Effects of Forearm Rotation on Wrist Flexor and Extensor Muscle Activities

This study examined the effect of commonly used long and short styles of commercially produced wrist extension orthoses on the activity of the proximal muscles of the shoulder and elbow and on wrist flexor and extensor muscle activity. While 17 women between 22 and 40 years of age (M = 26.6) performed a specified movement wearing each of the two styles of orthosis and without an orthosis, their motor unit recruitment of five proximal joint muscle groups, wrist extensors, and wrist flexors was measured by surface electromyography. Motor unit recruitment was significantly greater in both orthosis conditions for four of five proximal muscles and for wrist flexors. There were no significant differences between the short and long orthosis conditions for proximal muscle groups. Wearing a wrist extension orthosis appears to place additional stress on the proximal joint musculature beyond that found without splint use. The study has implications for the prescription of wrist extension orthoses, especially for patients whose proximal joints are already compromised.

Purpose. To investigate clinometric properties of an Anglo-Dutch spasticity measurement tool (ADSMT), an objective tool providing information about both neurophysiological and biomechanical aspects of spasticity about the wrist joint in the clinical setting.Method. ADSMT measurements were performed with 12 healthy and 11 participants with post-stroke spasticity, and consisted of assessing the maximum range of passive wrist movement (pROM) and passive wrist extension at different cycle rates. Outcome measures were wrist angle, flexor and extensor activation, and resistance to movement. Intra-class Correlation Coefficients (ICCs) were calculated for inter-rater and test-retest reliability. Validity was investigated by calculating Spearman's rho between ADSMT outcome measures and the Modified Ashworth Scale (n = 12), the Action Research Arm Test (n = 6), and a validated wrist rig (n = 6).Results. Impaired participants had higher flexor activity and higher resistance to movement during passive wrist extension compared to unimpaired participants. For all outcome measures inter-rater and test-retest reliability were satisfactory to good and concurrent validity was sufficient.Conclusions. Outcome measures related to wrist flexor activity and resistance to movement during extension are promising for spasticity assessment using the ADSMT. Further knowledge on reference values and practicality is necessary for this tool to become incorporated in the clinical setting.

Electromyographic activity, H-reflex modulation and corticospinal input to forearm motoneurones during active and passive rhythmic movements

Music provides a reward that can enhance learning and motivation in humans. While music is often combined with exercise to improve performance and upregulate mood, the relationship between music-induced reward and motor output is poorly understood. Here, we study music reward and motor output at the same time by capitalizing on music playing. Specifically, we investigate the effects of music improvisation and live accompaniment on motor, autonomic, and affective responses. Thirty adults performed a drumming task while (i) improvising or maintaining the beat and (ii) with live or recorded accompaniment. Motor response was characterized by acceleration of hand movements (accelerometry), wrist flexor and extensor muscle activation (electromyography), and the drum strike count (i.e., the number of drum strikes played). Autonomic arousal was measured by tonic response of electrodermal activity (EDA) and heart rate (HR). Affective responses were measured by a 12-item Likert scale. The combination of improvisation and live accompaniment, as compared to all other conditions, significantly increased acceleration of hand movements and muscle activation, as well as participant reports of reward during music playing. Improvisation, regardless of type of accompaniment, increased the drum strike count and autonomic arousal (including tonic EDA responses and several measures of HR), as well as participant reports of challenge. Importantly, increased motor response was associated with increased reward ratings during music improvisation, but not while participants were maintaining the beat. The increased motor responses achieved with improvisation and live accompaniment have important implications for enhancing dose of movement during exercise and physical rehabilitation.

