bluuebunny/crossref_metadata_2025 huggingface dataset:
Perceived and Actual Role of Secondary School Physical Educators
Authors: Ojeme Emmanuel O.
Published: August 2016

This paper describes a study conducted to determine the role perception and enactment (or performance) of secondary school physical educators as well as the magnitude of role deficits that physical educators experience in schools. The data for the study were collected using a 28-item test instrument classified into four role-subsets of teaching, coaching and sports administration, research and development, and student welfare roles. The results indicated that the physical educators studied possess an acceptable perception of their roles, and that they differentially enact or perform these roles. The coaching and sports administration role-subset is more enacted by physical educators than are teaching, research and development, and student welfare roles, respectively. Furthermore, the magnitude of role deficits experienced by physical educators is higher for teaching, research and development, and student welfare roles compared with role deficits in the coaching and sports administration role-subset. Further studies are required to ascertain the forces that shape the role of physical educators in the school system as well as the sources of role deficits.
The Effect of an Intervention on Academic Learning Time Provided by Preservice Physical Education Teachers
Authors: Randall Lynda E. , Imwold Charles H.
Published: August 2016

This study set out to determine the effect of a training program on the amount of academic learning time in physical education (ALT-PE) provided by student teachers. A treatment group/control group experimental design was used to test the effect of an intervention, and random selection was used in assigning subjects to either group. A total of 50 classes were observed. Descriptive analysis revealed that teachers in the treatment group produced more ALT-PE than teachers in the control group. Wilcoxon Rank Sum tests computed for this comparison showed that the distribution of ranks was significantly different (p<.01). Additional tests produced nonsignificant differences for the distribution of ranks within the variables of skill practice, game, management, and waiting (p>.01). However, the general trend of differences within these variables seemed to contribute to the overall provision of greater ALT-PE for the treatment group. These findings have some important implications for the implementation of theory into practice in the supervision of novice teachers.
Comparing Teaching Behaviors and Student Activity Levels in Classes Taught by P.E. Specialists versus Nonspecialists
Authors: Faucette Nell , Patterson Patricia
Published: August 2016

This study compared the teaching behaviors of elementary physical education specialists with those of classroom teachers (nonspecialists) while teaching physical education classes. Additionally, data were collected on student activity levels to detect similarities or differences in classes taught by specialists versus nonspecialists. Four specialists and 7 nonspecialists were observed during a 3-month period using the Teacher Observation Schedule (Rushall, 1977). The group time-sampling technique, Placheck recording, was used to gather data on the students’ levels of activity during the observed classes. It was found that specialists had significantly higher values in more effective teaching behaviors such as feedback/reward, questioning, and directing/explaining/informing, and significantly lower values in less effective teaching behaviors such as monitoring/attending. Additionally, there were significantly higher levels of activity for students in classes taught by specialists.
Meta-Analysis of the Placebo Effect in Nutritional Supplement Studies of Muscular Performance
Authors: Rawdon Tarra , Sharp Rick L. , Shelley Mack , Thomas Jerry R.
Published: August 2016

This paper is a meta-analysis of the role of nutritional supplements in strength training focusing on the effects of placebo treatments. We address specifically the results from meta-analysis of 334 fi.ndings from 37 studies of the effect of nutritional supplements and physical fitness interventions on strength, stamina, and endurance outcomes, controlling for main effects of the group on which the results were obtained (placebo, treatment, control, for pretest or posttest), with covariates for age, gender, randomization, double-blind procedures, study duration, training load, training frequency, and training status. Finding show that there are significant placebo effects accounting for a substantial portion of the effect size typically associated with treatment interventions. In addition to produce the best evaluations of treatment effects, both control and placebo groups should be included in a double-blind research design using participants who are well familiarized with the study procedures.
Right From the Start: Promotion of Health-Related Physical Activity in Preschoolers
Authors: Morgan Don W.
Published: August 2016

A growing body of literature has confirmed the health benefits of regular physical activity in school-aged youth. However, less systematic attention has been directed toward establishing activity profiles and evaluating the impact of community-based interventions designed to increase physical activity and reduce sedentary behavior in preschool children. In this paper, current findings are reviewed to determine whether preschoolers are achieving sufficient levels of structured and unstructured physical activity and to identify potential correlates of activity and sedentary behavior in the young child. In addition, promotion of physical activity among preschool-aged children in selected community settings is discussed and future research initiatives are highlighted. Given current trends in the overweight and obesity status of children aged two to five years, efforts aimed at increasing physical activity levels and documenting gains in health-related fitness and movement skillfulness in this pediatric population should be accelerated.
Strategy of Coordination of Two- and One-Joint Leg Muscles in Controlling an External Force
Authors: Prilutsky Boris I. , Gregor Robert J.
Published: August 2016

