bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Medio-LateraL Postural Perturbation Induced by Voluntary Arm Raising on the Biomechanical Organization of Rapid Step Initiation
Authors: Yiou Eric , Do Manh-Cuong
Published: August 2016

This study examined how the central nervous system organizes mediolateral (ML) “anticipatory postural adjustments” (APAs) for stepping initiation (SI) to take into account the postural perturbation induced by voluntary lateral arm raising. Subjects purposely stepped in isolation (“isolated stepping”) or in combination with lateral raising of dominant arm (“motor sequence”). SI was carried out with the leg ipsilateral or controlateral to raising arm. Results showed that APA amplitude increased from “ipsilateral isolated stepping” to “ipsilateral sequence”, but did not change in conditions involving controlateral leg; ML instability increased from “ipsilateral isolated stepping” to “ipsilateral sequence”, but decreased from “controlateral isolated stepping” to “controlateral sequence”. These changes were exacerbated when inertia was added at the hand during raising. These results suggest that APAs for SI are globally scaled as a function of the biomechanical consequences of forthcoming arm movement on ML postural stability.
A Test of the Rambling and Trembling Hypothesis: Multiple Sclerosis and Postural Control
Authors: Shin Sunghoon , Motl Robert W. , Sosnoff Jacob J.
Published: August 2016

The rambling-trembling analysis of postural control maintains that the center of pressure (COP) trajectory can be decomposed into deviations resulting from supraspinal (i.e., rambling; RM) and spinal processes (i.e., trembling; TM). The purpose of this investigation was to test the rambling and trembling hypothesis by comparing persons with multiple sclerosis (MS) who had either elevated or normal spinal reflexes to healthy controls. 16 subjects with MS and 16 age and gender matched control subjects completed a postural control task. The persons with MS were divided into groups with high (MShigh) or low (MSlow) H-reflex amplitude. The MShigh group had an elevated ratio of TM to COP compared with healthy controls, but no differences in the ratio between RM and COP. The findings are congruent with the assumptions of the rambling-trembling hypothesis. Further work is needed to determine if RM and TM represent distinct spinal and supraspinal mechanisms to postural control.
Exploring the Thresholds of Vision for Perception and Action
Authors: de Wit Matthieu M. , Masters Rich S.W. , van der Kamp John
Published: August 2016

Based upon evidence that vision for action has quicker access to visual information than vision for perception, we hypothesized that the two systems may have differentiated visual thresholds. There is also evidence that, unlike vision for perception, vision for action is insensitive to cognitive dual-task interference. Using visual masking, we determined the visual thresholds of 15 participants in a perception task, an action task and an action plus concurrent cognitive secondary task. There was no difference in threshold between the perception task and the action task, but the action plus concurrent secondary task was accompanied by a greater visual threshold than both the perception task and the action task alone, indicating dual-task interference. The action task was thus most likely informed by vision for perception. The implications of these results are reviewed in the context of recent discussions of the two visual systems model.
Examining Impulse-Variability in Overarm Throwing
Authors: Urbin M.A. , Stodden David , Boros Rhonda , Shannon David
Published: August 2016

The purpose of this study was to examine variability in overarm throwing velocity and spatial output error at various percentages of maximum to test the prediction of an inverted-U function as predicted by impulse-variability theory and a speed-accuracy trade-off as predicted by Fitts’ Law Thirty subjects (16 skilled, 14 unskilled) were instructed to throw a tennis ball at seven percentages of their maximum velocity (40–100%) in random order (9 trials per condition) at a target 30 feet away. Throwing velocity was measured with a radar gun and interpreted as an index of overall systemic power output. Within-subject throwing velocity variability was examined using within-subjects repeated-measures ANOVAs (7 repeated conditions) with built-in polynomial contrasts. Spatial error was analyzed using mixed model regression. Results indicated a quadratic fit with variability in throwing velocity increasing from 40% up to 60%, where it peaked, and then decreasing at each subsequent interval to maximum (p < .001, η2 = .555). There was no linear relationship between speed and accuracy. Overall, these data support the notion of an inverted-U function in overarm throwing velocity variability as both skilled and unskilled subjects approach maximum effort. However, these data do not support the notion of a speed-accuracy trade-off. The consistent demonstration of an inverted-U function associated with systemic power output variability indicates an enhanced capability to regulate aspects of force production and relative timing between segments as individuals approach maximum effort, even in a complex ballistic skill.
Reconstruction of the Unknown Optimization Cost Functions from Experimental Recordings During Static Multi-Finger Prehension
Authors: Niu Xun , Terekhov Alexander V. , Latash Mark L. , Zatsiorsky Vladimir M.
Published: August 2016

