Flexion Trials Research Articles

Upper arm muscle activity is influenced by both forearm posture and wrist exertion direction during isometric wrist flexion and extension

The purpose of this study was to determine how wrist exertion direction and forearm posture independently influence upper arm muscle activity during isometric wrist contractions. Surface electromyography was recorded from three muscles of the upper-limb: biceps brachii, triceps brachii, and brachioradialis. Participants were seated with their forearm supported in one of three postures (supinated/neutral/pronated) with an adjustable force transducer that could be placed either above, below, or to the right/left of the participant’s hand. Participants performed randomized trials of isometric wrist flexion or extension at five relative intensities: 20, 40, 60, 80, or 100% of maximal force. Trials lasted 4.5 s and both wrist force and electromyography data were assessed. In general, the elbow flexors were more active during wrist flexion, while the triceps were more active in wrist extension, but this pattern reversed in certain forearm postures and wrist exertion directions. Both forearm posture and wrist exertion direction resulted in unique effects on upper arm muscle activity. These findings suggest that muscle activity of the upper arm muscles is influenced independently by both posture and force direction, which should be carefully considered by both motor control specialists and ergonomists.

Muscle fatigue tracking during dynamic elbow flexion-extension movements with a varying hand load

Muscle fatigue monitoring, an important element in a fatigue risk management process, can help optimize work intensity and reduce risks for musculoskeletal injuries. An experiment was conducted to determine whether myoelectric manifestations of muscle fatigue can reflect the pace of fatigue development associated with varying load intensity. Twenty male participants performed elbow flexion-extension movements with alternating hand loads (2 kg vs. 1 kg) for 16 min. The pace of fatigue in the biceps brachii in response to load variation was quantified by electromyographic (EMG) fatigue measures collected during the dynamic elbow flexion-extension movements and periodic submaximal isometric elbow flexion trials. The isometric and dynamic EMG measures, except for the amplitude of dynamic EMG, indicated fatigue development during the 2-kg isotonic movements and partial recovery with the 1 kg load. Study results suggest the potential of EMG measures for fatigue monitoring during dynamic work tasks with varying load intensity.

How Many Trials Are Needed to Estimate Typical Lumbar Movement Patterns During Dynamic X-Ray Imaging?

Dynamic biplane radiographic (DBR) imaging measures continuous vertebral motion during in vivo, functional tasks with submillimeter accuracy, offering the potential to develop novel biomechanical markers for lower back disorders based on true dynamic motion rather than metrics based on static end-range of motion. Nevertheless, the reliability of DBR metrics is unclear due to the inherent variability in movement over multiple repetitions and a need to minimize radiation exposure associated with each movement repetition. The objectives of this study were to determine the margin of uncertainty (MOU) in estimating the typical intervertebral kinematics waveforms based upon only a small number of movement repetitions, and to determine the day-to-day repeatability of intervertebral kinematics waveforms measured using DBR. Lumbar spine kinematics data were collected from two participant groups who performed multiple trials of flexion-extension or lateral bending to assess the uncertainty in the mean estimated waveform. The first group performed ten repetitions on the same day. Data from that group were used to estimate MOU as a function of the number of repetitions. The second group performed five repetitions on each of two separate days. MOU was not only movement-specific, but also motion segment-specific. Using just one or two trials yielded a relatively high MOU (e.g., >4 deg or 4 mm), however, collecting at least three repetitions reduced the MOU by 40% or more. Results demonstrate the reproducibility of DBR-derived measurements is greatly improved by collecting at least three repetitions, while simultaneously minimizing the amount of radiation exposure to participants.

A Clinical Measure of Trunk Neuromuscular Function Predicts Falling in Older Adults With Chronic Low Back Pain.