The purpose of this study was to simulate the control of an external force using different strategies of muscle coordination and to compare the predicted patterns of muscle forces with those of electromyographic activity reported in the literature for the same task. We simulated a motor task in which a person sitting on a chair exerts an external force by pushing on the ground (or pulling a strap) in five different directions with two different force magnitudes. The results of this study suggest that during the control of an external force in pushing directions, more force is allocated to muscles with long moment arms and a large physiological cross-sectional area, and the number of simultaneously active muscles is increased. This strategy of muscle coordination corresponds to the strategy of minimizing muscle fatigue, and it is characterized by features of muscle coordination that agree with those reported in experimental studies of walking, running, jumping, and cycling.
Directions of Torques Produced About the Ankle Joint by Cat Medial Gastrocnemius Motor Units
Authors: Sokoloff Alan J. , Cope Timothy C. , Nichols T. Richard , English Arthur W.
Published: August 2016

Differences in the directions of torque produced by motor units might be used by the nervous system to coordinate posture and movement. Here we report plantar flexion and abduction isometric torques exerted at the ankle by 158 motor units in the cat medial gastrocnemius (MG) muscle. In five cats, motor unit torque direction differed by an average of 10°. Torque direction was weakly correlated with unit contraction time in 3 of 5 experiments, with tetanic force in 3 of 5 experiments, and with conduction velocity in 1 of 5 experiments. The direction of whole muscle torque, however, was constant at all levels of MG activation produced in sural and crossed extension reflexes. Thus, although there is a range in the direction of torque produced by motor units in the cat MG, we find no evidence for the ordering of motor units according to torque direction during MG activation.
Tradeoff between Response Speed and Pursuit Accuracy
Authors: Seya Yasuhiro , Mori Shuji
Published: August 2016

We examined simple and choice reaction times (RTs) to a visual target that appears during smooth pursuit. Participants pursued a moving fixation stimulus accurately before a target stimulus was presented either above or below the fixation stimulus. In the simple RT task, the participants responded to the onset of the target as soon as possible. In the choice RT task, they indicated the target position, i.e., above or below the fixation stimulus, as soon and as accurately as possible. The results showed that, in both tasks, the RTs during smooth pursuit at 10°/s were longer than those during stationary fixation, and the RTs decreased as the fixation stimulus velocity further increased to 40°/s. Since pursuit gains (the ratio of eye velocity to fixation stimulus velocity) decreased as the fixation stimulus velocity increased, these results suggest that there is a tradeoff between pursuit accuracy and RT.
Analyzing Variance in Multi-Degree-of-Freedom Movements: Uncovering Structure versus Extracting Correlations
Authors: Schöner Gregor , Scholz John P.
Published: August 2016

An important aspect of the study of multi-degree-of-freedom motor control is the analysis of high-dimensional variance data. Through the “uncontrolled manifold” (UCM) approach the structure in such data can be discovered and interpreted. The covariation by randomization (CR) approach provides nonlinear and potentially multi-dimensional measures of covariance. We critically examine these two approaches and compare them relative to the three fundamental issues of choice of variables, choice of model, and adoption of either a geometrical or a correlational view of variance. The UCM approach is a geometrical approach that seeks to discover the structure of variance in multi-degree-of-freedom task spaces in which all degrees of freedom have a common metric. The structure of variance in that space is interpreted in terms of its meaning for task variables. The CR approach seeks to uncover correlations between interpretable elemental variables. It requires a defined and common metric in the space of task variables, but not the elemental variables. Although the CR approach is better suited for systems with strong nonlinearities, variance structure that is not caused by correlation but by different amounts of variance in the different elemental variables is undetected by this approach.
Toward a New Theory of Motor Synergies
Authors: Latash Mark L. , Scholz John P. , Schöner Gregor
Published: August 2016

Driven by recent empirical studies, we offer a new understanding of the degrees of freedom problem, and propose a refined concept of synergy as a neural organization that ensures a one-to-many mapping of variables providing for both stability of important performance variables and flexibility of motor patterns to deal with possible perturbations and/or secondary tasks. Empirical evidence is reviewed, including a discussion of the operationalization of stability/flexibility through the method of the uncontrolled manifold. We show how this concept establishes links between the various accounts for how movement is organized in redundant effector systems.
Synergies in Intra- and Interpersonal Interlimb Rhythmic Coordination
Authors: Black David P. , Riley Michael A. , McCord Christopher K.
Published: August 2016

The authors conducted two experiments that served as a test bed for applying the recently developed uncontrolled manifold (UCM) approach to rhythmic motor coordination, which has been extensively investigated from a coordination dynamics perspective. The results of two experiments, one investigating withinperson and one investigating between-persons rhythmic movement coordination, identified synergistic behaviors in both of those types of coordination. Stronger synergies were identified for in-phase than antiphase coordination, at the endpoints of the movement cycles compared with the midpoints, for movement frequencies closer to the intrinsic frequency of the coordinated limbs, and for within-person coordination. Frequency detuning did not weaken the strength of interlimb rhythmic coordination synergies. The results suggest the synergistic behavior captured by the UCM analysis may be identifiable with the strength of coupling between the coordinated limbs. The UCM analysis appears to distinguish coordination parameters that affect coupling strength from parameters that weaken coordination attractors.
Muscle Activation Patterns and Postural Control Following Stroke
Authors: Garland S. Jayne , Gray Vicki L. , Knorr Svetlana
Published: August 2016

