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


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


Increased Role of the Secondary Passive Stabilizers Following Complete but Not Partial Loss of Anterior Cruciate Ligament Function During Post-Natal Growth

Robotic testing was performed with a 6-degree of freedom load cell in order to analyze functional contributions of the soft tissues in the knee under physiologically relevant loading conditions. Age groups ranging from 1.5 months to 18 months, porcine equivalent to early youth through late adolescent human ages, were studied. Complete ACL transection resulted in increased APTT and VVR across all ages (p<0.05), while injury to the AM bundle did not affect APTT or VVR. Additionally, increasing age resulted in decreased APTT normalized to the tibial plateau (p<0.05) and an average 19° decrease in VVR across states from 0 to 18 months of age (p<0.05). The ACL was the primary restraint against anterior drawer in the intact knee state [75-111%]. Following AM bundle dissection, the PL bundle carried the vast majority of the anterior load regardless of age [66-112%]. Following complete ACL transection, the MCL and medial meniscus carried most of the force across ages under anterior drawer. The LCL contributed increasing resistance to varus torque across states with age, as did the MCL under valgus torque.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science


Multigenerational growth approach to incorporate residual stress in an intervertebral disc finite element model with validation in multi-axial loading

Residual stresses are known to exist in human intervertebral discs but have not been incorporated in finite element models. A multigeneration model was applied to the annulus fibrosus of the intervertebral disc to simulate residual stresses arising from growth and remodeling. The intervertebral disc shape and compressive creep were used to verify that the multigeneration approach generates realistic values of residual stress. The model was then validated by comparing its 6 degree-of-freedom mechanical response to experimental data. Human intervertebral discs were tested in a custom-built hexapod in all 6 degrees-of-freedom (lateral shear, anterior-posterior shear, torsion, bending, flexion, and compression). Incorporating residual stresses resulted in a finite element model which can predict 4 degrees-of-freedom while excluding residual stresses produces a finite element model that can only predict 2 degrees-of-freedom.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research


In Vivo MRI Quantification of Human Disc Compression and Flexion/Extension

Disc function is mechanical, and measures of disc mechanical function are important to address spine function, degenerative disc disease, and low back pain. In vivo measures of disc mechanical function are needed, however the current standard in disc imaging is to acquire a single static image and classify the disc’s appearance using qualitative integer scales for degree of degeneration. Current grading standards are acknowledged as insufficient to identify symptomatic discs for treatment. In addition, static T2 weighted MRI cannot provide mechanical function information – mechanics must be measured as the change following a load or deformation perturbation. Because the disc experiences significant compression and height loss throughout the day, and because flexion-extension postures are often associated with low back pain, these physiological mechanical perturbations have potential to be used to quantify disc mechanics in vivo. The objective of this study was to use MRI-based methods to quantify in vivo disc function by measuring changes in disc geometry and T2 relaxation time with diurnal changes and with controllable posture. Quantification of in vivo disc mechanics by using diurnal loading or prescribed posture changes has potential to improve our ability to identify, evaluate, and treat degenerative disc disease. Symptomatic discs may have aberrant mechanics; if so, in vivo measurements of mechanical function may, with continued development, facilitate diagnosis of pathological discs.
Listed In: Biomechanical Engineering


Measuring Soft Tissue Contributions to Elbow Joint Motion and Virtual Ligament Modelling An In-Vitro Study

Knowledge of ligamentous contributions to joint stability is essential to restore normal joint range of motion and functionality through reconstruction procedures. Although, there has been numerous studies on the pathomechanics of the elbow joint, there have been very few rigorous and systematic attempts to characterize the roles of soft tissues during clinically relevant motions. Five fresh frozen cadaveric elbows from three male subjects were used for this study. In-vitro simulations were performed using a VIVO six degree-of-freedom (6-DOF) joint motion simulator (AMTI, Watertown, MA) capable of virtually simulating the effects of soft tissue constraints (virtual ligaments). This study introduces a unique, hybrid experimental-computational technique for measuring and simulating the biomechanical contributions of ligaments to elbow joint kinematics and stability. In vitro testing of cadaveric joints is enhanced by the incorporation of fully parametric virtual ligaments, which are used in place of the native joint stabilizers to characterize the contribution of elbow ligaments during simple flexion-extension motions using the principle of superposition. our results demonstrate the importance of AMCL and RCL structures as primary stabilizers under valgus and varus loading respectively. Virtual ligaments demonstrate the ability to restore the VV stability of the joint in the absence of any soft tissues attached to the osseous structures. This demonstrates the effectiveness of “virtual” ligaments for in vitro testing of elbow joint biomechanics, with applications in pre-clinical assessment of elbow implants.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research


More Push from your Push-Off: Joint-Level Modifications to Modulate Propulsive Forces in Old Age

Even prior to walking slower, older adults walk with a diminished push-off – decreased propulsive forces (FP) accompanied by reduced ankle moment and power generation. The purpose of this study was to identify age-related differences in the joint-level modifications used to modulate FP generation during walking. We posit that there are two possibilities for older adults to enhance FP generation. First, older adults may increase ankle power generation and thereby alleviate compensatory demands at the hip. Alternatively, older adults may opt to exacerbate their distal to proximal redistribution by relying even more on the hip musculature. 10 healthy young adults and 16 healthy older adults participated in this study. Subjects walked at their preferred speed while watching a video monitor displaying their instantaneous FP while instructed to modify their FP to match target values representing normal and ±10% and ±20% of normal. For all trials, we estimated lower extremity joint kinematics and kinetics. During normal walking, older adults exerted smaller FP and ankle power than young adults. Enhancing FP via biofeedback alleviated mechanical power demands at the hip, without changes in ankle power. Further, older adults walked with increased FP without increasing their total positive joint work. Thus, given the same total requisite power generation, older adults got ‘more bang for their ankle power buck’ using biofeedback.
Listed In: Biomechanical Engineering, Biomechanics, Gait


Does Corrective Surgery in Femoroacetabular Impingement Improve Joint Kinematics During Squatting?