The goal of the research is to reconstruct the unknown cost (objective) function(s) presumably used by the neural controller for sharing the total force among individual fingers in multifinger prehension. The cost function was determined from experimental data by applying the recently developed Analytical Inverse Optimization (ANIO) method (Terekhov et al. 2010). The core of the ANIO method is the Theorem of Uniqueness that specifies conditions for unique (with some restrictions) estimation of the objective functions. In the experiment, subjects (n = 8) grasped an instrumented handle and maintained it at rest in the air with various external torques, loads, and target grasping forces applied to the object. The experimental data recorded from 80 trials showed a tendency to lie on a 2-dimensional hyperplane in the 4-dimensional finger-force space. Because the constraints in each trial were different, such a propensity is a manifestation of a neural mechanism (not the task mechanics). In agreement with the Lagrange principle for the inverse optimization, the plane of experimental observations was close to the plane resulting from the direct optimization. The latter plane was determined using the ANIO method. The unknown cost function was reconstructed successfully for each performer, as well as for the group data. The cost functions were found to be quadratic with nonzero linear terms. The cost functions obtained with the ANIO method yielded more accurate results than other optimization methods. The ANIO method has an evident potential for addressing the problem of optimization in motor control.
Neural and Muscular Determinants of Dorsiflexor Weakness in Chronic Stroke Survivors
Authors: Klein Cliff S. , Power Geoffrey A. , Brooks Dina , Rice Charles L.
Published: August 2016

Few examined the contribution of neural and muscular deficits to weakness in the same stroke subject. We determined maximal voluntary contraction (MVC) and 50 Hz torques, activation (twitch interpolation), electromyographic (EMG) amplitude and antagonist coactivation, and muscle volume using magnetic resonance imaging (MRI) of the dorsiflexors bilaterally in 7 chronic stroke subjects (40–67 y). Recordings of MVC and 50 Hz torque were also done in 7 control subjects (24–69 y) without stroke. The MVC torque was smaller in the contralesional than ipsilesilesional limb (29.8 ± 21.3 Nm vs. 42.5 ± 12.0 Nm, p = .04), and was associated with deficits in activation (r2 = .77) and EMG amplitude (r2 = .71). Antagonist coactivation percentage was not significantly different between limbs. Muscle volume, 50 Hz torque, and specific torque (50Hz torque/muscle volume) were also not different between sides. The concept that atrophy is commonplace after stroke is not supported by the results. Our findings indicate that dorsiflexor weakness in mobile stroke survivors is not explained by atrophy or reduced torque generating capacity suggesting an important role for central factors.
Effect of Visual Feedback on Brain Activation During Motor Tasks: An fMRI Study
Authors: Noble Jeremy W. , Eng Janice J. , Boyd Lara A.
Published: August 2016

This study examined the effect of visual feedback and force level on the neural mechanisms responsible for the performance of a motor task. We used a voxelwise fMRI approach to determine the effect of visual feedback (with and without) during a grip force task at 35% and 70% of maximum voluntary contraction. Two areas (contralateral rostral premotor cortex and putamen) displayed an interaction between force and feedback conditions. When the main effect of feedback condition was analyzed, higher activation when visual feedback was available was found in 22 of the 24 active brain areas, while the two other regions (contralateral lingual gyrus and ipsilateral precuneus) showed greater levels of activity when no visual feedback was available. The results suggest that there is a potentially confounding influence of visual feedback on brain activation during a motor task, and for some regions, this is dependent on the level of force applied.
Age-Related Decline in the Rate of Force Development Scaling Factor
Authors: Bellumori Maria , Jaric Slobodan , Knight Christopher A.
Published: August 2016

Physical quickness is less in older adults with implications for fall prevention, movement initiation, and activities of daily living. The purpose was to compare control of rapid contractions in young and older adults within two diverse muscle groups: powerful elbow extensors (EE) and dexterous index finger abductors (IFA). Most-rapid force pulses to a variety of levels were recorded and peak force and rate of force development (RFD) were analyzed with linear regression. The resulting slope represents the dependent variable of interest, the RFD-scaling factor (RFD-SF). RFD-SF of EE and IFA strongly correlated both overall (r = .87, p < .01) and separately in young (r = .60, p < .05) and older (r = .77, p < .01) adults. RFD-SF values were different between muscle groups (F1,28 = 19.1, p < .001) and also less in elderly (F1,28 = 32.6, p < .001). We conclude that RFD-SF provides a sensitive assessment of muscle quickness that can be used to evaluate neuromuscular function in aging humans.
The Effect of Transcranial Direct Current Stimulation on Perception of Effort in an Isolated Isometric Elbow Flexion Task
Authors: Lampropoulou Sofia I. , Nowicky Alexander V.
Published: August 2016