The generation of the normal motor pattern for walking in mammals requires feedback from muscle proprioceptors. Two characteristics of the motor pattern particularly dependent on proprioceptive signals are (1) the magnitude of activity in knee and ankle extensor muscles and (2) the duration of extensor bursts during stance. Sensory regulation of these characteristics ensures that the level of activity in extensor muscles during stance is appropriate for the load carried by the leg and that the swing phase is not initiated when a leg is loaded. Many different groups of afferents from flexor and extensor muscles can influence the locomotor pattern. Most attention has focused on the action of group I afferents from ankle extensors. Electrical stimulation of these afferents during extension increases the duration and the magnitude of extensor activity. The prolongation of extensor activity depends in part on excitation of the extensor half-center by group Ib afferents from Golgi tendon organs. The enhancement of the magnitude of extensor bursts is produced primarily via disynaptic and polysynaptic pathways opened only during locomotion. The involvement of the proprioceptive signals in the generation of locomotor activity means that the gains in reflex pathways must be constantly calibrated according to the biomechanical properties of the locomotor system. Alteration of these properties by weakening ankle extensor muscles has recently been found to produce compensatory changes in proprioceptive influences on the locomotor pattern.

The effects upon the trajectories of practised slow (approximately 9 degrees/s) voluntary wrist-extension movements of applying vibration to the tendon of an antagonist muscle (flexor carpi radialis) during the course of the movement have been studied in patients with idiopathic Parkinson's disease and age-matched healthy individuals. In both patient and control groups, flexor vibration elicited undershooting of wrist-extension movements. Wrist extensor and flexor surface EMG recordings indicated that, in patients and controls, such undershooting resulted principally from sustained reductions in extensor (prime mover) activity. Small vibration reflexes were commonly elicited in the wrist flexors which, in both Parkinson's disease and healthy subjects, were usually otherwise virtually quiescent during these slow extension movements. The amplitudes of such vibration reflexes did not differ systematically between patient and control groups and appeared inadequate to have exerted an appreciable braking action upon the extension trajectories. However, the extent of vibration-induced undershooting was, on average, significantly less in the Parkinson's disease group. In a subgroup of patients with asymmetrical parkinsonism the effects of antagonist vibration upon wrist movements of the more and less affected limb were compared. The degree of vibration-induced undershooting was significantly smaller on the more affected side. This finding suggests that disturbed proprioceptive guidance of voluntary movements in Parkinson's disease is related to the severity of clinical motor deficits. A small number Parkinson's disease patients were studied 'ON' and 'OFF' their routine anti-parkinsonian medication. A non-significant tendency was found for vibration-induced errors to be less marked in the 'OFF' state. In a separate series of experiments, under isometric conditions, vibration-induced EMG changes were recorded whilst subjects attempted to maintain a steady (15% maximum) voluntary wrist extensor effort. Results in control subjects suggested that prolonged flexor vibration produced significant tonic reflex reciprocal inhibition of the extensor muscles. However, the strength of reflex inhibition appeared sufficient to account for only a small fraction of the undershooting observed during the movement tasks. Thus, our results are consistent with the existence of an abnormality of higher-level proprioceptive integration in Parkinson's disease in which there is a mismatch of sensory (proprioceptive) and motor (corollary discharge) information.

BackgroundLoss of elbow flexion due to traumatic palsy of the brachial plexus represents a major functional handicap.Then, the first goal in the treatment of the flail arm is to restore the elbow flexion by primary direct nerve surgery or secondary reconstructive surgery.There are various methods to restore elbow flexion which are well documented in the medical literature but the most known and used is Steindler flexorplasty.This review is intended to detail the author's experience with Steindler flexorplasty to restore elbow flexion in patients with brachial plexus palsy C5-C6-C7 where wrist extensors are paralyzed or weakened.MethodsWe conducted a retrospective follow-up study of 12 patients with absent or extremely weak elbow flexion (motor grade 2 or less), wrist/finger extensor and triceps palsy associated; who had undergone surgical reconstruction of the flail upper limb by tendon transfer (Steindler flexorplasty) and wrist arthrodesis to restore elbow flexion. The aetiology of elbow weakness was in all patients brachial plexus palsy (C5-C6-C7 deficit). Data were collected from medical records and from the information obtained during follow-up visits.Age, sex, preoperative strength (rated on a 0 to 5 scale for the flexors of the elbow, wrist flexors, pronator and triceps), previous surgery, length of follow-up, other associated operative procedures, results and complications were recorded.ResultsThe results are the follows: Eleven patients were found to have very good or good function of the transferred muscles. One patient had mild active flexion of the elbow despite the reconstructive procedure.There were no major intraoperative complications. Two patients experienced transient, intermittent nocturnal ulnar paresthesias postoperatively. In both patients these symptoms subsided without further surgery.ConclusionOur study suggests that in patients with C5-C6-C7 palsy where the wrist and finger extensors are paralyzed or weaked, the flexor-pronators muscles of the forearm are strong but the triceps is not available for transfer; Steindler flexorplasty to restore elbow flexion should be complemented with wrist arthrodesis.

