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Biomedical subjects

Richard R Neptune

Publications and source records attributed to Richard R Neptune.

16 recordsLinked to original sources
PubMed2007

Relationship between step length asymmetry and walking performance in subjects with chronic hemiparesis.

OBJECTIVE: To understand the relationship between step length asymmetry and hemiparetic walking performance. DESIGN: Descriptive. SETTING: Gait analysis laboratory. PARTICIPANTS: Convenience sample of 49 subjects with chronic hemiparesis. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Subjects walked at their self-selected walking speed over both an instrumented mat and forceplates to collect spatiotemporal parameters and ground reaction forces, respectively. Step length asymmetry was quantified by using a step length ratio (SLR) defined as paretic step length divided by nonparetic step length. Paretic leg propulsion, self-selected walking speed, hemiparetic severity (assessed by Brunnstrom stages of motor recovery), and some spatiotemporal walking parameters quantified the hemiparetic walking performance. Paretic leg propulsion was quantified by the paretic propulsion (P(P)) ratio, calculated as the percentage contribution of paretic leg to the total propulsive impulse. RESULTS: Significant negative correlation (r=-.78) was revealed between SLR and P(P), indicating that subjects generating less propulsive force with the paretic leg walked asymmetrically with longer paretic steps than nonparetic steps. SLR and self-selected walking speed revealed a weaker correlation (r=-.35), whereas hemiparetic severity correlated strongly with SLR (rho=-.53). CONCLUSIONS: Step length asymmetry is related to propulsive force generation during hemiparetic walking. Subjects generating least paretic propulsion walk with relatively longer paretic steps. This suggests that one of the mechanisms for the longer paretic step may be the relatively greater compensatory nonparetic leg propulsion. Further, those with more severe hemiparesis (those dependent on abnormal flexor and extensor synergies) walk with the longest paretic steps relative to nonparetic. Finally, our results indicated that asymmetrical step lengths may not necessarily limit the self-selected walking speed, likely due to other compensatory mechanisms.

Acceleration↗
PubMed2006

Mechanical energetic contributions from individual muscles and elastic prosthetic feet during symmetric unilateral transtibial amputee walking: a theoretical study.

Energy storage and return (ESAR) foot-ankle prostheses have been developed in an effort to improve gait performance in lower-limb amputees. However, little is known about their effectiveness in providing the body segment mechanical energetics normally provided by the ankle muscles. The objective of this theoretical study was to use muscle-actuated forward dynamics simulations of unilateral transtibial amputee and non-amputee walking to identify the contributions of ESAR prostheses to trunk support, forward propulsion and leg swing initiation and how individual muscles must compensate in order to produce a normal, symmetric gait pattern. The simulation analysis revealed the ESAR prosthesis provided the necessary trunk support, but it could not provide the net trunk forward propulsion normally provided by the plantar flexors and leg swing initiation normally provided by the biarticular gastrocnemius. To compensate, the residual leg gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in early stance and late stance into pre-swing, respectively, while the residual iliopsoas delivered increased energy to the leg in pre- and early swing to help initiate swing. In the intact leg, the soleus, gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in the first half of stance, while the iliopsoas increased the leg energy it delivered in pre- and early swing. Thus, the energy stored and released by the ESAR prosthesis combined with these muscle compensations was able to produce a normal, symmetric gait pattern, although various neuromuscular and musculoskeletal constraints may make such a pattern non-optimal.

Amputation, Surgical↗
PubMed2006

The neuromuscular demands of toe walking: a forward dynamics simulation analysis.

Toe walking is a gait deviation with multiple etiologies and often associated with premature and prolonged ankle plantar flexor electromyographic activity. The goal of this study was to use a detailed musculoskeletal model and forward dynamical simulations that emulate able-bodied toe and heel-toe walking to understand why, despite an increase in muscle activity in the ankle plantar flexors during toe walking, the internal ankle joint moment decreases relative to heel-toe walking. The simulations were analyzed to assess the force generating capacity of the plantar flexors by examining each muscle's contractile state (i.e., the muscle fiber length, velocity and activation). Consistent with experimental measurements, the simulation data showed that despite a 122% increase in soleus muscle activity and a 76% increase in gastrocnemius activity, the peak internal ankle moment in late stance decreased. The decrease was attributed to non-optimal contractile conditions for the plantar flexors (primarily the force-length relationship) that reduced their ability to generate force. As a result, greater muscle activity is needed during toe walking to produce a given muscle force level. In addition, toe walking requires greater sustained plantar flexor force and moment generation during stance. Thus, even though toe walking requires lower peak plantar flexor forces that might suggest a compensatory advantage for those with plantar flexor weakness, greater neuromuscular demand is placed on those muscles. Therefore, medical decisions concerning whether to reduce equinus should consider not only the impact on the ankle moment, but also the expected change to the plantar flexor's force generating capacity.