The purported ergogenic actions of transcranial direct current stimulation (tDCS) applied to motor cortex (M1) on force production and perception of effort were investigated using a 10-item numerical rating scale (0–10 NRS) in nonfatiguing bouts of a force-matching task utilizing isometric elbow flexion. Using a crossover design, 12 healthy volunteers received sham, anodal, and cathodal tDCS randomly for 10 min (1.5 mA, 62 μA/cm2) to the left M1 in a double-blind manner. Corticospinal excitability changes were also monitored using transcranial magnetic stimulation (TMS) with surface electromyography (sEMG) to monitor both motor evoked potentials (MEPs) and force-EMG from right m. biceps brachii and m. brachioradialis brachii. No significant differences between the verum and sham stimulation were obtained for elbow flexion maximum voluntary force, perception of effort, or sEMG. There were also no significant differences in MEP changes for the types of tDCS, which is consistent with reports that tDCS excitability effects are diminished during ongoing cognitive and motor activities.
Is Dynamical Systems Modeling Just Curve Fitting?
Authors: Rosenbaum David A.
Published: August 2016

The development of mathematical tools for describing dynamical systems has made it possible to characterize forms of behavior that could not be characterized before. This represents progress, but the enterprise runs the risk of being nothing more than curve fitting if investigators fail to identify the physical, biological, or psychological mechanisms which are common to systems that follow the same dynamical regime and which are not common to systems that do not follow the same dynamical regime.
Provision of External Cues and Movement Sequencing in Parkinson's Disease
Authors: Rogers Mark A. , Phillips James G. , Bradshaw John L. , lansek Robert , Jones Dean
Published: August 2016

The basal ganglia (BG) may play a part in motor sequencing. Individuals with Parkinson's disease (PD) may exhibit progressive slowing (sequence effect) during motor sequences such as writing (micrographia) and gait. In the present study, a serial two-way choice reaction time task was employed, in which advance information about each next movement was not provided until the participant began moving, thereby assessing the participant's ability to utilize advance information. Participants were 13 individuals with idiopathic PD and 13 age-matched controls. Both PD subjects and controls showed a significant sequence effect in the absence of advance information, possibly reflecting difficulty in initiating and maintaining movement without external cues. PD subjects and controls both exhibited a sequence effect at moderate levels of advance information. At high levels of advance information, PD subjects showed the effect but controls did not, suggesting that controls, unlike PD subjects, were able to use the extra information to facilitate performance, perhaps reflecting more frontal aspects of impairment in PD.
Does Having to Remember the Position of a Target Improve Reaction Time?
Authors: Parr-Brownlie Louise , Wickens Jeffrey , Anson J. Greg , Hyland Brian
Published: August 2016

In the monkey, reaction time in a precued delayed response task was found to be faster when the animals had to remember the precue than when it was continually available (Smyrnis, Taira, Ashe, & Georgopoulos, 1992). We investigated whether this reflects a general principle that applies to all types of precued tasks. However, we found the opposite result in a simpler task in humans. Our findings suggest that the beneficial effect of a memory requirement on reaction time in the monkey may reflect an effect of task difficulty, rather than a fundamental process involved in all precued movement tasks.
Coactivation to Reduce Variability in the Elderly
Authors: Seidler-Dobrin Rachael D. , He jiping , Stelmach George E.
Published: August 2016

The aim of this experiment was to determine whether elderly persons exhibit reciprocal phasing of muscle activity and scale EMG burst amplitude in the same manner as young people. Seven young and 7 elderly adults performed 30° elbow flexion movements at 800 ms duration to a visual target against varying inertial loads. The elderly were not able to achieve the required movement duration as frequently and spent a greater portion of the movement accelerating than the young. The young and the elderly subjects scaled EMG burst amplitude to the increasing loads in the same fashion, although the elderly subjects coactivated the agonisthtagonist muscles more than did the young subjects and thus did not accelerate the limb as rapidly. We hypothesized that the elderly used coactivation to reduce movement variability, and we developed a single-joint model with two muscles to examine this hypothesis. The model simulation correctly predicted the variability reduction due to coactivation. It appears, however, that this reduces the capability to accelerate rapidly.
A New View on Grasping
Authors: Smeets Jeroen B.J. , Brenner Eli
Published: August 2016

Reaching out for an object is often described as consisting of two components that are based on different visual information. Information about the object's position and orientation guides the hand to the object, while information about the object's shape and size determines how the fingers move relative to the thumb to grasp it. We propose an alternative description, which consists of determining suitable positions on the object—on the basis of its shape, surface roughness, and so on—and then moving one's thumb and fingers more or less independently to these positions. We modeled this description using a minimum-jerk approach, whereby the finger and thumb approach their respective target positions approximately orthogonally to the surface. Our model predicts how experimental variables such as object size, movement speed, fragility, and required accuracy will influence the timing and size of the maximum aperture of the hand. An extensive review of experimental studies on grasping showed that the predicted influences correspond to human behavior.
Computational Implications of Modeling Grasping as a Form of (Multiple-Parallel) Reaching
Authors: Morasso Pietro G. , Sanguineti Vittorio , Frisone Francesco
Published: August 2016

