Decoding kinetic parameters of grasping movements from single unit activity in monkey motor cortex

Development of neuronal prosthetics, where neuronal activity is used to control artificial limbs, has so far relied on decoding kinematic parameters of movements, such as movement position or velocity. In addition to kinematic control, proper control of forces exerted by the prosthetic device is necessary for successful interaction with the environment. In our study, we analysed the possibility of classifying and decoding different grasp related forces during active grasping. Two macaque monkeys were trained to reach, grasp and pull an object in response to visual cues. Cues instructed the monkeys to grasp the object with one out of two grip types (precision or side grip) and pull the object with one of two different forces (0.5N or 2N). Monkeys obtained a food reward after successfully performing the instructed grip and pull. During the task execution, we recorded electrophysiological signals from the multielectrode arrays implanted intracortically in the hand and arm area of the monkey’s motor cortex. Six different parameters of the grip: four pressure forces on each side of the object, pull force on the object and the object displacement, were recorded simultaneously with the neuronal activity. Recorded neuronal activity was used to classify different grip types or loading forces, and to decode the continuous traces of different forces during the grip. Our results show that kinetic grip parameters can be decoded with high accuracy, thereby improving the feasibility of constructing fully functional anthropomorphic neuronal prosthesis that relies on kinetic (force) control.

Listed In: Biomechanical Engineering, Neuroscience

Task-Invariant Learning of Continuous Joint Kinematics during Steady-State and Transient Ambulation Using Ultrasound Sensing

Natural control of limb motion is continuous and progressively adaptive to individual intent. While intuitive interfaces have the potential to rely on the neuromuscular input by the user for continuous adaptation, continuous volitional control of assistive devices that can generalize across various tasks has not been addressed. In this study, we propose a method to use spatiotemporal ultrasound features of the rectus femoris and vastus intermedius muscles of able-bodied individuals for task-invariant learning of continuous knee kinematics during steady-state and transient ambulation. The task-invariant learning paradigm was statistically evaluated against a task-specific paradigm for the steady-state (1) level-walk, (2) incline, (3) decline, (4) stair ascent, and (5) stair descent ambulation tasks. The transitions between steady-state stair ambulation and level-ground walking were also investigated. It was observed that the continuous knee kinematics can be learned using a task-invariant learning paradigm with statistically comparable accuracy to a task-specific paradigm. Statistical analysis further revealed that incorporating the temporal ultrasound features significantly improves the accuracy of continuous estimations (p < 0.05). The average root mean square errors (RMSEs) of knee angle and angular velocity estimation were 7.06° and 53.1°/sec, respectively, for the task-invariant learning compared to 6.00° and 51.8°/sec for the task-specific models. High accuracy of continuous task-invariant paradigms overcome the barrier of task-specific control schemes and motivate the implementation of direct volitional control of lower-limb assistive devices using ultrasound sensing, which may eventually enhance the intuitiveness and functionality of these devices towards a "free form" control approach.
Listed In: Biomechanical Engineering, Gait

Role of Biphasic Tissue Properties in Regulating Articulation-Induced Cartilage Rehydration

Healthy articular cartilage supports load bearing and frictional properties unmatched among biological tissues and man-made bearing materials. Balancing fluid exudation and recovery under loaded and articulated conditions is essential to the tissue’s biological and mechanical longevity. Our prior tribological investigations, which leveraged the convergent stationary contact area (cSCA) configuration, revealed that sliding alone can modulate cartilage interstitial fluid pressurization and the recovery and maintenance of lubrication under load through a mechanism termed ‘tribological rehydration.’ Our recent comparative assessment of tribological rehydration revealed remarkably consistent sliding speed-dependent fluid recovery and lubrication behaviors across femoral condyle cartilage from five mammalian species (equine/horse, bovine/cow, porcine/pig, ovine/sheep, and caprine/goat). In the present study, we identified and characterized key predictive relationships among tissue properties, sliding-induced tribological rehydration, and the modulation/recovery of lubrication within healthy articular cartilage. Using correlational analysis, we linked observed speed-dependent tribological rehydration behaviors to cartilage’s geometry and biphasic properties (tensile and compressive moduli, permeability). Together, these findings demonstrate that easily measurable tissue characteristics (e.g., bulk tissue material properties, compressive strain magnitude, and strain rates) can be used to predict cartilage’s rehydration and lubricating abilities, and ultimately its function in vivo.
Listed In: Biomechanical Engineering, Biotribology

