bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuromuscular Compartments of Cat Lateral Gastrocnemius Produce Different Torques about the Ankle Joint
Authors: Carrasco Dario I. , Lawrence John , English Arthur W.
Published: August 2016

The primary purpose of this study was to establish whether the neuromuscular compartments of cat lateral gastrocnemius produce different mechanical actions on the skeletal system, by determining the contributions made by these compartments to the torques produced about the ankle joint. It was postulated that neuromuscular compartments might represent output elements of the spinal circuits. If so, they should produce unique mechanical actions. Isometric torques about the center of the ankle joint produced by the neuromuscular compartments of the cat lateral gastrocnemius were measured with a multiaxis force-moment sensor connected to the plantar surface of the foot. Individual compartment torques were elicited by activation of the primary compartment branches of the lateral gastrocnemius nerve. The magnitude of the individual torque components, and thus of the resultant torque, was significantly different between compartments. In three of the four lateral gastrocnemius compartments, significantly different torque trajectories were noted. The results, together with those from previous studies demonstrating that compartments can be activated in a task-dependent manner, suggest that neuromuscular compartments represent anatomical substrates that can be used by the nervous system for regulating movement.
Minimizing Stress Is Not Enough
Authors: Gottlieb Gerald L.
Published: August 2016

Muscle stress is plainly one of the physical variables that the central nervous system probably wishes to minimize. This criterion does not uniquely define the patterns of muscle activation. It fails to explain the degree of coactivation of muscle antagonists that is widely found, and it cannot explain why two movements or movement segments that follow an identical trajectory driven by identical joint torques can be driven by different patterns of muscle activation. Muscle contraction provides for both net joint torque and limb stability. The minimization of the sum of muscle stresses, raised to any power, is an insufficient rule.
Subject Specific Coordination of Two- and One-Joint Muscles during Landings Suggests Multiple Control Criteria
Authors: McNitt-Gray Jill L.
Published: August 2016

The target article, thoughtfully constructed by Dr. Prilutsky, effectively synthesizes available data on multijoint movements regarding coordination patterns of major two- and one-joint muscles, provides evidence for an optimization criterion that predicts critical features of muscle activation patterns, and explores the functional consequences of muscle coordination. This work also provides a clear set of definitions and an organizational framework that is currently needed for a productive interdisciplinary discussion regarding the underlying control mechanisms used during realistic multijoint movements. Although identification of an optimization criterion that predicts muscle recruitment strategies would greatly simplify control logic required for rehabilitation and musculoskeletal modeling, our experimental data during landings indicate more than one criterion may exist. Preliminary review of our experimental landing data suggests the rules identified by Prilutsky apparently hold for some subjects during portions of the landing movements. The presence of more than one muscle activation pattern used to achieve the same NJMs demonstrates there may be more than one optimization criterion that predicts critical features of muscle activation patterns. The functional consequences of more than one control criterion may also prove to be an asset, particularly when adapting to different environmental constraints.
Some Mechanical Considerations on Muscle Coordination
Authors: Raikova Rositsa T.
Published: August 2016

This commentary emphasizes three points of discussion. (a) The terminology: The terms multifunctional, synergisic, antagonistic muscles, and synergistic and antagonistic coactivations are discussed and the conclusion is drawn that they could not be used without mentioning the particular joint motion. (b) The importance of the external joint moments for activation of the muscles is confirmed on the basis of logical and mechanical considerations. Not all experimental results, however, could be explained by this means. (c) The optimization criterion: Prilutsky's conclusion concerning the predicted muscle force proportionality to the muscle moment arm and PCSA is confirmed using a simple analytical solution of the optimization problem. It is shown, however, that the proportionality to the PCSA is a consequence of the chosen optimization criterion.
The Mechanical Action of Proprioceptive Length Feedback in a Model of the Cat Hindlimb
Authors: Burkholder Thomas J. , Nichols T. Richard
Published: August 2016

Postural regulation is an important part of a variety of motor tasks, including quiet standing and locomotion. Muscle length feedback, both the autogenic length feedback arising from a muscle's own spindles, and heterogenic length feedback, arising from its agonists and antagonists, is a strong modulator of muscle force and well suited to postural maintenance. The effects of this reflex feedback on 3-D force generation and limb mechanics are not known. In this paper, we present a mechanical model for relating 3-D changes in cat hindlimb posture to changes in muscle lengths. These changes in muscle length are used to estimate changes in both intrinsic muscle force generation and muscle activation by length feedback pathways. Few muscles are found to have directly agonist mechanical actions, and most differ by more than 20°. Endpoint force fields are largely uniform across the space investigated. Both autogenic and heterogenic feedback contribute to whole limb resistance to perturbation, autogenic pathways being most dramatic. Length feedback strongly reinforced a restoring force in response to end-point displacement.
Accuracy of Dynamic Isometric Force Production: The Influence of Age and Bimanual Activation Patterns
Authors: Harbst Kimberly B. , Lazarus Jo-Anne C. , Whitall Jill
Published: August 2016

