Ing Shiou Hwang

A rehabilitation robot with force-position hybrid fuzzy controller: hybrid fuzzy control of rehabilitation robot

The goal of this study was to design a robot system for assisting in the rehabilitation of patients with neuromuscular disorders by performing various facilitation movements. The robot should be able to guide patients wrist to move along planned linear or circular trajectories. A hybrid position/force controller incorporating fuzzy logic was developed to constrain the movement in the desired direction and to maintain a constant force along the moving direction. The controller was stable in the application range of movements and forces. Offline analyses of data were used to quantitatively assess the progress of rehabilitation. The results show that the robot could guide the upper limbs of subjects in linear and circular movements under predefined external force levels and apply a desired force along the tangential direction of the movements.

Assessment of soleus motoneuronal excitability using the joint angle dependent H reflex in humans

As variations in the amplitude of H reflex potentials can be influenced by changes in muscle length, motoneuronal excitability in terms of H reflex during free movement has long been argued. With the maximal M response controlled, the present study compared several H reflex parameters in order to assess motoneuronal excitability of the resting soleus for different ankle angles (plantarflexion 20 degrees, neutral, and dorsiflexion 20 degrees ). All H-related parameters were dependent on joint angle, suggesting that soleus motoneuronal excitability in the dorsiflexed position was significantly suppressed. By contrast, soleus motoneuronal excitability in the plantarflexed position was not effectively modulated since H-related parameters did not differ from their neutral-position analogs. Methodologically, assessment of joint angle-dependent modulation of motoneuronal excitability requires meticulous control of M responses and selection of appropriate parameters that are insensitive to possible physical modulation and spatial shift of the M recruitment curve confounded by geometrical factors.

Postural tremor and control of the upper limb in air pistol shooters

Abstract A postural tremor appears whenever someone attempts to maintain a steady position against gravity. We examined the postural tremor that occurred while air pistol shooters were taking aim so as to compare the coordinative control of the shooters and to identify the features critical to successful shooting. Ten elite and ten pre-elite athletes participated in pistol shooting at 10 m, and the postural tremors in the pistol and upper limb were recorded with lightweight accelerometers. Exploratory analysis showed that the elite shooters had smaller tremor amplitudes than the pre-elite shooters in the pistol and distal arm segments. Compared with the pre-elite shooters, the elite shooters had a smaller tremor amplitude in the lateral direction relative to that in the vertical direction, together with weaker tremor coupling in the lateral direction and stronger vertical coupling of the pistol–hand complex. The resulting shot performance was inversely related to the amplitude of the tremor and to the 8–12 Hz spectral peak of the lateral tremor in the pistol–hand complex. We conclude that the postural tremors of air pistol shooters are associated with the skill of the shooters, and that the elite shooters could optimize the control of the pistol–hand complex, which strongly determined success in shooting.

Postural Adjustment of Children With Spastic Diplegic Cerebral Palsy During Seated Hand Reaching in Different Directions

OBJECTIVES To examine the effect of reaching in different directions on postural adjustment in children with diplegic cerebral palsy (CP), and to examine the relationship between hand reach performance and postural adjustment, and between postural control ability and postural adjustment. DESIGN Cross-sectional study. SETTING A movement science laboratory at a medical university. PARTICIPANTS Children with CP (n=12) and typically developing (TD) children (n=16). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Two force platforms were used to measure the ground reaction force (GRF) and center of pressure (COP) data. Absolute peak COP velocity, COP sway ratio (SR), and mean GRF in the anterior posterior direction during the acceleration and deceleration segments of a reaching task were the main outcome measures. RESULTS Children with CP showed a greater absolute peak COP velocity in the medial lateral direction, a smaller SR (wider COP pattern), and greater amplitude of force modulation (exaggerated postural adjustments) than TD children in lateral or medial reaches. There was a moderate correlation between SR and total Pediatric Reach Test score. The chair SR was also negatively correlated with the hand movement units. CONCLUSIONS Children with CP showed wider, more crooked, and less efficient COP patterns than TD children, especially on medial or lateral reaches. Reaching medially or laterally involves trunk rotation, which produces more postural challenges than reaching anteriorly to children with CP. The patterns of postural adjustments in children with CP were correlated with their postural control ability and hand-reach smoothness.

Electromyographic analysis of locomotion for healthy and hemiparetic subjects--study of performance variability and rail effect on treadmill.

This study quantified the performance variability and effect of rail support on the ankle joint for normal and hemiparetic subjects during treadmill walking. Muscle activities of the anterior tibialis (TA) and medial gastrocnemius (MG) from six hemiparetic patients and 14 healthy subjects were assessed with EMG linear envelope and variance ratio of consecutive strides at self-selected cadences. Our results indicate that (1) performance consistency of the hemiparetic patients was significantly undermined; (2) habituated process during treadmill walking was notable in the MG but not in the TA; and (3) rail support could reduce performance variability of the ankle antagonist pairs.