Older adults with low back pain (LBP) are at risk for falling, but condition-specific mechanisms are unknown. Trunk neuromuscular function is critical for maintaining balance during mobility tasks and is often impaired in older adults with LBP. The purpose of this study was to assess whether aberrant lumbopelvic movements (or aberrant movements), a clinical index of trunk neuromuscular function, were associated with increased fall risk among older adults with chronic LBP over a 12-month follow-up period. This study analyzed data from a prospective cohort study of 250 community-dwelling older adults with chronic LBP. Participants were screened for 4 aberrant movements during 3 trials of forward flexion from a standing position: instability catch, painful arc, altered lumbopelvic rhythm, and Gower's sign. Aberrant movements were totaled to yield a summary score (ie, 0-4). Prospective falls were monitored via monthly fall calendars for 12 months. A generalized linear model with Poisson distribution and log link function was used to evaluate the association between aberrant movements and prospective fall risk. Age, sex, body mass index, LBP intensity, dynamic balance performance, prior falls, anxiolytic medication usage, and hip osteoarthritis characteristics were included as covariates in the model. Baseline aberrant movements were independently associated with greater fall risk (risk ratio = 1.249, 95% CI = 1.047-1.491, P = .014); each 1-unit increase in aberrant movement score imparted a 24.9% increase in the risk of falling. Aberrant movements increased the risk of falling among older adults with chronic LBP over a 1-year span.

An investigation of the flexion relaxation ratio in adults with and without a history of self-reported low back pain and transient sitting-induced pain

It is unknown whether the presence of sitting-induced pain or a clinical history of low back pain (LBP) changes spine function outcomes such as the flexion relaxation ratio (FRR). The purpose of this investigation was to determine whether sitting-induced pain or a history of non-specific LBP results in a different FRR. Forty-seven participants were instrumented with surface electromyography over erector spinae at L1, and accelerometers at L1 and S2. Standing maximum lumbar flexion trials were taken preceding and following a 1-hour sitting trial. Pain ratings during sitting and history of LBP were used to group participants for analysis. FRR values taken after the sitting exposures were compared between those that did and did not develop pain during sitting. Baseline FRR values were compared participants with and without a history of LBP. No significant differences in FRR were found for either pain groups (p = 0.11) or clinical history (p = 0.85). Lack of differences may be due to participants not currently experiencing a clinical episode of pain when the ratio was measured and/or because 1-hour sitting exposure was not long enough to induce pain modulation. The findings suggest that neither sitting-induced pain development or clinical history need to be controlled to prevent confounding of FRR.

A Preliminary Study to Design and Evaluate Pneumatically Controlled Soft Robotic Actuators for a Repetitive Hand Rehabilitation Task.

A stroke is an infarction in the cortical region of the brain that often leads to isolated hand paresis. This common side effect renders individuals compromised in their ability to actively flex or extend the fingers of the affected hand. While there are currently published soft robotic glove designs, this article proposed a unique design that allows users to self-actuate their therapy due to the ability to re-extend the hand using a layer of resistive flexible steel. The results showed a consistently achieved average peak of 75° or greater for each finger while the subjects’ hands were at rest during multiple trials of pneumatic assisted flexion. During passive assisted testing, human subject testing on 10 participants showed that these participants were able to accomplish 80.75% of their normal active finger flexion range with the steel-layer-lined pneumatic glove and 87.07% with the unlined pneumatic glove on average when neglecting outliers. An addition of the steel layer lowered the blocked tip force by an average of 18.13% for all five fingers. These data show strong evidence that this glove would be appropriate to advance to human subject testing on those who do have post stroke hand impairments.

Ultrasound-Derived Features of Muscle Architecture Provide Unique Temporal Characterization of Volitional Knee Motion.

Sonomyography, or dynamic ultrasound imaging of skeletal muscle, has gained significant interest in rehabilitation medicine. Previously, correlations relating sonomyography features of muscle contraction, including muscle thickness, pennation angle, angle between aponeuroses and fascicle length, to muscle force production, strength and joint motion have been established. Additionally, relationships between grayscale image intensity, or echogenicity, with maximum voluntary isometric contraction of muscle have been noted. However, the time relationship between changes in various sonomyography features during volitional motion has yet to be explored, which would highlight if unique information pertaining to muscle contraction and motion can be obtained from this real-time imaging modality. These new insights could inform how we assess muscle function and/or how we use this modality for assistive device control. Thus, our objective was to characterize the time synchronization of changes in five features of rectus femoris contraction extracted from ultrasound images during seated knee extension and flexion. A cross-correlation analysis was performed on data recorded by a handheld ultrasound system as able-bodied subjects completed seated trials of volitional knee extension and flexion. Changes in muscle thickness, angle between aponeuroses, and mean image echogenicity, a change in brightness of the grayscale image, preceded changes in our estimates of pennation angle and fascicle length. The leading nature of these features suggest they could be objective features for early detection of impending joint motion. Finally, multiple sonomyographic features provided unique temporal information associated with this volitional task.Clinical Relevance-This work evaluates the time relationship between five commonly reported features of skeletal muscle architecture during volitional motion, which can be used for targeted clinical assessments and intent detection.

