Joint Angular Position Research Articles

13.19 Lower limb kinetics changes during obstacles-crossingfollowing anterior cruciate ligament injury

Ankle-foot orthosis moment resisting plantarflexion has systematic effects on ankle and knee joint motion in individuals post-stroke. However, it is not known how much ankle-foot orthosis moment is generated to regulate their motion. The aim of this study was to quantify the contribution of an articulated ankle-foot orthosis moment to regulate ankle and knee joint motion during gait in individuals post-stroke.Gait data were collected from 10 individuals post-stroke using a Bertec split-belt instrumented treadmill and a Vicon 3-dimensional motion analysis system. Each participant wore an articulated ankle-foot orthosis whose moment resisting plantarflexion was adjustable at four levels. Ankle-foot orthosis moment while walking was calculated under the four levels based on angle-moment relationship of the ankle-foot orthosis around the ankle joint measured by bench testing. The ankle-foot orthosis moment and the joint angular position (ankle and knee) relationship in a gait cycle was plotted to quantify the ankle-foot orthosis moment needed to regulate the joint motion.Ankle and knee joint motion were regulated according to the amount of ankle-foot orthosis moment during gait. The ankle-foot orthosis maintained the ankle angular position in dorsiflexion and knee angular position in flexion throughout a gait cycle when it generated moment from − 0.029 (0.011) to − 0.062 (0.019) Nm/kg (moment resisting plantarflexion was defined as negative).Quantifying the contribution of ankle-foot orthosis moment needed to regulate lower limb joints within a specific range of motion could provide valuable criteria to design an ankle-foot orthosis for individuals post-stroke.

Kinematic analyses of semireclined leg cycling in able-bodied and spinal cord injured individuals

Retrospective descriptive study. To evaluate the leg kinematics and motion characteristics within able-bodied (AB) and spinal cord injured (SCI) individuals during stationary semireclined cycling. Functional Performance Laboratory, Connecticut, USA. Three SCI and three AB subjects participated in steady-state leg pedaling (50 revolutions per minute). The SCI group participated in electrical stimulation (FES)-induced cycling at resistances of 0, 6.25, and 12.5 Watts (W). The AB group cycled on the same ergometer without FES at resistances of 0, 60, and 120 W. Motion capture analysis recorded joint angular position, velocity, and acceleration at hip, knee, and ankle. Joint kinematics of hip, knee, and ankle were measured during steady-state leg cycling and comparisons were made between AB and SCI subjects as resistance proportionally and relatively increased. Intrasubject hip and knee movement patterns showed minimal variability across resistance levels. Comparisons between AB and SCI subjects showed that the hip and knee kinematics were very similar at all resistance levels. However, ankle movement patterns appeared to increase in variability (increased dorsiflexion) with increased resistance level in AB subjects and less so with SCI subjects. Overall, the ankle kinematics for AB and SCI subjects were dissimilar at resistance levels greater than zero. The joint kinematics of the hip, knee, and ankle were found to be periodic, but the differences in ankle kinematics in AB and SCI subjects suggest more emphasise should be placed on the current design of the bike-pedal and subject-specific seat configurations.

Joint position sense in elderly fallers: A preliminary investigation of the validity and reliability of the SENSERite measure

You SH. Joint position sense in elderly fallers: a preliminary investigation of the validity and reliability of the SENSERite measure. Arch Phys Med Rehabil 2005;86:346–52. Objectives To establish the validity and reliability of the SENSERite system and to determine and compare proprioceptive acuity thresholds (PATs) among 3 groups. Design Between groups, repeated measures, with randomized sequence. Setting University research laboratory. Participants Forty-six adults recruited into 1 of 3 groups: group 1, 10 healthy young adults (mean age, 22.20y); group 2, 22 healthy older adults (mean age, 73.12y); and group 3, 14 older adults with a history of falls (mean age, 73.21y). Interventions The validity of SENSERite’s joint position measure was determined by comparing the system’s performance with a validated goniometer measure. The test-retest reliability was determined by repeatedly measuring the established joint positions for the neutral, inversion, eversion, plantarflexion, and dorsiflexion on 2 separate occasions, approximately 24 hours apart. In addition, PATs were measured to determine group differences. Data were analyzed by means of a univariate analysis of variance (ANOVA), intraclass correlation coefficient (ICC 2,k), and paired t tests. Main outcome measures Error in active reproduction of position and PAT derived from the 5 respective joint position sense tests. Results Excellent clinical goniometer and SENSERite correlation (ICC 2,k=1.0, P<.05) was found. The test-retest reliability for the 5 respective position sense tests were excellent (ICC 2,k range, .88–.99; P<.05). ANOVA revealed a significant difference in PATs among the 3 groups. Post hoc analysis indicated that PAT was greater in groups 2 and 3 than in group 1. No significant difference in PAT was observed between groups 2 and 3. Conclusions The ability of the SENSERite to measure joint angular position was as good as that of a clinical goniometer; it had an adequate reliability when tested on 2 separate occasions. The device detected differences between elderly and young subjects, but it did not discriminate differences between fallers and nonfallers. This finding indicates that there is no significant difference between the fallers and nonfallers in proprioceptive acuity.

