The effect of attending to motor overflow on its voluntary inhibition in young and older adults

Impact of Upper Extremity Impairment and Trunk Control on Self-Care Independence in Children With Upper Motor Neuron Lesions

OBJECTIVE

The purpose of this study was to evaluate the relative importance of different approaches to measure upper extremity selective voluntary motor control (SVMC), spasticity, strength, and trunk control for explaining self-care independence in children affected by upper motor neuron lesions.

METHODS

Thirty-one patients (mean [SD] age = 12.5 [3.2] years) with mild to moderate arm function impairments participated in this observational study. Self-care independence was evaluated with the Functional Independence Measure for children (WeeFIM). Upper extremity SVMC was quantified with the Selective Control of the Upper Extremity Scale (SCUES), a similarity index (SISCUES) calculated from simultaneously recorded surface electromyography muscle activity patterns, and an accuracy and involuntary movement score derived from an inertial-measurement-unit-based assessgame. The Trunk Control Measurement Scale was applied and upper extremity spasticity (Modified Ashworth Scale) and strength (dynamometry) were assessed. To determine the relative importance of these factors for self-care independence, 3 regression models were created: 1 included only upper extremity SVMC measures, 1 included upper extremity and trunk SVMC measures (overall SVMC model), and 1 included all measures (final self-care model).

RESULTS

In the upper extremity SVMC model (total variance explained 52.5%), the assessgame (30.7%) and SCUES (16.5%) were more important than the SISCUES (4.5%). In the overall SVMC model (75.0%), trunk SVMC (39.0%) was followed by the assessgame (21.1%), SCUES (11.0%), and SISCUES (4.5%). In the final self-care model (82.1%), trunk control explained 43.2%, upper extremity SVMC explained 23.1%, spasticity explained 12.3%, and strength explained 2.3%.

CONCLUSION

Although upper extremity SVMC explains a substantial portion of self-care independence, overall trunk control was even more important. Whether training trunk control and SVMC can translate to improved self-care independence should be the subject of future research.

IMPACT

This study highlights the importance of trunk control and selective voluntary motor control for self-care independence in children with upper motor neuron lesions.

Voluntary suppression of associated activity decreases force steadiness in the active hand

Unilateral muscle contractions are often accompanied by the activation of the ipsilateral hemisphere, producing associated activity (AA) in the contralateral homologous muscles. However, the functional role of AA is not fully understood. We determined the effects of voluntary suppression of AA in the first dorsal interosseous (FDI), on force steadiness during a constant force isometric contraction of the contralateral FDI. Participants (n = 17, 25.5 years) performed two trials of isometric FDI contractions as steadily as possible. In Trial 1, they did not receive feedback or explicit instructions for suppressing the AA in the contralateral homologous FDI. In Trial 2, participants received feedback and were asked to voluntarily suppress the AA in the contralateral nontarget FDI. During both trials, corticospinal excitability and motor cortical inhibition were measured. The results show that participants effectively suppressed the AA in the nontarget contralateral FDI (-71%), which correlated with reductions in corticospinal excitability (-57%), and the suppression was also accompanied by increases in inhibition (27%) in the ipsilateral motor cortex. The suppression of AA impaired force steadiness, but the decrease in force steadiness did not correlate with the magnitude of suppression. The results show that voluntary suppression of AA decreases force steadiness in the active hand. However, due to the lack of association between suppression and decreased steadiness, we interpret these data to mean that specific elements of the ipsilateral brain activation producing AA in younger adults are neither contributing nor detrimental to unilateral motor control during a steady isometric contraction.