3D trunk orientation measured using inertial measurement units during anatomical and dynamic sports motions.

Trunk motion is related to the performance and risk of injuries during dynamic sports motions. Optical motion capture is traditionally used to measure trunk motion during dynamic sports motions, but these systems are typically constrained to a laboratory environment. Inertial measurement units (IMUs) might provide a suitable alternative for measuring the trunk orientation during dynamic sports motions. The objective of the present study was to assess the accuracy of the three‐dimensional trunk orientation measured using IMUs during dynamic sports motions and isolated anatomical trunk motions. The motions were recorded with two IMUs and an optical motion capture system (gold standard). Ten participants performed a total of 71 sports motions (19 golf swings, 15 one‐handed ball throws, 19 tennis serves, and 18 baseball swings) and 125 anatomical trunk motions (42, 41, and 42 trials of lateral flexion, axial rotation, and flexion/extension, respectively). The root‐mean‐square differences between the IMU‐ and optical motion capture‐based trunk angles were less than 5 degrees, and the similarity between the methods was on average across all trials “very good” to “excellent” (R ≥ 0.85; R 2 ≥ 0.80). Across the dynamic sports motions, even higher measures of similarity were found (R ≥ 0.90; R 2 ≥ 0.82). When aligned to the relevant segment, the current IMUs are a promising alternative to optical motion capture and previous presented IMU‐based systems for the field‐based measurement of the three‐dimensional trunk orientation during dynamic sports motions and the anatomical trunk motions.

Acute Muscle Damage Is Augmented After Exercise In PAD Patients: Evidence From Diffusion Tensor Imaging

Although the chronic myopathies associated with peripheral arterial disease (PAD) are well established, the acute muscular responses to exercise in this population are less clear. PURPOSE: This study used diffusion tensor imaging (DTI) to compare acute exercise related muscle damage between PAD patients and healthy controls. METHODS: Eight PAD patients and 7 healthy controls performed graded dynamic plantar flexion exercise in the bore of a 3T MRI scanner. In order to compare responses between the active and inactive legs, these plantar flexion trials were repeated during imaging of the exercising leg and imaging of the resting leg. Each exercise trial began at 2kg, and increased by 2kg every 2 minutes until fatigue, or until completion of 10kg. DTI images were collected from the widest portion of the calf pre and post exercise, and were analyzed for mean diffusivity (MD), fractional anisotropy (FA), and eigenvectors 1-3 (λ1-3) of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles. RESULTS: At baseline, there were no significant group differences in MD, FA, or any of the individual eigenvectors for the MG or TA of the exercising leg (P>0.34). However, results did indicate significantly greater increases in MD (+13.6 ± 10.6% and +2.5 ± 3.5%), λ1 (+13.7 ± 14.3% and +1.4 ± 3.1%), λ2 (+13.8 ± 10.5% and +3.0 ± 3.6%), and λ3 (+13.1 ± 7.1% and +3.7 ± 4.3%, all P<0.02) in the MG of the exercising leg in PAD patients compared to controls, respectively. Results also indicated a significantly greater increase in λ3 of the TA in the exercising leg in PAD patients compared to controls (2.1 ± 2.9% and -1.5 ± 1.4, respectively, P=0.01). In contrast, no significant group by time interactions were observed in the resting leg (all P>0.15). CONCLUSIONS: These data indicate that skeletal muscle diffusivity increases more in PAD patients compared to controls after exercise. Ultimately, this suggests that acute exercise related muscle damage is augmented in PAD patients. Supported by NIH P01-HL134609 (Sinoway) and UL1 TR002014 (Sinoway).

Effect of knee aspiration and intra-articular corticosteroid injection on gait biomechanics, strength, and patient-reported outcomes in patients with knee osteoarthritis