Musculoskeletal Modeling as a Tool for Biomechanical Analysis of Normal and Pathological Gait

In this work, a 3D lower limb musculoskeletal model and simulation of multiple sclerosis disease is presented. The Model was developed using the Musculoskeletal Modeling Software (MSMS), MSMS has the advantage that the model can be exported directly to Simulink allowing us to generate Functional Electrical Stimulation (FES) and evaluate different injuries. From the simulations, is possible to obtain the joint range of motion, joint torque, muscle-tendon length, force and moment arm, this is important not only to perform biomechanical analysis but also to design exoskeleton robots for rehabilitation and to generate reference trajectories for control purposes. In order to validate the results, a study case of a normal and pathological gait is presented, then, the results are compared with the literature and with real data obtained from a low cost, and a professional gait capture system.
Listed In: Biomechanical Engineering, Biomechanics, Gait

Stress influences performance: Insights into designing high cognitive load rehab tasks

The objective of this study was to investigate the effect of induced stress on the performance of each task during high cognitive load situations(HCLS). We hypothesized that induced stress leads to performance decrements during HCLS. In this study, the HCLS included standing while completing a secondary task(wire maze). The wire maze was composed of a metal wire path(maze) and a single ring, held in one hand that was moved over the maze without contacting the maze itself. Stress was induced through a loud buzzer when the ring contacted the maze. Participants were asked to randomly stand 1)quietly, or while completing the wire maze 2)with or 3)without the buzzer. Trials were three-minute long. A sample of 18 healthy young participants, (24.76±3.56 years) were randomly recruited. Perceived stress was obtained after each trial. Regularity of ground-reaction-force (GRF) in anterior-posterior and medial-lateral directions as well as wire maze error (ring-to-path contact) were calculated as primary and secondary task performance. GRF was more irregular during quietly standing compared to HCLS with and without the buzzer in both the AP and ML directions(p=0.02, p=0.001, respectively in anterior-posterior,η^2=0.28)&(p=0.004, p<0.0001, respectively in medial-lateral, η^2=0.39). Perceived stress was significantly lower during quietly standing compared to HCLS with(p=0.001, η^2=0.45) and without buzzer(p=0.007) conditions. Overall, the hypothesis was supported partially; during the most stressful HCLS, the high level of perceived stress coincided with less wire maze errors(P<0.0001, d= 0.72). Identifying the strategies underlying task prioritization can help clinicians design appropriate interventions to challenge patients appropriately to improve performance during HCLS.
Listed In: Biomechanical Engineering, Biomechanics, Physical Therapy, Posturography

Standing steadiness and variability of older adults on a step ladder

MOTIVATION: Ladder fall injury rates are highest among older adults. While standing stability has been quantified using center of pressure (COP) to classify general fall risk of older adults, it has not been applied to older adults’ balance and performance on ladders. This study investigates the standing stability of older adults while performing a task on a ladder. METHODS: One-hundred four older adults completed the Physiological Profile Assessment (PPA) to classify fall risk and climbed to the second step of a household step ladder to change a light bulb. Force plates under the step ladder were used to calculate the COP. COP parameters were extracted to assess stability on the step ladder including path length (time-normalized), RMS and elliptical area. Task time and COP parameters were compared between 10 participants with the highest fall risk and 10 participants with the lowest fall risk based on the PPA. RESULTS: Task time was 8.4 seconds (63.9%) longer for the high fall risk group. Time-normalized path lengths were similar between the two groups. The high fall risk group showed an increase in RMS by 18.1% and elliptical area by 44.6%. CONCLUSIONS: Differences in tasks time, RMS and elliptical area were observed between low and high fall risk groups. Larger RMS values and elliptical area indicate more movement away from the average COP location. This suggests high fall risk older adults to be more variable than low fall risk older adults in their standing stability when completing a task on a step ladder.
Listed In: Biomechanical Engineering, Biomechanics, Posturography