Hand opening is reduced by abnormal wrist and finger flexor activity in many individuals with stroke. This flexor activity also limits hand opening produced by functional electrical stimulation (FES) of finger and wrist extensor muscles. Recent advances in electrical nerve block technologies have the potential to mitigate this abnormal flexor behavior, but the actual impact of nerve block on hand opening in stroke has not yet been investigated. In this study, we applied the local anesthetic ropivacaine to the median and ulnar nerve to induce a complete motor block in 9 individuals with stroke and observed the impact of this block on hand opening as measured by hand pentagonal area. Volitional hand opening and FES-driven hand opening were measured, both while the arm was fully supported on a haptic table (Unloaded) and while lifting against gravity (Loaded). Linear mixed effect regression (LMER) modeling was used to determine the effect of Block. The ropivacaine block allowed increased hand opening, both volitional and FES-driven, and for both unloaded and loaded conditions. Notably, only the FES-driven and Loaded condition's improvement in hand opening with the block was statistically significant. Hand opening in the FES and Loaded condition improved following nerve block by nearly 20%. Our results suggest that many individuals with stroke would see improved hand-opening with wrist and finger flexor activity curtailed by nerve block, especially when FES is used to drive the typically paretic finger and wrist extensor muscles. Such a nerve block (potentially produced by aforementioned emerging electrical nerve block technologies) could thus significantly address prior observed shortcomings of FES interventions for individuals with stroke.

SIR–Our recent review on the effect of surgery of the spastic hand of children with cerebral palsy (CP) indicated that only studies with a low level of evidence were available, i.e. series of cases.1 The existing information indicated that surgery seems to have a positive effect on supination and dorsiflexion of the wrist, may improve grip strategy, and may induce an increase of the repertoire of grips and spontaneous use of the hand. The effect of surgery of the spastic hand on muscle coordination had only been addressed by three studies in a relatively systematic way.2–4 Unfortunately, it remained unclear, whether the putatively better hand function was the result of a better positioning of the hand and fingers and/or changes in muscle coordination induced by tendon transfer. Therefore, we started a pilot study in order to obtain insight into changes in muscle coordination and quality of reaching movements after surgical muscle transfers of the upper extremity in adolescents with unilateral CP. We hypothesised that surgery would result in more coordinated and more efficient muscle recruitment, i.e. in lower muscle activation rates, a reduction in recruitment of all arm muscles in concert, and in a temporal coordination which more closely resembles that of typically developing adolescents.4–7 In addition we evaluated whether surgery would result in qualitative improvement of motor behaviour during reaching. Three adolescents with unilateral CP who had surgery for their spastic hand to improve grip strategy and functional use of the paretic hand were studied. Hand posture, movement quality, and muscle coordination during a simple reaching task were assessed preoperatively and three times during the first postoperative year. Six age-matched typically developing adolescents had a single assessment to attain normative electromyography (EMG) data. Surgical procedures and patient characteristics are summarized in Table I.8–10 Postoperative treatment consisted of 5 weeks plaster immobilization, followed by a period of 6 weeks during which a removable splint was worn and intensive occupational therapy was applied. EMG was recorded continuously with bipolar surface electrodes of the following muscles: biceps brachii, triceps brachii, wrist extensors, and wrist flexors. A computer algorithm was used for the detection of phasic muscle activity.11 The analysis focused on (1) muscle activation rate, i.e. percentage of trials during which a muscle was activated; (2) ‘In concert’ muscle activation rate, i.e. percentage of trials during which all muscles were recruited; (3) percentage of trials during which a specific muscle was the ‘prime mover’; (4) onset latency of muscle activation; and (5) sequence of muscle activation: percentage of trials during which the sequence of activation consisted of (a) wrist Extensors, (b) biceps Brachii, and (c) wrist Flexors (EBF-sequence). The participants and their parents gave written informed consent and the procedures were approved by the ethics committee of the University Medical Center in Groningen. The operated hand showed in all three participants at 3 to 12 months postoperatively improvement in hand position and movement quality of wrist and fingers. This finding is in agreement with literature reports.12–15 The EMG-data indicated that surgery did not affect the rate of isolated or in concert muscle recruitment, the nature of the ‘prime mover’, or onset latencies. It did however affect muscle recruitment order: the atypical EBF-recruitment order decreased from 55% prior to surgery to 30%, 10%, and 10% at 3, 6, and 12 months respectively after the operation (Friedman: p=0.04. Fig. 1). Wrist Extensors, biceps Brachii, and wrist Flexors. (EBF)-sequence of non-dominant extremity of typically developing adolescents and adolescents with cerebral palsy pre -and post-operative. The findings of this pilot study suggest that surgery of the spastic hand does not only result in improved hand position, but also in a better quality of wrist and finger movements and a reduction of an atypical recruitment order of arm muscles. The latter may indicate that improved hand position may improve a person’s capacity to select a more efficient strategy out of the motor repertoire.5 Further investigation into the functional consequences of surgery of the spastic hand is highly recommended.