The purpose of this study was to investigate how children and adults control bimanual activities with the influence of kinematic variables minimized. Force and timing measures were analyzed in self-paced, isometric bimanual pinch tasks performed by 6-, 8-, 10-, 12-year-old, and adult subjects. Subjects (n = 84) performed four tasks (inphase symmetrical, antiphase reciprocal, inphase asymmetrical force-right high, inphase asymmetrical force-left high) cycling between low levels (10-30%) of maximal volitional force during three 15-s trials. Bimanual tasks requiring similar activation between the hands were performed more accurately, more quickly, and with less force and timing variability than tasks requiring different actions and/or levels of force to be produced simultaneously. Evidence of force entrainment between the hands was exhibited when force direction (increasing vs. decreasing) was similar between hands but greater relative force was required of the left hand. Lower accuracy and greater variability resulted when controlled decrement of force was required to reach the lower force targets as opposed to the upper force targets which required subjects to increase force. Subjects in the two youngest age groups exhibited lower force accuracy and greater force and timing variability relative to older children and adults. Twelve-year-old subjects approximated adults' performance in all variables.
Contributions of Gait and Trunk Movements to Prehension: Perspectives from World- and Body-Centered Coordinates
Authors: Marteniuk Ronald C. , Bertram Christopher P.
Published: August 2016

The present paper reviews a series of prehension experiments recently conducted at Simon Fraser University's Human Motor Systems Laboratory, and attempts to place them into the larger context of multi-segmental control theory. Two related lines of experiments are reported: (a) experiments involving prehension during walking, and (b) experiments involving trunk-assisted reaching. Three-dimensional analyses of movements were performed via both world-and body-centered coordinates. Our results are supportive of the idea that both types of tasks are carried out using task-specific synergies. Furthermore, we assert that the actions of these synergies are comprised of variable contributions of different movement systems and result in smooth, world-centered end-point trajectories. We show evidence that this “motor equivalence” is the result of increasing the complexity of a given task. Finally, the implications of the present findings on prevailing motor control theory are discussed in terms of the theoretical mechanisms underlying the coordination of the transport and grasp components of prehension.
Aerial Somersault Performance under Three Visual Conditions
Authors: Hondzinski Jan M. , Darling Warren G.
Published: August 2016

Experiments were designed to examine the visual contributions to performance of back aerial double somersaults by collegiate acrobats. Somersaults were performed on a trampoline under three visual conditions: (a) NORMAL acuity; (b) REDUCED acuity (subjects wore special contacts that blocked light reflected onto the central retina); and (c) NO VISION. Videotaped skill performances were rated by two NCAA judges and digitized for kinematic analyses. Subjects' performance scores were similar in NORMAL and REDUCED conditions and lowest in the NO VISION condition. Control of body movement, indicated by time-to-contact, was most variable in the NO VISION condition. Profiles of angular head and neck velocity revealed that when subjects could see, they slowed their heads prior to touchdown in time to process optical flow information and prepare for landing. There was not always enough time to process vision associated with object identification and prepare for touchdown. It was concluded that collegiate acrobats do not need to identify objects for their best back aerial double somersault performance.
Specificity versus Variability: Effects of Practice Conditions on the Use of Afferent Information for Manual Aiming
Authors: Tremblay Luc , Welsh Timothy N. , Elliott Digby
Published: August 2016

Although proponents of the motor schema theory hold that a decrease in the reliance on afferent information will occur with practice in consort with the development of motor programs, supporters of the specificity of practice hypothesis suggest that a performer's reliance on the available sources of afferent information during acquisition increases with the amount of practice. To reconcile these competing positions, four groups of 9 participants aimed to targets under either a constant or a variable practice schedule, with or without vision of the effector. After modest (15 trials) and moderate (150 trials) practice, participants were tested in both their own and in the alternate vision condition. Results indicate mat the utilization of online kinesthetic information was enhanced through practice regardless of the availability of vision during acquisition. This was especially true for the groups practicing under a variable practice schedule.
Inter-digit Individuation and Force Variability in the Precision Grip of Young, Elderly, and Parkinson's Disease Participants
Authors: Vaillancourt David E. , Slifkin Andrew B. , Newell Karl M.
Published: August 2016

