Programming Of Muscle Activity In Arm Movements In Relation To Force Requirements

Analysis of the relationship between movement kinematics and muscle activity is a widely used approach for understanding how the nervous system formulates motor commands to produce movements. In planar single joint movements, phasic muscle activity is highly correlated with specific kinematic variables. Such correlations have not proven to be as direct in complex movements. The rules used by the nervous system in movement coordination are thus poorly understood. The purpose of this study was first, to examine kinematics, dynamics and electromyographic (EMG) activity during single and two-joint arm movements to discern the common planning strategies between these movements; and second, to gain insight into the variables used in planning complex movements.;In single joint movements made in the vertical plane, all movements were characterized by time symmetric velocity profiles. Gravitational loading directly influenced muscle activity. This suggests that basic patterns of muscle activation are modulated in relation to external forces. In two-joint planar movements involving the wrist and elbow joints, the selection of muscle activation patterns at the wrist was dependent on the relative magnitude and direction of elbow reaction torques, in relation to wrist motion. Elbow joint movement is therefore an important consideration in planning wrist movement. The details of the actual wrist trajectory may not be specifically planned, but emerges from the integration of basic patterns of activity with the dynamic interaction between joints.;The influence of visual feedback information on movement coordination was also examined. Visual feedback of the endpoint targets as well as the subject\u27s endpoint limb position, were presented in a range of concrete to abstract representations. Changes were observed in the timing relationship between the two joints, and in the EMG patterns, in relation to visual feedback conditions.;Thus, in selecting the level and pattern of muscle activity of the distal joint during a two-joint movement, the nervous system requires information about the amplitude of the desired distal movement, and the magnitude and direction of acceleration of the proximal joint. Inter-joint coordination will further be influenced by the nature of visual feedback information

Health monitoring of young children with Down syndrome: A parent-report study

© 2019 John Wiley & Sons Ltd.Background: Children with Down syndrome have an increased risk of serious health conditions, particularly in early childhood. Published guidelines promote the identification and monitoring of health issues and adherence could reduce health inequalities, yet there is limited research about the extent to which health monitoring occurs as recommended. This study aimed to investigate the health monitoring of children with Down syndrome aged 0–5 years in the UK. Materials and Methods: Twenty-four parents of children with Down syndrome with a mean age of 32 months (10–65 months) participated. They completed a questionnaire about their child's healthcare usage, diagnoses of health conditions and whether health checks had been completed at birth and since birth. The results of the questionnaires were charted and compared to the schedule of checks produced by the Down Syndrome Medical Interest Group UK. Results: Children with Down syndrome had high usage of health services and reported significant health issues. There was high adherence to published guidelines for the majority of health checks at birth, although 38% of children had not received all recommended checks. Not all health domains had been monitored since birth for all children, particularly breathing and blood (excluding thyroid). With the potential exception of sleep apnoea, diagnosed conditions appeared to be monitored. Conclusions: This study suggests that health monitoring after birth and screening for nondiagnosed health conditions is variable for children with Down syndrome. Further research should examine convergence of these findings with medical records and clinicians' experiences across the UK.Peer reviewedFinal Accepted Versio

Returning Individuals to Activities and Participation...It's What We Do!

The evidence regarding the optimal rehabilitation management of concussion is clearly evolving. When can someone return to school, to work, to recreational exercise for fun, or to activities that could put them at risk for another injury like bike riding, ice skating, or trail running? We would argue that these questions, especially as they relate to physical activity, have long been our focus as physical therapists

Effects of gravitational forces on single joint arm movements in humans

We have examined the kinematics and muscle activation patterns of single joint elbow movements made in the vertical plane. Movements of different amplitudes were performed during a visual, step-tracking task. By adjusting shoulder position, both elbow flexion and extension movements were made under three conditions: (a) in the horizontal plane, (b) in the vertical plane against gravity, and (c) in the vertical plane with gravity. Regardless of the gravitational load, all movements were characterized by time symmetric velocity profiles. In addition, no differences were found in the relationships between movement duration, peak velocity, and movement amplitude in movements with or against gravity. The pattern of muscle activation was influenced however, by the gravitational load. Both flexion and extension movements made with gravity were characterized by a reciprocally organized pattern of muscle activity in which phasic agonist activity was followed by phasic antagonist activity. Flexion and extension movements made against gravity were characterized by early phasic antagonist activity occurring at about the same time as the initial agonist burst. These findings suggest that EMG patterns are modified in order to preserve a common temporal structure in the face of different gravitational loads.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46567/1/221_2004_Article_BF00239600.pd

Do we use a priori knowledge of gravity when making elbow rotations?