1. The question we addressed was the following: what rules does the CNS employ, given the initial and final positions of the arm for a pointing movement, to decide which shoulder and elbow muscles ("agonists") to activate for initiating movement? 2. Widely varying initial and final positions were used, so that the movements studied encompassed much of the reachable work space within the horizontal plane. For each movement, the initial electromyographic (EMG) activity at each joint was classified qualitatively in terms of the "sign," i.e., flexor or extensor muscle activity, and quantitatively in terms of the integral of the rectified EMG. 3. The sign of initial muscle activity at each joint was found to be related to the angular excursions at both joints during movement to the final position. 4. Two different hypothesized rules, derived from previously proposed strategies for control of multijoint limb movements, were tested for their ability to predict correctly the sign of initial muscle activity at each joint. Although four variables are needed to describe the initial and final positions of a two-segment arm, only two combinations of these four were relevant for testing the rules. The two positional variables were the spatial direction of the final tip position with respect to the initial forearm orientation (psi) and the initial elbow angle (theta Einit). 5. According to one of the rules tested, which was based on statics, the initial muscle activity at each joint should be such that the distal tip of the limb exerts an initial force in the direction of the final tip position. Our data concerning the sign of initial shoulder muscle activity clearly contradicted this rule in two distinct regions of the (psi, theta Einit) plane. 6. According to the other rule tested, which was based on dynamics, the initial muscle activity at each joint should be such that the initial acceleration of the distal tip is in the direction of the final tip position. The data contradicted the predicted sign of initial shoulder muscle activity for a certain range of psi. This shows that the activation of muscles is not always appropriate even qualitatively for a straight-line path. Furthermore, the effects of added inertial loads predicted by this rule were not observed for trials in which a 1.8-kg mass was attached to the distal portion of the limb.(ABSTRACT TRUNCATED AT 400 WORDS)