Although it is true that the specific research on grasping has been dominated in recent years by the canonical transport + grip model originally formulated by Jeannerod (1984), still one can find in the research on reaching a number of links and anticipations to the new view on grasping made explicit by the authors of the target article. This paper reviews some of the relevant concepts and outlines a modeling framework that aims at biological plausibility.
What Can Be Learned from Smeets and Brenner's Model about the Control of Grasping?
Authors: Steenbergen Bert
Published: August 2016

The present reaction on the paper of Smeets and Brenner focuses on two premises of their proposed model The first is that grasping is nothing more than pointing with two fingers. It is argued that this assumption cannot be upheld in light of the differences between both actions with respect to neuromuscular structures, muscular innervation, use of visual feedback, and basic function The second premise of the model is that the velocity profile of the transport component is symmetrical and independent of intrinsic object properties. It is shown that the symmetrical velocity profile represents a boundary condition and is influenced by intrinsic object properties. Given these concerns, it is doubtful that the model in its present form will add much to our understanding of the control of grasping.
Grip Formation as an Emergent Property. Response to Commentaries on “A New View on Grasping”
Authors: Smeets Jeroen B.J. , Brenner Eli
Published: August 2016

We begin our response by discussing the commentators' arguments concerning our proposal to abandon the classical distinction between transport and grip. In the second section, we argue that the minimum-jerk model is not fundamental to our approach, but very convenient. In the third section, we discuss how the experimental results that the commentators mention fit into our new approach. We conclude that the predictive capacity of our model, combined with its simplicity, makes it very useful for understanding grasping.
Effects of Direction and Curvature on Variable Error Pattern of Reaching Movements
Authors: Jaric Slobodan , Tortoza Charli , Fatarelli Ismael F.C. , Almeida Gil L.
Published: August 2016

A number of studies have analyzed various indices of the final position variability in order to provide insight into different levels of neuromotor processing during reaching movements. Yet the possible effects of movement kinematics on variability have often been neglected. The present study was designed to test the effects of movement direction and curvature on the pattern of movement variable errors. Subjects performed series of reaching movements over the same distance and into the same target. However, due either to changes in starting position or to applied obstacles, the movements were performed in different directions or along the trajectories of different curvatures. The pattern of movement variable errors was assessed by means of the principal component analysis applied on the 2-D scatter of movement final positions. The orientation of these ellipses demonstrated changes associated with changes in both movement direction and curvature. However, neither movement direction nor movement curvature affected movement variable errors assessed by area of the ellipses. Therefore it was concluded that the end-point variability depends partly, but not exclusively, on movement kinematics.
Coordination of Two- and One-Joint Muscles: Functional Consequences and implications for Motor Control
Authors: Prilutsky Boris l.
Published: August 2016

The purpose of this paper is three-fold: (a) to summarize available data on coordination of major two- and one-joint muscles in multijoint tasks and identify basic features of muscle coordination, (b) to demonstrate that there may exist an optimization criterion that predicts essential features of electromyographic activity of individual muscles in a variety of tasks, and (c) to address the functional consequences of the observed muscle coordination and underlying mechanisms of its control. The analysis of the literature revealed that basic features of muscle coordination are similar among different voluntary motor tasks and reflex responses. It is demonstrated that these basic features of coordination of one- and two-joint muscles in two-dimensional tasks are qualitatively predicted by minimizing the sum of muscle stresses cubed. Functional consequences of the observed coordination of one- and two-joint muscles are (a) reduction of muscle force as well as stress, mechanical and metabolic energy expenditure, muscle fatigue, and perceived effort; (b) a spring-like behavior of a multi-joint limb during maintenance of an equilibrium posture; and (c) energy transfer between joints via two-joint muscles. A conceptual scheme of connections between motoneuron pools of one- and two-joint muscles, which accounts for the observed muscle coordination, is proposed. An important part of this scheme is the force-dependent inhibition and excitation from two-joint to one-joint synergists and antagonists, respectively.
Too Early to Explain All Experimental Data with a Single Model
Authors: Gielen C.C.A.M.
Published: August 2016

The target article by Prilutsky gives an excellent overview of the predictions of the Crowninshield and Brand model and about the relevant literature about muscle coordination. However, we do not agree with the claim that the Crowninshield and Brand model can explain the coordination between one-joint and two-joint muscles. In this commentary we will make three claims: (a) The Crowninshield and Brand model cannot explain all aspects of muscle coordination, (b) there is good experimental evidence that different constraints and models may be necessary to explain muscle coordination in different motor tasks, and (c) the reason for the lack of quantitative fits between predictions about muscle force and experimental data is that it is hard to measure muscle force in man. As a compromise one has to rely on EMG activity as a measure of muscle force. Because of the complex relationship between EMG and muscle force, a quantitative test of models is difficult.
Soleus Stretch Reflex during Cycling
Authors: Grey Michael J. , Pierce Charles W. , Milner Theodore E. , Sinkjaer Thomas
Published: August 2016