We examine the force fluctuations in the control of grip force to determine if force variability increases or decreases in relation to the degree of inter-digit individuation. This relation was examined in young (n = 7) and elderly (n = 7) participants, and in participants diagnosed with Parkinson's disease (n = 7). Force was produced under different force levels (5%, 25%, 50% MVC) with and without visual feedback. Force variability was assessed using the standard deviation and root mean square error, and inter-digit individuation was examined using cross-approximate entropy. Force variability increased with the force level, the removal of visual feedback, and also in the Parkinson's disease compared to the young and elderly matched control participants. There was a reduction in the degree of inter-digit individuation, with increases in force level, the removal of visual feedback, and in Parkinson's disease participants compared to the matched controls. Overall, there was a negative correlation between the degree of inter-digit individuation and force variability. The force fluctuations in precision grip revealed a continuum for the degree of inter-digit individuation in which task constraints, aging, and Parkinson's disease alter the coupling between the digits in controlling grip force.
Visual Perception of Movement Kinematics and the Acquisition of “Action Prototypes”
Authors: Sparrow William A. , Shinkfield Alison J. , Day Ross H. , Hollitt Sarah , Jolley Damien
Published: August 2016

Recognizing a class of movements as belonging to a “nominal” action category, such as walking, running, or throwing, is a fundamental human ability. Three experiments were undertaken to test the hypothesis that common (“prototypical”) features of moving displays could be learned by observation. Participants viewed moving stick-figure displays resembling forearm flexion movements in the saggital plane. Four displays (presentation displays) were first presented in which one or more movement dimensions were combined with 2 respective cues: direction (up, down), speed (fast, slow), and extent (long, short). Eight test displays were then shown, and the observer indicated whether each test display was like or unlike those previously seen. The results showed that without corrective feedback, a single cue (e.g., up or down) could be correctly recognized, on average, with the proportion correct between .66 and .87. When two cues were manipulated (e.g., up and slow), recognition accuracy remained high, ranging between .72 and .89. Three-cue displays were also easily identified. These results provide the first empirical demonstration of action-prototype learning for categories of human action and show how apparently complex kinematic patterns can be categorized in terms of common features or cues. It was also shown that probability of correct recognition of kinematic properties was reduced when the set of 4 presentation displays were more variable with respect to their shared kinematic property, such as speed or amplitude. Finally, while not conclusive, the results (from 2 of the 3 experiments) did suggest that similarity (or “likeness”) with respect to a common kinematic property (or properties) is more easily recognized than dissimilarity.
Learning a New Bimanual Coordination Pattern Is Influenced by Existing Attractors
Authors: Wenderoth Nicole , Bock Otmar , Krohn Rainer
Published: August 2016

The present study investigates whether the acquisition of a rhythmical bimanual coordination pattern is influenced by existing intrinsic coordination tendencies. Participants were required to learn 1 of 5 new coordination patterns, whose relative phase ϕ was either 36, 60, or 90° away from the 0° and 180° attractors, respectively. They performed 35 trials, each consisting of 2 conditions: In the augmented feedback condition, continuous visual guidance was provided, while in the normal feedback condition participants were required to rely on normal vision of their arms. We found that all to-be-learned patterns were performed with higher accuracy in the visually guided condition, whereas interference with pre-existing coordination tendencies was more pronounced in the normal vision condition. Comparing the learning progress of the 5 groups, we found for patterns close to anti-phase, a smaller improvement and significantly larger phase errors than for patterns close to in-phase. This indicates that the acquisition of a new phase relationship is influenced by existing attractors and that the 180º attractor interfered more strongly with the to-be-learned pattern than the 0º attractor.
Bimanual Coordination Dynamics in Adults with Down Syndrome
Authors: Ringenbach Shannon D. , Chua Romeo , Maraj Brian K. V. , Kao James C. , Weeks Daniel J.
Published: August 2016

Previous experiments involving discrete unimanual tasks have shown that individuals with Down syndrome (DS) have auditory/verbal-motor deficits. The present study investigated unimanual and bimanual continuous perceptual-motor actions in adults with DS. Ten adults with DS, 10 typical adults, and 10 children drew continuous circles at increasing periods bimanually and unimanually with each hand. Movement was paced by either a visual or an auditory metronome. The results revealed that for circle shape and coordination measures, children and adults were more accurate with the visual metronome, whereas adults with DS were more accurate with the auditory metronome. In the unimanual tasks, adults with DS displayed hand asymmetries on spatial measures. In the bimanual task, however, adults with DS adopted an in-phase coordination pattern and stability more similar to adults than children. These results suggest that bimanual coordination in adults with DS is functioning effectively despite hand asymmetries evident in unimanual performance.
When Is Behavioral Data Evidence for a Control Theory? Tau-Coupling Revisited
Authors: Brouwer Anne-Marie , Brenner Eli , Smeets Jeroen B.J.
Published: August 2016

Before an aspect of a movement that is predicted by a control theory can be considered as evidence for that theory, it should be clear that this aspect is not the result of some other property of the movement. We investigate whether this condition is met in studies that claim to provide evidence for the tau-coupling theory. This theory proposes that moving targets are intercepted at a specified goal zone by maintaining a constant ratio between the tau (time to closure) of the gap between the hand and the goal zone and the tau of the gap between the hand and the moving target. In line with the theory, previous research has found a linear relationship between these two decreasing taus during the last part of such a movement. To investigate whether this linear relationship was a side-effect of smooth successful movements, we modeled smooth ballistic hand movements that were independent of the target's movement but led to successful interception. We found that the resulting taus of decreasing gaps were also related linearly. We conclude that this relationship cannot be considered as evidence for the tau-coupling theory.
Slow Motor Performance in Girls with Turner Syndrome Is Not Related to Increased Neuromotor Noise
Authors: der Sanden Maria W.G. Nijhuis-Van , Van Asseldonk Edwin H.F. , Eling Paul A.T.M. , Van Galen Gerard P.
Published: August 2016

