Flexion Task Research Articles

Crossed Corticospinal Facilitation Between Arm and Trunk Muscles Correlates With Trunk Control After Spinal Cord Injury.

Objective: To investigate whether crossed corticospinal facilitation between arm and trunk muscles is preserved following spinal cord injury (SCI) and to elucidate these neural interactions for postural control during functional arm movements.Methods: Using transcranial magnetic stimulation (TMS) in 22 subjects with incomplete SCI motor evoked potentials (MEPs) in the erector spinae (ES) muscle were examined when the contralateral arm was at rest or performed 20% of maximal voluntary contraction (MVC) of biceps brachii (BB) or triceps brachii (TB). Trunk function was assessed with rapid shoulder flexion and forward-reaching tasks.Results: MEP amplitudes in ES were increased during elbow flexion in some subjects and this facilitatory effect was more prominent in subjects with thoracic SCI than in the subjects with cervical SCI. Those who showed the increased MEPs during elbow flexion had faster reaction times and quicker anticipatory postural adjustments of the trunk in the rapid shoulder flexion task. The onset of EMG activity in ES during the rapid shoulder flexion task correlated with the trunk excursion in forward-reaching.Conclusions: Our findings demonstrate that crossed corticospinal facilitation in the trunk muscles can be preserved after SCI and is reflected in trunk control during functional arm movements.

Aspects of cortical area responsibilities while learning a visually cued spatiotemporal motor task.

Aspects of cortical area responsibilities while learning a visually cued spatiotemporal motor task.

Crosstalk in Mechanomyographic Signals From Elbow Flexor Muscles During Submaximal to Maximal Isometric Flexion, Pronation, and Supination Torque Tasks.

This study analyzed the crosstalk in mechanomyographic (MMG) signals from elbow flexors during isometric muscle actions from 20% to 100% maximum voluntary isometric contraction (MVIC). Twenty-five young, healthy, male participants performed the isometric elbow flexion, forearm pronation, and supination tasks at an elbow joint angle of 90 deg. The MMG signals from the biceps brachii (BB), brachialis (BRA), and brachioradialis (BRD) muscles were recorded using accelerometers. The cross-correlation coefficient was used to quantify the crosstalk in MMG signals, recorded in a direction transverse to muscle fiber axis, among the muscle pairs (P1: BB and BRA, P2: BRA and BRD, and P3: BB and BRD). In addition, the MMG RMS and MPF were quantified. The mean normalized RMS and mean MPF exhibited increasing (r > 0.900) and decreasing (r < -0.900) trends, respectively, with increases in the effort levels in all three tasks. The magnitude of crosstalk ranged from 0.915% to 21.565% in all three muscle pairs. The crosstalk was found to exhibit high positive correlations with submaximal to maximal flexion [P1 (r = 0.970), P2 (r = 0.951), and P3 (r = 0.824)], pronation [P1 (r = 0.811), P2 (r = 0.763), and P3 (r = 0.901)] and supination [P1 (r = 0.898), P2 (r = 0.838), and P3 (r = 0.852)] torque levels (eight out of nine p-values were < 0.05). Regardless of the high positive correlation between crosstalk and level of effort, the crosstalk remained at a low range (0.915-21.565%) with increases in the torque levels.

Relationship between force-velocity-power profiles and inter-limb asymmetries obtained during unilateral vertical jumping and singe-joint isokinetic tasks

ABSTRACT We explored the associations between force-velocity-power (FVP) profiles and inter-limb asymmetries in FVP profiles obtained during unilateral jumping and single-leg isokinetic knee extension and flexion tasks. Thirty (13 senior and 17 junior) basketball players performed unilateral jumps with different levels of unloading (0–40% body mass) and isokinetic knee extension and flexion at different angular velocities (60–300°/s) with each leg. Senior and junior basketball players exhibited similar jump performance, normalized knee extensor and flexor strength, and relatively similar jumping and isokinetic FVP profiles. No significant associations between unilateral jump and isokinetic knee extension and flexion FVP parameters were found (all r ≤ 0.26; p > 0.05). Inter-limb asymmetries had no or very weak associations with unilateral jump height (−0.2 < r < 0.2; all p > 0.1); also, inter-limb asymmetries in jump and isokinetic FVP parameters were generally weakly associated (median r < 0.1). Finally, unilateral jump height was weakly-to-moderately associated with isokinetic F0, jumping Pmax, and normalized knee extension isokinetic peak torque at 60°/s and 240°/s (r = 0.35–0.57). These results suggest that the generalizability of the FVP profile of isolated muscle groups to complex ballistic tasks is weak.