Adult↗
PubMed2006

Compensatory strategies during normal walking in response to muscle weakness and increased hip joint stiffness.

Compared to young adults, older adults exhibit a slower walking speed, smaller step length, shorter swing phase time and decreased range of motion in their lower extremity joints. The underlying mechanisms causing these gait adaptations is not well understood, with various musculoskeletal parameters being put forth as contributing factors, including increased joint stiffness and decreased isometric muscle strength. The objective of this study was to identify the necessary compensatory mechanisms to overcome such musculoskeletal deficits and regain a normal walking pattern. Understanding these mechanisms has important implications for designing effective rehabilitation interventions for older adults that target specific muscle groups and properties (e.g., isometric strength versus joint stiffness) to improve gait performance. Muscle-actuated forward dynamics simulations of normal walking were analyzed to quantify compensatory mechanisms in the presence of muscle weakness in specific muscle groups and increased hip joint stiffness. Of particular importance were the compensatory mechanisms provided by the plantar flexors, which were shown to be able to compensate for many musculoskeletal deficits, including diminished muscle strength in the hip and knee flexors and extensors and increased hip joint stiffness. This importance was further highlighted when a normal walking pattern could not be achieved through compensatory action of other muscle groups when the uniarticular and biarticular plantar flexor strength was decreased as a group. Thus, rehabilitation or preventative exercise programs may consider focusing on increasing or maintaining plantar flexor strength, which appears critical to maintaining normal walking mechanics.

Adaptation, Physiological↗
PubMed2006

Anterior-posterior ground reaction forces as a measure of paretic leg contribution in hemiparetic walking.

BACKGROUND AND PURPOSE: Walking after stroke is characterized by slow gait speed, poor endurance, reduced quality and adaptability of walking patterns, and an inability to coordinate the legs. Estimates based on mechanical work calculations have suggested that the paretic leg does 30% to 40% of the total mechanical work over the gait cycle, regardless of hemiparetic severity, but these work estimates may not describe the contribution of each leg to forward propulsion. The purpose of this study was to establish a quantifiable link between hemiparetic severity and paretic leg contribution to propulsion during walking, which we propose to quantify using a measure based on the anterior-posterior ground reaction forces (A-P GRFs). METHODS: A total of 47 participants with chronic hemiparesis walked at self-selected speeds to collect spatiotemporal parameters and 3D GRFs. A 16-person subset also participated in a pedaling protocol to compare A-P GRF measures to established measures of paretic leg output. RESULTS: A-P GRF measures were correlated with both walking speed and hemiparetic severity. These measures were also strongly correlated with positive work and net work values obtained during the pedaling task. The percentage of total propulsion generated by the paretic leg (PP) was calculated and found to be 16%, 36%, and 49% for those with high, moderate, and low hemiparetic severity, respectively. CONCLUSIONS: PP was found to provide a quantitative measure of the coordinated output of the paretic leg. Further research on this measure of forward propulsion may lead to the provision of an effective tool for distinguishing functional compensation from physiological restitution.

Aged↗
PubMed2006

The effect of foot and ankle prosthetic components on braking and propulsive impulses during transtibial amputee gait.