Many stroke survivors have residual sensorimotor deficits that impact negatively on balance and quality of life. The purpose of this review is to provide an overview of the impairments in motor control following stroke and the impact of those impairments on muscle activation patterns during postural control in stroke. Motor control impairments following stroke result in force production that is slow, weak and lacking in precision making it difficult to produce a fast rate of force development with sufficient magnitude to be effective for postural responses. Whether postural perturbations require feedback or feedforward responses, there is impairment to the timing, magnitude and sequencing of muscle activation following stroke. The impairment in muscle activation is dependent on the extent of the motor control impairments and strategies used by the individuals following stroke to compensate for the impairments. The central nervous system uses a variety of mechanisms to improve the muscle activation patterns needed for the recovery of postural responses following stroke.
Measurement and Modulation of Plasticity of the Motor System in Humans Using Transcranial Magnetic Stimulation
Authors: Chen Robert , Udupa Kaviraja
Published: August 2016

Several techniques that involve transcranial magnetic stimulation (TMS) can be used to measure brain plasticity noninvasively in humans. These include paired-associative stimulation (PAS), repetitive transcranial magnetic stimulation (rTMS) and theta burst stimulation (TBS). Some of these techniques are based the principle of use dependent plasticity or are designed to mimic protocols used to induce long-term potentiation or depression in animal studies. These studies have been applied to certain neurological and psychiatric disorders to investigate their pathophysiology. For example, PAS induced plasticity is enhanced in dystonia and stroke but is reduced in Huntington’s disease and schizophrenia. Furthermore, TMS may be used to modulate brain plasticity and has therapeutic potential in neurological and psychiatric disorders such as stroke, Parkinson’s disease, dystonia and depression.
Effect of Working Memory and Spatial Attention Tasks on Gait in Healthy Young and Older Adults
Authors: Nadkarni Neelesh K. , Zabjek Karl , Lee Betty , McIlroy William E. , Black Sandra E.
Published: August 2016

Changes in gait parameters induced by the concomitant performance of one of two cognitive tasks activating working memory and spatial attention, was examined in healthy young adults (YA) and older adults (OA). There was a main effect of task condition on gait-speed (p = .02), stride-length (p < .001) and double-support time (p = .04) independent of the group. There were no significant differences between working memory and spatial attention associated gait changes. Working-memory and spatial-attention dual-tasking led to a decrease in gait-speed (p = .09 and 0.01) and stride-length (p = .04 and 0.01) and increase in double-support time (p = .01 and 0.03) in YA and decrease in stride-length (p = .04 and 0.01) alone in OA. Cognitive task associated changes in gait may be a function of limited attentional resources irrespective of the type of cognitive task.
Effects of Task Complexity on Coordination of Inter-Limb and Within-Limb Forces in Static Bimanual Manipulation
Authors: Krishnan Vennila , Jaric Slobodan
Published: August 2016

Coordination of the hand grip (G; acting normally to the grasping surface) and load forces (L; acting in parallel) in bimanual static tasks was studied. L symmetry (either the magnitude or direction) and frequency were manipulated in healthy participants (N = 14). More complex tasks (i.e., the higher frequency and/or asymmetric ones) revealed expected deterioration in both the task performance (accuracy of the prescribed L force profiles) and force coordination (G/L ratio and G-L correlation) suggesting importance of L frequency and symmetry in prehension activities. However, the same tasks revealed a more prominent deterioration of interlimb than the within-limb force coordination. This could be interpreted by two partly different and noncompeting neural control mechanisms where the coordination of interlimb forces may be based on ad-hoc and task-specific muscle coordination (often referred to as muscle synergies) while the within-limb coordination of G and L could be based on more stable and partly reflex mechanisms.
Parkinson’s Disease Influences the Structural Variations Present in the Leg Swing Kinematics
Authors: Ivkovic Vladimir , Kurz Max J.
Published: August 2016

This study investigated the nature of the structural variations found in the motor output of individuals with Parkinson’s disease (PD). Young (n = 21; 19.9 ± 1.3 yrs.), aged (n = 9; 74.8 ± 6.8 yrs.) and individuals with PD (n = 9; 73.4 ± 6.6 yrs.) swung their leg at a pendular frequency and frequencies that were 20% faster and slower. This study had three key findings. First, individuals with PD have greater variability in the leg swing angular kinematics and swing times. These variations appear to be related to the 0–15 Hz band of the of angular displacement power spectrum. Second, changes in the structural variations appear to not be derived from a stochastic source. Third, the magnitude of the variations and the structure of the variations are influenced by the frequency that the leg is swung. These results are consistent with the viewpoint that changes in the magnitude of the variations and the regularity of the structural variations are dependent upon health and adaptability to the task dynamics.
Supervised Resistance Training Results in Changes in Postural Control in Patients with Multiple Sclerosis
Authors: Huisinga Jessie M. , Filipi Mary L. , Stergiou Nicholas
Published: August 2016

