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ItemMechanisms of coordination between one- and two-joint synergist muscles(Georgia Institute of Technology, 2016-04-15) Mehta, RickyMajor muscle groups (e.g. triceps surae, quadriceps, hamstrings, triceps brachii) contain synergist muscles that cross either one or two joints; they are called one- and two-joint muscles. The functional significance of this musculoskeletal design, extensively studied in the past, has been suggested to increase the economy and efficiency of movement. Much less attention has been paid to the mechanisms responsible for the differential activation, or coordination, between one- and two-joint synergists. The understanding of these mechanisms will not only add to the basic knowledge of neural control of movement but also contribute to prevention and therapeutic interventions of muscle injuries that often occur in two-joint muscles. Previous work has suggested that mechanical intermuscular interactions, resultant muscle moment requirements at the adjacent joints, movement speed, and muscle length-velocity related sensory feedback can affect this coordination. Additionally, the comparison of motoneuronal and muscle activity patterns between fictive and real locomotion in cats suggests a greater influence of motion related sensory feedback on activity of proximal two-joint muscles (i.e., rectus femoris and hamstrings) compared to one-joint muscles and distal two-joint muscles (medial and lateral gastrocnemius). Therefore, the first goal of this work was to test the possible contribution of mechanical intermuscular interactions between one- and two-joint ankle extensors in the cat. The second goal was to examine the role of joint moment requirements, movement speed and length-velocity related feedback in distinct activation of distal one- and two-joint muscles (soleus and gastrocnemius). The third goal was to investigate the effect of removal of length-velocity sensory feedback from proximal one- and two-joint muscles (vastii and rectus femoris) on coordination of these muscles. To address the above goals, an array of motor tasks with different speeds and combinations of joint moments were studied in cats and humans. The tasks included level, downslope and upslope walking and paw shake response in cats, as well as back and leg load lifting and jumping in humans. Motion capture and force plate data were recorded to analyze kinematics and joint moments, sonomicrometry was used to measure muscle fascicle length in cats, and electromyography (EMG) was used to quantify muscle activity. Length-velocity related sensory feedback was removed in cats by muscle self-reinnervation. Results show that mechanical intermuscular interactions via myofascial force transmission should be considered in the coordination between adjacent one- and two-joint synergist muscles in certain pathological conditions leading to increased muscle lengths. Coordination between distal and proximal one- and two-joint synergists depends on joint moment requirements, and the differential inhibition of soleus and excitation of gastrocnemius does not depend on movement speed or length-velocity related sensory feedback. Removal of length-velocity related sensory feedback has a strong effect on coordination between the studied proximal synergist pair (vastii and rectus femoris) but not on coordination of the distal synergist pair (soleus and gastrocnemius). Findings presented here expand on understanding the role of mechanical interactions, sensory feedback and feedforward control in the coordination between one- and two-joint muscles. These findings have potential implications for developing targeted rehabilitation strategies/treatment and implementation of new control strategies for robotics and prosthetics to improve movement efficiency.
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ItemDynamic stability of quadrupedal locomotion: animal model, cortical control and prosthetic gait(Georgia Institute of Technology, 2012-11-13) Farrell, Bradley J.The ability to control balance and stability are essential to prevent falls during locomotion. Maintenance of stable locomotion is challenging especially when complicated by amputation and prosthesis use. Humans employ several motor strategies to maintain stability during walking on complex terrain: decreasing walking speed, adjusting stride length and stance width, lowering the center of mass, and prolonging the double support time. The mechanisms of selecting these motor strategies by the primary motor cortex are unknown and cannot be studied directly in humans. There is also little information about dynamic stability of prosthetic gait with bone-anchored prostheses, which are thought to provide sensory feedback to the amputee through osseoperception. Therefore, the Specific Aims of my research were to (1) evaluate dynamic stability and the activity of the primary motor cortex during walking with different constraints on the base of support and (2) develop an animal model to evaluate mechanics and stability of prosthetic gait with a bone-anchored prosthesis. To address these aims, I developed a feline model that allows for investigating (1) the role of the primary motor cortex in regulation of dynamic stability of intact locomotion, (2) skin and bone integration with a percutaneous porous titanium implant facilitating prosthetic attachment, and (3) dynamic stability of walking on a bone-anchored prosthesis. The results of Specific Aim 1 demonstrated that the area and shape of the base of support influence the margins of dynamic stability during quadrupedal walking. For example, I found that the animal is dynamically unstable in the sagittal plane and frontal plane (although to a lesser degree) during a double-support by a forelimb and the contralateral hindlimb. Elevated neuronal activity from the right forelimb representation in the primary motor cortex during these phases suggests that the motor cortex may contribute to selection of paw placement location and thus to regulation of stability. The results of Specific Aim 2 on the development of skin-integrated bone-anchored prostheses demonstrated the following. Skin ingrowth into 3 types of porous titanium pylons (pore sizes 40-100 μm and 100-160 μm and nano-tubular surface treatment) implanted under skin of rats was seen 3 and 6 weeks after implantation, and skin filled at least 30% of available implant space. The duration of implantation, but not implant pore size (in the studied range) or surface treatment statistically influenced skin ingrowth; pore size and time of implantation affected the implant extrusion length (p<0.05). The implant type with the slowest extrusion rate (pore size 40-100 μm) was used in a feline model of prosthetic gait with skin-integrated bone-anchored prosthesis. The developed implantation methods, rehabilitation procedures and feline prostheses allowed 2 animals to utilize skin- and bone-integrated prostheses for dynamically stable locomotion. Prosthetic gait analysis demonstrated that the animals loaded the prosthetic limb, but increased reliance on intact limbs for weight support and propulsion. The obtained results and developed animal model improve the understanding of locomotor stability control and integration of skin with percutaneous implants.