The modulation and strength of the human soleus short latency stretch reflex was investigated by mechanically perturbing the ankle during an unconstrained pedaling task. Eight subjects pedaled at 60 rpm against a preload of 10 Nm. A torque pulse was applied to the crank at various positions during the crank cycle, producing ankle dorsiflexion perturbations of similar trajectory. The stretch reflex was greatest during the power phase of the crank cycle and was decreased to the level of background EMG during recovery. Matched perturbations were induced under static conditions at the same crank angle and background soleus EMG as recorded during the power phase of active pedaling. The magnitude of the stretch reflex during the dynamic condition was not statistically different from that during the static condition throughout the power phase of the movement. The results of this study indicate that the stretch reflex is not depressed during active cycling as has been shown with the H-reflex. This lack of depression may reflect a decreased susceptibility of the stretch reflex to inhibition, possibly originating from presynaptic mechanisms.
During Slow Wrist Movements, Distance Covered Affects EMG at a Given External Force
Authors: Welter Tom G. , Bobbert Maarten F.
Published: August 2016

This study investigates the hypothesis that EMG measured from a muscle at a given force, length, and low-shortening velocity depends on the contraction history, specifically the distance over which the muscle has shortened. Slow linear horizontal wrist movements (3 cm/s) involving shoulder and elbow rotations towards a test position of 90° elbow flexion were performed. REMG was measured at the test position after wrist displacements over 6.5 and 13 cm. Muscle contraction speed was below 1% of maximum. A constant force (25 N) causing flexion torque in the elbow was exerted by the wrist. Inertial load was minimal. Two main elbow flexors (biceps caput longum and breve) showed significantly higher (14 and 24%) concentric REMG after 13-cm wrist movement than alter 6.5-cm. Eccentric EMG did not differ between the 6.5-and 13-cm conditions. It is concluded that adaptation of muscle activation is required to counteract the effects of contraction history on the force producing capacity of the muscle.
Spatial Interactions during Bimanual Coordination Patterns: The Effect of Directional Compatibility
Authors: Bogaerts Hedwig , Swinnen Stephan P.
Published: August 2016

Whereas previous bimanual coordination research has predominantly focused on the constraining role of timing, the present study addressed the role of spatial (i.e., directional) constraints during the simultaneous production of equilateral triangles with both upper limbs. In addition to coordination modes in which mirror-image and isodirectional movements were performed (compatible patterns), new modes were tested in which the left limb lagged with respect to the right by one triangle side (non-compatible patterns). This resulted in the experimental manipulation of directional compatibility between the limbs. In addition. triangles with either horizontal or vertical orientations were to be drawn in order to assess the role of static images on movement production. Results supported the important role of directional constraints in bimanual coordination. Furthermore, triangles in vertical orientations (with a vertical symmetry axis, i.e., one apex pointing up) were drawn more successfully than those in horizontal orientations (with a horizontal symmetry axis, i.e., one apex pointing left or right), suggesting that the static aspects of a geometric form may affect movement dynamics. Finally, evidence suggested that cognitive processes related to integration of the submovements into a unified plan mediate the performance of new coordination patterns. The implications of the present findings for clinical populations are discussed.
Planning Reaching and Grasping Movements: Theoretical Premises and Practical Implications
Authors: Rosenbaum David A. , Meulenbroek Ruud G.J. , Vaughan Jonathan
Published: August 2016

This paper presents the background, premises, and results of a model of movement planning. The model's central claims are fourfold: (a) A task is defined by a set of prioritized requirements, or what we call a constraint hierarchy; (b) movement planning works first by specifying a goal posture and then by specifying a movement to that goal posture; (c) movements have characteristic forms; and (d) movements can be shaped through simultaneous performance of different movements, even by the same effector. We review the model and then speculate on its implications for clinical concerns, especially spasticity.
Effects of Changing Gravity on Anticipatory Grip Force Control during Point-to-Point Movements of a Hand-Held Object
Authors: Nowak Dennis A. , Hermsdörfer Joachim , Philipp Jens , Marquardt Christian , Glasauer Stefan , Mai Norbert
Published: August 2016

We investigated the quality of predictive grip force control during gravity changes induced by parabolic flight maneuvers. During these maneuvers gravity varied: There were 2 periods of hypergravity, in which terrestrial gravity nearly doubled, and a 20-s period of microgravity, during which a manipulated object was virtually weightless. We determined grip and load forces during vertical point-to-point movements of an instrumented object. Point-to-point movements were a combination of static (stationary holding) and dynamic (continuous movements) task conditions, which were separately analyzed in our previous studies. Analysis of the produced grip forces revealed that grip adjustments were closely linked to load force fluctuations under each gravity condition. In particular, grip force maxima coincided closely in time with load force peaks, although these occurred at different phases of the movement depending on the gravity level. However, quantitative analysis of the ratio of maximum grip force to the corresponding load force peak revealed an increased force ratio during microgravity when compared to that during normal and hypergravity, We hypothesize that the impaired precision of force coupling with respect to force magnitude during microgravity results from reduced feedback information about the object's mass during the stationary holding of the object in between each movement. The results indicate that the temporal grip force regulation is highly automatized and stable, whereas economical planning of force magnitude is more flexible and might reflect changes of the external loading condition.
Separate Sources of Spatial Information for Distance and Location in Rapid Aiming Movements
Authors: Khan Michael A. , Hale Trevor , Carry Michael I. , Franks Ian M.
Published: August 2016