Flexion Angle Dependent Differences in Joint Kinematics and ACL Force In Response to Applied Loads Are Conserved Throughout Skeletal Growth in the Porcine Stifle Joint

The anterior cruciate ligament (ACL) stabilizes the lower limb against translational and rotational loads while the knee is is multiple postures. Surgical reconstruction, the most common treatment for ACL tears, is intended to replicate the biomechanical function of the native ACL in the postures and activities related to daily living and high-impact activities. In order to improve outcomes from ACL reconstructions in patients in pediatric and adolescent age groups, we need to improve our understanding of the knee posture dependent biomechanical function of the ACL. As such, the objective of this study was to quantify flexion angle dependent changes in the response of the ACL and the total knee to applied loads in the anterior-posterior and varus-valgus directions using a skeletally immature porcine model. To do this, we collected stifle (knee) joints from female Yorkshire-cross pigs at ages ranging from 1.5 to 18 months (n=30 total). The joints were tested using a 6 degree-of-freedom universal force sensing robotic system under applied anterior-posterior loads and varus-valgus moments at 40° and 60° of flexion. Studied parameters included anterior-posterior tibial translation (APTT), varus-valgus rotation (VVR), and anterior force carried by the ACL and its anteromedial and posterolateral bundles. We found increased knee laxity (APTT and VVR) was associated with both younger age and increased knee flexion. Greater anterior force carried in the ACL, and specifically in the anteromedial bundle, was associated with increased flexion, regardless of age. These findings have implications in intraoperative graft assessment and biomechanical models.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science

Gait as a Potential Marker of Cognitive Decrements in Type 2 Diabetes (T2DM): Early Results from the ENBIND Study

Background and Aim: Type 2 Diabetes (T2DM) in midlife represents a potent risk factor for the development of dementia in later life. Early indicators to highlight particular individuals with T2DM who are at risk of cognitive decline are lacking. Subtle abnormalities in gait (and particularly dual-task gait with a cognitive task) have emerged as a potential predictor of cognitive decline in older adults, but have not been investigated in patients with T2DM. The ENBIND Study (Exploring Novel Biomarkers of Brain health IN Diabetes) aims to assess patients with T2DM in midlife without cognitive impairment and follow participants over the course of several years to establish early predictors of cognitive decline in this poorly characterised yet high-risk group. Methods: Patients with midlife T2DM (40-65 yrs) were recruited at the time of their diabetic clinic appointment. Patients were excluded if they had a diagnosis of peripheral neuropathy, peripheral vascular disease, musculoskeletal disease, previous stroke, any form of diagnosed cognitive impairment or diabetic retinopathy/nephropathy. Patients underwent medical/diabetes assessment and examination by a physician. Cognition was screened using the Montreal Cognitive Assessment (MoCA) and assessed using a computerised cognitive battery designed for prodromal Alzheimer's Disease (CANTAB®). Gait was then assessed using both a raw clinical measure (stopwatch) and Shimmer® Inertial Measurement Units (IMUs) across four tasks: (i) 30 metre walk at a normal pace (turn at 15m), (ii) 30 metre fast walk (turn at 15m) (iii) dual cognitive-gait task (reciting alternate letters of the alphabet) and (iv) a long walk at a self-selected pace. Between group differences were assessed using t-tests and appropriate non-parametric equivalents Results: 20 participants with T2DM (52.05 yrs ± 2.13) and 10 matched healthy volunteers (mean age 52.2 yrs ± 2.74) were recruited. T2DM was associated with a significantly lower score on the MoCA (29.2 vs 27.6; p=0.0452). Participants with T2DM had slower but non-significant self-selected (0.87 ms-1 vs 0.8ms-1) and fast gait speed (0.66 ms-1 vs 0.59 ms-1). On the dual-cognitive task, participants with T2DM made more errors (1.1 vs 0.6), and had higher dual-task cost (9.17% vs 2.7%, p=0.014). Dual-task cost (the percentage decrement in walking speed due to introduction of the cognitive task) was significantly correlated with total MoCA score (R2 = 0.17, p =0.031). Discussion: Otherwise healthy participants with midlife T2DM display significantly poorer scores on MoCA. Performance on the dual-cognitive gait task was significantly correlated with MoCA score. Our study adds evidence to the presence of cognitive decrements in midlife T2DM, in-keeping with its role as a potent risk factor for the later development of dementia. We provide early data to support the utility of simple clinical gait analysis, particularly where a dual-cognitive paradigm is employed. Expansion of the sample size of patients in this study as well as longitudinal follow up should afford more detailed insight into using gait as a potential marker for cognition in this high risk cohort
Listed In: Biomechanical Engineering, Biomechanics, Gait, Neuroscience