The role of shortening reaction in mediating rigidity in Parkinson?s disease

Rigidity in Parkinson's disease (PD) is defined as an increased resistance to passive movement of a joint. The plastic-type rigidity is uniform and constant throughout the entire range of motion, whereas the cogwheel-type rigidity is accompanied by tremor. Rigidity in PD has been understudied. Thus, its pathophysiological basis remains unclear. The purpose of the study is to examine neuromuscular/biomechanical properties of PD rigidity and to provide its physiological characteristics. We hypothesize that PD rigidity presents as a flattened trace of joint torque vs. angular position (torque-angle relation) of the wrist, because the forces generated by lengthening muscles are offset by activation of the antagonist, i.e. show "shortening reaction" (SR). Experiments were conducted on six PD subjects medication OFF and ON. PD severity was assessed based on the unified Parkinson's disease rating scale. Each subject sat on a chair and was instructed to relax, with the wrist coupled to the device. The servomotor applied constant velocity displacement to create wrist flexion/extension. Electromyographic (EMG) responses were monitored from wrist muscles, along with position, velocity and torque. EMG magnitudes were computed over the movement period. Slopes were derived from the torque-angle trace. Results showed that SRs were routinely recorded OFF medication, but substantially reduced ON medication. Due to the interaction of SR, torque-angle relation was flatter OFF medication and became steeper ON medication. Correlation analyses showed that a strong correlation (R=0.65) existed between SR and torque-angle slope OFF medication, exclusively. We suggest that SR may play an important role in mediating the mechanical features of PD rigidity.

Kinematics of wrist joint flexion in overarm throws made by skilled subjects.

Previous studies of multijoint arm movements have shown that the CNS holds arm kinematics constant in different situations by predictively compensating for the effects of interaction torques. We determined whether this was also the case for wrist joint flexion in natural overarm throws performed by skilled subjects in 3D, a situation where large passive torques can occur at the wrist. Specifically, we investigated whether wrist flexion amplitudes are held constant in throws of different speeds. Joint rotations were recorded at 1,000 Hz with the search-coil technique. Contrary to a previous study on constrained 2D throwing, indirect evidence was found that in fast throws passive torques associated with forearm deceleration were exploited to increase wrist flexion velocity. This increase in wrist flexion velocity was associated with constant wrist flexion amplitudes at ball release (mean 27 degrees) for throws of different speeds. Furthermore, final wrist flexion positions after ball release were similar for a particular subject irrespective of the speed of the throw. This was associated in faster throws with increased magnitudes of wrist flexor and wrist extensor EMG activity which damped passive torques associated with forearm angular deceleration. It is concluded that wrist flexion in overarm throws of different speeds is produced by central signals which precisely control net joint torque by both exploiting and damping passive torques during different parts of the throw to keep wrist joint angular position parameters constant. As such the results show that control strategies for natural 3D throwing are different from those for constrained 2D throwing.