The purpose of this research was to examine the role of distance and location information in the production of rapid aiming movements. Participants performed an aiming task consisting of horizontal left-handed elbow flexion movements that translated to movements of a cursor on an oscilloscope screen. The location of the home position and the target on the oscilloscope screen were fixed but me initial angle of the elbow was varied randomly. Participants were informed mat the required distance was always constant. Initial impulse and error correction phases were analyzed to examine whether separate spatial codes for distance and position were used in the control of these two movement phases. The results indicated mat initial impulse endpoints and the final positions of the limb overshot the target from the leftmost starting positions, while they undershot me target from me rightmost starting positions. Also, varying the initial angle of the elbow had a greater influence on me final position of the limb than initial impulse endpoints.
A New Look at Posturographic Analysis in the Clinical Context: Sway-Density versus Other Parameterization Techniques
Authors: Baratto Luigi , Morasso Pietro G. , Re Cristina , Spada Gino
Published: August 2016

In order to identify useful guidelines for the clinical practitioner as regards the use of static posturographic analysis, we collected a set of posrurograms from 3 groups of participants (normal participants. Parkinsonian patients, and osteoporotic patients), according to the Romberg test. From each posturogram, we extracted global parameters (in the time domain and frequency domain) and structural parameters (based on diffusion plots and sway-density plots), with a total of 38 parameters. The discriminative power of each parameter was evaluated by means of statistical analysis in relation to the condition effect (open vs. closed eyes) and the pathology effect (normal participants vs. patients). The initial set of 38 parameters was reduced to 24 by identifying clear redundancies, and then to 18 by eliminating the parameters that did not pass the condition effect with normal participants. These parameters were analyzed for reliability and discriminative power in the general framework of a biomechanic model of postural stabilization. At the end of this analysis, we suggested that a set of 4 parameters is particularly valuable in the clinical practice: 2 global parameters (sway-path and frequency band of the posturogram) and 2 structural parameters (mean value of peaks and mean inter-peak distance in the sway-density plots).
A Role of the Basal Ganglia in Movement: The Effect of Precues on Discrete Bi-directional Movements in Parkinson's Disease
Authors: Johnson Andrew M. , Vernon Philip A. , Almeida Quincy J. , Grantier Linda L. , Jog Mandar S.
Published: August 2016

The effect of a precue on improving movement initiation (i.e., reaction time; RT) is well understood, whereas its influence on movement execution (i.e., movement time; MT) has rarely been examined. The current study investigated the influence of a directional precue (i.e., left vs. right) on the RT and MT of simple and discrete bi-directional movements in a large sample of Parkinson's disease patients and healthy control participants. Both patients and controls were tested twice, with testing sessions separated by 2 hours. Patients were tested first following an overnight levodopa withdrawal and again after they had taken their medication. Both patients and controls demonstrated a significant RT improvement when information was provided in advance. MT in both healthy participants and medicated patients was, however, slower with the provision of advance information, while unmedicated patients showed no significant MT effects. These results suggest that while the basal ganglia may not be involved in motor program selection, they may dynamically modulate movement execution.
Differential Effects of Target Height and Width on 2D Pointing Movement Duration and Kinematics
Authors: Bohan Michael , Longstaff Mitchell G. , Van Gemmert Arend W.A. , Rand Miya K. , Stelmach George E.
Published: August 2016

This study examined the impact of target geometry on the trajectories of rapid pointing movements. Participants performed a graphic point-to-point task using a pen on a digitizer tablet with targets and real time trajectories displayed on a computer screen. Circular- and elliptical-shaped targets were used in order to systematically vary the accuracy constraints along two dimensions. Consistent with Fitts' Law, movement time increased as target difficulty increased. Analysis of movement kinematics revealed different patterns for targets constrained by height (H) and width (W). When W was the constraining factor, movements of greater precision were characterized by a lower peak velocity and a longer deceleration phase, with trajectories that were aimed relatively farther away from the center of the target and were more variable across trials. This indicates an emphasis on reactive, sensory-based control. When H was the constraining factor, however, movements of greater precision were characterized by a longer acceleration phase, a lower peak velocity, and a longer deceleration phase. The initial trajectory was aimed closer to the center of the target, and the trajectory path across trials was more constrained. This suggests a greater reliance on both predictive and reactive control.
Motion Enslaving among Multiple Fingers of the Human Hand
Authors: Li Zong-Ming , Dun Shouchen , Harkness Daniel A. , Brininger Teresa L.
Published: August 2016