Behavioural and cerebral asymmetries of mirror movements are specific to rhythmic task and related to higher attentional and executive control

Mirror movements (MM) refer to the involuntary movements or contractions occurring in homologous muscles contralateral to the unilateral voluntary movements. This behavioural manifestation increases in elderly. In right-handed adults, some studies report asymmetry in MM production, with greater MM in the right dominant hand during voluntary movements of the left non-dominant hand than the opposite. However, other studies report contradictory results, suggesting that MM asymmetry could depend on the characteristics of the task. The present study investigates the behavioural asymmetry of MM and its associated cerebral correlates during a rhythmic task and a non-rhythmic task using low-force contractions (i.e., 25 % MVC). We determined the quantity and the intensity of MM using electromyography (EMG) and cerebral correlates through electroencephalography (EEG) in right-handed healthy young and middle-aged adults during unimanual rhythmic vs. non-rhythmic tasks. Overall, results revealed (1) behavioural asymmetry of MM specific to the rhythmic task and irrespective of age, (2) cerebral asymmetry of motor activations specific to the rhythmic task and irrespective of age and (3) greater attentional and executive activations in the rhythmic task compared to the non-rhythmic task. In line with our hypotheses, behavioural and cerebral motor asymmetries of MM seem to be specific to the rhythmic task. Results are discussed in terms of cognitive-motor interactions: greater attentional and executive control required in the rhythmic tasks could contribute to the increased occurrence of involuntary movements in both young and middle-aged adults.

Validity and reliability of an electromyography-based upper limb assessment quantifying selective voluntary motor control in children with upper motor neuron lesions

Current clinical assessments evaluating selective voluntary motor control are measured on an ordinal scale. We combined the Selective Control of the Upper Extremity Scale (SCUES) with surface electromyography to develop a more objective and interval-scaled assessment of selective voluntary motor control. The resulting Similarity Index (SI) quantifies the similarity of muscle activation patterns. We aimed to evaluate the validity and reliability of this new assessment named SISCUES (Similarity Index of the SCUES) in children with upper motor neuron lesions. Thirty-three patients (12.2 years [8.8;14.9]) affected by upper motor neuron lesions with mild to moderate impairments and 31 typically developing children (11.6 years [8.5;13.9]) participated. We calculated reference muscle activation patterns for the SISCUES using data of 33 neurologically healthy adults (median [1st; 3rd quantile]: 32.5 [27.9; 38.3]). We calculated Spearman correlations (ρ) between the SISCUES and the SCUES and the Manual Ability Classification System (MACS) to establish concurrent validity. Discriminative validity was tested by comparing scores of patients and healthy peers with a robust ANCOVA. Intraclass correlation coefficients2,1 and minimal detectable changes indicated relative and absolute reliability. The SISCUES correlates strongly with SCUES (ρ = 0.76, p < 0.001) and moderately with the MACS (ρ = -0.58, p < 0.001). The average SISCUES can discriminate between patients and peers. The intraclass correlation coefficient2,1 was 0.90 and the minimal detectable change was 0.07 (8% of patients' median score). Concurrent validity, discriminative validity, and reliability of the SISCUES were established. Further studies are needed to evaluate whether it is responsive enough to detect changes from therapeutic interventions.

Voluntary Inhibition of Physiological Mirror Activity: An EEG-EMG Study

Physiological mirror activity (pMA), observed in healthy human adults, describes the involuntary co-activation of contralateral homologous muscles during unilateral limb movements. Here we provide novel evidence, using neuromuscular measurements (electromyography; EMG), that the amplitude of pMA can be voluntarily inhibited during unilateral isometric contractions of intrinsic hand muscles after informing human participants (10 male, 10 female) about its presence and establishing a basic understanding of pMA mechanisms through a standardized protocol. Importantly, significant suppression of pMA was observed immediately after participants were asked to inhibit it, despite the absence of any online feedback during task execution and without special training. Moreover, we observed that the decrease of pMA was specifically accompanied by an increase in relative frontal δ power recorded with electroencephalography (EEG). Correlation analysis further revealed an inverse association between the individual amplitude of pMA and frontal δ power that reached significance once participants started to inhibit. Taken together, these results suggest that δ power in frontal regions might reflect executive processes exerting inhibitory control over unintentional motor output, in this case pMA. Our results provide an initial reference point for the development of therapeutic applications related to the neurorehabilitation of involuntary movements which could be realized through the suppression of pMA observed in the elderly before it would fully manifest in undesirable overt movement patterns.

Validity and reliability of an accelerometer-based assessgame to quantify upper limb selective voluntary motor control

INTRODUCTION

Current clinical assessments measure selective voluntary motor control (SVMC) on an ordinal scale. We introduce a playful, interval-scaled method to assess SVMC in children with brain lesions and evaluate its validity and reliability.