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ItemMotor control in persons with a trans-tibial amputation during cycling(Georgia Institute of Technology, 2011-07-06) Childers, Walter LeeMotor control of any movement task involves the integration of neural, muscular and skeletal systems. This integration must occur throughout the sensorimotor system and focus its efforts on controlling the system endpoint, e.g. the foot during locomotion. A person with a uni-lateral trans-tibial amputation has lost the foot, ankle joint, and muscles crossing those joints, hence the residuum becomes the new terminus of the motor system. The amputee must now adjust to the additional challenges of utilizing a compromised motor system as well as the challenges of controlling an external device, i.e. prosthesis, through the mechanical interface between the residuum and prosthetic socket. The obvious physical and physiologic asymmetries between the sound and amputated limbs are also involved in strategies for locomotion involving kinematic and kinetic asymmetries (Winter&Sienko, 1988). There are many questions as to why these asymmetric locomotor strategies are selected and what factors may be influencing that strategy. Factors influencing a change in locomotor strategy could be related to 1) the central nervous system accounting for the loss of sensorimotor feedback, 2) the altered mechanics of this new human/prosthetic system, or some combination of these factors. Understanding how the human motor system adjusts to the amputation and to the addition of an external mechanical device can provide useful insight into how robust the human control system may be and to adaptations in human motor control. This research uses a group of individuals with a uni-lateral trans-tibial amputation and a group of intact individuals using an Ankle Foot Orthosis (AFO) performing a cycling task to understand the "motor adjustments" necessary to utilize an external device for locomotion. Results of these experiments suggest 1) the motor system does account for the activation-contraction dynamics when coordinating muscle activity post amputation, 2) the motor system also changes joint kinetics and muscle activity, 3) these changes are related to control of the interface between the limb and the external device, and 4) the motor system does not alter kinetic asymmetries when kinematic asymmetries are minimized, contrary to a common practice in rehabilitation (Kapp, 2004). Results suggest that control of the external device, i.e. prosthesis or AFO, via the interface between the limb and the device reflect "motor adjustments" made by the nervous system and may be viewed in the context of tool use. Clinical goals in rehabilitation currently focus on minimizing gait deviations whereas the clinical application of these results suggest these deviations from normal locomotion are motor adjustments necessary to control a tool, i.e. prosthesis, by the motor system. Examining amputee locomotion in the context of tool use changes the clinical paradigm from one designed to minimize deviations to one intended to understand this behavior as related to interface control of the device thereby shifting the focus to improving function of the limb/prosthesis system. Kapp SL. (2004) Atlas amp limb def: surg pros rehab princ. 3rd ed: 385 - 394. Winter&Sienko. (1988) J Biomech, 21: 361 - 367.
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ItemMotor learning and its transfer during bilateral arm reaching.(Georgia Institute of Technology, 2011-06-09) Harley, Linda RosemaryHave you ever attempted to rub your abdomen with one hand while tapping your head with the other? Separately these movements are easy to perform but doing them together (bilateral task) requires motor adaptation. Motor adaptation is the process through which the Central Nervous System improves upon performance. Transfer of learning is the process through which learning a motor task in one condition improves performance in another condition. The purpose of this study was to determine whether transfer of learning occurs during bilateral goal-directed reaching tasks. It was hypothesized that transfer of learning would occur from the non-dominant to the dominant arm during bilateral tasks and that position and load feedback from the arms would affect the rate of adaptation and transfer of learning. During the experiments, subjects reached with one or both their index finger(s) to eight targets while a velocity dependent force perturbation (force environment) was applied to the arm(s). Three groups of bilateral tasks were examined: (1) unilateral reaching, where one arm learned to reach in a force environment, while the other arm remained stationary and therefore did not provide movement related position or load feedback; (2) bilateral reaching single load, where both arms performed reaching movements but only one arm learned a force environment and therefore the other arm provided movement related position feedback but not load feedback; (3) bilateral reaching two loads, where both arms performed reaching movements and both learned a force environment, while providing movement related position and load feedback. The rate of adaptation of the force environment was quantified as the speed at which the perturbed index finger trajectory became straight over the course of repeated task performance. The rate of adaptation was significantly slower for the dominant arm during the unilateral reaching tasks than during the bilateral reaching single load tasks (p<0.05). This indicates that the movement related position feedback from the non-dominant arm improved significantly the motor adaptation of the dominant arm; therefore transfer of learning occurred from the non-dominant to the dominant arm. The rate of adaptation for the non-dominant arm did not differ significantly (p>0.05) between the unilateral reaching and bilateral reaching single load tasks. Results also indicated that the rate of adaptation was significantly (p<0.05) faster for both the non-dominant and the dominant arms during the bilateral reaching two loads tasks than during the bilateral reaching single load tasks. The latter results indicate that transfer of learning occurred in both directions - from the dominant to the non-dominant arm and from the non-dominant to the dominant arm - when position and load feedback was available from both arms, but only when the force environment acted in the same joint direction. This study demonstrated that transfer of learning does occur during bilateral reaching tasks and that the direction and degree of transfer of learning may be modulated by the position and load feedback that is available to the central nervous system. This information may be used by physical therapists in order to improve rehabilitation strategies for the upper extremity.