A musculoskeletal model to perform high knee flexion tasks: Application to ACL injury prevention

A musculoskeletal model to perform high knee flexion tasks: Application to ACL injury prevention

Importance of the Primary Motor Cortex in Development of Human Hand/Finger Dexterity.

Hand/finger dexterity is well-developed in humans, and the primary motor cortex (M1) is believed to play a particularly important role in it. Here, we show that efficient recruitment of the contralateral M1 and neuronal inhibition of the ipsilateral M1 identified by simple hand motor and proprioceptive tasks are related to hand/finger dexterity and its ontogenetic development. We recruited healthy, right-handed children (n = 21, aged 8–11 years) and adults (n = 23, aged 20–26 years) and measured their brain activity using functional magnetic resonance imaging during active and passive right-hand extension–flexion tasks. We calculated individual active control-related activity (active–passive) to evaluate efficient brain activity recruitment and individual task-related deactivation (neuronal inhibition) during both tasks. Outside the scanner, participants performed 2 right-hand dexterous motor tasks, and we calculated the hand/finger dexterity index (HDI) based on their individual performance. Participants with a higher HDI exhibited less active control-related activity in the contralateral M1 defined by the active and passive tasks, independent of age. Only children with a higher HDI exhibited greater ipsilateral M1 deactivation identified by these tasks. The results imply that hand/finger dexterity can be predicted by recruitment and inhibition styles of the M1 during simple hand sensory–motor tasks.

Pericapsular hip muscle activity in people with and without femoroacetabular impingement. A comparison in dynamic tasks

ObjectivesCompare anterior pericapsular muscle activity between individuals with and without femoroacetabular impingement syndrome (FAIS) during dynamic tasks, to investigate whether muscle activity is consistent with a role in retracting the capsule to prevent impingement and active restraint of the femoral head in walking. DesignCross-sectional. SettingUniversity-laboratory. ParticipantsThirteen athletes with FAIS and 13 pain-free controls. Main outcome measuresMuscle activity was recorded using fine-wire (Iliocapsularis, iliacus and anterior gluteus minimus) and surface (rectus femoris) electromyography (EMG), during three hip flexion tasks (active and assisted hip flexion; squatting) and four walking trials. ResultsIliocapsularis EMG amplitude was no different between active and assisted hip flexion tasks around 90° of hip flexion in FAIS. There was no difference in EMG between groups in squatting. The pattern of burst activity preceding peak hip extension in iliacus, iliocapsularis, and anterior gluteus minimus was similar in both groups during walking. ConclusionIn FAIS, similar activation of iliocapsularis during active and assisted hip flexion, despite reduced flexion torque demand in the latter, suggests a role in capsular retraction or enhanced hip joint protection. Pericapsular muscle activity in advance of peak hip extension during walking is consistent with a proposed contribution to femoral head control.

Corticomotor Network Activity Does Not Contribute To The Bilateral Deficit Phenomenon