OBJECTIVE: To assess the influence of energy storage and return (ESAR) prosthetic feet and multi-axis ankles on ground reaction forces and loading asymmetry between lower limbs in transtibial amputees. DESIGN: Subjects wore 2 different prosthetic feet with and without a multi-axis ankle and were analyzed using a blind repeated-measures multivariate analysis-of-variance design. SETTING: Gait analysis laboratory. PARTICIPANTS: Fifteen healthy unilateral transtibial amputees (>55 y) who had an amputation at least 1 year before testing because of vascular disorders. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The anteroposterior ground reaction force impulse, peak ground reaction forces, and braking and propulsion impulse duration were analyzed as subjects walked at a self-selected speed while wearing each of the 4 foot-ankle prosthesis combinations. Statistical analyses were used to determine if there was a significant foot, ankle, or foot-ankle interaction effect on the outcome measures for each foot (P<.05). RESULTS: Amputees generated a significantly greater propulsive impulse with the residual leg when wearing a multi-axis ankle with the ESAR and non-ESAR foot, which improved the propulsive symmetry between the residual and intact legs. There was no prosthetic foot effect on these measures. There were no significant differences in the peak residual-leg braking or propulsive ground reaction forces or the impulse durations due to the prosthetic foot, ankle, or foot-ankle interactions, although an increase in the propulsive impulse duration approached significance (P=.062) with a multi-axis ankle. CONCLUSIONS: These results suggest that amputee gait may improve with the prescription of multi-axis ankles that allow for greater propulsive impulses by the residual leg, which improve the loading symmetry between legs.

Amputation, Surgical↗
PubMed2006

An experimental and theoretical framework for manufacturing prosthetic sockets for transtibial amputees.

Selective laser sintering (SLS) is a powerful manufacturing technology that does not require part-specific tooling or significant human intervention and provides the ability to easily generate parts with complex geometric designs. The present work focuses on developing a manufacturing framework using this technology to produce subject-specific transtibial amputee prosthetic sockets made of Duraform PA, which is a nylon-based material. The framework includes establishing an overall socket design (using the patellar-tendon bearing approach), performing a structural analysis using the finite element method (FEM) to ensure structural reliability during patient use, and validating the results by comparing the model output with experimental data. The validation included quantifying the failure conditions for the socket through a series of bending moment and compression tests. In the case study performed, the FEM results were within 3% of the experimental failure loads for the socket and were considered satisfactory.

Amputation Stumps↗
PubMed2005

Differences in muscle function during walking and running at the same speed.

Individual muscle contributions to body segment mechanical energetics and the functional tasks of body support and forward propulsion in walking and running at the same speed were quantified using forward dynamical simulations to elucidate differences in muscle function between the two different gait modes. Simulations that emulated experimentally measured kinesiological data of young adults walking and running at the preferred walk-to-run transition speed revealed that muscles use similar biomechanical mechanisms to provide support and forward propulsion during the two tasks. The primary exception was a decreased contribution of the soleus to forward propulsion in running, which was previously found to be significant in walking. In addition, the soleus distributed its mechanical power differently to individual body segments between the two gait modes from mid- to late stance. In walking, the soleus transferred mechanical energy from the leg to the trunk to provide support, but in running it delivered energy to both the leg and trunk. In running, earlier soleus excitation resulted in it working in synergy with the hip and knee extensors near mid-stance to provide the vertical acceleration for the subsequent flight phase in running. In addition, greater power output was produced by the soleus and hip and knee extensors in running. All other muscle groups distributed mechanical power among the body segments and provided support and forward propulsion in a qualitatively similar manner in both walking and running.

Biomechanical Phenomena↗
PubMed2005

Muscle mechanical work and elastic energy utilization during walking and running near the preferred gait transition speed.

Mechanical and metabolic energy conservation is considered to be a defining characteristic in many common motor tasks. During human gait, the storage and return of elastic energy in compliant structures is an important energy saving mechanism that may reduce the necessary muscle fiber work and be an important determinant of the preferred gait mode (i.e., walk or run) at a given speed. In the present study, the mechanical work done by individual muscle fibers and series-elastic elements (SEE) was quantified using a musculoskeletal model and forward dynamical simulations that emulated a group of young healthy adults walking and running above and below the preferred walk-run transition speed (PTS), and potential advantages associated with the muscle fiber-SEE interactions during these gait modes at each speed were assessed. The simulations revealed that: (1) running below the PTS required more muscle fiber work than walking, and inversely, walking above the PTS required more muscle fiber work than running, and (2) SEE utilization in running was greater above than below the PTS. These results support previous suggestions that muscle mechanical energy expenditure is an important determinant for the preferred gait mode at a given speed.

Adult↗
PubMed2005

The quasi-static response of compliant prosthetic sockets for transtibial amputees using finite element methods.