This study examined the relationship between decreased speed-accuracy tradeoff and increased neuromotor noise in girls with Turner Syndrome (TS). Fifteen girls with TS and 15 age-matched controls performed isometric force contractions with both index fingers separately at 5 force levels, based on their maximum voluntary contraction. The results revealed that (a) groups did not differ in speed-accuracy tradeoff or neuromotor noise, (b) output-variability increased linearly with force level, (c) signal-to-noise ratio changed according to an inverted U-shaped function, (d) broadening in the frequency profile is highest at the lower force levels, (e) with increasing force level, the power peak in the 0–4 Hz domain dominates, (f) frequency profile broadens more in the dominant hand. These findings suggest that, in girls with TS, motor performance is not diminished in an isometric force task, that motor recruitment is intact, and that neuromotor noise is not increased. The findings are discussed with respect to motor control and neuromotor noise.
On the Nature of Stopping an Earlier Intended Voluntary Action
Authors: McGarry Tim , Franks Ian M.
Published: August 2016

The ability to inhibit an earlier intended action in a stop-signal task is commonly assessed using the measures of latency and probability. The usual findings from stop-signal trials of lower response probabilities and shorter reaction latencies at reduced stop-signal delays were reported, as described in previous studies in terms of an independent race between stochastic processes (see Logan & Cowan, 1984). In addition, using the less common measure of amplitude, a continuum of reductions in surface EMG onsets was reported. Weakened motor discharges have yet to be explained in terms of a mechanism of inhibitory control. Using computer simulations of neural functioning, the properties of independence and non-independence were examined for their effects on motor pool output in terms of probability, latency, and EMG onsets. The data provided support to question the requirement of independent processes for a theory of inhibitory control.
The Utilization of Visual Feedback in the Control of Movement Direction: Evidence from a Video Aiming Task
Authors: Khan Michael A. , Lawrence Gavin P. , Franks Ian M. , Elliott Digby
Published: August 2016

The purpose of the present study was to establish the contribution of visual feedback in the correction of errors during movement execution (i.e., online) and the utilization of visual feedback from a completed movement in the programming of upcoming trials (i.e., offline). Participants performed 2 dimensional sweeping movements on a digitizing tablet through 1 of 3 targets, which were represented on a video monitor. The movements were performed with and without visual feedback under 4 criterion movement times (150, 250, 350, 450 msec). We analyzed the variability in directional error at 25%, 50%, 75%, and 100% of the distance between the home position and the target. There were significant differences in variability between visual conditions at each movement time. However, in the 150-msec condition, the form of the variability profiles did not differ between visual conditions, suggesting that the contribution of visual feedback was due to offline processes. In the 250-, 350-, and 450-msec conditions, there was evidence for both online and offline control, as the form of the variability profiles differed between the vision and no vision conditions.
When Motor Execution Is Selectively Impaired: Control of Manipulative Finger Forces in Amyotrophic Lateral Sclerosis
Authors: Nowak Dennis A. , Hermsdörfer Joachim , Topka Helge
Published: August 2016

Amyotrophic lateral sclerosis is a degenerative motor neuron disorder with progressive and exclusive loss of motor neurons in the spinal cord, brainstem, and motor cortex. Five patients with amyotrophic lateral sclerosis, and 5 age-matched, healthy control subjects performed vertical point-to-point arm movements with an instrumented hand-held object. In between the movements, the object was held stationary. Compared with healthy controls, all patients generated greater grip forces during the phase of stationary holding of the object and greater ratios between grip and load force maximums during the arm movements. We conclude that in amyotrophic lateral sclerosis, the ability to scale the grip force magnitude efficiently according to the actual loading requirements is impaired. When performing upward movements, controls increased grip force in parallel with load force right from the movement onset; during downward movements, controls anticipated an early decrease of load force by constant or decreasing grip forces. In contrast, 3 of 5 patients showed an early increase of grip force during both upward and downward movements, indicating that in amyotrophic lateral sclerosis, the differential regulation of the grip force output according to the direction-dependent load force profile may be impaired. In motor neuron disease, the inaccurate grip force scaling and the impaired temporal coupling between grip and load force profiles may either directly result from deficient motor execution or be secondary to accompanying symptoms, such as dyscoordination of hand and finger muscles due to spasticity.
The Control of Memory-Guided Reaching Movements in Peripersonal Space
Authors: Heath Matthew , Westwood David A. , Binsted Gordon
Published: August 2016