Human grip is commonly used in sport and recreational activities and involves the coordinated activation of forearm muscles. Lateral epicondylalgia (LE) is a common musculoskeletal disorder that involves pathology of the tendon of extensor carpi radialis brevis (ECRB) at its insertion onto the lateral epicondyle of the humerus. LE presents clinically as pain provoked by gripping activities and has a major impact on function. This results in days off work and time off sport. Despite considerable research into the pathophysiology of LE, it remains poorly understood whether forearm muscles activity is altered during gripping in individuals with LE. This thesis aimed to comprehensively understand the extent of current knowledge and provide new data of activity of the wrist/forearm muscles in LE. Study 1 clarifies the current understanding of muscle activity in LE by way of systematic review with quantitative analysis. This review identified that studies of individuals with LE revealed altered motor unit morphology, abnormal patterns of muscle activity during resisted wrist extension and tennis strokes, fewer cortical peaks and less distance between cortical representation of muscles (mapped with transcranial magnetic stimulation), and delayed activation of wrist extensor muscles during gripping, when contrasted to pain-free controls. The latter finding was also present on the asymptomatic limb. Importantly, this systematic review identified limited understanding of gripping despite the clinical importance of this task in provocation of LE. The only study that had investigated muscle activity during this task had severe limitations that compromise the interpretation of the results. Limitations included the use of surface electromyography (which does not record from individual muscles), and performance of sustained contraction with high grip force (50% maximum voluntary contraction), which is likely to be provocative of pain in some individuals with LE. On the basis of some evidence of sensorimotor changes in the asymptomatic limb of individuals with unilateral LE, Study 2 was conducted as a systematic review with meta-analysis to determine the extent bilateral differences in sensorimotor function between individuals with unilateral tendinopathy and pain-free controls. Study 2 identified evidence for several sensory and motor system differences, and evidence for tendon pathology in the asymptomatic limb of individuals with other unilateral tendinopathies (Achilles tendinopathy) but not LE when contrasted to pain-free controls. On the foundation that tendon pathology was present in asymptomatic limb of individuals with Achilles tendinopathy, Study 3 investigated whether there was a greater prevalence of tendon pathology of the asymptomatic common extensor tendon of individuals with LE than pain-free controls. Unlike the findings in the Achilles tendon, Study 3 did not identify greater tendon pathology in the asymptomatic limb of individuals with unilateral LE than that present in the tendons of pain-free individuals. As no studies had explored specific muscle activation during a low level grip, Study 4 compared the contribution of forearm muscle activity to gripping between the symptomatic and asymptomatic sides in individuals with unilateral LE and pain-free individuals. This study highlighted altered muscle activity in LE characterised by a lower contribution of ECRB in the symptomatic arm and a greater contribution of extensor digitorum communis (EDC) and flexor digitorum profundus (FDP) to total EMG bilaterally, in individuals with LE than pain-free individuals. Modified distribution of activity between the synergist wrist extensor muscles ECRB and EDC has potential to impact on the functional performance of grip. The strategy used by individuals with might compromise efficient grip as finger flexor muscles (FDP) would need to overcome finger extensor muscle activity (EDC). Although potentially negative for grip, the different motor pattern could have consequences for ECRB pathology by unloading the muscle. This could provide a benefit of pain reduction, but also potential negative effects from stress shielding of the tendon. Study 5 investigated potential differences in muscle synergies (defined as groups of muscles working together to simplify central nervous system processing) between individuals with LE and pain-free individuals. For both groups, analysis with non-negative matrix factorization identified two muscle synergies involved in control of forearm muscles during repetitive gripping. Comparison between groups indicated the variance accounted for by the muscle synergies was lower in the LE group than pain-free individuals, which suggests more variation in muscle activation pattern for that group. The studies outlined in this thesis identified differences in the control of forearm muscles between individuals with and without LE. The findings imply that EDC provides a greater contribution and ECRB a lesser contribution to the gripping task in individuals with LE than pain-free controls. Given the cross-sectional study design it is not possible to clarify whether the differences preceded or followed LE, but in both cases rehabilitation of muscle activation is likely to be beneficial for recovery. Clinical interventions to modify forearm muscle activity may provide clinical benefit, but future research is needed to determine whether altered muscle activity can be changed and whether this improves outcomes.