A NORMATIVE DATABASE OF ISOKINETIC UPPER-EXTREMITY JOINT STRENGTHS: TOWARDS THE EVALUATION OF DYNAMIC HUMAN PERFORMANCE

The objective of this study was to provide a normative database of dynamic upper-extremity (shoulder and elbow) joint strengths to fill the current void in literature for multidimensional strength capacity profiles. The isokinetic strength of the elbow and shoulder joints was tested for twenty normal males and females. The independent variables consisted of joint angular position, joint angular velocity, direction of exertion, and gender. The measured joint strength (torque, Nm) was the only defined dependent variable. The majority of existing joint strength prediction models and normative databases are static (isometric) in nature. The few available dynamic models are reported in the form of torque as a function of joint angle. Since joint strength is a function of both the joint angular position and angular velocity, descriptive models should take this interaction into consideration. The dynamic joint strengths of the subjects were studied using the KIN_COM 125E Plus. A second-order multiple regression analysis was used to model the dynamic 3-D strength surface response of each joint in each direction of exertion. Analysis of variance (ANOVA) with repeated measures design was used to test for the effects of gender, angular position, angular velocity, and direction on the dynamic strength of each joint, joint strength was significantly influenced by dynamic parameters such as the angular velocity. The interaction between angular position and velocity was highly significant. 3-D strength surface representation may be used as a "performance capacity envelope" to comprehensively characterize an individual's dynamic joint strength performance.

Surface Responses of Maximum Isokinetic Ankle Torque Generation Capability

The majority of existing normative torque generation capability (torque capability for short) databases are reported in the form of torque as a function of joint angle. although it is well recognized that torque capability is a function of both the joint angular position and angular velocity. The main objective of this study was to develop the methodology of 3-D dynamic representation of torque capability using the ankle joint as an example. The ankle torque capability of 20 males and females was assessed at 5 levels of ankle joint angular positions and velocities in each direction of plantar and dorsi flexion. The ANOVA results indicated significant main effects of joint angular position, angular velocity, direction, and gender, in addition to the interaction effect of angular position and velocity (p &lt; .003) on the torque capability of the ankle joint. The regression analysis indicated that an individualized quadratic surface response performed significantly belter than the models developed for each gender or the whole population using the coefficient of determination and standard error of the regression as criteria. Such 3-D representation of torque capability has a broad spectrum of applications ranging from rehabilitation and ergonomic to biomechanical applications.

Determination of the effect of lift characteristics on dynamic performance profiles during manual materials handling tasks

In any quantitative gait or occupational biomechanics investigation, the quantification of the different kinematic, kinetic, and electromyographic parameters is essential towards assessment of functional capacity and development of a biomechanical profile of the task demands. In the current study, the authors presented a methodology for using inferential statistics to evaluate the effect of lift characteristics on phase-dependent and phase-independent variability in performance. Using a database of kinematic and kinetic profiles obtained from a manual lifting study, the phase-dependent effects of lift characteristics: box mass (load), mode (technique of lift), and speed (frequency of lift) were investigated through the use of analysis of variance (ANOVA) techniques, which recognize the vectorial constitution of the profiles. In addition, the Karhunen-Loeve Expansion (KLE) feature extraction method was used for representing the lifting patterns of measured joint angular position, velocity, acceleration, and net muscular torque profiles obtained from a 2-D biomechanical lifting model in order to study the phase-independent effects. In comparison to traditional descriptive statistical analyses currently used in various occupational biomechanics experimental investigations, this method allows the significant information content of the time varying signal to be captured, enhancing the sensitivity of subsequent hypothesis testing procedures. The application of this technique to MMH investigations allows identification of the lift characteristics that dominate the variability of task demands, hence aiding in the design and assessment of ergonomic solutions.

Reduced-order observer-based point-to-point and trajectory controllers for robot manipulators

This paper presents a design procedure for a reduced-order observer-based controller dedicated to n-joint robot manipulators. It is assumed that only the joint angular positions are measured. The joint angular velocities are estimated via an exponential reduced-order observer. Two types of control laws based on this observer are studied: point-to-point control with gravity compensation and trajectory control. Sufficient conditions to ensure the closed-loop stability are given. Performances of the reduced-order observer used with these two control laws are illustrated in a simulation study of a two-degrees-of-freedom robot manipulator.

Reduced-Order Observer-Based Point-to-Point and Trajectory Controllers for Robot Manipulators

This note presents a design procedure of a reduced-order observer-based controller for a n-joint robot manipulators. We assume that only the joint angular positions are measured. The joint angular velocities are estimated via an exponential reduced-order observer. Two types of control laws based on this observer are studied: a point-te-point control with gravity compensation and a trajectory control. Sufficient conditions to ensure the closed-loop stability are given. Performances of the reduced-order observer used with these two control laws are illustrated in a simulation study of a two degrees-of-freedom robot manipulator.

Note: A statistical problem in testing invariance of movement using the phase plane model.

Invariant positions on a phase plane of joint angular position and velocity have been proposed as a means by which interlimb coordination may be achieved. This note identifies a problem in the testing, using conventional statistics, of hypotheses derived using the phase plane model. A possible solution is proposed based on directional statistics. Conclusions regarding phase angle invariance, which are based on conventional statistics, must be viewed with some caution.