Postural disturbances are one of the first reported symptoms in patients with Multiple Sclerosis (MS). The purpose of this study was to investigate the effect of supervised resistance training on postural control in MS patients. Postural control was assessed using amount of sway variability [Root Mean Square (RMS)] and temporal structure of sway variability [Lyapunov Exponent (LyE)] from 15 MS patients. Posture was evaluated before and after completion of three months of resistance training. There were significant differences between MS patients pretraining and healthy controls for both LyE (p = .000) and RMS (p = .002), but no differences between groups after training. There was a significant decrease in RMS (p = .025) and a significant increase in LyE (p = .049) for MS patients pre- to posttraining. The findings suggested that postural control of MS patients could be affected by a supervised resistance training intervention.
Gait Variability Measures Reveal Differences Between Multiple Sclerosis Patients and Healthy Controls
Authors: Kaipust Jeffrey P. , Huisinga Jessie M. , Filipi Mary , Stergiou Nicholas
Published: August 2016

The purpose of this study was to determine the differences in gait variability between patients with multiple sclerosis (MS) and healthy controls during walking at a self-selected pace. Methods: Kinematics were collected during three minutes of treadmill walking for 10 patients with MS and 10 healthy controls. The Coefficient of Variation (CoV), the Approximate Entropy (ApEn) and the Detrended Fluctuation Analysis (DFA) were used to investigate the fluctuations present in stride length and step width from continuous strides. Results: ApEn revealed that patients with MS had significantly lower values than healthy controls for stride length (p < .001) and step width (p < .001). Conclusions: ApEn results revealed that the natural fluctuations present during gait in the stride length and step width time series are more regular and repeatable in patients with MS. These changes implied that patients with MS may exhibit reduced capacity to adapt and respond to perturbations during gait.
Asymmetric Interference Associated With Force Amplitude and Hand Dominance in Bimanual Constant Isometric Force
Authors: Hu Xiaogang , Newell Karl M.
Published: August 2016

This study investigated the asymmetry of bilateral interference in relation to the relative difference of force amplitude between hands and the hand dominance. In Experiment 1, one hand produced a fixed constant force of 5% maximum voluntary contraction (MVC) while the other hand produced different constant forces of 5%, 20%, and 50% MVC in blocked conditions. Asymmetric interference in force amplitude alone was evident in that the hand producing the fixed low force showed a stronger interference than the hand performing the higher force. Asymmetric interference in hand dominance was also found in that more interference was observed when the nondominant left hand produced the higher force, a finding that does not support the hemisphere specialization hypothesis. Experiment 2 was performed to rule out the fixed force level interpretation compared with the low force level account and the fixed force was set at 50% MVC. The results were consistent with the findings in Experiment 1 showing asymmetric interference with force amplitude rather than with fixed force level. The findings revealed that without a timing constraint the task demand associated with force amplitude alone can induce the asymmetric bilateral interference. The external task asymmetry and intrinsic asymmetry of the organism interact and influence the bimanual force coordination and control patterns.
Influence of Vestibular Afferent Input on Common Modulation of Human Soleus Motor Units During Standing
Authors: Monsour Marc , Ivanova Tanya D. , Wilson Tim D. , Garland S. Jayne
Published: August 2016

The purpose of this study was to investigate whether application of bipolar galvanic vestibular stimulation (GVS) would influence the common modulation of motor unit discharge rate in bilateral soleus muscles during quiet standing. Soleus motor unit activity was recorded with fine wire electrodes in each leg. Subjects stood, with eyes closed, on two adjacent force platforms to record postural sway with the head facing straight ahead, turned to right, or turned left. Subjects also swayed voluntarily without GVS to the same position as evoked during the GVS. There was no difference in the common drive to bilateral soleus motoneurons during quiet standing and voluntary sway tasks. Common drive was significantly lower during right cathode GVS with the head straight or turned to the right. These results demonstrate that manipulation of vestibular afferent input influences the common modulation of bilateral soleus motor unit pairs during quiet standing.
Fractionated Reflex and Reaction Times in Children with Developmental Coordination Disorder
Authors: Raynor Annette J.
Published: August 2016

The patellar tendon reflex (PTR) and simple visual reaction time (VRT) were fractionated and compared in 40 subjects with developmental coordination disorder (DCD) and normal coordination (NC) in two age groups. Four equal groups of subjects, 6 years DCD (6DCD), 6 years NC (6NC), 9 years DCD (9DCD), and 9 years NC (9NC) were compared using ANOVA for the main effects of coordination and age. PTR and its components of reflex latency and motor time were not significantly affected by the level of coordination; however, a significant coordination by age interaction (p < .05) revealed an increased motor time in the 6DCD group. VRT, premotor time, and motor time were all significantly (p < .05) increased in children with DCD; the increased VRT and premotor time support earlier findings, whereas the increased motor time has not previously been found. These findings suggest that the processing of reflexive and volitional responses by children with DCD differs from that of their NC peers.
Grasp Stiffness as a Function of Grasp Force and Finger Span
Authors: Van Doren Clayton L.
Published: August 2016