Purpose: Synovial inflammation is associated with pain and disease progression in knee OA and may adversely affect joint biomechanics. The presence of knee inflammation is associated with quadriceps avoidance gait (decreased external knee flexion moment) and decreased quadriceps and hamstring strength. The effect of decreasing knee inflammation on gait biomechanics and strength is unknown. Here, we investigate the effects of inflammation on gait biomechanics in patients with knee OA and inflammation on ultrasound (US), testing the effects of knee aspiration and intra-articular corticosteroid injection on gait, strength, and clinical outcomes. Methods: Forty-five patients with knee OA, synovitis and effusion underwent US, gait biomechanics and strength assessments, and completed the Knee Injury and Osteoarthritis Outcome Score (KOOS), before and 3 weeks after receiving a knee aspiration and 40 mg triamcinolone injection under US guidance (Table 1). Ultrasound assessments were performed by a Canadian Rheumatology Ultrasound Society (CRUS) trained examiner using a 12 Hz linear probe. The suprapatellar recess was scanned in the long axis view medially, laterally and in the midline with the knee flexed to 30o. All US exams were graded using previously validated OMERACT grading criteria for synovitis, synovial hyperplasia, effusion, and power Doppler (6-point scale). Three-dimensional quantitative gait analysis was completed using a 12-camera motion capture system and floor mounted force plate and used to calculate knee angles and moments during walking. Strength testing was completed using an isokinetic dynamometer. Patients completed three maximal knee extension and flexion trials at 90 degrees per second. US, gait and strength tests were completed by the same examiner. Paired t-tests were used to assess mean differences in gait, strength and KOOS scores. Results: There was a significant (p < 0.05) increase in external knee flexion moment [mean change (95%CI)]: 0.32 %BW*ht (0.07, 0.57), peak quadriceps strength [5.95 Nm (0.99, 10.91)], and peak hamstring strength [4.03 Nm (0.56, 7.51)] 3 weeks after injection. There were significant (p < 0.05) improvements in US composite scores [-0.86 (-1.30, -0.42)], and KOOS Subscales for Symptoms [6.16 (1.63, 10.69)], Pain [6.43 (1.17, 11.69)], Function in Daily Living [5.61 (0.80, 10.42)] and Function in Sport and Recreation [9.37 (0.56, 18.18)]. There were no other significant changes in gait (Table 2). Conclusions: Patients undergoing aspiration and injection for knee synovitis and effusion experience increased knee flexion moments during walking and increased maximal quadriceps and hamstring strength. These results suggest a link between inflammation and joint biomechanics in patients with knee OA; interventions that induce changes in knee inflammation detectable by US can improve knee biomechanics during walking.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Investigating the Muscular and Kinematic Responses to Sudden Wrist Perturbations During a Dynamic Tracking Task

Sudden disturbances (perturbations) to the hand and wrist are commonplace in daily activities and workplaces when interacting with tools and the environment. It is important to understand how perturbations influence forearm musculature and task performance when identifying injury mechanisms. The purpose of this work was to evaluate changes in forearm muscle activity and co-contraction caused by wrist perturbations during a dynamic wrist tracking task. Surface electromyography was recorded from eight muscles of the upper-limb. Participants performed trials consisting of 17 repetitions of ±40° of wrist flexion/extension using a robotic device. During trials, participants received radial or ulnar perturbations that were delivered during flexion or extension, and with known or unknown timing. Co-contraction ratios for all muscle pairs showed significantly greater extensor activity across all experimental conditions. Of all antagonistic muscle pairs, the flexor carpi radialis (FCR)-extensor carpi radialis (ECR) muscle pair had the greatest change in co-contraction, producing 1602% greater co-contraction during flexion trials than during extensions trials. Expected perturbations produced greater anticipatory (immediately prior to the perturbation) muscle activity than unexpected, resulting in a 30% decrease in wrist displacement. While improving performance, this increase in anticipatory muscle activity may leave muscles susceptible to early-onset fatigue, which could lead to chronic overuse injuries in the workplace.

What is the best way to collect maximum forward lumbar spine flexion values for normalizing posture to range of motion?

Spine angles are an important measure in biomechanics research and are commonly normalized to a percentage of range of motion. However, standardized methods to collect the reference posture trials for this normalization do not exist. The purpose of this study was to determine posture (seated or standing) and number of trials that should be collected and how to calculate the angle that best represents the maximum range. Forty healthy adults (22 females, 18 males) completed 12 reference trials: 1 upright standing, 5 standing flexion, and 5 seated flexion trials. The maximum lumbar angle was found for each flexion trial. Additionally, different methods to calculate the maximum were applied by taking the maximum of the 5 standing, 5 seated, and all 10 flexion trials. An interaction was found between posture, order, and trial number. 42.5% and 57.5% of participants reached their maximum angle during seated and standing flexion respectively which may be due to back- vs hip-dominant movement strategies. 85% of participants achieved their maximum at some point during the first six flexion trials.The maximum angle of all 10 flexion trials was significantly greater than the angle of the first standing or seated trial only but not significantly greater than the maximum of all seated or standing flexion trials respectively. Secondarily, no differences in the maximum lumbar angle were found between sexes. This study suggests that 6 flexion trials, involving both standing and seated flexion, should be collected to best represent the maximum end range of spine flexion.