Reciprocal influences on performances of a postural–suprapostural task by manipulating the level of task-load

The objective of this study was to investigate the reciprocal influences of stance pattern (bilateral stance vs. unilateral stance) and thumb-index precision grip task (static target vs. dynamic target) on postural-suprapostural tasks by manipulating task-load. Fifteen healthy volunteers participated in four postural-suprapostural tasks, including static force-matching in bilateral/unilateral stance (BS_static; US_static), dynamic force-matching in bilateral/unilateral stance (BS_dynamic; US_dynamic), and two control tasks in bilateral and unilateral stances without a finger task. The normalized force error (NFE), reaction time (RT) of the finger tasks, and normalized change in center of pressure sway (Delta NCoP) were measured. For suprapostural task performance, a significant interaction effect between postural and suprapostural tasks on NFE of the finger tasks was noted (static: BS<US; dynamic: BS>US), but RT was not different among the four tasks. For postural task performance, negative Delta NCoP during unilateral stance indicated a spontaneous reduction in postural sway due to added force-matching. In contrast, addition of force-matching tended to increase postural sway during bilateral stance, but postural fluctuations decreased as task-load of suprapostural task increased (BS_dynamic<BS_static). In conclusion, performance of postural-suprapostural tasks was differently modulated by task-load increment. Our observations favored adaptive resource-sharing and implicit expansion of resource capacity for a postural task with a motor suprapostural goal.

Reorganization of multidigit physiological tremors after repetitive contractions of a single finger

In light of the interplay among physiological finger tremors, this study was undertaken to investigate the transfer effect of fatigue on coordinative strategies of multiple fingers. Fourteen volunteers performed prolonged position tracking with a loaded middle finger while measures of neuromuscular function, including electromyographic activities of the extensor digitorum (ED)/flexor digitorum superficialis (FDS) and physiological tremors of the index, middle, ring, and little fingers, were monitored. The subjects exhibited inferior tracking congruence and an increase in ED activity at the end of the tracking. Fatigue spread was manifested in a remarkable increase in tremor across fingers, in association with enhanced involuntary tremor coupling among fingers that was topologically organized in relation to the distance of the digits from the middle finger. Principal component analysis suggested that an enhanced 8- to 12-Hz central rhythm contributed primarily to the tremor restructure following fatigue spread. The observed tremor reorganization validated the hypothesis that the effect of fatigue was not limited to the instructed finger and that fatigue functionally decreased independence of the digits. The spreading of fatigue weakens neural inputs that diverge to motor units acting on various digits because of fatigue-related enhancement of common drive at the supraspinal level.

Modulation of soleus H-reflex amplitude and variance during pretibial contraction-effects of joint position and effort level

To investigate the effects of joint position and effort level of antagonist contraction on reciprocal inhibition, experiments with 15 healthy volunteers were performed to compare the changes of standardized soleus H reflex during dorsiflexion contraction (0%, 25%, 50%, 75% maximal voluntary contraction [MVC] associated with different ankle positions (plantarflexion 20, neutral, and dorsi -flexion 20). The results indicated that a decrease of the soleus H response was dependent on the level of pretibial contraction, but a significant interaction of ankle position and pretibial contraction was noted (p. 05). These findings suggest that progressive reciprocal inhibition was position relevant pertaining to joint stability as well as force variability.

Eye-Hand Synergy and Intermittent Behaviors during Target-Directed Tracking with Visual and Non-visual Information

Visual feedback and non-visual information play different roles in tracking of an external target. This study explored the respective roles of the visual and non-visual information in eleven healthy volunteers who coupled the manual cursor to a rhythmically moving target of 0.5 Hz under three sensorimotor conditions: eye-alone tracking (EA), eye-hand tracking with visual feedback of manual outputs (EH tracking), and the same tracking without such feedback (EHM tracking). Tracking error, kinematic variables, and movement intermittency (saccade and speed pulse) were contrasted among tracking conditions. The results showed that EHM tracking exhibited larger pursuit gain, less tracking error, and less movement intermittency for the ocular plant than EA tracking. With the vision of manual cursor, EH tracking achieved superior tracking congruency of the ocular and manual effectors with smaller movement intermittency than EHM tracking, except that the rate precision of manual action was similar for both types of tracking. The present study demonstrated that visibility of manual consequences altered mutual relationships between movement intermittency and tracking error. The speed pulse metrics of manual output were linked to ocular tracking error, and saccade events were time-locked to the positional error of manual tracking during EH tracking. In conclusion, peripheral non-visual information is critical to smooth pursuit characteristics and rate control of rhythmic manual tracking. Visual information adds to eye-hand synchrony, underlying improved amplitude control and elaborate error interpretation during oculo-manual tracking.

Behavioral data and neural correlates for postural prioritization and flexible resource allocation in concurrent postural and motor tasks

This study was undertaken to investigate the reciprocity effect between postural and suprapostural performances and its underlying neural mechanisms wherein subjects executed a perceptual‐motor suprapostural task and maintained steady upright postures. Fourteen healthy individuals conducted force‐matching maneuvers (static vs. dynamic) under two stance conditions (bipedal stance vs. unipedal stance); meanwhile, force‐matching error, center of pressure dynamics, event‐related potentials (ERPs), and the movement‐related potential (MRP) were monitored. The behavioral results showed that force‐matching error and postural sway were differently modulated by variations in stance pattern and force‐matching version. Increase in postural challenge undermined the precision of static force‐matching but facilitated a dynamic force‐matching task. Both static and dynamic force‐matching tasks improved postural control of unipedal stance but not of bipedal stance, in reference to the control conditions. ERP results revealed a stance‐dependent N1 response, which was greater around the parietal cortex in the unipedal stance conditions. Instead, P2 was modulated by the effect of the suprapostural motor task, with a smaller P2 in the right parietal cortex for dynamic force‐matching. Spatiotemporal evolution of the MRP commenced at the left frontal‐central area and spread bilaterally over the frontal‐central and parietal cortex. MRP onset was subject to an analogous interaction effect on force‐matching performance. Our findings suggest postural prioritization and a structural alternation effect of stance pattern on postural performance, relevant to implicit expansion and selective allocation of central resources for relative task‐loads of a postural‐suprapostural task. Hum Brain Mapp, 2013.