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Perception of limb position and motion combines sensory information from spindles in muscles that span one joint (monoarticulars) and two joints (biarticulars). This anatomical organization should create interactions in estimating limb position. We developed two models, one with only monoarticulars and one with both monoarticulars and biarticulars, to explore how biarticulars influence estimates of arm position in hand ( x , y ) and joint ( shoulder, elbow ) coordinates. In hand coordinates, both models predicted larger medial-lateral than proximal-distal errors, although the model with both muscle groups predicted that biarticulars would reduce this bias. In contrast, the two models made significantly different predictions in joint coordinates. The model with only monoarticulars predicted that errors would be uniformly distributed because estimates of angles at each joint would be independent. In contrast, the model that included biarticulars predicted that errors would be coupled between the two joints, resulting in smaller errors for combinations of flexion or extension at both joints and larger errors for combinations of flexion at one joint and extension at the other joint. We also carried out two experiments to examine errors made by human subjects during an arm position matching task in which a robot passively moved one arm to different positions and the subjects moved their other arm to mirror-match each position. Errors in hand coordinates were similar to those predicted by both models. Critically, however, errors in joint coordinates were only similar to those predicted by the model with monoarticulars and biarticulars. These results highlight how biarticulars influence perceptual estimates of limb position by helping to minimize medial-lateral errors. NEW & NOTEWORTHY It is unclear how sensory information from muscle spindles located within muscles spanning multiple joints influences perception of body position and motion. We address this issue by comparing errors in estimating limb position made by human subjects with predicted errors made by two musculoskeletal models, one with only monoarticulars and one with both monoarticulars and biarticulars. We provide evidence that biarticulars produce coupling of errors between joints, which help to reduce errors.

Context: Sport-related concussion (SRC) often presents with multidimensional and subtle neurologic deficits that are difficult to detect with standard clinical tests. New assessment approaches that efficiently quantify deficits across multiple neurologic domains are needed., Objective: To quantify impairments in postural movements during an assessment of rapid, bimanual motor ability in athletes within 10 days of experiencing an SRC and evaluate relationships between impairments in upper extremity and postural performance., Design: Cohort study., Setting: Sports medicine clinic., Patients or Other Participants: Initial baseline assessments were completed for 711 athletes. Seventy-five athletes (age = 15.8 ± 3.3 years at baseline) sustained SRCs and were reassessed within 10 days. Seventy-eight athletes (age = 15.5 ± 2.0 years) completed 2 assessments in a healthy state., Main Outcome Measure(s): Athletes stood on force plates and performed a rapid, bimanual motor task, termed the object-hit task, delivered using a Kinesiological Instrument for Normal and Altered Reaching Movements endpoint robot. Measures of postural stability that quantified center-of-pressure movements and measures of upper extremity performance were used to characterize task performance., Results: Performance changes across assessments were converted to reliable change indices. We observed a difference in reliable change indices values between athletes with SRC and healthy control athletes on the combined postural measures (P = .01). Using measures to evaluate the change in postural movements from the early, easier portion of the task to the later, more difficult portion, we identified the highest levels of impairment (19%-25% of the sample impaired). We also noted a difference between individuals with concussion and healthy individuals on the combined upper extremity measures (P = .003), but these impairments were largely unrelated to those identified in the postural movements., Conclusions: Measurement of postural movements during the object-hit task revealed impairments in postural stability that were not related to impairments in upper extremity performance. The findings demonstrated the benefits of using assessments that simultaneously evaluate multiple domains of neurologic function (eg, upper extremity and postural control) after SRC., (© by the National Athletic Trainers' Association, Inc.)

