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A Neuroscientific Approach to the Examination of Concussions in Student-Athletes

Concussions are occurring at alarming rates in the United States and have become a serious public health concern. The CDC estimates that 1.6 to 3.8 ...

Elon University

Fifteen older adults (M = 68 years old) and 15 young adults (M = 23 years old) participated in a speed-accuracy task in which aiming movements were performed on a digitizing tablet to assess movement slowing and variability in older adults. Target-size and movement amplitude influences were analyzed separately to determine if they affected the performance of the young and older adults differently. When target size was increased, older adults did not increase the relative distance traveled in the primary submovement. When movement amplitude was increased, older adults did not scale movement velocities to the same magnitude as young adults did. Both the inability to scale velocity and the inability to increase the relative distance traveled in the primary submovement contribute to slower, more variable movements observed in older adults depending on task parameters. Thus, these data reveal that manipulation of target size and movement amplitude yield two distinct factors that contribute to slowness of movement in older adults.

Age-related kinematic differences as influenced by task difficulty, target size, and movement amplitude.

Influence of mechanical interactions between the shoulder and elbow on production of different coordination patterns during horizontal arm movements is investigated in the present study. Subjects performed cyclical movements along a circle and along lines of 4 different orientations. Cycling frequency was manipulated to highlight control features responsible for interactive torque regulation. When the shoulder was involved in motion, torque analysis revealed that this joint was controlled similarly during all movement types. At the elbow, however, each movement type required a specific pattern of regulation of interactive torque with muscle torque. When interactive torque acted in the direction of the required elbow rotation, the demands for active control were lower than when the interactive torque resisted elbow motion and had to be actively suppressed. Kinematic analysis demonstrated that increases in cycling frequency systematically deformed the fingertip path. The amount of these deformations differed across movement types, being more pronounced for movements where the interactive torque resisted joint motion. It appears that interactive torque can assist or resist movement at the joints, making control of some movement types more difficult than others.

Influence of biomechanical constraints on horizontal arm movements.

Parkinson's disease patients are known to suffer loss of dopaminergic input to the rostral caudate nucleus. Recent functional magnetic resonance imaging (fMRI) studies have implicated this structure in the transformation of spatial information in memory to guide action, suggesting that memory to motor transformations may be selectively impaired in Parkinson's disease. In order to investigate this possibility we tested a group of Parkinson's disease patients (PDs) using a memory-guided pointing task. Of interest was whether patients showed reduced accuracy in the task as a function of memory load. Twelve PD patients and 13 elderly controls were asked to recall single or four step target sequences with 2 time delays (500 and 3,500 ms). In all memory-guided conditions PD patients showed increased variability in memory-guided movement end-points. This effect was not affected by delay, number of items, or the sequence familiarity. The results are consistent with increased variability in memory-motor transformations in early PD, due to dopamine depletion within the rostral caudate nucleus.

Memory-motor transformations are impaired in Parkinson's disease.

The underlying mechanisms of the neural control of movement have long been explored, with a focus primarily on central control aspects and often overlooking the intrinsic mechanical properties of the motor system. To fully understand the control and regulation of movements, the biomechanical properties of the moving subject, specifically interactive torques, must be considered in the design, evaluation, and interpretation of empirical data. We first discuss the difficulty of extrapolating information from a wide variety of tasks due to their varying inherent task constraints. Examples are subsequently given where a biomechanical perspective provides a more informative interpretation of existing data. Finally, we focus on research examining the role of interactive torques with a discussion of how discoordinated movements may be explained by an inability to modulate interactive torques. Inclusion of biomechanical considerations in motor control research is a step toward incorporating multilevel methodologies and interpretations into the field, and providing a more comprehensive understanding of the neural control and regulation of movement.

Multijoint movement control: the importance of interactive torques.

The present study investigates whether regulation of interactive torque during multijoint movements decays with advanced age as a result of declines in the motor system. Young and elderly adults repeatedly drew a circle and ovals oriented in different directions using shoulder and elbow joint movements. Each template was traced at three levels of cycling frequency with and without vision. Although vision did not affect performance, increases in cycling frequency caused distortions of movement trajectories in both groups. The pattern of distortions differed, however, between the groups. These differences were accounted for by differences in elbow control. Young adults provided regulation of elbow amplitude and timing by matching muscle torque magnitude with increased interactive torque. In contrast, elderly adults did not increase muscle torque magnitude and modulated torque timing for elbow motion regulation. This strategy is discussed as adaptation to decrements in the aging motor system.

Age-related differences in the control of multijoint movements.

Impairments in control of multi-joint arm movements in Parkinson's Disease (PD) were investigated. The PD patients and age-matched elderly participants performed cyclical arm movements, tracking templates of a large circle and four differentially oriented ovals on a horizontal table. The wrist was immobilized and the movements were performed with shoulder and elbow rotations. The task was performed with and without vision at a cycling frequency of 1.5 Hz. Traces of the arm endpoint, joint-motion parameters represented by range of motion and relative phase, and joint-control characteristics represented by amplitude and timing of muscle torque were analyzed. The PD patients provided deformations of the template shapes that were not observed in movements of elderly controls. The deformations were consistent for each shape but differed across the shapes, making quantification of impairments in the endpoint movement difficult. In contrast, the characteristics of joint control and motion demonstrated systematic changes across all shapes in movements of PD patients, although some of these changes were observed only without vision. A specification of the PD influence was observed at the level of joint control and it was not distinguishable in joint and endpoint motion, because of the property of multi-joint movements during which control at each joint influences motion at the other joints. The results suggest that inability of PD patients to provide fine muscle torque regulation coordinated across the joints contributes to the altered endpoint trajectories during multi-joint movements. The study emphasizes the importance of the torque analysis when deficits in multi-joint movements are investigated, because specific impairments that can be detected in joint-control characteristics are difficult to trace in characteristics of joint and endpoint kinematics, because of interactions between joint motions.