In vivo changes in adjacent segment kinematics after lumbar decompression and fusion

The pathogenesis of lumbar adjacent segment disease is thought to be secondary to altered biomechanics resulting from fusion. Direct in vivo evidence for altered biomechanics following lumbar fusion is lacking. This study’s aim was to describe in vivo kinematics of the superior adjacent segment relative to the fused segment before and after lumbar fusion. This study analyzed seven patients with symptomatic lumbar degenerative spondylolisthesis (5 M, 2F; age 65 ± 5.1 years) using a biplane radiographic imaging system. Each subject performed two to three trials of continuous flexion of their torso according to established protocols. Synchronized biplane radiographs were acquired at 20 images per second one month before and six months after single-level fusion at L4-L5 or L5-S1, or two-level fusion at L3-L5 or L4-S1. A previously validated volumetric model-based tracking process was used to track the position and orientation of vertebrae in the radiographic images. Intervertebral flexion/extension and AP translation (slip) at the superior adjacent segment were calculated over the entire dynamic flexion activity. Skin-mounted surface markers were tracked using conventional motion analysis and used to determine torso flexion. Change in adjacent segment kinematics after fusion was determined at corresponding angles of dynamic torso flexion. Changes in adjacent segment motion varied across patients, however, all patients maintained or increased the amount of adjacent segment slip or intervertebral flexion/extension. No patients demonstrated both decreased adjacent segment slip and decreased rotation. This study suggests that short-term changes in kinematics at the superior adjacent segment after lumbar fusion appear to be patient-specific.

Blinded by magic: Electrophysiological correlates of change blindness

Magicians can often hide their method for a trick in plain sight by effecting a phenomenon known as change blindness. The purpose of this study was to find the reason for why an individual is induced with change blindness. Alpha oscillations are known to impair detection of visual stimuli, but it is unclear if this is due to increased guess rate or decreased fidelity of the mental representation. Here we estimated fidelity and guess rate as a function of pre-stimulus alpha oscillations using a change blindness task. In this study, each trial began with an array of 6 Gabor patches with a fixated dot that subjects were instructed to keep their eyes on. As the array traveled to the center of the screen, it either changed direction vertically at 90 degrees or continued horizontally. When the array switched direction, one of the Gabor patches rotated 30 degrees simultaneously. Subjects were then asked to identify which patch rotated. EEG (electroencephalography) data was simultaneously recorded with eye-tracking as subjects performed the task. Twenty-eight participants performed this task, which included six blocks of forty-eight trials. There were two different types of trials: flexion, in which the array changed direction, and control, in which the array did not change direction. Reaction time tended to be slower in flexion trials, and we found that the change in direction affected the subject’s ability to see the Gabor patch rotation. Based on the event-related potential results, which are an average of EEG signals aligned to the start of a trial, we could see that the P300 differed between correct flexion, incorrect flexion, and control trials. The P300 can be interpreted as a marker of consciousness. This difference demonstrates that the subject’s attention is automatically drawn to a larger change in stimuli.

Shoulder Flexion Torque Is Augmented by a Volitional Abdominal Isometric Contraction.

Cacolice, PA, Carcia, CR, and Scibek, JS. Shoulder flexion torque is augmented by a volitional abdominal isometric contraction. J Strength Cond Res 35(4): 920-923, 2021-A stable core provides a solid base to facilitate effective extremity function. It is unclear whether an individual is able to produce a greater amount of upper extremity torque while performing a volitional core contraction when compared with the independent contraction that occurs subconsciously. Therefore, the purpose of this study was to determine whether peak shoulder flexion torque values were different with and without a concurrent volitional core isometric contraction. Thirty healthy, recreationally active college-aged students participated. Surface electromyography from the rectus abdominis (RA) was captured using a telemetry system interfaced with a software acquisition system and personal computer. In a counterbalanced alternating order, subjects completed 3 trials of maximal isometric shoulder flexion at 90° with and without a volitional abdominal contraction. Percent activation of the RA was greater when subjects volitionally contracted their core (15.8 ± 12.7%) compared with the subconscious contracted condition (6.3 ± 4.8%) (p ≤ 0.001). Isometric shoulder flexion peak torque was greater when the core was actively contracted (44.6 ± 18.9 N × m) compared with when the core was recruited subconsciously (30.7 ± 15.7 N × m) (p ≤ 0.001). These findings suggest the clinician should encourage the individual to activate their core musculature when performing upper extremity strength activities.