METHODS

Thirty-one neurologically intact children (median [1st-3rd quartile]: 11.6 years [8.5-13.9]) and 33 patients (12.2 years [8.8-14.9]) affected by upper motor neuron lesions with mild to moderate impairments participated. Using accelerometers, they played a movement tracking game (assessgame) with isolated joint movements (shoulder, elbow, lower arm [pro-/supination], wrist, and fingers), yielding an accuracy score. Involuntary movements were recorded simultaneously and resulted in an involuntary movement score. Both scores were normalized to the performance of 33 neurologically intact adults (32.5 years [27.9; 38.3]), which represented physiological movement patterns. We correlated the assessgame outcomes with the Manual Ability Classification System, Selective Control of the Upper Extremity Scale, and a therapist rating of involuntary movements. Furthermore, a robust ANCOVA was performed with age as covariate, comparing patients to their healthy peers at the age levels of 7.5, 9, 10.5, 12, and 15 years. Intraclass correlation coefficients and smallest real differences indicated relative and absolute reliability.

RESULTS

Correlations (Kendall/Spearman) for the accuracy score were τ = 0.29 (p = 0.035; Manual Ability Classification System), ρ = - 0.37 (p = 0.035; Selective Control of the Upper Extremity Scale), and ρ = 0.64 (p < 0.001; therapist rating). Correlations for the involuntary movement metric were τ = 0.37 (p = 0.008), ρ = - 0.55 (p = 0.001), and ρ = 0.79 (p < 0.001), respectively. The robust ANCOVAs revealed that patients performed significantly poorer than their healthy peers in both outcomes and at all age levels except for the dominant/less affected arm, where the youngest age group did not differ significantly. Robust intraclass correlation coefficients and smallest real differences were 0.80 and 1.02 (46% of median patient score) for the accuracy and 0.92 and 2.55 (58%) for involuntary movements, respectively.

CONCLUSION

While this novel assessgame is valid, the reliability might need to be improved. Further studies are needed to determine whether the assessgame is sensitive enough to detect changes in SVMC after a surgical or therapeutic intervention.

Age-related differences in bimanual coordination performance

Purpose. The purpose of this article was to determine how characteristics of bimanual coordination tasks affect the quality of performance and to determine the impact of these characteristics on muscular activation of the upper limbs, with consideration of age-related differences. Methods. The research was carried out on two groups consisting of 25 people aged 20-30 and 60-67 years. The subjects performed seven tasks that varied in coordination mode, tracking mode and outline-tracing. The main measures of task performance were calculated on the basis of the difference between the position of the target and tracing cursors. Cohen's d value was calculated to show differences in measures between groups. Results. There were higher values of error and variability measures for elderly people compared to young. Complex tasks showed the largest difficulty, which suggests that, when performed, such tasks have the greatest potential to improve coordination skills. Tasks during which both limbs contribute to the movement of one cursor proved the most appropriate. Conclusion. The tracking mode is of great importance for the quality of performance in motor coordination tasks, while the performance of tasks with imposed speed is much more strongly age-sensitive than performance with a freely chosen speed.

First validation of a novel assessgame quantifying selective voluntary motor control in children with upper motor neuron lesions

The question whether novel rehabilitation interventions can exploit restorative rather than compensatory mechanisms has gained momentum in recent years. Assessments measuring selective voluntary motor control could answer this question. However, while current clinical assessments are ordinal-scaled, which could affect their sensitivity, lab-based assessments are costly and time-consuming. We propose a novel, interval-scaled, computer-based assessment game using low-cost accelerometers to evaluate selective voluntary motor control. Participants steer an avatar owl on a star-studded path by moving the targeted joint of the upper or lower extremities. We calculate a target joint accuracy metric, and an outcome score for the frequency and amplitude of involuntary movements of adjacent and contralateral joints as well as the trunk. We detail the methods and, as a first proof of concept, relate the results of select children with upper motor neuron lesions (n = 48) to reference groups of neurologically intact children (n = 62) and adults (n = 64). Linear mixed models indicated that the cumulative therapist score, rating the degree of selectivity, was a good predictor of the involuntary movements outcome score. This highlights the validity of this assessgame approach to quantify selective voluntary motor control and warrants a more thorough exploration to quantify changes induced by restorative interventions.