The goal of the present investigation was to explore the putative contributions of feedforward- and feedback-based processes in the control of memory-guided reaching movements. Participants (N= 4) completed an extensive number of reaching movements (2700) to 3 midline targets (20, 30, 40 cm) in 6 visual conditions: full-vision, open-loop, and four memory-guided conditions (0, 200, 400, and 600 ms of delay). To infer limb control, we used a regression technique to examine the within-trial correspondence between the spatial position of the limb at peak acceleration, peak velocity, peak deceleration, and the ultimate movement endpoint. A high degree of within-trial correspondence would suggest that the final position of the limb was largely specified prior to movement onset and not adjusted during the action (i.e., feedforward control); conversely, a low degree of within-trial correspondence would suggest that movements were modified during the reaching trajectory (i.e., feedback control). Full-vision reaches were found to be more accurate and less variable than open-loop and memory-guided reaches. Moreover, full-vision reaches demonstrated only modest within-trial correspondence between the spatial position of the limb at each kinematic marker and the ultimate movement endpoint, suggesting that reaching accuracy was achieved by adjusting the limb trajectory throughout the course of the action. Open-loop and memory-guided movements exhibited strong within-trial correspondence between final limb position and the position of the limb at peak velocity and peak deceleration. This strong correspondence indicates that the final position of the limb was largely determined by processes that occurred before the reach was initiated; errors in the planning process were not corrected during the course of the action. Thus, and contrary to our previous findings in a video-based aiming task, it appears that stored target information is not extensively (if at all) used to modify the trajectory of reaching movements to remembered targets in peripersonal space.
Functional Changes in Brain Activity during Acquisition and Practice of Movement Sequences
Authors: van Mier Hanneke I. , Perlmutter Joel S. , Petersen Steven E.
Published: August 2016

In the present study, brain activations were measured using positron emission tomography (PET) over the course of practice. Fourteen right-handed participants were scanned during six 1-min periods of practice tracing a cutout maze design with their eyes closed. Practice-related decreases were found in the right premotor and posterior parietal cortex and left cerebellum, increases in the supplementary motor area (SMA) and primary motor cortex. The decrease in right premotor activity and the increase in SMA was significantly correlated with a decrease in the number of stops, implying involvement in learning and storing the movement sequence. The significant correlation between decreases in errors and left cerebellar and right posterior parietal activity suggests a role in accuracy. Involvement of the primary motor cortex in motor execution is suggested by the correlation of increased activation and movement speed. These results suggest that different neural structures (involving a premotor-parietal-cerebellar circuit) play a role in a sequential maze learning task.
Using the Framework of the Kinematic Theory for the Definition of a Movement Primitive
Authors: Woch Anna , Plamondon Réjean
Published: August 2016

This article reviews the current status of the movement primitives problem, especially the question of their description and identification, and points out some challenges that are stillwhich remain unsolved by the approaches that are frequently adopted to study human movements. We use the framework of the kinematic theory proposed by Plamondon (1995 and 1998) as an example of a hybrid model thatthat allows a precise and flexible quantitative description of human movements. It is shown that the theory can be used to encompass the various types of rapid movement encountered in the field. Namely, tThe principal aim of this article is to highlight the fact that the notion of movement primitive movements should not necessarily be confined to movements with a single velocity peak, as it is still often assumed in many models. The model allows, for example, a simple description of a movement primitivethat, which might contain up to two direction reversals.
Effects of Adaptation to Altered Display Gain on the Control of Single Aimed Movements
Authors: van Doorn Robert R.A. , Unema Pieter J.A.
Published: August 2016

A display gain setting defines the mapping of a movement to the real-time visual display. In two experiments we investigated how the acquired adaptation to low and high display gain affected motor control of single aimed stylus movements. Experiments differed with respect to how gain was varied. In Experiment 1, gain was realized by manipulating the surface displacements with a constant display. The results show an expected linear decrease of movement time and spatial accuracy, which is in sharp contrast with the often-reported U-shaped relation. Experiment 2 was run to study the influence of visual feedback in low- and high-gain conditions. The manipulation of gain was realized by display variation with unaltered surface displacements. The linear increase of movement time and feedback processing with gain and the unaltered spatial accuracy across conditions, suggested that participants actively adapted to the displayed visual information in altered gain conditions.
The Effect of Movement Frequency on Interlimb Coupling during Recumbent Stepping
Authors: Kao Pei-Chun , Ferris Daniel P.
Published: August 2016