The bilateral deficit (BLD) phenomenon is an inability to maximally contract bilaterally as compared to the sum of the corresponding unilateral contractions, and is expressed as an index (BI). The underlying mechanism is unknown, but altered transcallosal inhibition (TCI) and diminished voluntary activation (VA) during bilateral homologous (BH), as compared to bilateral non-homologous (BNH) and unilateral tasks, is considered the most likely mechanism. PURPOSE: To examine corticospinal activity during BH, BNH, and unilateral maximal contractions, and resultant changes from task practice. METHODS: Eleven healthy adults (6 women/5 men, 25.6±3.7years; 171.81±11.44cm; 74.4±21.2kg) participated in the counterbalanced repeated measures study. TCI and VA were assessed with transcranial magnetic stimulation for BH, BNH, and unilateral dominant flexion (DF) sessions 1 and 7. For sessions 2-6, five of each BH elbow flexion, BNH flexion/extension, and DF maximal voluntary isometric contraction (MVIC) tasks were practiced. Paired t-tests or Wilcoxon signed-rank tests, as appropriate, were used to test TCI and VA between sessions 1 and 7. Pearson or Spearman correlation coefficients, as appropriate, between VA and TCI measures and BLD and peak force measures were used to assess any association between neurological and performance variables on test days 1 and 7. RESULTS: There were no differences in VA or TCI between BH, BNH, and DF. BH VA decreased from day 1 (95.14±4.3%) to day 7 (92.2±4.4%, p = 0.014), but did not exceed the minimal detectable change (6.47). VA for BH (r = -0.655; p = 0.039) and DF (r = -0.636; p = 0.035) was associated with BH BI on day 1. When associated with peak force, day 7 BH (r = -0.627, p = 0.039) and BNH (r = -0.682, p = 0.021) TCI was correlated. CONCLUSION: BI was similar to prior research, but neurophysiological measures did not explain these differences. This is similar to previous equivocal research between BH and unilateral maximal force and TCI and/or VA, suggesting differences in BH and BNH BI are not solely influenced by neural drive modifications. Of interest, TCI was highly correlated with force, revealing neurophysiological influence between tasks, but differences in bilateral and unilateral force may be influenced by outside mechanisms.

Dexterous Force Estimation during Finger Flexion and Extension Using Motor Unit Discharge Information.

With the development of advanced robotic hands, a reliable neural-machine interface is essential to take full advantage of the functional dexterity of the robots. In this preliminary study, we developed a novel method to estimate isometric forces of individual fingers continuously and concurrently during dexterous finger flexion and extension. Specifically, motor unit (MU) discharge activity was extracted from the surface high-density electromyogram (EMG) signals recorded from the finger extensors and flexors, respectively. The MU information was separated into different groups to be associated with the flexion or extension of individual fingers and was then used to predict individual finger forces during multi-finger flexion and extension tasks. Compared with the conventional EMG amplitude-based method, our method can obtain a better force estimation performance (a higher correlation and a smaller estimation error between the predicted and the measured force) when a linear regression model was used. Further exploration of our method can potentially provide a robust neural-machine interface for intuitive control of robotic hands.

Altered Corticomuscular Coherence (CMCoh) Pattern in the Upper Limb During Finger Movements After Stroke.

Background: Proximal compensation to the distal movements is commonly observed in the affected upper extremity (UE) of patients with chronic stroke. However, the cortical origin of this compensation has not been well-understood. In this study, corticomuscular coherence (CMCoh) and electromyography (EMG) analysis were adopted to investigate the corticomuscular coordinating pattern of proximal UE compensatory activities when conducting distal UE movements in chronic stroke.Method: Fourteen chronic stroke subjects and 10 age-matched unimpaired controls conducted isometric finger extensions and flexions at 20 and 40% of maximal voluntary contractions. Electroencephalogram (EEG) data were recorded from the sensorimotor area and EMG signals were captured from extensor digitorum (ED), flexor digitorum (FD), triceps brachii (TRI), and biceps brachii (BIC) to investigate the CMCoh peak values in the Beta band. EMG parameters, i.e., the EMG activation level and co-contraction index (CI), were analyzed to evaluate the compensatory muscular patterns in the upper limb.Result: The peak CMCoh with statistical significance (P < 0.05) was found shifted from the ipsilesional side to the contralesional side in the proximal UE muscles, while to the central regions in the distal UE muscle in chronic strokes. Significant differences (P < 0.05) were observed in both peak ED and FD CMCohs during finger extensions between the two groups. The unimpaired controls exhibited significant intragroup differences between 20 and 40% levels in extensions for peak ED and FD CMCohs (P < 0.05). The stroke subjects showed significant differences in peak TRI and BIC CMCohs (P < 0.01). No significant inter- or intra-group difference was observed in peak CMCoh during finger flexions. EMG parameters showed higher EMG activation levels in TRI and BIC muscles (P < 0.05), and higher CI values in the muscle pairs involving TRI and BIC during all the extension and flexion tasks in the stroke group than those in the control group (P < 0.05).Conclusion: The post-stroke proximal muscular compensations from the elbow to the finger movements were cortically originated, with the center mainly located in the contralesional hemisphere.