Variations in Static Force Control and Motor Unit Behavior with Error Amplification Feedback in the Elderly

Error amplification (EA) feedback is a promising approach to advance visuomotor skill. As error detection and visuomotor processing at short time scales decline with age, this study examined whether older adults could benefit from EA feedback that included higher-frequency information to guide a force-tracking task. Fourteen young and 14 older adults performed low-level static isometric force-tracking with visual guidance of typical visual feedback and EA feedback containing augmented high-frequency errors. Stabilogram diffusion analysis was used to characterize force fluctuation dynamics. Also, the discharge behaviors of motor units and pooled motor unit coherence were assessed following the decomposition of multi-channel surface electromyography (EMG). EA produced different behavioral and neurophysiological impacts on young and older adults. Older adults exhibited inferior task accuracy with EA feedback than with typical visual feedback, but not young adults. Although stabilogram diffusion analysis revealed that EA led to a significant decrease in critical time points for both groups, EA potentiated the critical point of force fluctuations [Formula: see text], short-term effective diffusion coefficients (Ds), and short-term exponent scaling only for the older adults. Moreover, in older adults, EA added to the size of discharge variability of motor units and discharge regularity of cumulative discharge rate, but suppressed the pooled motor unit coherence in the 13-35 Hz band. Virtual EA alters the strategic balance between open-loop and closed-loop controls for force-tracking. Contrary to expectations, the prevailing use of closed-loop control with EA that contained high-frequency error information enhanced the motor unit discharge variability and undermined the force steadiness in the older group, concerning declines in physiological complexity in the neurobehavioral system and the common drive to the motoneuronal pool against force destabilization.

Age-related differences in bimanual movements: A systematic review and meta-analysis

BACKGROUND

With increasing age motor functions decline. The additional challenges of executing bimanual movements further hinder motor functions in older adults. The current systematic review and meta-analysis determined the effects of healthy aging on performance in bimanual movements as compared to younger adults.

METHODS

Our comprehensive search identified 27 studies that reported bimanual movement performance measures. Each study included a between groups comparison of older (mean age=68.79years) and younger adults (mean age=23.14years). The 27 qualified studies generated 40 total outcome measure comparisons: (a) accuracy: 18, (b) variability: 14, and (c) movement time: eight.

RESULTS

Our meta-analysis conducted on a random effects model identified a relatively large negative standardized mean difference effect (ES=-0.93). This indicates that older adults exhibited more impaired bimanual movement performance in comparison to younger adults in our group of studies. Specifically, a moderator variable analysis revealed large negative effects in both accuracy (ES=-0.94) and variability (ES=-1.00), as well as a moderate negative effect (ES=-0.71) for movement time. These findings indicate that older adults displayed reduced accuracy, greater variability, and longer execution time when executing bimanual movements.

CONCLUSION

These meta-analytic findings revealed that aging impairs bimanual movement performance.

Abdominal Bracing Increases Ground Reaction Forces and Reduces Knee and Hip Flexion During Landing

STUDY DESIGN

Controlled laboratory study.

BACKGROUND

Abdominal bracing (AB) is a widely advocated method of increasing spine stability, yet the influence of AB on the execution of sporting movements has not been quantified. Landing is a common task during sporting endeavors; therefore, investigating the effect of performing AB during a drop-landing task is relevant.

OBJECTIVE

To quantify the effect of AB on kinematics (ankle, knee, hip, and regional lumbar spine peak flexion angles) and peak vertical ground reaction force (vGRF) during a drop-landing task.

METHODS

Sixteen healthy adults (7 female, 9 male; mean ± SD age, 27 ± 7 years; height, 170.6 ± 8.1 cm; mass, 68.0 ± 11.3 kg) were assessed using 3-D motion analysis, electromyography (EMG), and a force platform while performing a drop-landing task with and without AB. Abdominal bracing was achieved with the assistance of real-time internal oblique EMG feedback. Lower-limb and regional lumbar spine kinematics, peak vGRF, and normalized EMG of the left and right internal obliques and lumbar multifidus were quantified. Paired-samples t tests were used to compare variables between the AB and no-AB conditions.