In this study, we aim to investigate whether motor commands, emanating from movement planning, are customized to movement orientation relative to gravity from the first trial on. Participants made fast point-to-point elbow flexions and extensions in the transverse plane. We compared movements that had been practiced in reclined orientation either against or with gravity with the same movement relative to the body axis made in the upright orientation (neutral compared to gravity). For each movement type, five rotations from reclined to upright orientation were made. For each rotation, we analyzed the first trial in upright orientation and the directly preceding trial in reclined orientation. Additionally, we analyzed the last five trials of a 30-trial block in upright position and compared these trials with the first trials in upright orientation. Although participants moved fast, gravitational torques were substantial. The change in body orientation affected movement planning: we found a decrease in peak angular velocity and a decrease in amplitude for the first trials made in the upright orientation, regardless of whether the previous movements in reclined orientation were made against or with gravity. We found that these decreases disappeared after participants familiarized themselves with moving in upright position in a 30-trial block. These results indicate that participants used a general strategy, corresponding to the strategy observed in situations with unreliable or limited information on external conditions. From this, we conclude that during movement planning, a priori knowledge of gravity was not used to specifically customize motor commands for the neutral gravity condition

An EEG study on the somatotopic organisation of sensorimotor cortex activation during action execution and observation in infancy

Previous studies have shown that sensorimotor cortex activation is somatotopically-organised during action execution and observation in adulthood. Here we aimed to investigate the development of this phenomenon in infancy. We elicited arm and leg actions from 12-month-old infants and presented them, and a control group of adults, with videos of arm and leg actions while we measured their sensorimotor alpha suppression using EEG. Sensorimotor alpha suppression during action execution was somatotopically organised in 12-month-old infants: there was more suppression over the arm areas when infants performed reaching actions, and more suppression over the leg area when they performed kicking actions. Adults also showed somatotopically-organised activation during the observation of reaching and kicking actions. In contrast, infants did not show somatotopically-organised activation during action observation, but instead activated the arm areas when observing both reaching and kicking actions. We suggest that the somatotopic organisation of sensorimotor cortex activation during action observation may depend on infants’ understanding of the action goal and their expectations about how this goal will be achieved

Does dysfunction of the mirror neuron system contribute to symptoms in amyotrophic lateral sclerosis?

There is growing evidence that mirror neurons, initially discovered over two decades ago in the monkey, are present in the human brain. In the monkey, mirror neurons characteristically fire not only when it is performing an action, such as grasping an object, but also when observing a similar action performed by another agent (human or monkey). In this review we discuss the origin, cortical distribution and possible functions of mirror neurons as a background to exploring their potential relevance in amyotrophic lateral sclerosis (ALS). We have recently proposed that ALS (and the related condition of frontotemporal dementia) may be viewed as a failure of interlinked functional complexes having their origins in key evolutionary adaptations. This can include loss of the direct projections from the corticospinal tract, and this is at least part of the explanation for impaired motor control in ALS. Since, in the monkey, corticospinal neurons also show mirror properties, ALS in humans might also affect the mirror neuron system. We speculate that a defective mirror neuron system might contribute to other ALS deficits affecting motor imagery, gesture, language and empathy

Unconstrained three-dimensional reaching in Rhesus monkeys

To better understand normative behavior for quantitative evaluation of motor recovery after injury, we studied arm movements by non-injured Rhesus monkeys during a food-retrieval task. While seated, monkeys reached, grasped, and retrieved food items. We recorded three-dimensional kinematics and muscle activity, and used inverse dynamics to calculate joint moments due to gravity, segmental interactions, and to the muscles and tissues of the arm. Endpoint paths showed curvature in three dimensions, suggesting that maintaining straight paths was not an important constraint. Joint moments were dominated by gravity. Generalized muscle and interaction moments were less than half of the gravitational moments. The relationships between shoulder and elbow resultant moments were linear during both reach and retrieval. Although both reach and retrieval required elbow flexor moments, an elbow extensor (triceps brachii) was active during both phases. Antagonistic muscles of both the elbow and hand were co-activated during reach and retrieval. Joint behavior could be described by lumped-parameter models analogous to torsional springs at the joints. Minor alterations to joint quasi-stiffness properties, aided by interaction moments, result in reciprocal movements that evolve under the influence of gravity. The strategies identified in monkeys to reach, grasp, and retrieve items will allow the quantification of prehension during recovery after a spinal cord injury and the effectiveness of therapeutic interventions

Low-frequency oscillations employ a general coding of the spatio-temporal similarity of dynamic faces

Brain networks use neural oscillations as information transfer mechanisms. Although the face perception network in occipitotemporal cortex is well-studied, contributions of oscillations to face representation remain an open question. We tested for links between oscillatory responses that encode facial dimensions and the theoretical proposal that faces are encoded in similarity-based “face spaces”. We quantified similarity-based encoding of dynamic faces in magnetoencephalographic sensor-level oscillatory power for identity, expression, physical and perceptual similarity of facial form and motion. Our data show that evoked responses manifest physical and perceptual form similarity that distinguishes facial identities. Low-frequency induced oscillations (< 20 Hz) manifested more general similarity structure, which was not limited to identity, and spanned physical and perceived form and motion. A supplementary fMRI-constrained source reconstruction implicated fusiform gyrus and V5 in this similarity-based representation. These findings introduce a potential link between “face space” encoding and oscillatory network communication, which generates new hypotheses about the potential oscillation-mediated mechanisms that might encode facial dimensions