The finite element method (FEM) is a very powerful tool for analyzing the behavior of structures, especially when the geometry and mechanics are too complex to be modeled with analytical methods. This study focuses on the analysis of patellar tendon bearing prosthetic sockets with integrated compliant features designed to relieve contact pressure between the residual limb and socket. We developed a FEM model composed of a socket, liner and residual limb and analyzed it under quasi-static loading conditions derived from experimentally measured ground reaction forces. The geometry of the residual limb, liner and socket were acquired from computed tomography (CT) data of a transtibial amputee. Three different compliant designs were analyzed using FEM to assess the structural integrity of the sockets and their ability to relieve local pressure at the fibula head during normal walking. The compliant features consisted of thin-wall sections and two variations of spiral slots integrated within the socket wall. One version of the spiral slots produced the largest pressure relief, with an average reduction in local interface pressure during single-leg stance (20-80% of the stance phase) from 172 to 66.4 kPa or 65.8% compared to a baseline socket with no compliant features. These results suggest that the integration of local compliant features is an effective method to reduce local contact pressure and improve the functional performance of prosthetic sockets.

Amputation, Surgical↗
PubMed2005

Design and analysis of orthogonally compliant features for local contact pressure relief in transtibial prostheses.

A very attractive advantage of manufacturing prosthetic sockets using solid freeform fabrication is the freedom to introduce design solutions that would be difficult to implement using traditional manufacturing techniques. Such is the case with compliant features embedded in amputee prosthetic sockets to relieve contact pressure at the residual limb-socket interface. The purpose of this study was to present a framework for designing compliant features to be incorporated into transtibial sockets and manufacturing prototypes using selective laser sintering (SLS) and Duraform material. The design process included identifying optimal compliant features using topology optimization algorithms and integrating these features within the geometry of the socket model. Using this process, a compliant feature consisting of spiral beams and a supporting external structure was identified. To assess its effectiveness in reducing residual limb-socket interface pressure, a case study was conducted using SLS manufactured prototypes to quantify the difference in interface pressure while a patient walked at his self-selected pace with one noncompliant and two different compliant sockets. The pressure measurements were performed using thin pressure transducers located at the distal tibia and fibula head. The measurements revealed that the socket with the greatest compliance reduced the average and peak pressure by 22% and 45% at the anterior side distal tibia, respectively, and 19% and 23% at the lateral side of the fibula head, respectively. These results indicate that the integration of compliant features within the socket structure is an effective way to reduce potentially harmful contact pressure and increase patient comfort.

Amputees↗
PubMed2005

Coordination of hemiparetic locomotion after stroke rehabilitation.

OBJECTIVES: Determine whether a rehabilitation program targeting functional motor recovery of persons with poststroke hemiparesis improved motor coordination. METHODS: A subgroup of 20 persons with poststroke hemiparesis (n = 11 in intervention and n =9 in control group) was investigated from within a larger randomized controlled single-blind clinical trial of 100 patients. Motor coordination was measured using a pedaling task, and subjects in the intervention group pedaled during an intensive broad-based home exercise program that targeted flexibility, strength, balance, and endurance. Coordination variables based on paretic leg pedal forces and EMG of 4 thigh muscles were measured while pedaling pre- and postintervention. RESULTS: Despite extensive pedaling practice, up to 30 half-hour sessions that were progressively more intense, there was no effect (P > 0.05) of the intervention on percent of total work done by the paretic leg, quantitative measures of EMG, or pedaling speed. However, walking speed was improved and pedaling and walking faster were associated after the intervention. CONCLUSIONS: There is no evidence of improved locomotor coordination postintervention. The increased walking and pedaling speed was likely achieved by a more proficient use of the same impaired pattern without EMG timing changes, likely because of increased strength and endurance postintervention. A more task-specific intervention may be required to improve coordination, consistent with principles of use-dependent plasticity.

Aged↗
PubMed2005

Ankle plantar flexor force production is an important determinant of the preferred walk-to-run transition speed.