The purpose of this study was to determine whether direct measurements of grasp stiffness agreed with stiffness inferred from the slopes of isovolitional force-span characteristics derived from previous grasp-effort matching data. Grasp stiffness for three-finger pinch was measured as a function of initial force and finger span using step displacements applied in a do-not-intervene paradigm. Subjects pinched a free-floating, motorized manipulandum in each hand and squeezed both with equal effort; one of the hands was perturbed at random. Stiffness was calculated from the initial and final steady-state values of force and span. The effects of step amplitude, rise-time, and initial load stiffness were investigated; grasp stiffness decreased significantly for larger steps, increased slightly for longer rise-times, and was unaffected by load stiffness. Grasp stiffness then was measured as a function of initial force and span using a single set of step parameters. Stiffness increased significantly in proportion to force but was changed only slightly by span. It was concluded that the perturbation and effort-matching measures of stiffness are not equivalent and represent different components of motor behavior.
Limb Stiffness and Postural Tremor in the Arm
Authors: Morrison Steven , Newell Karl M.
Published: August 2016

The relation between limb stiffness and postural tremor in the upper arm was investigated during a pointing task. The task goal was to minimize the amount of motion (tremor) at the index finger under levels of increasing limb stiffness. This study investigated the influence of increasing limb stiffness on the pattern of intra- and interlimb dynamics. The frequency profile of the tremor for all limb segments across all conditions displayed two peaks, one between 2-4 Hz and another between 8-12 Hz. A third, higher frequency component (20-22 Hz) was present in the index finger. Increasing limb stiffness through voluntary co-contraction of antagonistic muscle pairs effectively constrained the segments of the upper limb to increasingly operate as a single biomechanical degree of freedom. Higher levels of limb stiffness typically led to an increase in the frequency and power of the 2-4 and 8-12 Hz peaks. There was also a decrease in the frequency of the 20-22 Hz component of finger tremor. The act of reducing the effective degrees of freedom in joint space through voluntarily stiffening of the upper limbs also resulted in decreased performance as determined by an increase in finger tremor. In the preferred, natural level of limb stiffness, specific intralimb segment relations were observed but there was no significant interlimb coupling. The intralimb segment correlations were characterized by compensatory (out of phase) coupling between the upper arm/forearm and hand/index finger segment pairs of each limb that were organized about the action of the wrist joint. Increasing the degree of limb stiffness led to a decrease in the level of intralimb coupling. The findings suggest that the most efficient mechanism for reducing tremor at the periphery is that of compensatory coupling between relevant intralimb segments with a low level of limb stiffness.
Control Variables in Mechanical Muscle Models: A Mini-Review and a New Model
Authors: Shapiro Mark B. , Kenyon Robert V.
Published: August 2016

A new mechanical model of isolated muscle is proposed in which spring with variable slack length is the force-generating element. Based on the review of experimental studies in isolated muscle, it is suggested that spring slack lengthX0is the control variable in the model and is a function of motor unit firing rate. In the presence of sensory feedback, the Sliding Spring model is equivalent to the Rack and Pinion model. However, sensory feedback is essential in the Rack and Pinion model but complementary in the Sliding Spring model. How the new control variable in the model of isolated muscle affects the interpretation of control processes up the motor system hierarchy is discussed in light of certain controversies associated with the Lambda and Alpha models of control of movement. It is argued that the Sliding Spring model of isolated muscle can be used as a basis for developing models of control of movement.
Forward versus Backward Oriented Stepping Movements in Parkinsonian Patients
Authors: Gantchev Nikolai , Viallet François , Aurenty Roselyne , Massion Jean
Published: August 2016

The primary purpose of this paper was to compare the effect of reversing the direction of step initiation in Parkinson's disease. Forward (FDS) and backward (BDS) oriented stepping initiation analyses were conducted on combined kinematic and kinetic data recorded on Parkinsonian patients (PD) and healthy age-matched subjects. Two successive phases were examined: a postural phase from T1 (onset of the center of pressure [CP] displacement) to T2 (onset of the malleolus displacement), which was followed by a stepping phase from T2 to T3 (end of the malleolus displacement; i.e., the end of the step). In healthy subjects, the duration of the postural phase remained unchanged regardless of the direction in which the step was initiated. The stepping phase duration and the first step length were reduced in BDS in comparison with FDS. In both tasks, the absolute value of the horizontal force in sagittal plane (Fx) remained unchanged. The maximal velocity of the iliac crest marker (estimated whole body center of gravity [CG]) in the sagittal plane (Vmax CG) remained within the same range regardless of direction of stepping. In Parkinsonian patients, the duration of the postural phase was markedly prolonged in both tasks in comparison with healthy subjects. The mean duration of stepping phase was approximately the same as in normal subjects, but the first step length was considerably reduced, as were horizontal force (Fx) and Vmax CG. This impairment, which was due to a decrease in the propulsive forces, was significantly more pronounced in BDS that in FDS.
Grip and Load Force Coordination during a Manual Transport Movement: Findings in Healthy Participants
Authors: Hejduková Blanka , Hosseini Nasser , Johnels Bo , Ingvarsson Pall E. , Steg Goran , Olsson Torsten
Published: August 2016