The purpose of the current study was to examine motion enslaving characteristics of multiple fingers during isolated flexion of the distal interphalangeal joints. Because the distal interphalangeal joints are flexed by multiple tendons of the single flexor digitorum profundus, the current experimental design provided a unique advantage to understand inter-finger enslaving effects due to the flexor digitorum profundus. Eight subjects were instructed to flex the distal inter-phalangeal joint of each individual finger from the fully extended position to the fully flexed position as quickly as possible. Maximal angular displacements, velocities, or accelerations of individual fingers were used to calculate the enslaving effects. An independence index, defined as the ratio of the maximal displacement of a master finger to the sum of the maximal displacements of the master and slave fingers, was used to quantify relative independence of each finger. The angular displacements of the index, middle, ring, and little fingers were 68.6° (±7.7), 68.1° (±10.1), 68.1° (±9.7), and 74.7° (±13.3), respectively. The motion of a master finger was invariably accompanied by motion of 1 or 2 slave fingers. Angular displacements of master and slave fingers increased to maximum values with time monotonically. Velocity curves demonstrated bell-shaped profile, and the acceleration curves were sinusoidal. Enslaving effects were generated mainly on the neighboring fingers. The amount of enslaving on the middle and ring fingers exceeded more than 60% of their own maximum angular displacements when a single adjacent finger moved. The index finger had the highest level of independence as indicated by the lowest enslaving effects on other fingers or by other fingers. The independence indices of the index, middle, ring, and little fingers were 0.812 (±0.070), 0.530 (±0.051), 0.479 (±0.099), and 0.606 (±0.148), respectively. In all tasks, motion of slave fingers always lagged with respect to the master finger. Time delays, on average, ranged from 7.8 (±5.0) to 35.9 (±22.1) ms. Our results suggest that there exist relatively large enslaving effects among the compartments of the flexor digitorum profundus, and functional independence of fingers in daily activities is likely enhanced through synergistic activities of multiple muscles, including flexors and extensors.
Dynamic Stability of Gait Cycles as a Function of Speed and System Constraints
Authors: Buzzi Ugo H. , Ulrich Beverly D.
Published: August 2016

The purpose of this study was to examine the dynamic stability of two groups of children with different dynamic resources in changing contexts. The stability of the lower extremity segments of preadolescent children (8–10 years old) with and without Down syndrome (DS) was evaluated as children walked on a motorized treadmill at varying speeds. Tools from nonlinear dynamics, maximum Lyapunov exponent, and approximate entropy were used to assess the behavioral stability of segmental angular displacements of the thigh, shank, and foot. Our results suggest that children with DS show decreased dynamic stability during walking in all segments and that this might be a consequence of inherently different subsystem constraints between these groups. Differences between groups also varied, though not uniformly, with speed, suggesting that inherent differences could further constrain the behavioral response to changing task demands.
Submovements Grow Larger, Fewer, and More Blended during Stroke Recovery
Authors: Rohrer Brandon , Fasoli Susan , Krebs Hermano Igo , Volpe Bruce , Frontera Walter R , Stein Joel , Hogan Neville
Published: August 2016

Submovements are hypothesized building blocks of human movement, discrete ballistic movements of which more complex movements are composed. Using a novel algorithm, submovements were extracted from the point-to-point movements of 41 persons recovering from stroke. Analysis of the extracted submovements showed that, over the course of therapy, patients' submovements tended to increase in peak speed and duration. The number of submovements employed to produce a given movement decreased. The time between the peaks of adjacent submovements decreased for inpatients (those less than 1 month post-stroke), but not for outpatients (those greater than 12 months post-stroke) as a group. Submovements became more overlapped for all patients, but more markedly for inpatients. The strength and consistency with which it quantified patients' recovery indicates that analysis of submovement overlap might be a useful tool for measuring learning or other changes in motor behavior in future human movement studies.
Finger-Tapping Ability in Male and Female Pianists and Nonmusician Controls
Authors: Aoki Tomoko , Furuya Shinichi , Kinoshita Hiroshi
Published: August 2016

Using fast tapping tasks with each of the four fingers (single-finger tapping) and with two of the fingers used alternately (double-finger tapping), the ability to make rapid tapping movement by the individual fingers was compared between expert pianists and nonmusician controls in both genders. Maximal pinch and grasp forces were also measured to assess strength of individual fingers and whole hand, respectively. Movement of the ring and little fingers was slower than that of the index and middle fingers in both the pianists and controls. The slowness of the ring and little fingers was, however, much less evident in the pianists than the controls in both tapping tasks. The pianists also had smaller intertap interval variability for the index and middle fingers. No pianist–control difference was found for the pinch and grasp forces. Piano training, therefore, effectively changed the ability to move individual fingers rapidly, but not their flexor strength. No gender difference was found in any of the tapping tasks though males had greater strength. Gender thus does not appear to be a factor differentiating the ability to move individual fingers rapidly.
Information Processing and Constraints-based Views of Skill Acquisition: Divergent or Complementary?
Authors: Anson Greg , Elliott Digby , Davids Keith
Published: August 2016