The mechanisms that govern the voluntary transition from walking to running as walking speed increases in human gait are not well understood. The objective of this study was to examine the hypothesis that plantar flexor muscle force production is greatly impaired at the preferred transition speed (PTS) due to intrinsic muscle properties and, thus, serves as a determinant for the walk-to-run transition. The plantar flexors have been shown to be important contributors to satisfying the mechanical energetic demands of walking and are the primary contributors to the observed ground reaction forces (GRFs) during the propulsion phase. Thus, if the plantar flexor force production begins to diminish near the PTS despite an increase in muscle activation, then a corresponding decrease in the GRFs during the propulsion phase would be expected. This expectation was supported. Both the peak anterior/posterior and vertical GRFs decreased during the propulsion phase at walking speeds near the PTS. A similar decrease was not observed during the braking phase. Further analysis using forward dynamics simulations of walking at increasing speeds and running at the PTS revealed that all lower extremity muscle forces increased with walking speed, except the ankle plantar flexors. Despite an increase in muscle activation with walking speed, the gastrocnemius muscle force decreased with increasing speed, and the soleus force decreased for walking speeds exceeding 80% PTS. These decreases in force production were attributed to the intrinsic force-length-velocity properties of muscle. In addition, the running simulation analysis revealed that the plantar flexor forces nearly doubled for similar activation levels when the gait switched to a run at the PTS due to improved contractile conditions. These results suggest the plantar flexors may serve as an important determinant for the walk-to-run transition and highlight the important role intrinsic muscle properties play in determining the specific neuromotor strategies used in human locomotion.

Adult↗
PubMed2003

Biomechanics and muscle coordination of human walking: part II: lessons from dynamical simulations and clinical implications.

Principles of muscle coordination in gait have been based largely on analyses of body motion, ground reaction force and EMG measurements. However, data from dynamical simulations provide a cause-effect framework for analyzing these measurements; for example, Part I (Gait Posture, in press) of this two-part review described how force generation in a muscle affects the acceleration and energy flow among the segments. This Part II reviews the mechanical and coordination concepts arising from analyses of simulations of walking. Simple models have elucidated the basic multisegmented ballistic and passive mechanics of walking. Dynamical models driven by net joint moments have provided clues about coordination in healthy and pathological gait. Simulations driven by muscle excitations have highlighted the partial stability afforded by muscles with their viscoelastic-like properties and the predictability of walking performance when minimization of metabolic energy per unit distance is assumed. When combined with neural control models for exciting motoneuronal pools, simulations have shown how the integrative properties of the neuro-musculo-skeletal systems maintain a stable gait. Other analyses of walking simulations have revealed how individual muscles contribute to trunk support and progression. Finally, we discuss how biomechanical models and simulations may enhance our understanding of the mechanics and muscle function of walking in individuals with gait impairments.

Biomechanical Phenomena↗
PubMed2002

Biomechanics and muscle coordination of human walking. Part I: introduction to concepts, power transfer, dynamics and simulations.

Current understanding of how muscles coordinate walking in humans is derived from analyses of body motion, ground reaction force and EMG measurements. This is Part I of a two-part review that emphasizes how muscle-driven dynamics-based simulations assist in the understanding of individual muscle function in walking, especially the causal relationships between muscle force generation and walking kinematics and kinetics. Part I reviews the strengths and limitations of Newton-Euler inverse dynamics and dynamical simulations, including the ability of each to find the contributions of individual muscles to the acceleration/deceleration of the body segments. We caution against using the concept of biarticular muscles transferring power from one joint to another to infer muscle coordination principles because energy flow among segments, even the adjacent segments associated with the joints, cannot be inferred from computation of joint powers and segmental angular velocities alone. Rather, we encourage the use of dynamical simulations to perform muscle-induced segmental acceleration and power analyses. Such analyses have shown that the exchange of segmental energy caused by the forces or accelerations induced by a muscle can be fundamentally invariant to whether the muscle is shortening, lengthening, or neither. How simulation analyses lead to understanding the coordination of seated pedaling, rather than walking, is discussed in this first part because the dynamics of pedaling are much simpler, allowing important concepts to be revealed. We elucidate how energy produced by muscles is delivered to the crank through the synergistic action of other non-energy producing muscles; specifically, that a major function performed by a muscle arises from the instantaneous segmental accelerations and redistribution of segmental energy throughout the body caused by its force generation. Part II reviews how dynamical simulations provide insight into muscle coordination of walking.

Bicycling↗