During transport of an object using the precision grip with thumb and index finger, a modulation of the grip force is needed in response to the forces evoked by the movement. We measured the grip force (GF) and the load force (LF) in 10 healthy participants moving a 640-g object forward and upward. The task was repeated with various speeds. There were considerable changes with speed of the LF trajectory but not of the GF trajectory. A loss of synergy between GF and LF appeared in fast lifts. This is in contrast to the close coupling between load force and grip force repeatedly demonstrated during simple lifts. We suggest that (a) speed should be considered as an input parameter for movement planning, and (b) regulation of GF and of LF are independent under certain conditions. We discuss whether the grip-load force synergy should be considered a special case rather than a more general principle.
Interactions between Rhythmic and Discrete Components in a Bimanual Task
Authors: Wei Kunlin , Wertman Gary , Sternad Dagmar
Published: August 2016

An asymmetric bimanual task was investigated in which participants performed a rhythmic movement with their dominant arm and initiated a second movement with their nondominant arm at a random phase of the continued oscillations. The objective was to examine whether different constraints existed between rhythmic and discrete movements and, more generally, whether rhythmic and discrete movements can be regarded as two different movement primitives. Participants performed rhythmic forearm rotations at 1 of 4 prescribed metronome periods. After a random interval, a trigger signaled to initiate either a discrete or rhythmic movement with the left forearm as fast as possible while continuing the oscillations. Analyses extracted the mutual influences that the two movements exerted on each other and contrasted discrete-rhythmic and rhythmic-rhythmic coupling. (a) The initiation of the rhythmic movement was constrained to occur in-phase with the ongoing rhythmic movement, while the discrete movement could be initiated at any arbitrary phase. (b) Reaction time of the initiated rhythmic movement scaled with the oscillation period, while the discrete movement's reaction time was invariant across periods. (c) Peak velocity of the initiated movement scaled with the oscillatory period in both tasks but more strongly in the discrete movement. (d) Synchronization of EMG bursts of both arm flexors was evident in both tasks but more strongly in the rhythmic-rhythmic combination. The results are interpreted as support for the hypothesis that discrete and rhythmic actions are two different control regimes, and coupling occurs at a higher level in the central nervous system.
Can a Visual Representation Support the Online Control of Memory-Dependent Reaching? Evidence from a Variable Spatial Mapping Paradigm
Authors: Heath Matthew , Westwood David A.
Published: August 2016

We investigated whether a representation of a visual target can be stored in memory and used to support the online control of reaching movements. To distinguish between the use of a stored target representation for movement planning versus online control, we employed a novel movement environment in which participants could not fully plan their action in advance of movement initiation; that is, the spatial mapping between the movement of a computer mouse and the on-screen movement of a cursor was randomly varied from trial to trial. As such, participants were required to use online control to reach the target position. Reaches were examined in full-vision and three memory-dependent conditions (0, 2, and 5 s of delay). Absolute constant error did not accumulate between full-vision and brief delay trials (i.e., the 0-s delay), suggesting a stored representation of the visual target can be used for online control of reaching given a sufficiently brief delay interval. Longer delay trials (2 and 5 s) were less accurate and more variable than brief delay trials; however, the residual accuracy of these memory-dependent actions suggests that the motor system may have access to a stored representation of the visual target for online control processes for upwards of 5 s following target occlusion.
Assessment of Postural Response after a Self-initiated Perturbation
Authors: Termoz Nicolas , Martin Luc , Prince François
Published: August 2016

The aim of this study was to assess postural response efficiency to a self-initiated perturbation using an original method based on the inverted pendulum model. Eight young subjects were asked to perform bilateral arm raising and lowering at 3 different speeds while standing on a force plate. The time necessary to recover a steady state following the movement was computed by analyzing the time evolution of the coefficient of determination between the center of pressure and center of mass difference variable (COP-COM) and the horizontal acceleration of the COM. Results show a spatial reorganization (hip strategy) of the segments following the perturbation and a strong influence of the linear relationship to the arm velocity. However, the conditions of arm velocity did not have any effect on the time response of the postural control, suggesting that this parameter would be an invariant characteristic of the movement. These results support the existence of an internal representation of the inertial constraints related to the movement execution.
Disruption of Coordination between Arm, Trunk, and Center of Pressure Displacement in Patients with Hemiparesis
Authors: Ustinova Ksenia I. , Goussev Valery M. , Balasubramaniam Ramesh , Levin Mindy F.
Published: August 2016