Since the middle of the nineteenth century, movement scientists have been challenged to explain processes underlying the control, coordination, and acquisition of skill. Information processing and constraints-based approaches represent two distinct, often perceived as opposing, views of skill acquisition. The purpose of this article is to compare information processing and constraints-based approaches through the lens of Fitts’ three-stage model and Newell’s constraints-based model, respectively. In essence, both models can be identified, at least in spirit, with ideas about skill described by Bernstein (1967, 1996). Given that the product of “skill acquisition” is the same, although the explanation of the processes might differ, it is perhaps not surprising that similarities between the models appear greater than the differences. In continuing to meet the challenge to explain skill acquisition, neural-based models provide a glimpse of the cutting edge where behavior and biological mechanisms underpinning processes of control, coordination, and acquisition of skill might meet.
Balance Training with Visual Feedback in Children with Hemiplegic Cerebral Palsy: Effect on Stance and Gait
Authors: Ledebt Annick , Becher Jules , Kapper Janneke , Rozendaal Rianne M. , Bakker Rachel , Leenders Iris C. , Savelsbergh Geert J.P.
Published: August 2016

The aim of the present study was to examine the effects of balance training with visual feedback on stance and gait in school-age children with hemiplegic cerebral palsy. Ten participants between 5 and 11 years of age were assigned to either the training or the control group according to an aged-stratified randomization. The training corresponded to three sessions per week during six weeks. Stance and gait parameters, based on force plate data, were assessed three times in both groups: (a) at the beginning of the study (before training); (b) after six weeks; (c) after ten weeks. Spatial and temporal parameters were calculated. The results for stance showed that the training improved the performances on the tasks that were trained. More interesting, the results for gait showed that the walking pattern became more symmetrical after the training.
Physiologic Characteristics and Team Performance of Female High School Runners
Authors: Cunningham Lee N.
Published: August 2016

This study compared team performances of adolescent female cross-country runners in relation to maximal oxygen consumption (V̇O2 max), ventilatory threshold, and running economy (RE). Twenty female runners (M age = 16.0 yrs) from four high school teams that competed in the Massachusetts All-State Cross-Country Championship Meet underwent maximal treadmill testing. When physiologic parameters were grouped by team, significant differences were observed for only V̇O2 max and percent V̇O2 at a 215 m • min−1 pace. The mean VO2 max for Team 1 (the All-State Meet champions) was found to be significantly higher than that of Teams 3 and 4 (70.7 ± 4 vs. 56.5±4, and 58.6 ± 4 ml • kg−1 • min−1, respectively). When running on the treadmill at a 215 m • min−1 pace, members of Team 1 were working at a significandy lower percent of VO2 max than Team 3 (70 ± 3 vs. 84 ± 4). The estimated physiologic requirements for running the All-State Meet based upon data derived from physiologic testing were not statistically different between teams (p>0.05). In conclusion, most of the physiologic variables investigated were not sensitive enough to separate out performance differences between top high school cross-country teams. Of these variables, VO2 max is suggested to be the primary physiologic determinant for team success for this age group of female runners.
Predicting Maximal Oxygen Uptake in Children: Modification of the Astrand–Ryhming Test
Authors: Buono Michael J. , Roby Julia J. , Micale Frank G. , Sallis James F.
Published: August 2016

The Astrand-Ryhming est was modified to overcome problems of predicting V̇O2max in children. V̇O2max was measured directly during a maximal treadmill test and estimated by means of a submaximal protocol in a test group of 51 subjects ages 10–18 years. A multiple regression equation was developed with directly measured V̇O2max as the dependent variable and age, body weight, and V̇O2max estimated from the Astrand nomogram as independent variables. The validity and reliability of this equation to predict V̇O2max in children and adolescents was cross-validated. No significant difference was found between the measured V̇O2max and that estimated from the equation. The correlation coefficient between measured and estimated V̇O2max for the cross-validation group was 0.89, with a standard error of estimate of 12%. Test-retest reliability was 0.95. It was concluded that this modification of the Astrand nomogram provides a valid and reliable prediction of V̇O2max in children and adolescents.
Maturation and Exercise Training in Children
Authors: Plowman Sharon Ann
Published: August 2016

This paper describes the effects of exercise training on the somatic, skeletal, and sexual maturation of children. Young athletes of both sexes grow at the same rate and to the same extent as young nonathletes. However, there is evidence that the pubertal development of young female athletes may be delayed. Menarche is more consistently late than either thelarche or pubarche. Genetic and environmental factors are explored in an attempt to determine causative mechanisms. Longitudinal training data are needed for both boys and girls on a variety of physical and hormonal variables. Until such data are available, it is recommended that all children engage in regular physical activity but that maturational progress be monitored in those involved in strenuous competitive training.