A parameter identification method for robot dynamic models using a balancing mechanism

SUMMARYAccurate modeling of robot dynamics is a prerequisite for the design of model-based control schemes and enhancement of the performance of the robot. The dynamic parameters associated with a pseudo-inertia matrix are often difficult to identify accurately because the inertia torques are small in comparison to gravity loadings, thus creating signal processing problem. The identification method presented in this paper utilizes a balancing mechanism which increases the estimation accuracy of the dynamic parameters. The balancing mechanism has the effect of amplifying the inertia-related torque signal by eliminating gravity loadings acting on the robot joints. A series of motion data were experimentally obtained through sequential test steps. By incorporating the measured information about joint torques, angular positions, velocities and accelerations the least square algorithm was used to identify the dynamic parameters. The estimated values were converted to those of the original robot model to obtain its dynamic model parameters. The identified robot dynamic model was shown to be accurate enough to predict the actual robot motions.

Design and Modeling of a Computer- Controlled Planar Manipulator

This paper describes the design of a computer-controlled planar manipulator and the modeling necessary to derive the dynamic equations of motion. The planar manipulator was built as an experimental research device for work in kine matics, dynamics, controls, design, and sensor development. The device consists of three joints and three links with a gripper and operates in a horizontal plane on air bearings. The planar manipulator was instrumented for position, veloc ity, and torque feedback from each joint and is controlled either manually, using a teach pendant, or directly from a computer. A modularity feature was also designed into the robot to allow for interchanging any electromechanical com ponents and to enable structural substitutions for investiga tions into flexibility and vibrations. The completed robot successfully exceeded performance specifications and design criteria. The next phase of the research focused on the development and evaluation of a computer model designed to simulate the open-loop dynamic behavior of the three-link, three-jointed, high-speed planar manipulator. Describing equations were developed for both the servo actuator and arm dynamics at each joint. Significant terms included were coulomb, viscous, and hysteresis damping; and centripetal, Coriolis, and cou pling inertial effects induced by relative motions of the arm structure. The model used the voltage into the power ampli fiers for each servo drive as the system input, and the joint angular position, velocity, and acceleration as the system output. Results from various inputs including a step-input function, a sinusoidal-input function, and a ramp-input func tion were found to compare closely with experimental data measured from the actual planar manipulator built during the course of the research.

Coordination of three-joint digit movements for rapid finger-thumb grasp.

Human thumb and index finger kinematics were examined for multiple repetitions of a simple grasp task as a means to evaluate motor planning and execution of these important hand movements. Subjects generated a rapid (approximately 90-ms duration) pinch movement of the index finger and thumb from an open-hand position. Approximately 400 repetitions were obtained from four naive subjects. The two-dimensional trajectory of the fingertip and the angular positions of the metacarpophalangeal (MP) and proximal interphalangeal (PIP) joints of the index finger were recorded along with the angular position of the thumb interphalangeal joint (TH). Individual joint angular positions were transduced using planar electrogoniometers of an exoskeletal linkage design. Except for consistent single-peaked joint angle and digit trajectory velocity profiles, most kinematic features of the grasp varied considerably across trials, including fingertip spatial position at contact, specific finger paths, finger and thumb path distances, finger and thumb peak tangential velocities, and 5) individual joint rotation magnitudes and peak velocities. However, this kinematic variability was not random. Variable TH angular positioning was paralleled by complementary two-dimensional variations in the finger path. These fingertip adjustments were accomplished by actively controlled, reciprocal angular positioning of the MP and PIP joints. Specifically, with natural reductions in thumb flexion, MP flexion was greater while PIP flexion was reduced and vice versa. These adjustments acted to minimize variations in the point contact of the finger on the thumb and yielded a robust and seemingly natural preference for finger-thumb contact at the more distal surfaces of the digits. The kinematic variability was not due to the finger and thumb movements being controlled independently of digit contact. The variable appositional movements of the finger and thumb and the associated contact force were generated as a single action. This was indicated by an absence of kinematic or force adjustments after contact, smooth digit trajectories with a single peak in their tangential velocities, and finger-thumb contact that consistently occurred well after peak velocity. Likewise, because the variability in the kinematics of the grasp was systematic, it apparently was not due simply to sloppiness or noise in motor execution.(ABSTRACT TRUNCATED AT 400 WORDS)