During passive lower limb movement, active use of the upper limbs increases unintentional lower limb muscle activation. We hypothesized that faster movement frequencies would amplify lower limb muscle activation during upper limb exertion but would not affect lower limb muscle activation when the upper limbs were relaxed. We studied 10 healthy participants exercising on a recumbent stepping machine that mechanically coupled the four limbs via handles and pedals. Participants exercised at four frequencies (30, 60, 90, 120 steps/min) under four conditions of active and passive movement. Self-driven lower limb motion resulted in greater muscle activation compared to externally driven lower limb motion. Muscle activation amplitude increased with frequency for all conditions except for externally driven stepping. These results indicate that fast upper limb movement facilitates neuromuscular recruitment of lower limb muscles during stepping tasks. If a similar effect occurs in neurologically impaired individuals during active stepping, self-assisted exercise might enhance neuromuscular recruitment during rehabilitation.
Anticipatory Planning of Movement Sequences in Hemiparetic Cerebral Palsy
Authors: Mutsaarts Marcel , Steenbergen Bert , Bekkering Harold
Published: August 2016

Anticipatory planning was examined in detail for a complex object manipulation task by capitalizing on both the complexity and the number of elements in the movement sequences in seven individuals with hemiparetic cerebral palsy (HCP) and seven left-handed control participants. Participants had to grasp a hexagonal knob using one of five possible grasping patterns as quicklly as possible following a starting cue (condition I), and sometimes, they had to rotate it subsequently either 60˚ or 120˚ clockwise or counterclockwise (condition II). In the first condition, the HCP participants appear to anticipate the comfort of the different grasping patterns before movement onset, as controls did. However, when the task consisted of more than one movement part, HCP participants did not complete their planning processes before movement onset, which was contrary to controls. Instead, the results suggest that they use a step-by-step planning strategy, that is, they planned the latter parts of a movement sequence as the movement unfolds. The results are discussed in the light of possible capacity limitations of an internal model for grip selection, and a recent model on the planning and on-line control of movement performance.
Anaerobic and Aerobic Capacities of Children
Authors: Zwiren Linda D.
Published: August 2016

This paper deals with the measurement of aerobic and anaerobic power in children, and how these capacities are affected by growth and training. The type of tests available, the selection of ergometer, establishment of criteria for determining whether a maximal value has been attained, and the limitations of the various expressions of maximal values are discussed. Aerobic capacity, when expressed in liters per minute, has been observed to increase with growth; when expressed relative to body weight, aerobic capacity has been shown to remain the same or decrease with age. Anaerobic capacity increases with age no matter how the values are expressed. Limited evidence suggests that training during prepubescence does not increase aerobic capacity beyond that expected from growth. Several methodological limitations of longitudinal studies are examined.
Individual Differences in Relative Endurance and Physiological Response for Prepubescents, Adolescents, and Adults
Authors: Sady Stanley P. , Katch Victor L. , Berg Kris , Villanacci John
Published: August 2016

The extent of individual differences in relative endurance and physiological response was examined in adolescent boys (n=22) and compared to data of prepubescent boys (n = 21) and adult men (n = 21). Subjects performed two (test and retest) relative endurance cycle ergometer tests at an initial rate of 105% V̇O2 max, which they attempted to maintain for 8 minutes. Relative endurance performance was defined as the revolutions for each minute of the test (RPM). There were no differences among groups for the total revolutions turned or the total percent dropoff from the initial rate. All groups had similar patterns for consistency of RPM except for Minute 3. The prepubescent boys exhibited the greatest within-individual variation (Si) for HR, especially after Minute 4 (p<.05). On the average, a greater proportion of the total variability in HR was due to Si in comparison to true individual differences (St) for the prepubescents (47%) than either the adolescents (13%) or the adults (11%). The adolescents had the lowest proportion of total variability in V̇O2 due to Si (adolescents 9%, adults 16%, prepubescents 26%). The data support an earlier hypothesis of a threshold age effect on the stability of individual differences for physiological response during relative endurance exercise. A change may occur during adolescence.
Measurement of Cardiac Output in Children during Exercise: A Review
Authors: Driscoll David J. , Staats Bruce A. , Beck Kenneth C.
Published: August 2016

Knowledge of cardiac output changes during exercise is helpful for understanding normal exercise physiology and the effect of disease upon exercise performance. There are four noninvasive techniques applicable to measurement of cardiac output in children: Indirect Fick, acetylene rebreathing, electrical bioimpedance, and Doppler. Each technique requires substantial operator experience to obtain reliable and reproducible results.
Exercise and Cystic Fibrosis: A Review
Authors: Cerny Frank J. , Armitage Lisa M.
Published: August 2016

Cystic fibrosis (CF) results in chronic obstructive pulmonary disease with progressive increases in areas of the lung with poor gas exchange (dead space). The pulmonary response to exercise is characterized by a higher than expected minute ventilation (V̇E). In some patients the elevated V̇E is inadequate to overcome the large dead space, resulting in decreases in arterial oxygen and/or increases in arterial carbon dioxide levels during exercise. Chronic lung hyperinflation in patients with severe disease limits the ability to increase tidal volume, and therefore V̇E, during exercise. Most patients can exercise without decreases in arterial oxygen and should be encouraged to participate in regular activity. Oxygen supplementation during exercise allows many patients with severe lung dysfunction to participate in some form of activity. Regular exercise has been shown to be of some benefit and should be encouraged on an individual basis in patients with CF.
The Relationship between Peak Oxygen Uptake and Physical Activity in 6- to 8-Year-Old Children
Authors: Fenster Juliane R. , Freedson Patty S. , Washburn Richard A. , Ellison R. Curtis
Published: August 2016

