the first PC of the three ADLs were all less than 10[Formula: see text]. Level walking and stair climbing needed at least two PCs to reach 95% VAF. In addition, the motion pattern was different between the two ADLs. Moreover, the angle between the first PC of the two ADLs was around 90[Formula: see text]. In the coronal plane, the five ADLs except contralateral pick-up arrived at 90% VAF with two PCs. The motion pattern and the angle between the first PC both demonstrated larger differences among the five ADLs. Conclusion: Two PCs were essential to represent level walking and stair climbing, indicating a complex control strategy used by the NS. Trunk bending, ipsilateral pick-up and contralateral pick-up could be described with one PC in the sagittal plane, showing a strong coupling and simple motion pattern. In addition, the motion pattern varied considerably among these ADLs. The outcomes of this study can help clinicians to select suitable ADLs for the patients with various joint or disc diseases and to conduct corresponding functional test and rehabilitation.

Identification of Changing Lower Limb Neuromuscular Activation in Parkinson's Disease during Treadmill Gait with and without Levodopa Using a Nonlinear Analysis Index

Analysis of electromyographic (EMG) data is a cornerstone of research related to motor control in Parkinson's disease. Nonlinear EMG analysis tools have shown to be valuable, but analysis is often complex and interpretation of the data may be difficult. A previously introduced algorithm (SYNERGOS) that provides a single index value based on simultaneous multiple muscle activations (MMA) has been shown to be effective in detecting changes in EMG activation due to modifications of walking speeds in healthy adults. In this study, we investigated if SYNERGOS detects MMA changes associated with both different walking speeds and levodopa intake. Nine male Parkinsonian patients walked on a treadmill with increasing speed while on or off medication. We collected EMG data and computed SYNERGOS indices and employed a restricted maximum likelihood linear mixed model to the values. SYNERGOS was sensitive to neuromuscular modifications due to both alterations of gait speed and intake of levodopa. We believe that the current experiment provides evidence for the potential value of SYNERGOS as a nonlinear tool in clinical settings, by providing a single value index of MMA. This could help clinicians to evaluate the efficacy of interventions and treatments in Parkinson's disease in a simple manner.

Biologically inspired kinematic synergies enable linear balance control of a humanoid robot

Despite many efforts, balance control of humanoid robots in the presence of unforeseen external or internal forces has remained an unsolved problem. The difficulty of this problem is a consequence of the high dimensionality of the action space of a humanoid robot, due to its large number of degrees of freedom (joints), and of non-linearities in its kinematic chains. Biped biological organisms face similar difficulties, but have nevertheless solved this problem. Experimental data reveal that many biological organisms reduce the high dimensionality of their action space by generating movements through linear superposition of a rather small number of stereotypical combinations of simultaneous movements of many joints, to which we refer as kinematic synergies in this paper. We show that by constructing two suitable non-linear kinematic synergies for the lower part of the body of a humanoid robot, balance control can in fact be reduced to a linear control problem, at least in the case of relatively slow movements. We demonstrate for a variety of tasks that the humanoid robot HOAP-2 acquires through this approach the capability to balance dynamically against unforeseen disturbances that may arise from external forces or from manipulating unknown loads.

Squat-to-reach task in older and young adults: kinematic and electromyographic analyses

The purpose of this study was to compare the two-dimensional kinematic and electromyographic (EMG) changes during the squat-to-reach task in older and young adults. Twenty-six older adults and thirty-three young adults were studied. A 16-channel telemetry system was used for recording muscular activity and kinematic data during two trials of a squat-to-reach task. Surface EMG data were recorded on select muscles of the trunk and the lower extremity on the dominant side. An electrogoniometer was fixed over the knee joint, and an inclinometer was fastened on the head and thigh to record kinematic data. The task was split into six movement phases based on the angular displacement and velocities of the knee joint. The mean values of the maximal displacements in the sagittal plane of the head, knee, and thigh were significantly (p<0.05) lower, but those in the frontal plane of the head and thigh were significantly (p<0.05) higher in older adults than in young adults. Thigh muscle activities were significantly (p<0.05) higher in older adults than in young adults throughout the movements. The trunk and leg muscles contracted earlier, but the hip adductors contracted later in older adults compared to young adults (p<0.05). The older adults squatted in a shallow and heel-off posture during forward reaching tasks. Therefore, older adults had increased lateral flexion of the head to compensate for insufficient knee flexion during the squat-to-reach movement and required increased activity of the posture muscles to maintain lateral stability.