This study aimed to examine whether isokinetic exercises applied to the intact wrist could reduce muscle strength loss and prevent the development of Complex Regional Pain Syndrome (CRPS) type I in adults with distal radius fractures. Forty-two patients with distal radius fractures were randomized into two groups: a Cross-Education (CE) group (n = 21) and a control group (n = 21). Both groups received a standard home exercise program. In addition, the CE group performed 12 supervised sessions of isokinetic wrist strengthening exercises on the non-fractured side during the immobilization period. After cast removal, isometric muscle strength of the fractured wrist was evaluated, and patients were monitored for the development of CRPS type I. The CE group showed significantly higher isometric muscle strength in wrist flexors and extensors compared with the control group (wrist flexors: d = 0.73, p = 0.024; wrist extensors: d = 0.87, p = 0.008). Furthermore, the incidence of CRPS type I was significantly lower in the CE group (p = 0.03). Cross-Education training applied during immobilization can prevent muscle weakness and decrease the risk of CRPS in fracture rehabilitation. These findings highlight CE as a safe and effective early intervention strategy that may enhance functional outcomes and reduce complications in patients with distal radius fractures.

Formation of the central pattern generator for locomotion in the rat and mouse

Following peripheral nerve injury, moderate daily exercise conducted on a level treadmill results in enhanced axon regeneration and modest improvements in functional recovery. If the exercise is conducted on an upwardly inclined treadmill, even more motor axons regenerate successfully and reinnervate muscle targets. Whether this increased motor axon regeneration also results in greater improvement in functional recovery from sciatic nerve injury was studied. Axon regeneration and muscle reinnervation were studied in Lewis rats over an 11 wk postinjury period using stimulus evoked electromyographic (EMG) responses in the soleus muscle of awake animals. Motor axon regeneration and muscle reinnervation were enhanced in slope-trained rats. Direct muscle (M) responses reappeared faster in slope-trained animals than in other groups and ultimately were larger than untreated animals. The amplitude of monosynaptic H reflexes recorded from slope-trained rats remained significantly smaller than all other groups of animals for the duration of the study. The restoration of the amplitude and pattern of locomotor EMG activity in soleus and tibialis anterior and of hindblimb kinematics was studied during treadmill walking on different slopes. Slope-trained rats did not recover the ability to modulate the intensity of locomotor EMG activity with slope. Patterned EMG activity in flexor and extensor muscles was not noted in slope-trained rats. Neither hindblimb length nor limb orientation during level, upslope, or downslope walking was restored in slope-trained rats. Slope training enhanced motor axon regeneration but did not improve functional recovery following sciatic nerve transection and repair.

IntroductionIpsilateral motor evoked potentials (iMEPs) are difficult to obtain in distal upper limb muscles of healthy participants but give a direct insight into the role of ipsilateral motor control.MethodsWe tested a new high-intensity double pulse transcranial magnetic stimulation (TMS) protocol to elicit iMEPs in wrist extensor and flexor muscles during four different bimanual movements (cooperative—asymmetric, cooperative—symmetric, non-cooperative—asymmetric and non-cooperative—symmetric) in 16 participants.ResultsNine participants showed an iMEP in the wrist extensor in at least 20% of the trials in each of the conditions and were classified as iMEP+ participants. iMEP persistence was greater for cooperative (50.5 ± 28.8%) compared to non-cooperative (31.6 ± 22.1%) tasks but did not differ between asymmetric and symmetric tasks. Area and amplitude of iMEPs were also increased during cooperative (area = 5.41 ± 3.4 mV × ms; amplitude = 1.60 ± 1.09 mV) compared to non-cooperative (area = 3.89 ± 2.0 mV × ms; amplitude = 1.12 ± 0.56 mV) tasks and unaffected by task-symmetry.DiscussionThe upregulation of iMEPs during common-goal cooperative tasks shows a functional relevance of ipsilateral motor control in bimanual movements. The paired-pulse TMS protocol is a reliable method to elicit iMEPs in healthy participants and can give new information about neural control of upper limb movements. With this work we contribute to the research field in two main aspects. First, we describe a reliable method to elicit ipsilateral motor evoked potentials in healthy participants which will be useful in further advancing research in the area of upper limb movements. Second, we add new insight into the motor control of bimanual movements. We were able to show an upregulation of bilateral control represented by increased ipsilateral motor evoked potentials in cooperative, object-oriented movements compared to separate bimanual tasks. This result might also have an impact on neurorehabilitation after stroke.