Neural Control of Individual Finger Movements Using Intracortical Recordings From a Person With Tetraplegia

Abstract INTRODUCTION Intracortical microelectrode arrays have allowed people to control robotic arm movements such as reaching and grasping. However, to restore dexterous movement, control of fingers will be required. We aimed to control individual finger movements of a virtual-reality hand on a person with tetraplegia. METHODS A 31-yr-old man with a C5/6 ASIA B spinal cord injury was implanted with two 88-channel intracortical microelectrode arrays (4 × 4 mm footprint, 1.5 mm shank-length) in the left motor cortex. Across 4 d, a 6-class linear discriminant classifier was used as an online decoder that output finger velocity commands every 20 ms. We quantified the number of channels and location significantly modulating each attempted finger movement using a Kolmogorov-Smirnov test. We also report the success rate to reach targets for flexing each of the five fingers and thumb abduction. RESULTS On average, there were 28 channels modulated by attempted finger movement on the lateral array as compared to 19 on the medial array. Attempted thumb flexion exhibited the highest (n = 18, P &lt; .05) while ring finger had the fewest (n = 13, P &lt; .05) modulated channels. The mean success rate was 61 ± 15% (chance: 17%). The participant was successful for 81% of the thumb flexion trials, while thumb abduction, index, middle, ring and pinky flexion achieved average accuracies of 75%, 63%, 49%, 38%, and 56% respectively. Of the failed trials, 93% failed due to co-activation of adjacent fingers, with middle and ring being the most interdependent. For example, the ring finger successfully flexed on 93% of the “ring finger” trials (high sensitivity), but middle was co-activated during 53% of the same trials (low specificity) resulting in trial failure. CONCLUSION A person with tetraplegia was able to use a brain-computer interface to control individual digits of a virtual robotic hand. Failed trials typically resulted from movement of adjacent fingers. This co-dependence should be accounted for in future control schemes.

McArdle Sign: A Specific Sign of Multiple Sclerosis

ObjectiveTo measure McArdle sign (rapidly reversible weakness induced by neck flexion) both qualitatively and quantitatively and to evaluate its specificity and clinical utility for diagnosis of multiple sclerosis (MS). Patients and MethodsIn this prospective study, McArdle sign was evaluated by a technician blinded to diagnosis by measuring changes in finger extensor strength in successive trials of neck extension and flexion, first clinically and then with a torque measurement device. We studied 25 healthy controls and 81 patients with finger extensor weakness. Patients were not selected for having McArdle sign. Fifty-two patients had MS, 24 had other myelopathies, and 5 had peripheral nerve lesions accounting for their weakness. The study was conducted between February 1, 2016, and June 30, 2017. ResultsThe median clinical McArdle sign and the 2 quantitative measures of neck flexion–induced strength reduction were greater in patients with MS than in the other groups (P<.001). Baseline strength did not confound the difference. The area under the receiver operating characteristic curve was 0.84 (95% CI, 0.75-0.93) comparing patients with MS vs healthy controls and 0.84 (95% CI, 0.75-0.93) comparing MS vs patients with other myelopathies. The 2 quantitative and 1 clinical measurement of McArdle sign by the technician who performed the quantitative testing were correlated (r=.57 and r=.58; P<.001), and in turn, the technician's and unblinded referring physician's clinical assessments were correlated (r=.58; P<.001). McArdle sign was evident in some patients who had minor disability and who were in early phases of MS. ConclusionMcArdle sign, when defined as greater than 10% neck flexion–induced reduction in strength, is entirely specific and 65% sensitive for a diagnosis of MS when compared with other conditions that mimic MS-associated myelopathy. It may facilitate diagnosis in certain clinical situations. Trial Registrationclinicaltrials.gov Identifier: NCT03122873.

Feedforward and Feedback Control Share an Internal Model of the Arm's Dynamics.