The relationship between physical activity measured using the LSI (Large Scale Integrated Activity Monitor), and questionnaire, with physical work capacity 170 (PWC 170) and aerobic capacity (peak V̇O2) was evaluated in 6- to 8-year-old children (n = 18). The mean (± SD) peak V̇O2 was 44.1 ± 5.6 ml • kg−1 • min−1. Peak V̇O2 was not significantly different for children (n = 8) who had completed two treadmill trials (45.4 vs. 43.5 ml • kg−1 • min−1; R = 0.67, p<0.05). The log LSI expressed as counts per hour (M ± SD = 2.1 ±.22 cts/hr) was the only activity method significantly related to peak V̇O2 (r = 0.59, p<0.05). The correlation between peak V̇O2 with the questionnaire was positive but nonsignificant (r = 0.20). PWC 170 was not related to peak V̇O2 (r = 0.21) or the activity variables (r = 0.12 questionnaire; r = 0.18 log LSI). When the group was divided into high and low peak V̇O2 groups (high: M = 48.8 ml • kg−1 • min−1; low: M = 39.5 ml • kg−1 • min−1), the log LSI was able to distinguish significant differences in activity levels (high: 2.23 ±. 19 cts/hr; low: 1.99±.19 cts/hr). This study suggests that activity measured with the LSI and aerobic capacity are related in this sample of 6- to 8-year-old children.
Energy Expenditure among Children: Implications for Childhood Obesity I: Resting and Dietary Energy Expenditure
Authors: Puhl Jackie L.
Published: August 2016

The increasing prevalence of childhood obesity, persistence of obesity over time, and health risks associated with it place childhood obesity among the highest national health concerns. The extent to which excess caloric intake or insufficient energy expenditure contribute to childhood obesity has not yet been clearly delineated. This report examines the components of the energy alance equation, focusing on the major components of energy expenditure (rest, thermic effect of food, and physical activity) whereby differences may affect energy balance and promote or perpetuate obesity among children. Some implications of differences in energy expenditure to childhood obesity and areas of needed research are suggested.
Oxygen Uptake and Endurance Fitness in Children: A Developmental Perspective
Authors: Rowland Thomas W.
Published: August 2016

In adults, maximum oxygen uptake (VO2max) serves as a useful indicator of cardiopulmonary reserve as well as performance in endurance exercise events. Whether VO2max can be interpreted in the same manner in children is less certain, since maximal oxygen uptake per kg body weight remains essentially stable during the growing years while endurance performance improves dramatically. Gains in ability in endurance events may be achieved through improved submaximal exercise economy, qualitative changes in oxygen delivery not indicated by VO2max, or the development of nonaerobic factors (speed, strength). Maximal oxygen uptake in children may therefore be a less valid indicator of cardiopulmonary function, endurance capacity, and response to training than in adult subjects.
The Exercising Child: Injuries
Authors: Micheli Lyle J.
Published: August 2016

The majority of injuries in exercising children affect the musculoskeletal system. These injuries result from two mechanisms: single, acute macrotrauma or repetitive microtrauma. The injuries resulting from repetitive microtrauma—overuse injuries—appear to be occurring with increased frequency in this age group. A number of risk factors for overuse injury from exercise have been identified, including training error, muscle imbalance, anatomic malalignment, footwear, surface, nutritional factors, and cultural factors. The development of scientific criteria for exercise prescription in this age group that will enhance fitness and avoid injury awaits techniques for noninvasive assessment of musculoskeletal tissue fitness. In the interim, many of these injuries can be prevented or decreased in severity by slow progression of exercise intensity and qualified adult supervision.
The Accumulated Oxygen Deficit Measure and Its Application in Pediatric Exercise Science
Authors: Naughton Geraldine A. , Carlson John S.
Published: August 2016

A definitive measure for assessing the energy contribution of anaerobic pathways during exhaustive exercise remains inconclusive. The accumulated oxygen deficit (AOD) has been used in several studies to estimate energy contribution. The underlying assumptions of the AOD measure have been criticized for underestimating the true contribution of anaerobic metabolism in high intensity exercise. Indeed, the AOD measure has been the subject of much controversy. Several of the physiological exercise responses of children may lead to an even greater underestimation of the anaerobic energy contribution to high intensity exercise in children than adults when AOD measures are calculated.
Metabolic and Perceptual Responses to Short-Term Cycle Training in Children
Authors: Duncan Glen E. , Howley Edward T.
Published: August 2016

