The relationship between task difficulty and motor performance complexity

Single-Session Cerebellar Transcranial Direct Current Stimulation Improves Postural Stability and Reduces Ataxia Symptoms in Spinocerebellar Ataxia

Spinocerebellar ataxia (SCA) results in balance and coordination impairment, and current treatments have limited efficacy. Recent evidence suggests that combining postural training with cerebellar transcranial direct current stimulation (ctDCS) can improve these symptoms. However, the combined effects of ctDCS and postural training on individuals with spinocerebellar ataxia remain underexplored. Ten volunteers with (SCA type 3) participated in a triple-blind, randomized, crossover study to receive a single session of ctDCS (2 mA for 20 min) and a sham ctDCS session separated by at least one week. The Biodex Balance System was used to assess balance at each session, measuring overall stability index, anteroposterior stability index, and medial-lateral stability index. As secondary outcomes, cerebellar ataxia symptoms were evaluated using the 8-item Scale for Assessment and Rating of Ataxia. The assessments were conducted before and after each session. The results indicated that ctDCS enhanced the overall stability index when compared to sham ctDCS (Z = -2.10, p = 0.03), although it did not significantly affect the anteroposterior or medial-lateral stability indices. Compared to the baseline, a single session of ctDCS reduced appendicular symptoms related to cerebellar ataxia, as evidenced by improvements in the nose-finger test (Z = -2.07, p = 0.04), fast alternating hand movements (Z = -2.15, p = 0.03), and heel-to-shin slide (Z = -1.91, p = 0.05). In conclusion, our study suggests that a single session of ctDCS, in combination with postural training, can enhance balance and alleviate ataxia symptoms in individuals with cerebellar ataxia. This study was approved by the local research ethics committee (No. 2.877.813) and registered on clinicaltrials.org (NCT04039048 - https://www.clinicaltrials.gov/study/NCT04039048 ) on 2019-07-28.

Biomechanical Assessment Methods Used in Chronic Stroke: A Scoping Review of Non-Linear Approaches

Non-linear and dynamic systems analysis of human movement has recently become increasingly widespread with the intention of better reflecting how complexity affects the adaptability of motor systems, especially after a stroke. The main objective of this scoping review was to summarize the non-linear measures used in the analysis of kinetic, kinematic, and EMG data of human movement after stroke. PRISMA-ScR guidelines were followed, establishing the eligibility criteria, the population, the concept, and the contextual framework. The examined studies were published between 1 January 2013 and 12 April 2023, in English or Portuguese, and were indexed in the databases selected for this research: PubMed®, Web of Science®, Institute of Electrical and Electronics Engineers®, Science Direct® and Google Scholar®. In total, 14 of the 763 articles met the inclusion criteria. The non-linear measures identified included entropy (n = 11), fractal analysis (n = 1), the short-term local divergence exponent (n = 1), the maximum Floquet multiplier (n = 1), and the Lyapunov exponent (n = 1). These studies focused on different motor tasks: reaching to grasp (n = 2), reaching to point (n = 1), arm tracking (n = 2), elbow flexion (n = 5), elbow extension (n = 1), wrist and finger extension upward (lifting) (n = 1), knee extension (n = 1), and walking (n = 4). When studying the complexity of human movement in chronic post-stroke adults, entropy measures, particularly sample entropy, were preferred. Kinematic assessment was mainly performed using motion capture systems, with a focus on joint angles of the upper limbs.

Influence of daily physical activity on fine motor skills of adults around a Fitts task

INTRODUCTION

Achieving our daily tasks depends on the speed-accuracy conflict. Physical activity plays a role in the development of our motor skills. However, the relationship between physical activity level (PAL) and fine motor skills remains largely unexplored.