Recent work has shown that, when countering external forces, the nervous system adjusts not only predictive (i.e., feedforward) control of reaching but also reflex (i.e., feedback) responses to mechanical perturbations. Here we show that altering the physical properties of the arm (i.e., intersegmental dynamics) causes the nervous system to adjust feedforward control and that this learning transfers to feedback responses even though the latter were never directly trained. Forty-five human participants (30 females) performed a single-joint elbow reaching task and countered mechanical perturbations that created pure elbow motion. In our first experiment, we altered intersegmental dynamics by asking participants to generate pure elbow movements when the shoulder joint was either free to rotate or locked by the robotic manipulandum. With the shoulder unlocked, we found robust activation of shoulder flexor muscles for pure elbow flexion trials, as required to counter the interaction torques that arise at the shoulder because of forearm rotation. After locking the shoulder joint, which cancels these interaction torques, we found a substantial reduction in shoulder muscle activity over many trials. In our second experiment, we tested whether such learning transfers to feedback control. Mechanical perturbations applied to the arm with the shoulder unlocked revealed that feedback responses also account for intersegmental dynamics. After locking the shoulder joint, we found a substantial reduction in shoulder feedback responses, as appropriate for the altered intersegmental dynamics. Our work suggests that feedforward and feedback control share an internal model of the arm's dynamics.SIGNIFICANCE STATEMENT Here we show that altering the physical properties of the arm causes people to learn new motor commands and that this learning transfers to their reflex responses to unexpected mechanical perturbations, even though the reflex responses were never directly trained. Our results suggest that feedforward motor commands and reflex responses share an internal model of the arm's dynamics.

Trueness and Minimal Detectable Change of Smartphone Inclinometer Measurements of Shoulder Range of Motion

Digital inclinometer applications using data from embedded sensors on smartphone/multi-purpose pocket computers or "smart digital inclinometers" (SDIs) are now used to clinically assess range of motion (ROM). The objectives of this study were to assess, compared with a biomechanical gold standard (GS), the trueness and minimal detectable change (MDC) of shoulder range of motion (SROM) measurements obtained from an SDI. Twenty-five (n = 25) asymptomatic healthy participants performed three trials of shoulder flexion (SF), shoulder abduction (SA), and shoulder external rotation (SER) at full-range and mid-range. SROM was measured concurrently from sensor data (pitch, yaw, roll angles) from an iPod Touch installed on the posterior aspect of the humerus and 3D orientation of the upper arm obtained from an optical motion tracking system GS. The mean level of bias between SDI and the GS across all SROM measurements was 3.4°, with a 95% confidence interval varying between -8.9° and 15.8°. The mean and standard deviation absolute difference of SDI measurements with the GS were 5.8° ± 3.7° for SF, 8.7° ± 5.2° for SA, and 1.7° ± 1.4° for SER. The trueness of these values varied according to the movement. MDC was 1.9° for SF, 2° for SA, and 0.3° for SER. SROM measures in SER with an SDI seem to be accurate and robust for clinical use. However, SROM measures in other planes of motion should be interpreted with caution depending on the evaluation objective, the plane of motion assessed, and the range of ROM measured.

Intra- and Intersession Reliability of Surface Electromyography on Muscles Actuating the Forearm During Maximum Voluntary Contractions.

The aim of this study is to determine the intra- and intersession reliability of nonnormalized surface electromyography (sEMG) on the muscles actuating the forearm during maximum voluntary isometric contractions (MVIC). A subobjective of this study is to determine the intra- and intersession reliability of forearm MVIC force or torque, which is a prerequisite to assess sEMG reliability. Eighteen healthy adults participated at 4 different times: baseline, 1-h post, 6-h post, and 24-h post. They performed 3 MVIC trials of forearm flexion, extension, pronation, and supination. sEMG of the biceps brachii short head, brachialis, brachioradialis, triceps brachii long head, pronator teres, and pronator quadratus were measured. The intraclass correlation coefficient (ICC) on MVIC ranged from 0.36 to 0.99. Reliability was excellent for flexion, extension, and supination MVIC for both intra- and intersession. The ICC on sEMG ranged from 0.58 to 0.99. sEMG reliability was excellent for brachialis, brachioradialis, and pronator quadratus, and good to excellent for triceps brachii, biceps brachii, and pronator teres. This study shows that performing 3 MVICs is sufficient to obtain highly reliable maximal sEMG over 24 h for the main muscles actuating the forearm. These results confirm the potential of sEMG for muscle motor functional monitoring.