Upper Limb End-Effector Force Estimation During Multi-Muscle Isometric Contraction Tasks Using HD-sEMG and Deep Belief Network.

In this study, research was carried out on the end-effector force estimation of two representative multi-muscle contraction tasks: elbow flexion and palm-pressing. The aim was to ascertain whether an individual muscle or a combination of muscles is more suitable for the end-effector force estimation. High-density surface electromyography (HD-sEMG) signals were collected from four primary muscle areas of the upper arm and forearm: the biceps brachii (BB), brachialis (BR), triceps brachii (TB), brachioradialis (BRD), and extensor digitorum communis (EDC). The wrist pulling and palm-pressing forces were measured in elbow flexion and palm-pressing tasks, respectively. The deep belief network (DBN) was adopted to establish the relation between HD-sEMG and the measured force. The representative signals of the four primary areas, which were considered as the input signal of the force estimation model, were extracted by HD-sEMG using the principle component analysis (PCA) algorithm, and fed separately or together into the DBN. An index termed mean impact value (MIV) was proposed to describe the priority of different muscle groups for estimating the end-effector force. The experimental results demonstrated that, in multi-muscle isometric contraction tasks, the dominant muscles with the highest activation degree could track variations in the end-effector force more effectively, and are more suitable than a combination of muscles. The main contributions of this research are as follows: (1) To fuse the activation information from different muscles effectively, DBN was adopted to establish the relationship between HD-sEMG and the generated force, and achieved highly accurate force estimation. (2) Based on the well-trained DBN force estimation model, an index termed MIV was presented to evaluate the priority of muscles for estimating the generated force.

Functional Index-3: A Valid and Reliable Functional Outcome Assessment Measure in Patients With Dermatomyositis and Polymyositis.

Patients with dermatomyositis (DM) and polymyositis (PM) have reduced muscle endurance.The aim of this study was to streamline the Functional Index-2 (FI-2) by developing the Functional Index-3 (FI-3) and to evaluate its measurement properties, content and construct validity, and intra- and interrater reliability. A dataset of the previously performed and validated FI-2 (n = 63) was analyzed for internal redundancy, floor, and ceiling effects. The content of the FI-2 was revised into the FI-3. Construct validity and intrarater reliability of FI-3 were tested on 43 DM and PM patients at 2 rheumatology centers. Interrater reliability was tested in 25 patients. The construct validity was compared with the Myositis Activities Profile (MAP), Health Assessment Questionnaire (HAQ), and Borg CR-10 using Spearman correlation coefficient. Spearman correlation coefficients of 63 patients performing FI-3 revealed moderate to high correlations between shoulder flexion and hip flexion tasks and similar correlations with MAP and HAQ scores; there were lower correlations for neck flexion task. All FI-3 tasks had very low to moderate correlations with the Borg scale. Intraclass correlation coefficients (ICC) of FI-3 tasks for intrarater reliability (n = 25) were moderate to good (0.88-0.98). ICC of FI-3 tasks for interrater reliability (n = 17) were fair to good (range 0.83-0.96). The FI-3 is an efficient and valid method for clinically assessing muscle endurance in DM and PM patients. FI-3 construct validity is supported by the significant correlations between functional tasks and the MAP, HAQ, and Borg CR-10 scores.