A preliminary examination of the contextual interference effect on trained trick retention in domestic dogs

This study sought to enhance current dog training practices by determining whether a finding from human motor skill learning research, the contextual interference (CI) effect, could be replicated in a trick-training paradigm with companion dogs. In humans, research shows that practicing skills in random order, as compared with blocked order, improves learning of those skills. To test this question in dogs, we randomly allocated 17 dogs to blocked training (low CI) or random training (high CI). The dogs performed three behaviors of varying difficulty. After training, we conducted a retention test in which half of the dogs in each group performed the tasks in blocked order and the other half in random order. We scored each trick, measured duration, and measured whether dogs required one or two tries to perform a behavior. We found no significant differences between dogs who practiced three tricks in random or in blocked order during training and during a retention test. This study is the first to apply the CI effect to dog trick training. Although no evidence of the CI effect was found, the current research provides a preliminary framework for future studies with potential implications for increasing retention of trained skills.

Human Information Processing of the Speed of Various Movements Estimated Based on Trajectory Change

Fitts' approach, which examines the information processing of the human motor system, has the problem that the movement speed is controlled by the difficulty index of the task, which the participant uniquely sets, but it is an arbitrary speed. This study rigorously aims to examine the relationship between movement speed and information processing using Woodworth's method to control movement speed. Furthermore, we examined movement information processing using an approach that calculates probability-based information entropy and mutual information quantity between points from trajectory analysis. Overall, 17 experimental conditions were applied, 16 being externally controlled and one being self-paced with maximum speed. Considering that information processing occurs when irregularities decrease, the point at which information processing occurs switches at a movement frequency of approximately 3.0-3.25 Hz. Previous findings have suggested that motor control switches with increasing movement speed; thus, our approach helps explore human information processing in detail. Note that the characteristics of information processing in movement speed changes that were identified in this study were derived from one participant, but they are important characteristics of human motor control.

Analytical-stochastic model of motor difficulty for three-dimensional manipulation tasks

Multiple models exist for the evaluation of human motor performance; some of these rely on the Index of Difficulty (ID), a measure to evaluate the difficulty associated to simple reaching tasks. Despite the numerous applications of the ID in reaching movements, the existing formulations are functions of the geometrical features of the task and do not consider the motor behaviour of subjects performing repetitive movements in interaction with the environment. Variability of movements, length of trajectories, subject-specific strength and skill, and required interaction with the environment are all factors that contribute to the motor difficulty experienced by a moving agent (e.g., human, robot) as it repeatedly interacts with the environment during a given task (e.g., target-reaching movement, locomotion, etc.). A novel concept of motor difficulty experienced by an agent executing repetitive end-effector movements is presented in this study. A stochastic ID formulation is proposed that captures the abovementioned factors and applies to general three-dimensional motor tasks. Natural motor variability, inherent in the proposed model, is representative of the flexibility in motor synergies for a given agent-environment interaction: the smaller the flexibility, the greater the experienced difficulty throughout the movement. The quantification of experienced motor difficulty is demonstrated for the case of young healthy subjects performing three-dimensional arm movements during which different objects are manipulated. Results show that subjects’ experienced motor difficulty is influenced by the type of object. In particular, a difference in motor difficulty is observed when manipulating objects with different grasp types. The proposed model can be employed as a novel tool to evaluate the motor performance of agents involved in repetitive movements, such as in pick and place and manipulation, with application in both industrial and rehabilitation contexts.

Effects of different tools and working height on physical workload in vertical cleaning tasks applying ambient control techniques

This study aimed to investigate the effects of different tools and working heights on physical workloads in vertical cleaning tasks. Thirty healthy adults were recruited to use a rag and a long-handle tool (LHT) to simulate cleaning operations on the Wii Fit board surfaces of 3 different heights, respectively. Participants used a lower 50th percentile force but were required to spend a longer time to finish the task while using an LHT than using a rag. The tool preferences were the main factors considered for efficiency and personal subjective workload and physiological load. 76.6% of the participants preferred to use the LHT instead of the rag at a high task height, but 70% preferred to use the rag when working at a medium task height. For low workload cleaning tasks on vertical surfaces, employers should provide cleaners with different handle lengths tools to choose from to reduce the cleaner's workload.