INTRODUCTION: Cam femoroacetabular impingement (FAI) is characterized by an osseous overgrowth on the femoral head-neck junction [1], leading to pain and limited range of motion (ROM) during daily life activities [2]. Corrective surgery is highly recommended and performed in order to reduce or eliminate pain and further development of osteoarthritis (OA). However, it is still unclear whether it would lead to improved functional mobility. The purpose was to compare kinematic variables of the operated limb between FAI patients when performing a squat task pre-surgery and at around 2-year follow-up. A secondary objective consisted of express the results in a biomechanical functional score to quantify the joint kinematics of FAI patients compared to healthy control (CTRL) participants. METHODS: Eleven male patients (7 arthroplasty: 34.6±8.1 years, 25.7±3.2 kg/m2; 4 open: 33.3±7.1 years, 24.9±1.9 kg/m2) and 21 CTRL (2F/19M, 33.4±6.7 years, 25.4±3.3 kg/m2) participants were recruited from the orthopaedic surgeon’s clinical practice. Patients were assigned to either an arthroplasty or open FAI surgery correction. The participants signed prior to their participation a consent form approved by the hospital and university ethics board. Patients agreed to undergo motion analysis prior to and 2 years after the surgery. The CTRL were selected based on similar age and BMI as the FAI group and underwent the same motion analysis protocol. At the local hospital, CT scan was performed in all participants to confirm an alpha-angle higher than 55º and also establish their pelvic and knee bony landmarks. At the motion laboratory, the participants were outfitted with 45 reflective markers and performed a minimum of five trials of deep squat at a self-selected pace. Three-dimensional joint kinematics (200 Hz) of the lower limbs were captured using a ten-camera motion analysis system (Vicon, UK). Kinematics data were processed in Nexus 1.8.3 (Vicon, UK) using a modified Plug-In-Gait model and exported with a custom MATLAB script (Mathworks, USA) to calculate group averages and extract relevant variables. All trials were time-normalized based on a full squat cycle (descent and ascent phases) and individual averages for each participant were calculated across the trials. Four kinematic variables were included in the analysis: pelvis, hip, knee, and ankle sagittal angles. The normalized root-mean-square deviation (nRMSD) was calculated between the FAI and the CTRL groups for both pre- and post-surgery conditions, expressed by
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research


An Assessment of a novel approach for determining the player kinematics in elite rugby union players

Rugby is intrinsically an impact sport which results in concussions being a frequent injury within the game. Repeated concussion is linked to early-onset dementia and depression, and the rules for limiting repeated concussion are an ongoing controversy. Therefore a greater understanding of the dynamics of head impacts in rugby and the mechanism of concussion is required. Accordingly, this study focuses on assessing the use of Model Based Image Matching (MBIM) and multi-camera view video for measuring six degree of freedom head kinematics during an impact event in rugby union. The matching is performed on video evidence using 3-D animation software Poser 4. The surroundings are built in the virtual environment based on the real dimensions of the sport field. A skeleton model is then used to fit the player’s anthropometry for each video frame thus allowing player kinematics to be measured. The results from this initial study suggest that the MBIM method can be applied to head impact cases in rugby union. The head kinematics results from this case are similar to those reported in literature. The MBIM method should be applied to a number of head impact cases to establish thresholds for concussion injuries in rugby. The data gained from the MBIM method can allow for more reliable kinematic data to be inputted into finite element analysis and rigid body simulations of concussion impacts. This can allow multi-axis force measurements to be measured within the brain and neck. This can ultimately lead to an improvement in concussion injury prevention and management.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Sports Science


MUSCULAR FATIGUE INFLUENCES MOTOR SYNERGIES DURING PUSH-UPS

Objectives: The conventional push-up is a popular exercise used by the American College of Sports Medicine to test participant muscular endurance. Push-ups require changes in the ground reaction forces generated at each point of contact with the ground (all four extremities) which are achieved through muscular contractions. Although this exercise is common, the motor control mechanisms used in this motion are relatively unknown. We investigated whether humans adjust individual limb forces (push-up synergies) as they reached volitional fatigue and evaluated the hypothesis that muscular fatigue influences synergistic actions between the forces produced at the hand contact points. Approach: Twenty-one volunteers participated in a single motion capture trial where they performed as many push-ups as possible, stopping at self-determined failure. Push-ups were completed to a controlled three-beat rhythm (down, up, hold plank) at a rate of 24 repetitions per minute. Participants were instructed to arrange themselves in a plank position with each extremity within the bounds of an embedded force platform and analog data was collected at a frequency of 1000Hz. An index of synergy, defined as correlations between vertical forces, was calculated for every downward and upward motion within the push-up trial. Findings: Between-arm vertical forces were positively correlated during upward and downward motion. Positive correlation indicates that limbs worked together to produce increases or decreases needed for center of mass movement. Upward limb synergy significantly (p ≤ 0.00) decreased as participants neared volitional fatigue while downward limb synergy did not significantly change (p = 0.77). Conclusions: We found that muscular fatigue affected the synergistic actions between limbs in upward motion but not in downward motion. After muscular fatigue, between arm synergy was reduced only during concentric muscle contractions. Public Health Significance: Better understanding the synergistic changes produced by fatigue could be used to evaluate or better understand control changes behind pathologic gait or movement adaptations.
Listed In: Biomechanical Engineering, Biomechanics, Neuroscience