BCI-based sensorimotor rhythm training can affect individuated finger movements

ABSTRACT Brain-computer interface (BCI) technology can restore communication and control to people who are severely paralyzed. BCI technology might also be able to enhance rehabilitation of motor function. We have previously shown that pre-movement sensorimotor rhythm (SMR) amplitude affects reaction time and performance on a joystick-based cursor movement task. The present study explores in adults without motor impairment the possibility that pre-movement SMR amplitude affects performance of individuated finger movements. In Phase 1, 8 individuals performed a finger flexion task that was monitored by an exoskeleton. During a 1-sec preparatory period, two colored targets on a video monitor cued flexion of the index finger, middle finger, both fingers, or neither finger; sudden color change then triggered the movement (or non-movement). SMR features (i.e. EEG amplitudes in specific frequency bands at specific scalp locations) in the pre-movement EEG that correlated with movement versus no movement were identified. In Phase 2, the participants learned to increase or decrease these SMR features to control a two-target BCI task. Finally, in Phase 3, they were asked to increase or decrease the SMR features to initiate the finger flexion task of Phase 1 and the impact on finger flexion performance was assessed. After BCI training, pre-movement SMR feature amplitude affected performance in a subset of individuals: lower amplitude was associated with shorter movement onset. In a subset of individuals, the beneficial effect on performance of lower SMR amplitude was greater when both fingers were flexed than when one was flexed and the other remained extended; thus, the impact of SMR amplitude modulation depended on the specificity of the subsequent motor task. These results indicate that BCI-based training of SMR activity in the pre-movement preparatory period can affect finger movements in a subset of individuals. They encourage studies that integrate such training into rehabilitation protocols and examine its capacity to enhance restoration of useful hand function.

Effect of ankle joint position on triceps surae motor unit firing rates

The triceps surae is an interesting model to study the effect of muscle length changes on motor unit properties for two reasons. First, the gastrocnemii components show lower motor unit discharge rates (MUDRs) when shortened by knee joint flexion as compared to an extended knee joint, whereas all other muscles studied display either higher or similar MUDRs in a shortened compared to a lengthened position. Second, the soleus receives strong afferent feedback due to its predominantly type I muscle fiber composition indicating that muscle length changes may have a great effect on its motor unit properties. The limited previous studies have not explored how changes in ankle joint position affect the triceps surae muscles. Thus, the purpose of this study was to compare MUDRs of the bi‐articular medial gastrocnemius (MG) and mono‐articular soleus at two ankle joint positions, 30° dorsiflexion and 20° plantar flexion, during the common task of plantar flexion. Four young, healthy men (~24 years old) were seated upright in a leg dynamometer with both the hip and knee joint angles at 90°. Subjects performed two ~3s isometric plantar flexion maximal voluntary contractions (MVC) at each ankle joint position. Tungsten electrodes were then used to record MUDRs from the MG and soleus during separate steady state 3–10s isometric plantar flexion contractions at 25, 50, 75, and 100% MVC at one ankle joint position. After a series of contractions, the ankle joint angle was changed and the subjects performed another series of plantar flexion contractions at each torque level. Initial ankle joint position and the order of contractions performed were randomized prior to each testing session. Subjects visited the lab multiple times to repeat the intervention in order to sample from many motor units. The mean MVC torque was 53% lower in the shortened (20° plantar flexion; 105Nm) compared to the lengthened (30° dorsiflexion; 223Nm) position. A total of 487 motor units from the MG (n=228) and soleus (n=259) were identified. Mean MG MUDRs at 25, 50, 75 and 100% MVC were lower by 8, 0, 17 and 14%, respectively in the dorsiflexed compared to the plantar flexed position. Similarly, mean soleus MUDRs were lower by 8, 12, 25 and 25% at 25, 50, 75 and 100% MVC, respectively in the dorsiflexed compared to the plantar flexed position. These preliminary findings indicate that shortening the MG and soleus by placing the ankle joint in a plantar flexed position leads to higher MUDRs as compared to a dorsiflexed position. This may serve as a compensatory mechanism for the decreased torque producing capability of the triceps surae in a shortened (plantar flexed) position.Support or Funding InformationFunded by NSERC.

A Comparison of Motor Unit Control Strategies between Two Different Isometric Tasks.