Estimating Information Processing of Human Fast Continuous Tapping from Trajectories

Fitts studied the problem of information capacity and transfer in the speed–accuracy motor paradigm using a theoretical approach developed from Shannon and Weaver’s information theory. The information processing (bit/s) estimated in Fitts’ study is calculated from the movement time required to achieve the required task index of difficulty but is essentially different from Shannon’s information entropy. Thus, we estimated the information entropy of multiple human movement trajectories and the mutual information among trajectories for the continuous aiming task in Fitts’ paradigm. Further, we estimated the information processing moment by moment. Two methods were considered: (1) encoded values encompassing the coordinates of the three dimensions and (2) coordinate values associated with each direction in the three dimensions. Information entropy indicates the magnitude of variation at each time point, and the structure of this variation varies with the index of difficulty. The ratio of entropy to mutual information was examined, and it was found that information was processed from the first half of the trajectory in difficult tasks. In addition, since these values calculated from the encoded method were higher than those from the conventional method, this method may be able to estimate these values successfully.

Can Increased Locomotor Task Difficulty Differentiate Knee Muscle Forces After Anterior Cruciate Ligament Reconstruction?

Changes in knee mechanics following anterior cruciate ligament (ACL) reconstruction are known to be magnified during more difficult locomotor tasks, such as when descending stairs. However, it is unclear if increased task difficulty could distinguish differences in forces generated by the muscles surrounding the knee. This study examined how knee muscle forces differ between individuals with ACL reconstruction with different graft types (hamstring tendon and patellar tendon autograft) and "healthy" controls when performing tasks with increasing difficulty. Dynamic simulations were used to identify knee muscle forces in 15 participants when walking overground and descending stairs. The analysis was restricted to the stance phase (foot contact through toe-off), yielding 162 separate simulations of locomotion in increasing difficulty: overground walking, step-to-floor stair descent, and step-to-step stair descent. Results indicated that knee muscle forces were significantly reduced after ACL reconstruction, and stair descent tasks better discriminated changes in the quadriceps and gastrocnemii muscle forces in the reconstructed knees. Changes in quadriceps forces after a patellar tendon graft and changes in gastrocnemii forces after a hamstring tendon graft were only revealed during stair descent. These results emphasize the importance of incorporating sufficiently difficult tasks to detect residual deficits in muscle forces after ACL reconstruction.

Low-Frequency Oscillations and Force Control Capabilities as a Function of Force Level in Older Women

Force variability is potentially related to altered low-frequency oscillations in motor outputs. This study examines the contributions of low-frequency oscillations in force to altered force control performances from lower to higher targeted force levels in older women. Fourteen older women executed unilateral hand-grip force control tasks at 10% and 40% of maximum voluntary contraction (MVC). Force control performances were estimated by calculating force accuracy (root-mean-square-error), force variability (standard deviation), and force regularity (approximate entropy). We additionally quantified low-frequency oscillations in force using absolute powers across four different frequency bands: (a) 0–0.5 Hz, (b) 0.5–1.0 Hz, (c) 1.0–1.5 Hz, and (d) 1.5–2.0 Hz. The findings reveal that from lower to higher targeted force level older women show greater force error, force variability, and force regularity with increased values of absolute power in force across the four frequency bands. The multiple regression models identified a significant relationship between greater force frequency power below 0.5 Hz and more impairments in force control performances. These findings suggest that force frequency oscillation below 0.5 Hz is a key predictor indicating altered stability of task performances across different targeted force levels in older women.