Background. Corticospinal tract (CST) damage is considered a biomarker for stroke recovery. Several methods have been used to define CST damage and examine its relationship to motor performance, but which method is most useful remains unclear. Proprioceptive impairment also affects stroke recovery and may be related to CST damage. Methods. Robotic assessment quantified upper-limb motor and proprioceptive performance at 2 weeks and 6 months poststroke (n = 149). Three previously-established CST lesion metrics were calculated using clinical neuroimaging. Diffusion magnetic resonance imaging quantified CST microstructure in a subset of participants (n = 21). Statistical region of interest (sROI) analysis identified lesion locations associated with motor and proprioceptive deficits. Results. CST lesion metrics were moderately correlated with motor scores at 2 weeks and 6 months poststroke. CST fractional anisotropy (FA) was correlated with motor scores at 1 month poststroke, but not at 6 months. The FA ratio of the posterior limb of the internal capsule was not correlated with motor performance. CST lesion metrics were moderately correlated with proprioceptive scores at 2 weeks and 6 months poststroke. sROI analysis confirmed that CST damage was associated with motor and proprioceptive deficits and additionally found that putamen, internal capsule, and corticopontocerebellar tract lesions were associated with poor motor performance. Conclusions. Across all methods used to quantify CST damage, correlations with motor or proprioceptive performance were moderate at best. Future research is needed to identify complementary or alternative biomarkers to address the complexity and heterogeneity of stroke recovery.

Kinesthesia is an essential component of proprioception allowing for perception of movement. Due to neural injury, such as stroke, kinesthesia can be significantly impaired. Throughout neurorehabilitation, clinicians may encourage use of vision to guide limb movement to retrain impaired kinesthesia. However, little evidence exists that vision improves kinesthetic performance after stroke. We examined behavioral and neuroanatomical characteristics of kinesthesia post-stroke to determine if these impairments improve with vision. Stroke subjects (N = 281) performed a robotic kinesthetic matching task (KIN) without and with vision at ∼10 days post-stroke. A robotic exoskeleton moved the stroke-affected arm while subjects mirror-matched the movement with the opposite arm. Performance was compared to 160 controls. Spatial and temporal parameters were used to quantify kinesthetic performance. A Kinesthetic Task Score was calculated to determine overall performance on KIN without and with vision. Acute stroke imaging (N = 236) was collected to determine commonalities in lesion characteristics amongst kinesthetic impairment groups. Forty-eight percent (N = 135) of subjects had post-stroke impairment in kinesthesia both without and with vision. Only 19% (N = 52) improved to control-level performance with vision. Of the 48% of subjects that failed to improve with vision, many (N = 77, 57%) had neglect and/or field deficits. Notably 58 subjects (43%) did not have these deficits and still failed to improve with vision. Subjects who failed to improve with vision often had lesions affecting corticospinal tracts, insula, and parietal cortex, specifically the supramarginal gyrus and inferior parietal lobule. Many individuals could not use vision of the limb to correct for impaired kinesthesia after stroke. Subjects that failed to improve kinesthesia with vision had lesions affecting known sensorimotor integration areas. Our results suggest that integration of spatial information is impaired in many individuals post-stroke, particularly after parietal cortex damage. The result is a disconnect between kinesthetic and visuomotor processing necessary for visual limb guidance., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Proprioceptive deficits are common after stroke and have been associated with poorer recovery. Relatively little is known about the brain regions beyond primary somatosensory cortex that contribute to the percept of proprioception in humans. We examined a large sample (n = 153) of stroke survivors longitudinally to determine which brain regions were associated with persistent post-stroke proprioceptive deficits. A robotic exoskeleton quantified two components of proprioception, position sense and kinesthesia (movement sense), at 2 weeks and again at 6 months post-stroke. A statistical region of interest (sROI) analysis compared the lesion-behaviour relationships of those subjects with cortical and subcortical stroke (n = 136). The impact of damage to brainstem and cerebellum (n = 17) was examined separately. Results indicate that damage to the supramarginal gyrus, the arcuate fasciculus, and Heschl's gyrus are associated with deficits in position sense and kinesthesia at 6 months post-stroke. These results suggest that regions beyond the primary somatosensory cortex contribute to our sense of limb position and movement. This information extends our understanding of proprioceptive processing and may inform personalized interventions such as non-invasive brain stimulation where specific brain regions can be targeted to potentially improve stroke recovery., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Proprioception is the sense of the position and movement of our limbs, and is vital for executing coordinated movements. Proprioceptive disorders are common following stroke, but clinical tests for measuring impairments in proprioception are simple ordinal scales that are unreliable and relatively crude. We developed and validated specific kinematic parameters to quantify proprioception and compared two common metrics, Euclidean and Mahalanobis distances, to combine these parameters into an overall summary score of proprioception., Methods: We used the KINARM robotic exoskeleton to assess proprioception of the upper limb in subjects with stroke (N = 285. Mean days post-stroke = 12 ± 15). Two aspects of proprioception (position sense and kinesthetic sense) were tested using two mirror-matching tasks without vision. The tasks produced 12 parameters to quantify position sense and eight to quantify kinesthesia. The Euclidean and Mahalanobis distances of the z-scores for these parameters were computed each for position sense, kinesthetic sense, and overall proprioceptive function (average score of position and kinesthetic sense)., Results: A high proportion of stroke subjects were impaired on position matching (57%), kinesthetic matching (65%), and overall proprioception (62%). Robotic tasks were significantly correlated with clinical measures of upper extremity proprioception, motor impairment, and overall functional independence. Composite scores derived from the Euclidean distance and Mahalanobis distance showed strong content validity as they were highly correlated (r = 0.97-0.99)., Conclusions: We have outlined a composite measure of upper extremity proprioception to provide a single continuous outcome measure of proprioceptive function for use in clinical trials of rehabilitation. Multiple aspects of proprioception including sense of position, direction, speed, and amplitude of movement were incorporated into this measure. Despite similarities in the scores obtained with these two distance metrics, the Mahalanobis distance was preferred.