Background: This study examined the motor unit (MU) control strategies for non-fatiguing isometric elbow flexion tasks at 40% and 70% maximal voluntary isometric contraction. Methods: Nineteen healthy individuals performed two submaximal tasks with similar torque levels: contracting against an immovable object (force task), and maintaining the elbow joint angle against an external load (position task). Surface electromyographic (EMG) signals were collected from the agonist and antagonist muscles. The signals from the agonist were decomposed into individual action potential trains. The linear regression analysis was used to examine the MU recruitment threshold (RT) versus mean firing rates (MFR), and RT versus derecruitment threshold (DT) relationships. Results: Both agonist and antagonist muscles’ EMG amplitudes did not differ between two tasks. The linear slopes of the MU RT versus MFR and RT versus DT relationships during the position task were more negative (p = 0.010) and more positive (p = 0.023), respectively, when compared to the force task. Conclusions: To produce a similar force output, the position task may rely less on the recruitment of relatively high-threshold MUs. Additionally, as the force output decreases, MUs tend to derecruit at a higher force level during the position task.

Differential neural coordination of bilateral hand and finger movements.

Cooperative hand movements (e.g., opening a bottle) require a close coordination of the hands. This is reflected in a neural coupling between the two sides. The aim of this study was to investigate in how far neural coupling is present not only during bilateral hand but also during bilateral finger movements. For this purpose unilateral mechanical and electrical nerve stimuli were delivered during bilateral sequentially and synchronously performed finger movements on a keyboard and, for comparison, during bilateral hand flexion movements. Electromyographic (EMG) activity and reflex responses in forearm flexor and extensor muscles of both sides were recorded and analyzed. Confounding EMG activity related to hand movements during the finger task was limited by wrist fixating braces. During the hand flexion task, complex reflex responses appeared in the forearm muscles of both sides to unilateral stimulation of the ulnar nerve (mean latency 57 ms), reflecting neural coupling between the two hands. In contrast, during the bilateral finger movement task, unilateral electrical nerve or mechanical stimulation of the right index finger was followed by dominant ipsilateral reflex responses (latency 45 and 58 ms, respectively). The results indicate that in contrast to the coupled hand movements, finger movements may not be coupled but can move independently on each side. Functionally this makes sense because during most activities of daily living, a close cooperation of the hands but not of individual fingers is needed. This independence of individual finger movements may rely on strong, specific, contralateral cortico‐motoneuronal control.

Relationship Between Hamstring Flexibility and Extensor Muscle Activity During a Trunk Flexion Task

ObjectiveThe purpose of this study was to investigate the relationship between hamstring flexibility and electromyography (EMG) muscle parameters in back and lower limb extensor muscles during a trunk flexion task. MethodsThirty healthy women aged 18 to 30 years with normal hip movement were recruited for this study. Hamstring muscle flexibility was measured with the 90-90 active straight leg raise test. Surface EMG activities were simultaneously recorded from the lumbar erector spinae, gluteus maximus, biceps femoris, semitendinosus, lateral gastrocnemius, and medial gastrocnemius muscles during forward bending. Muscle activity onset and offset, amplitude, and duration were calculated with technical computer software (MATLAB, version 1.6.0). Linear regression analysis was used to investigate the relationships between hamstring flexibility test results and EMG parameters during trunk flexion. In addition, the Friedman test was used to determine the recruitment activity pattern in women with low versus normal hamstring flexibility. ResultsDuring flexion, the back extensor muscles in individuals with lower hamstring flexibility test scores were activated and deactivated later, which can lead to delayed flexion-relaxation. Regression analysis did not disclose any significant correlations between hamstring flexibility and other EMG parameters (duration and amplitude) in back extensor muscles. Activation and deactivation recruitment patterns differed between the groups with normal and low hamstring flexibility. ConclusionThe findings of this study suggest that hamstring flexibility plays an important role in the patterns of trunk and lower limb muscle activity onset, offset, and recruitment.

The effects of transcranial static magnetic fields stimulation over the supplementary motor area on anticipatory postural adjustments

We investigated the influence of transcranial static magnetic field stimulation (tSMS) over the supplementary motor area (SMA) on anticipatory postural adjustments (APAs), in which the activation of the postural muscles of the legs and trunk that control standing posture precedes the activation of the prime mover muscles during rapid shoulder flexion movement. Eighteen subjects performed a self-paced rapid shoulder flexion task before, during, and after tSMS. Electromyogram (EMG) activity was recorded from the deltoid anterior (AD) as the prime mover muscle and the biceps femoris (BF) as the postural muscle during the task. The EMG latency difference (ΔEMG onset) between the two muscles was calculated by subtracting the EMG burst onset of the BF from that of the AD. The ΔEMG onset was significantly shortened, but center-of-pressure parameters were not affected after tSMS stimulation. These findings suggest that tSMS applied over the SMA could inhibitively modulate APAs function.

