Evidence of movement variability patterns during a repetitive pointing task until exhaustion

Simulation Study of the Upper-Limb Isometric Wrench Feasible Set With Glenohumeral Joint Constraints

The aim of this work is to improve musculoskeletal-based models of the upper-limb wrench feasible set (WFS), i.e., the set of achievable maximal wrenches at the hand for applications in collaborative robotics and computer aided ergonomics. In particular, a recent method performing wrench capacity evaluation called the iterative convex hull method (ICHM) is upgraded in order to integrate nondislocation and compression limitation constraints at the glenohumeral (GH) joint not taken into account in the available models. Their effects on the amplitude of the force capacities at the hand, glenohumeral joint reaction forces and upper-limb muscles coordination in comparison to the original iterative convex hull method are investigated in silico. The results highlight the glenohumeral potential dislocation for the majority of elements of the wrench feasible set with the original iterative convex hull method and the fact that the modifications satisfy correctly stability constraints at the glenohumeral joint. Also, the induced muscles coordination pattern favors the action of stabilizing muscles, in particular the rotator-cuff muscles, and lowers that of known potential destabilizing ones according to the literature.

Few sex-specific effects of fatigue on muscle synergies in a repetitive pointing task

Previous studies have identified some sex differences in how individual muscles change their activation during repetitive multi-joint arm motion-induced fatigue. However, little is known about how indicators of multi-muscle coordination change with fatigue in males and females. Fifty-six (29 females) asymptomatic young adults performed a repetitive, forward-backward pointing task until scoring 8/10 on a Borg CR10 scale while surface electromyographic activity of upper trapezius, anterior deltoid, biceps brachii, and triceps brachii was recorded. Activation coefficient, synergy structure, and relative weight of each muscle within synergies were calculated using the non-negative matrix factorization method. Two muscle synergies were extracted from the fatiguing task. The synergy structures were mostly preserved after fatigue, while the activation coefficients were altered. A significant Sex × Fatigue interaction effect showed more use of the anterior deltoid in males especially before fatigue in synergy 1 during shoulder stabilization (p = 0.04). As for synergy 2, it was characterized by variations in the relative weight of biceps, which was higher by 16 % in females compared to males (p = 0.04), and increased with fatigue (p = 0.03) during the elbow flexion acceleration phase and the deceleration phase of the backward pointing movement. Findings suggest that both sexes adapted to fatigue similarly, using fixed synergy structures, with alterations in synergy activation patterns and relative weights of individual muscles. Results support previous findings of an important role for the biceps and anterior deltoid in explaining sex differences in patterns of repetitive motion-induced upper limb fatigue.

Characterizing upper extremity kinematics in typically developing children during box and blocks test

Upper extremity kinematics are important for understanding functional ability and performance improvements. The Box and Blocks test (BBT) is a standardized functional test used to measure manual dexterity when evaluating children or patients following a stroke. The BBT measures the number of blocks moved in one minute and therefore, kinematic measures and compensatory strategies cannot be assessed. This study examined the correlation between upper extremity kinematics and cycle time per block movement during the BBT in three age groups (7-, 9-, and 11-year-olds). Participants completed one BBT session while test scores and kinematic measures (hand velocity and position and shoulder, elbow, and wrist range of motion and peak joint angles) were captured using standard three-dimensional motion capture techniques. Kinematic measures were determined for block movements during the middle of each BBT trial. A mixed-effects model was used to identify group differences (α = 0.05). BBT score was different (p = 0.005) between the 7- (44.88 ± 6.03) and the 11-year-old age group (56.95 ± 8.37) along with peak shoulder flexion (p = 0.024) and abduction (p = 0.022). Peak elbow flexion was different (p = 0.049) between the 9- and 11-year-old age groups. No differences were seen between the 7- and 9-year-old age groups. Pearson's Correlation Coefficients were determined between cycle time and each significant kinematic measure, where the cycle time is specific to each block movement (BBT score) and is correlated to the BBT score. This resulted in weak correlations for all the comparisons. Therefore, using BBT score alone is not representative of UE kinematics and both should be collected during this task to provide insight into movement mechanics in a pediatric population.

A guide to inter-joint coordination characterization for discrete movements: a comparative study

Characterizing human movement is essential for understanding movement disorders, evaluating progress in rehabilitation, or even analyzing how a person adapts to the use of assistive devices. Thanks to the improvement of motion capture technology, recording human movement has become increasingly accessible and easier to conduct. Over the last few years, multiple methods have been proposed for characterizing inter-joint coordination. Despite this, there is no real consensus regarding how these different inter-joint coordination metrics should be applied when analyzing the coordination of discrete movement from kinematic data. In this work, we consider 12 coordination metrics identified from the literature and apply them to a simulated dataset based on reaching movements using two degrees of freedom. Each metric is evaluated according to eight criteria based on current understanding of human motor control physiology, i.e, each metric is graded on how well it fulfills each of these criteria. This comparative analysis highlights that no single inter-joint coordination metric can be considered as ideal. Depending on the movement characteristics that one seeks to understand, one or several metrics among those reviewed here may be pertinent in data analysis. We propose four main factors when choosing a metric (or a group of metrics): the importance of temporal vs. spatial coordination, the need for result explainability, the size of the dataset, and the computational resources. As a result, this study shows that extracting the relevant characteristics of inter-joint coordination is a scientific challenge and requires a methodical choice. As this preliminary study is conducted on a limited dataset, a more comprehensive analysis, introducing more variability, could be complementary to these results.