Fitts' law when errors are not allowed: Quantification of reciprocating trajectories and estimating information processing

There are circumstances in which humans are required to move in environments wherein accuracy should be maximized, such as golf putting or surgeons' hand movements during surgical procedures. Fitts' law expresses human movement by movement time and task difficulty, which is determined by one's distance from the target and the targets' size. Additionally, this law is considered as the most universal expression of human movement. However, it is calculated based on the possibility of failure, mainly because a tap error ratio of ~4% occurred in the continuous tap task used by Fitts. Thus, this study aimed to examine how movement changes can occur with an error rate of 0%, and whether Fitts' law can be applied to human movement in such a setting. The continuous tap task was performed under two conditions: a conventional one, and a new condition where the devised error rate becomes 0%. To measure movement change during tapping, the variation of the entire trajectory was quantified by principal component analysis, and changes in the quantified values of the trajectory toward the target were examined. For the new condition, no tapping errors occurred; the quantified value of the trajectory toward the target decreased compared with the conventional condition. It was considered that this related to the process of feedback control, and that this process related to an increase in movement time per tap. We suggest that increased information processing may account for these changes. Furthermore, the Fitts' law model, shown from the regression lines for movement time and difficulty, displayed a high fit for both conditions. However, it was difficult to evaluate movement time with the highest index of difficulty for the new condition using the model for the conventional condition. Therefore, we conclude that the conventional model may need to be modified for conditions where the error rate is 0%.

Proof of Concept of Novel Visuo-Spatial-Motor Fall Prevention Training for Old People

Falls in the geriatric population are one of the most important causes of disabilities in this age group. Its consequences impose a great deal of economic burden on health and insurance systems. This study was conducted by a multidisciplinary team with the aim of evaluating the effect of visuo-spatial-motor training for the prevention of falls in older adults. The subjects consisted of 31 volunteers aged 60 to 92 years who were studied in three groups: (1) A group under standard physical training, (2) a group under visuo-spatial-motor interventions, and (3) a control group (without any intervention). The results of the study showed that visual-spatial motor exercises significantly reduced the risk of falls of the subjects.

Impact of Distracting Emotional Stimuli on the Characteristics of Movement Performance: A Kinematic Study

It is well-documented that emotional stimuli impact both the cognitive and motor aspects of “goal-directed” behavior. However, how emotional distractors impact motor performance remains unclear. This study aimed to characterize how movement quality was impacted during emotional distractors. We used a modified oddball paradigm and documented the performance of pure movement. Participants were designated to draw a triangle or a polygon, while an emotional stimulus was presented. Speed was assessed using reaction time and movement time. The quality and precision of movement were assessed by calculating the accuracy and root-mean-square error (RMSE). Compared to drawings of triangles, polygons had higher accuracy under negative stimuli, but lower RMSE under positive stimuli. The results indicate that distracting emotional stimuli impact different aspects of movement quality, with movement complexity influencing accuracy under negative distractors and precision under positive distractors. This study provides further evidence that movement precision is an important feature of emotional embodiment that should be incorporated in future studies.

Step Response of Human Motor System as a Measure of Postural Stability in Children

Postural sway is a product of the neuromuscular system that is commonly used in contemporary labs and clinics for the assessment of postural stability. In this study, we analyzed the transient responses of the neuromuscular system during the rise-on-toes (ROT) movement in eighteen 11 yrs old girls. Their center of pressure (COP) trajectories were recorded with standard force-platform during the transition from quiet stance to standing on toes. To assess the robustness of children's postural stability, we compared the ROT trajectories while the movement was performed with and without vision. Our results confirmed that the dynamic characteristics of the COP step response were significantly modified by visual feedback. In particular, the ROT test performed with eyes closed (EC) was characterized by a four-fold increase of COP chaotic oscillations at the target (tiptoe) position. This resulted in a substantial increase in the movement's index of difficulty (ID) thus to achieve adequate accuracy of the target-oriented movement the COP velocity was decreased accordingly. This inherent strategy of the brain controller allowed for precise positioning of the COP within the reduced size of the target. In conclusion, the dynamics of the ROT movement is always precisely adjusted to the stability of the upright posture, and thus, the dynamic characteristics of the COP step response are also sensitive measures of postural stability and the ROT can be recommended as a useful test for this assessment in the general population.