Metabolic and perceptual responses to cycle training were investigated in children in a training group (TG, N = 10) and control group (CG, N = 13). Prior to training, aerobic power (VO2peak) was assessed, and children performed submaximal exercise at graded power outputs. Substrate use was calculated for each level using the respiratory exchange ratio (RER) and metabolic rate, and ratings of perceived exertion (RPE) were obtained to estimate perceptual effort. Training consisted of 12 sessions (three 10-min work bouts 3 times/week, 50% VO2peak) on a cycle ergometer. After 4 weeks, RER and RPE were reevaluated at the same absolute intensities. Overall difference scores indicated a decrease in RER and RPE in the TG and an increase in RER with * no change in RPE in the CG. These data demonstrate that short-term cycle training in children results in enhanced fat use and diminished perception of effort during submaximal exercise.
Teaching Landing to Children with and Without Developmental Coordination Disorder
Authors: Larkin Dawne , Parker Helen E.
Published: August 2016

This study investigated landing patterns of children aged 7–9 years with either developmental coordination disorder (DCD) or without coordination problems (NC). Initially, 16 DCD and 15 NC children were videotaped performing two-foot landings from a height of 21.5 cm onto a force platform sampling at 500 Hz. Each landing was videotaped at 60 Hz. Regression modeling of the data identified that 72% of peak maximum loading force was explained by landing time, knee angle at touchdown, and hip joint range of motion. Dis-criminant function analysis using landing force, landing time and lower limb joint kinematic variables reliably separated the groups. In the second part, 12 DCD and 10 NC children participated in 6 weekly landing lessons. The only significant adjustment produced by the program was a decrease in the range of motion at the hip in response to instructions to look straight ahead and sit into the landing.
Can Conceptual Physical Education Promote Physically Active Lifestyles?
Authors: Dale Darren , Corbin Charles B. , Cuddihy Thomas F.
Published: August 2016

This study examined the physical activity participation of students in a large southwestern high school 1–3 years after they had been exposed to a 9th-grade conceptual physical education program. Comparisons were made to students exposed to traditional physical education. Students were assessed using physical activity questions from the 1995 Youth Risk Behavior Survey. Students from the conceptual program met adolescent guidelines for physical activity, especially those who participated in the program in its first year of operation. Females were significantly less likely to report sedentary behaviors if they had been exposed to the conceptual, rather than traditional, high school physical education program.
Immune Responses to Exercise and Training: A Comparison of Children and Young Adults
Authors: Shore Susan , Shephard Roy J.
Published: August 2016

Immune responses have been examined in 11 children aged 10.3 ± 0.6 years before and after 12 weeks of aerobic training. Initial resting data showed high total lymphocyte, CD3+ and CD8+ counts, a low CD4+/CD8+ ratio and a low CD25+ count relative to young adults. Acute exercise (30 min at ventilatory threshold) initially increased CD4+, CD8+, and CD56+ counts, and decreased CD4+/CD8+ ratio, but CD56+ count did not decrease during recovery. After training, relative aerobic power remained unchanged at 50 ±3 ml · kg−1 · min−1. However, resting leukocyte, CD3’ and CD25’ counts were decreased, and acute exercise induced smaller changes in leukocyte and subset counts. We conclude that immune responses to exercise are generally similar in children and young adults.
Changes Over Time in the Determinants of Sport Commitment
Authors: Carpenter Paul J. , Scanlan Tara K.
Published: August 2016

The purpose of this study was to examine whether changes over time in the determinants of sport commitment would be related to predicted changes in commitment. Male and female (N = 103) high school soccer players completed surveys toward the middle and at the end of their regular season. A simultaneous multiple regression analysis indicated that commitment was significantly predicted by changes in involvement opportunities. Examination of the mean magnitude of changes in the determinants and corresponding changes in commitment using a series of correlated t-tests revealed significant effects for sport enjoyment and involvement opportunities. For those players whose sport enjoyment and involvement opportunities had declined, there was a corresponding decrease in their commitment. For those players whose involvement opportunities had increased, there was a corresponding increase in their commitment. Combined, these results provided support for a priori hypotheses regarding changes in the determinants of commitment over time and corresponding changes in commitment.
Contribution of Organized Sports Participation to Estimated Daily Energy Expenditure in Youth
Authors: Katzmarzyk Peter T. , Malina Robert M.
Published: August 2016

The contribution of organized sport participation to the total daily energy expenditure (TDEE) of youth was estimated in a sample of 90 males and 93 females, 12-14 years of age. TDEE and moderate-to-vigorous energy expenditure (MVEE) were estimated using a 3-day activity record. Males expended 20.4% of TDEE in youth sports; the corresponding estimate for females was 16.3%. Males and females expended 55% and 64.6%, respectively, of MVEE in youth sports. Youth who participated in organized sports had greater TDEE and MVEE, and spent less time watching television than those who did not participate. Thus, organized sport participation appears to be a significant component of daily energy expenditure among youth.