Disruptions in joint control during drawing arm movements in Parkinson's disease.

The authors investigated whether visual fixations during a continuous graphical task were related to arm endpoint kinematics, joint motions, or joint control. The pattern of visual fixations across various shapes and the relationship between temporal and spatial events of the moving limb and visual fixations were assessed. Participants (N=16) performed movements of varying shapes by rotating the shoulder and elbow joints in the transverse plane at a comfortable pace. Across shapes, eye movements consisted of a series of fixations, with the eyes leading the hand. Fixations were spatially related to modulation of joint motion and were temporally related to the portions of the movement where curvature was the highest. Gathering of information related to modulation of interactive torques arising from passive forces from movement of a linked system occurred when the velocity of the movement (a) was the lowest and (b) was ahead of the moving limb, suggesting that that information is used in a feedforward manner.

The role of vision in the control of continuous multijoint movements.

The present study addresses the influence of aging on the ability to regulate mechanical effects arising during arm movements due to the multi-joint structure of the arm. Two mechanical factors were considered, interaction torque (IT) and inertial resistance (IR). Regulation of these two factors can be demanding in terms of the timing and magnitude of the required muscle torque (MT), specifically during fast movements. We hypothesized that aging exacerbates the challenge regarding the regulation of these effects with muscular control due to declines in the motor system. This hypothesis was tested by comparing performance of a cyclic line-drawing task in two age groups, young and older adults. Only two joints, the shoulder and elbow, participated in motion. Four orientations of the lines were used to provide variations in the requirements for regulation of IT and IR. Cyclic frequency was manipulated to emphasize the dependence of the mechanical factors on movement speed. Various characteristics of fingertip motion showed that there were no age-related deteriorations in accuracy of line drawing. However, older adults were systematically slower, particularly in the directions of high IR. A detailed analysis of the magnitude of MT and the contribution of this torque to production of net torque at each joint demonstrated that older adults modified joint control and decreased the demands for MT by skillful exploitation of IT in a way specific for each particular line orientation. The results point to a tendency in older adults to decrease the production of muscle force. Nevertheless, older adults also demonstrated an ability to partially compensate for declines in the force production by developing sophisticated strategies of joint control that exploit the multi-joint mechanical structure of the arm. This ability suggests that the internal representation of inter-segmental dynamics and the capability to use it for movement control does not decay with age. The study emphasizes the importance of analysis of joint motion and control characteristics for the investigation of arm movements and for comparison of these movements between different subject populations.

Efficient control of arm movements in advanced age.

Research has shown that movement impairments following stroke are typically associated with the limb contralateral to the side of the stroke. Prior studies identified ipsilateral motor declines across a variety of tasks.

Targeted aiming movements are compromised in nonaffected limb of persons with stroke.

The authors sought to determine if principles of the Leading Joint Hypothesis, when applied to a multijoint, bimanual coordination task, could provide insight into the contribution of intralimb dynamics to interlimb coordination. Participants repetitively traced ellipse templates with an isodirectional motion of the end effectors (both hands moving counterclockwise [CCW]) at two cycling frequencies. Ellipse templates were oriented either tilted right or tilted left, yielding a total of 4 left arm-right arm leading-joint combinations. Analysis of torque sign and impulse data indicated that the 4 ellipse-tracing conditions resulted in 4 distinct left arm-right arm leading-joint combinations: 2 conditions with similar leading joints and 2 conditions with different leading joints. Isodirectional CCW ellipse tracing was more stable when produced with similar leading joints compared with when produced with different leading joints. The authors discuss results within the context of intralimb control contributions to the stability of interlimb coordination patterns.

Identifying leading joint strategies in a bimanual coordination task: does coordination stability depend on leading joint strategy?

: Concussions in collegiate athletics can affect student-athletes both on the field and in the classroom. As policies are made to outline return-to-play decisions and timelines, this article will make the case that return-to-academics should also be included and follow a step-wise protocol. Complete cognitive rest is a cornerstone of concussion recovery and slow reintroduction to academics should precede return-to-play. The college structure allows for student-athletes to begin small doses of cognitive activity after the recommended complete cognitive rest. It is recommended that return-to-academics involves a team approach to help the student-athlete navigate the responsibilities of course work while healing from a brain injury.

Caroline J. Ketcham

Department of Exercise Science

Elon University

A Neuroscientific Approach to the Examination of Concussions in Student-Athletes

Caroline J. Ketcham

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Exercise Science

Elon University

A Neuroscientific Approach to the Examination of Concussions in Student-Athletes

Department of Exercise Science