Fluid load support in the migrating contact area: How much migration is necessary?

It is well-accepted that cartilage maintains interstitial fluid load support under long-term joint loading because contact migration leaves insufficient time for fluid exudation. However, it’s also evident that the benefits of migration dissipate as range of motion first approaches the contact length, a situation typical of moving diarthrodial joints, and then zero—typical of static joints. This study aims to elucidate the transition from full fluid load support to zero fluid load support under restricted ranges of motion. Testing was performed on osteochondral plugs using varied probe sizes, loads and track-lengths at Pe >> 1; fluid load support, contact area, and contact stress were quantified in-situ. Fluid load support depended primarily on the migration length per unit contact length (S*) and maintained maximal magnitude (F*=100%) at S* > 10. At S* < 10, it varied as a sigmoidal function of S*, falling to F* = 50% by S* = 0.1 on average. This transition migration length was independent of probe radius and varied slightly, yet significantly with contact area, load, and contact stress over the ranges tested. When migration length approached the contact length, the fluid load support of cartilage fell below that predicted by the established mechanics of migrating contacts. Based on our results, we propose a simple analytical correction that should be used when S*<10. These results demonstrate that fluid retention and load support are impaired by reduced activity and reduced ranges of motion, especially given the relatively short tracks of most joints at full range of motion.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology

Could lowering the tackle height law to below the chest in rugby union reduce long-term brain degeneration?

The tackle height law in rugby union has been an area of concern for many years. It is currently set at the line of the ball carrier’s shoulder. The goal of this study is to use Model-Based Image-Matching (MBIM) and human volunteer tackles in a marker-based 3D motion analysis laboratory to examine the severity of a legal tackle to the shoulder/chest of the ball carrier (with no head contact) and the effect of tackles above and below the chest on ball carrier inertial head kinematics, respectively. From the real-world tackles, the estimated ball carrier peak resultant change in head angular velocity was 30.4 rad/s (23.1 rad/s, 14.0 rad/s and 21.8 rad/s in the coronal, sagittal and transverse direction, respectively). In the staged tackles, the median peak resultant head linear and angular acceleration and change in head angular velocity values for tackles above the chest were greater than for below the chest. The results support the proposition of lowering the current tackle height law. Due to the real-world tackle (MBIM), the ball carrier head kinematics indicated a greater than 75% chance of sustaining a concussion, based on the literature. This was the case even though no contact was made with the ball carrier’s head. Therefore, repeatedly engaging in this type of legal tackle may be detrimental for long-term brain health. However, by lowering the tackle height law to below the chest, ball carrier inertial head kinematics can be reduced significantly, thus reducing the repetitive loading placed on the brain.
Listed In: Biomechanical Engineering, Biomechanics, Sports Science