The effect of head and gaze orientation on spine kinematics during forward flexion

Compound, or awkward, spine postures have been suggested as a biomechanical risk factor for low back injury. This experiment investigates the influence of head (i.e. head-on-torso) and gaze (i.e. eye-in-head) orientation on three-dimensional (3D) neck and spine range of motion (ROM) during forward flexion movements. To emulate previous experimental protocols and replicate real-world scenarios, a sample of ten young, healthy males (mean ± standard deviation: age: 20.8 ± 1.03 years, height: 180.2 ± 7.36 cm, and mass: 81.9 ± 6.47 kg) completed forward flexion movements with a constrained and unconstrained pelvis, respectively. Surface kinematics were gathered from the head and spine (C7-S1). Movements were completed under a baseline condition as well as upward, downward, leftward, and rightward head and gaze orientations. For each condition, mean neck angle and inter-segmental spine (C7T1 through L5S1) ROM were evaluated. The results demonstrate that directed head and gaze orientations can influence the ROM of specific spine regions during a forward flexion task. With leftward and rightward directed head and gaze orientations, the neck became increasingly twisted and superior thoracic segments (i.e. C7T1-T2T3) were significantly more twisted during the leftward head orientation condition than the baseline condition. With upward and downward directed head and gaze orientations, a similar effect was observed for neck and superior thoracic (i.e. C7T1-T4T5) flexion-extension. Interestingly, it was also demonstrated that changes in upward/downward head orientation can also change flexion-extension kinematics of the thoracolumbar region as well (i.e. T7T8-L1L2), suggesting that head postures requiring neck extension may also promote extension throughout these spine regions. These findings provide evidence for a functional link between changes in neck flexion-extension posture and flexion-extension movement of the thoracolumbar region of the spine.

MotoRneuron: an open-source R toolbox for time-domain motor unit analyses

Motor unit synchronization is the tendency of motor neurons and their associated muscle fibers to discharge near-simultaneously. It has been theorized as a control mechanism for force generation by common excitatory inputs to these motor neurons. Magnitude of synchronization is calculated from peaks in cross-correlation histograms between motor unit discharge trains. However, there are many different methods for detecting these peaks and even more indices for calculating synchronization from them. Methodology is diverse, typically laboratory-specific and requires expensive software, like Matlab or LabView. This lack of standardization makes it difficult to draw definitive conclusions about motor unit synchronization. A free, open-source toolbox, “motoRneuron”, for the R programming language, has been developed which contains functions for calculating time domain synchronization using different methods found in the literature. The objective of this paper is to detail the toolbox’s functionality and present a case study showing how the same synchronization index can differ when different methods are used to compute it. A pair of motor unit action potential trains were collected from the forearm during a isometric finger flexion task using fine wire electromyography. The motoRneuron package was used to analyze the discharge time of the motor units for time-domain synchronization. The primary function “mu_synch” automatically performed the cross-correlation analysis using three different peak detection methods, the cumulative sum method, the z-score method, and a subjective visual method. As function parameters defined by the user, only first order recurrence intervals were calculated and a 1 ms bin width was used to create the cross correlation histogram. Output from the function were six common synchronization indices, the common input strength (CIS), k′, k′ − 1, E, S, and Synch Index. In general, there was a high degree of synchronization between the two motor units. However, there was a varying degree of synchronization between methods. For example, the widely used CIS index, which represents a rate of synchronized discharges, shows a 45% difference between the visual and z-score methods. This singular example demonstrates how a lack of consensus in motor unit synchronization methodologies may lead to substantially differing results between studies. The motoRneuron toolbox provides researchers with a standard interface and software to examine time-domain motor unit synchronization.