To determine how arm movements influence postural sway in the upright position after stroke, interactions between arm, trunk, and center of pressure (CoP) displacements in the sagittal direction were investigated in participants with hemiparesis and healthy subjects. Participants swung both arms sagittally in either of 2 directions (in-phase, anti-phase) and at 2 speeds (preferred, fast) while standing on separate force plates. Variables measured included amplitude and frequency of arm swinging, shoulder and trunk range of motion, CoP displacements under each foot and of the whole body, and the relationships between the arm, trunk, and CoP displacements. CoP displacements under the non-paretic leg were greater than those under the paretic leg, which may in part be related to the larger amplitude of swinging of the non-paretic arm. CoP displacements under each foot were not related to arm swinging during in-phase swinging at the preferred speed in healthy subjects. When speed of arm swinging was increased, however, the CoP moved in a direction opposite to the arm movement. In contrast, in individuals with hemiparesis, CoPs and arms moved in the same direction for both speeds. During anti-phase swinging in healthy subjects, the trunk counterbalanced the arm movements, while in participants with hemiparesis, the trunk moved with the affected arm. Results show that stroke resulted in abnormal patterns of arm-trunk-CoP interactions that may be related to a greater involvement of the trunk in arm transport, an altered pattern of coordination between arm and CoP displacements, and an impaired ability of the damaged nervous system to adapt postural synergies to changes in movement velocity.
The Sway-Density Curve and the Underlying Postural Stabilization Process
Authors: Jacono Marco , Casadio Maura , Morasso Pietro G. , Sanguineti Vittorio
Published: August 2016

The sway-density curve (SDC) is computed by counting, for each time instant, the number of consecutive samples of the statokinesigram falling inside a circle of “small” radius R. The authors evaluated the sensitivity of the curve to the variation of R and found that in the range 3–5 mm the sensitivity was low, indicating that SDC is a robust descriptor of posturographic patterns. In addition, they investigated the relationship between SDC and the underlying postural stabilization process by decomposing the total ankle torque into three components: a tonic component (over 69% of the total torque), an elastic torque caused by ankle stiffness (about 19%), and an anticipatory active torque (about 12%). The last component, although the smallest in size, is the most critical for the overall stability of the standing posture and appears to be correlated with the SDC curve.
Connecting Sciences Using Graphonomic Research
Authors: Van Gemmert Arend W. A. , Teulings Hans-Leo
Published: August 2016

The term graphonomics refers to the scientific and technological effort involved in identifying relationships between the planning and generation of handwriting and drawing movements, the resulting spatial traces of writing and drawing instruments (either conventional or electronic), and the dynamic features of these traces (International Graphonomics Society, 1987). Since the term graphonomics was coined in 1982, the multidisciplinary nature of graphonomic research has attracted scientists in several fundamental and applied areas, including motor control, motor learning, motor development, movement disorders, neuropsychology, biophysics, forensic science, computer science, cognitive science, artificial intelligence, among others. The many different research areas that are represented at the biennial conferences of the International Graphonomic Society (IGS) are exemplified by the variety of research papers published in special issues and books resulting from these conferences (cf. Meulenbroek & Van Gemmert, 2003; Simner & Girouard, 2000; Van Galen & Morasso, 1998; Simner, Leedham, & Thomassen, 1996; Faure, Keuss, Lorette, & Vinter, 1994; Simner, Hulstijn, & Girouard, 1994; Plamondon, 1993; Van Galen & Stelmach, 1993; Van Galen, Thomassen, & Wing, 1991; Wann, Wing, & Søvik, 1991; Plamondon & Leedham, 1990; Plamondon, Suen, & Simner, 1989; Kao, Van Galen, & Hoosain, 1986; Thomassen, Keuss, Van Galen, & Grootveld, 1983). Starting at the 10th IGS conference in Nijmegen, 2001, the influence of multidisciplinary collaborations and technical advancements expanded the scope of paradigms of researchers interested in graphonomics (e.g., finger control, isometric force control, brain imaging). This expansion of paradigms and the multidisciplinary nature of graphonomic research was pushed further into the center of fine motor control at the 11th IGS conference held in Scottsdale, 2003. This special issue of Motor Control, containing papers from this conference, exemplifies this progress.
Visuomotor Adaptation in Children with Developmental Coordination Disorder
Authors: Kagerer Florian A. , Bo Jin , Contreras-Vidal Jose L. , Clark Jane E.
Published: August 2016

Although one of the criteria for the diagnosis of developmental coordination disorder (DCD) suggests learning impairments, there is a lack of studies investigating motor adaptation in these children. This study examined the ability of 7 children with DCD to adapt to a novel visuomotor relationship by exposing them to a 45° visual feedback rotation while they performed a center-out drawing task, and compared their performance with that of 7 normally developing children. The results show that the children with DCD were less affected by the feedback distortion than the control children, and did not show aftereffects, suggesting they had a less well-defined internal model. A principal component analysis of the performance variables during early and late exposure showed that the variables accounting for most of the variance in the trajectories are different between the 2 groups, suggesting that underlying control processes might operate differently in the 2 groups of children.
The Negotiation of Stationary and Moving Obstructions during Walking: Anticipatory Locomotor Adaptations and Preservation of Personal Space
Authors: Gérin-Lajoie Martin , Richards Carol L. , McFadyen Bradford J.
Published: August 2016

