Glenohumeral stabilizing roles of the scapulohumeral muscles: Implications of muscle geometry.

Dynamic stability provided by muscles is integral for function and integrity of the glenohumeral joint. Although the high degree of inter-individual variation that exists in musculoskeletal geometry is associated with shoulder injuries, there is limited research associating the effects of muscle geometry on the potential stabilizing capacities of shoulder muscles. The purpose of this investigation was to evaluate the stabilizing functions of the scapulohumeral muscles using computational modeling and to quantify the sensitivity of muscle stabilizing roles to changes in muscle geometry.

Modeling the effects of musculoskeletal geometry on scapulohumeral muscle moment arms and lines of action.

Biomechanical investigations examining shoulder function commonly observe a high degree of inter-individual variability in muscle activity and kinematic patterns during static and dynamic upper extremity exertions. Substantial differences in musculoskeletal geometry between individuals can alter muscle moment arms and lines of action that, theoretically, alter muscle activity and shoulder kinematics. The purposes of this research were to: (i) quantify model-predicted functional roles (moment arms, lines of action) of the scapulohumeral muscles, (ii) compare model predictions to experimental data in the literature, and (iii) evaluate sensitivity of muscle functional roles due to changes in muscle attachment locations using probabilistic modeling.

Iterative Spatial Updating During Forward Linear Walking Revealed Using a Continuous Pointing Task.

The continuous pointing task uses target-directed pointing responses to determine how perceived distance traveled is estimated during forward linear walking movements. To more precisely examine the regulation of this online process, the current study measured upper extremity joint angles and step-cycle kinematics in full vision and no-vision continuous pointing movements. Results show perceptual under-estimation of traveled distance in no-vision trials compared to full vision trials.

Examining the effect of state anxiety on compensatory and strategic adjustments in the planning of goal-directed aiming.

The anxiety-perceptual-motor performance relationship may be enriched by investigations involving discrete manual responses due to the definitive demarcation of planning and control processes, which comprise the early and late portions of movement, respectively. To further examine the explanatory power of self-focus and distraction theories, we explored the potential of anxiety causing changes to movement planning that accommodate for anticipated negative effects in online control. As a result, we posed two hypotheses where anxiety causes performers to initially undershoot the target and enable more time to use visual feedback ("play-it-safe"), or fire a ballistic reach to cover a greater distance without later undertaking online control ("go-for-it").

The influence of intrapersonal sensorimotor experiences on the corticospinal responses during action-observation.

The coupling of perception and action has been strongly indicated by evidence that the observation of an action primes a response in the observer. It has been proposed that these primed responses may be inhibited when the observer is able to more closely distinguish between self- and other-generated actions - the greater the distinction, then the greater the inhibition of the primed response. This self-other distinction is shown to be enhanced following a period of visual feedback of self-generated action.

Extending Energy Optimization in Goal-Directed Aiming from Movement Kinematics to Joint Angles.

Energy optimization in goal-directed aiming has been demonstrated as an undershoot bias in primary movement endpoint locations, especially in conditions where corrections to target overshoots must be made against gravity. Two-component models of upper limb movement have not yet considered how joint angles are organized to deal with the energy constraints associated with moving the upper limb in goal-directed aiming tasks. To address this limitation, participants performed aiming movements to targets in the up and down directions with the index finger and two types of rod extensions attached to the index finger.

The Impact of Strategic Trajectory Optimization on Illusory Target Biases During Goal-Directed Aiming.

During rapid aiming, movements are planned and executed to avoid worst-case outcomes that require time and energy to correct. As such, downward movements initially undershoot the target to avoid corrections against gravity. Illusory target context can also impact aiming bias.

The modulation of motor contagion by intrapersonal sensorimotor experience.

Sensorimotor experiences can modify the internal models for action. These modifications can govern the discrepancies between predicted and actual sensory consequences, such as distinguishing self- and other-generated actions. This distinction may also contribute toward the inhibition of movement interference, which is strongly associated with the coupling of observed and executed actions.

The violation of Fitts' Law: an examination of displacement biases and corrective submovements.

Fitts' Law holds that, to maintain accuracy, movement times of aiming movements must change as a result of varying degrees of movement difficulty. Recent evidence has emerged that aiming to a target located last in an array of placeholders results in a shorter movement time than would be expected by the Fitts' equation-a violation of Fitts' Law. It has been suggested that the violation emerges because the performer adopts an optimized movement strategy in which they partially pre-plan an action to the closest placeholder (undershoot the last placeholder) and rely on a secondary acceleration to propel the limb toward the last location when it is selected as the target (Glazebrook et al.

Common vs. independent limb control in sequential vertical aiming: The cost of potential errors during extensions and reversals.