Proprioception is an important aspect of function that is often impaired in the upper extremity following stroke. Unfortunately, neurorehabilitation has few evidence based treatment options for those with proprioceptive deficits. The authors consider potential reasons for this disparity. In doing so, typical assessments and proprioceptive intervention studies are discussed. Relevant evidence from the field of neuroscience is examined. Such evidence may be used to guide the development of targeted interventions for upper extremity proprioceptive deficits after stroke. As researchers become more aware of the impact of proprioceptive deficits on upper extremity motor performance after stroke, it is imperative to find successful rehabilitation interventions to target these deficits and ultimately improve daily function.

Two decades of research on robots and upper extremity rehabilitation has resulted in recommendations from systematic reviews and guidelines on their use in stroke. Robotics are often cited for their ability to encourage mass practice as a means to enhance recovery of movement. Yet, stroke recovery is a complex process occurring across many aspects of neurologic function beyond movement. As newer devices are developed and enhanced assessments are integrated into treatment protocols, the potential of robotics to advance rehabilitation will continue to grow.

Background: Impairment of position sense of the upper extremity (UE) may impede activities of daily living and limit motor gains after stroke. Most clinical assessments of position sense rely on categorical or ordinal ratings by clinicians that lack sensitivity to change or the ability to discriminate subtle deficits., Objective: Use robotic technology to develop a reliable, quantitative technique with a continuous scale to assess UE position sense following stroke., Methods: Forty-five patients recruited from an inpatient stroke rehabilitation service and 65 age-matched healthy controls performed an arm position matching task. Each UE was fitted in the exoskeleton of a KINARM device. One UE was passively placed in one of 9 positions, and the subject was told to match his or her position with the other UE. Patients were compared with statistical distributions of control data to identify those with deficits in UE position sense. Test-retest sessions using 2 raters established interrater reliability., Results: Two thirds of left hemiparetic and one third of right hemiparetic patients had deficits in limb position sense. Left-affected stroke subjects demonstrated significantly more trial-to-trial variability than right-affected or control subjects. The robotic assessment technique demonstrated good interrater reliability but limited agreement with the clinical thumb localizing test., Conclusions: Robotic technology can provide a reliable quantitative means to assess deficits in limb position sense following stroke.