This article introduces a novel, ecological, obstructed walking paradigm. Gait adaptations to circumvent obstacles undergoing uncertain displacements, and the effect of revealing the obstacle’s action beforehand, were investigated in young adults. The personal space (PS) maintained during walking was quantified for the first time under different environmental factors including auditory distractions. Obstacle movement and its uncertainty resulted in gait adjustments aimed at gaining time to assess the situation. Early gait adaptations and constant clearances around the obstacle suggest that anticipation and preplanning are involved in such navigational tasks. Participants systematically maintained an elliptical PS during circumvention, but they adjusted its size according to different environmental factors. There was a relationship between the size of PS and level of attention, which suggests that the regulation of PS is used to control locomotion. This novel paradigm has important implications for the assessment and training of locomotor ability within real world environments.
Planning and Control in a Manual Collision Avoidance Task by Children with Hemiparesis
Authors: te Velde Arenda F. , van der Kamp John , Becher Jules G. , van Bennekom Coen , Savelsbergh Geert J.P.
Published: August 2016

We examined whether deficits in planning and control during a manual collision avoidance task in children with hemiparesis are associated with damage to the left or right hemisphere (LHD and RHD). Children pushed a doll across a scale-size road between two approaching toy cars. Movement onset and velocity served as indicators of planning and control. In Experiment 1, children with hemiparesis collided more frequently, and controlled velocity less appropriately compared to typically-developing children. Children with LHD initiated their movement later than children with RHD. Experiment 2 compared the preferred and non-preferred hand of children with LHD and RHD. Children with RHD crossed less with their non-preferred hand, while children with LHD initiated later than children with RHD. Moreover, the groups showed differences in velocity control. It is argued that planning deficits may be related to LHD. The hypothesized association between control deficits and RHD, however, was not confirmed.
Field Monitoring of Physical Activity in Children
Authors: Freedson Patty S.
Published: August 2016

Precise quantification of physical activity is necessary in order to evaluate the relationship between physical activity and various types of disease and/or risk factors associated with disease. With the emergence of the study of the origins of coronary heart disease risk factors in children, it is imperative that accurate measurement of physical activity in the pediatric population be obtained. This review critically evaluates various field measures of physical activity in children including motion sensors, questionnaires, and heart rate. A new heart-rate quantification procedure is also presented that may provide an index of the quality of physical activity.
Longitudinal Changes of Aerobic Fitness in Youth Ages 12 to 23
Authors: Kemper Han C.G. , Verschuur Robbert , de Mey Langha
Published: August 2016

In the Amsterdam Growth and Health Study, 103 girls and 97 boys were studied five times on a longitudinal basis over a period of 8 years, covering the teenage years from 12 to 17 until young adulthood at 22/23 years. Measured were anthropometric variables such as height, weight (BW), and body fat, and physiological variables such as maximal aerobic power (V̇O2max) and endurance performance (max slope). During the teenage period, V̇O2max/BW remains constant in boys and decreases in girls whereas endurance performance increases in boys and remains constant in girls. By young adulthood V̇O2max/BW and maximal slope have declined in both sexes, and in the case of females are even lower than at the beginning of their teens. Boys superiority in aerobic fitness and the decline in aerobic fitness in both sexes is mainly caused by the differences in the intensity of daily physical activity level.
Cardiorespiratory Responses of Trained Boys to Treadmill and Arm Ergometry: Effect of Training Specificity
Authors: Al-Hazzaa Hazzaa M. , Al-Refaee Saeed A. , Sulaiman Muhammed A. , Dafterdar Ma’ed Y. , Al-Herbish Abdullah S. , Chukwuemeka Andrew C.
Published: August 2016

The purpose of this study was to examine the maximal cardiorespiratory responses of trained adolescent male swimmers (SWM, N = 18), soccer players (SOC, N = 18), and moderately active reference subjects (CON, N = 16) to treadmill running (TRD) and arm ergometry (ARM). Mean values (±SD)for skeletal age were similar among the three groups (12.5± 1.9, 12.7 ± 1.1, and 12.5 ± 1.6 years, for the SWM, SOC, and CON, respectively). Allometric scaling procedures, relating VO2max and body mass, were used and mass exponents of .80 and .74 were identified for TRD and ARM data, respectively. During TRD testing SOC attained significantly higher VO2max values when expressed in ml · kg−1 · min−1, or ml · kg−0.80 · min−1 than the other two groups. However, during ARM testing, the SWM achieved significantly higher VO2peak values (ml · kg−0.74 · min−1 and scaled to arm-CSA) than SOC. The ratio of ARM-VAT to TRD-VAT was significantly higher in SWM (50.1± 9%) compared to SOC (41.2±5%), or CON (41.9 ± 6%).