The following study explored movement kinematics in two-component aiming contexts that were intended to modulate the potential cost of overshoot or undershoot errors in up and down directions by having participants perform a second extension movement (Experiment 1) or a reversal movement (Experiment 2). For both experiments, the initial movement toward a downward target took longer, and had lower peak acceleration and peak velocity than upward movements. These movement characteristics may reflect a feedback-based control strategy designed to prevent energy-consuming limb modifications against gravitational forces.

The use of action phrases in individuals with Autism Spectrum Disorder.

Previous research has shown that individuals with Autism Spectrum Disorder (ASD) may be able to perceive the intentions of another individual through tool use (e.g., Aldridge et al.

Age-related changes in postural control to the demands of a precision task.

Optimal sensorimotor integration is needed to maintain the precision of a visuomotor postural task. Furthermore, cognitive resources have been suggested to be involved in maintaining balance, especially in older adults. This study investigated how older and younger adults differed in employing sensorimotor strategies in a dual-task situation.

Effector mass and trajectory optimization in the online regulation of goal-directed movement.

Goal-directed aiming movements are planned and executed so that they optimize speed, accuracy and energy expenditure. In particular, the primary submovements involved in manual aiming attempts typically undershoot targets in order to avoid costly time and energy overshoot errors. Furthermore, in aiming movements performed over a series of trials, the movement planning process considers the sensory information associated with the most recent aiming attempt.

The influence of visual feedback and prior knowledge about feedback on vertical aiming strategies.

Two experiments were conducted to examine time and energy optimization strategies for movements made with and against gravity. In Experiment 1, the authors manipulated concurrent visual feedback, and knowledge about feedback. When vision was eliminated upon movement initiation, participants exhibited greater undershooting, both with their primary submovement and their final endpoint, than when vision was available.

Separating responses based on demand characteristics and phenomenological-spatial associations.

Previous researchers have found that participants associate higher frequencies with locations that are higher in space and lower frequencies with lower locations, creating a phenomenological-spatial association for the frequency of auditory tones. With such an association, the frequency of an auditory tone could potentially bias movements along multiple axes. This hypothesis was tested.

The gunslinger effect: why are movements made faster when responding to versus initiating an action?

The authors replicated and extended results from the gunfight paradigm (A. Welchman, J. Stanley, M.

Gaze-down endoscopic practise leads to better novice performance on gaze-up displays.

Objectives: It is well known that precision skills are best learned when they are practised in the sensorimotor context that is present when performance is most important. However, a particular skill may vary with respect to the sensorimotor context in which it is performed. Certain sensorimotor variations can make a task more or less complex than others.

Spinal manipulation impacts cervical spine movement and fitts' task performance: a single-blind randomized before-after trial.

Objective: The objective of this study was to determine if active cervical range of motion (ROM) and Fitts' task movement time differences occurred after high-velocity low-amplitude cervical spinal manipulation (SM) across various indexes of difficulty.

Methods: A single-blind randomized before-after trial was performed in a motor performance laboratory. Fifteen volunteers (21-42 years) with asymptomatic palpable intervertebral motion restriction at the C1-C2 level were randomly assigned to an SM group or to a no-intervention (NI) group.

Spatial properties of perceived pitch: influence on reaching movements.

We present three experiments that show a clear influence of pitch on reaching movements. The first experiment shows that when there are incompatibilities between the spatial representations of target coordinates and perceived pitches, response times are longer than when spatial representations are congruous. The second experiment shows that pitch can influence motor responses, biasing their direction.

Attentional and motor response priming in a bimanual task.

This study examined the performance of the upper limbs during responses to previously cued and un-cued locations. Participants made unimanual and bimanual responses under homologous and non-homologous muscular control, within a cuetarget (Experiment 1; n = 10), and a target-target (Experiment 2; n = 10) aiming protocol. The inhibition of return (IOR) to a target location was expected to increase with (a) an increase in the organization of the movement response required, and (b) the decrease in the muscular coupling under which the bimanual movement was performed.

The effect of the Müller-Lyer illusion on the planning and control of manual aiming movements.

Two experiments used Müller-Lyer stimuli to test the predictions of the planning-control model (S. Glover, 2002) for aiming movements. In Experiment 1, participants aimed to stimuli that either remained the same or changed upon movement initiation.

African-American grandmothers as health educators in the family.

More than 18,000 adolescents die each year in the United States from bicycle, motorcycle, car, and truck accidents. This study sought to understand the role of African-American grandmothers as prevention-oriented health educators in the family. Full Model Fitted Regression Analyses were conducted on a sample of African-American grandmothers (N = 105) with 10- to 19-year-old grandchildren.

Does Joe influence Fred's action? Inhibition of return across different nervous systems.

Inhibition of return (IOR) refers to the slowing of responses to a target that appears in the same location as a previous event. Many researchers have speculated that IOR arises from inhibitory neural processes that have developed through evolution to facilitate efficient search patterns by biasing the action and/or attention of an individual towards novel locations. Throughout evolution, however, humans conducted searches as individuals as well as members of a group.