RESULTS

Abdominal bracing resulted in significantly reduced knee and hip flexion and increased peak vGRF during landing. No differences in lumbar multifidus EMG or lumbar spine kinematics were observed.

CONCLUSION

Abdominal bracing reduces impact attenuation during landing. These altered biomechanics may have implications for lower-limb and spinal injury risk during dynamic tasks.

Use of Postural Reconstruction® physiotherapy to treat an adolescent with asymmetric bilateral genu varum and idiopathic scoliosis

OBJECTIVE

To document the effect of Postural Reconstruction® physiotherapy on two postural disorders commonly observed in adolescents: genu varum and idiopathic scoliosis.

PATIENT AND METHODS

A case report on a 16-year-old boy suffering from knee pain and presenting with bilateral genu varum and mild scoliosis. At the initial evaluation (T0), the intercondylar space was 7 cm and the Cobb angles for the right lumbar curve and left thoracic curve were 18° and 13°, respectively. The boy was treated with Postural Reconstruction(®), a neuromuscular physiotherapy intervention using facilitation/inhibition techniques. The outcomes used to quantify the effect of 6 months (T1), 12 months (T2) and 26 months (T3) of treatment were pain levels, the intercondylar space, the lumbar gibbosity and the lumbar and thoracic Cobb angles.

RESULTS

The knee pain disappeared rapidly. At T3, the intercondylar space had decreased by 4 cm, the lumbar gibbosity angle had decreased by 2° and the lumbar and thoracic Cobb angles had decreased by 8° and 7°, respectively.

CONCLUSION

This non-invasive physiotherapy intervention appears to have considerable promise for the long-term correction of postural disorders.

Excessive motor overflow reveals abnormal inter-hemispheric connectivity in Friedreich ataxia

This study sought to characterise force variability and motor overflow in 12 individuals with Friedreich ataxia (FRDA) and 12 age- and gender-matched controls. Participants performed a finger-pressing task by exerting 30 and 70 % of their maximum finger force using the index finger of the right and left hand. Control of force production was measured as force variability, while any involuntary movements occurring on the finger of the other, passive hand, was measured as motor overflow. Significantly greater force variability in individuals with FRDA compared with controls is indicative of cortico-cerebellar disruption affecting motor control. Meanwhile, significantly greater motor overflow in this group provides the first evidence of possible abnormal inter-hemispheric activity that may be attributable to asymmetrical neuronal loss in the dentate nucleus. Overall, this study demonstrated a differential engagement in the underlying default processes of the motor system in FRDA.

Does Training of the Nondominant Upper Extremity Reduce the Surgeon’s Muscular Strain During Laparoscopy?

Introduction. In laparoscopy, suboptimal ergonomics frequently lead to morbidity for surgeons. Physical complaints are more commonly reported on the dominant upper extremity. This may be the consequence of challenging laparoscopic tasks being easier to perform with the dominant side. The authors hypothesized that specific training of the nondominant upper extremity may equip this side better and lead to a more equal distribution of physical load. Materials and methods. Participants (medical doctors) were randomized to a 3-week training schedule or no training. The training program consisted of training the nondominant upper extremity. Participants were not allowed to train on a laparoscopic box or virtual reality trainer during the study period. Baseline and outcome measurements after 3 weeks were examined with the use of EMG measurements during a validated task on a laparoscopic box trainer. Muscle strain of the trapezius and deltoid muscles and effective alternation of brachioradial and abductor pollicis brevis muscles were used as outcome variables. Results. In all, 26 participants were included. EMG analysis revealed that participants in both intervention and control groups showed a decrease in muscle strain of trapezius and deltoid muscles. However, there were no significant differences between groups. Those in the intervention group showed significantly better alternation in the brachioradial muscle. Conclusion. Training the nondominant upper extremity leads to better alternated use of lower-arm muscles during a validated box trainer task. Repeating the task after 3 weeks led to less muscle tension in the trapezius and deltoid muscles.

Task-related enhancement in corticomotor excitability during haptic sensing with the contra- or ipsilateral hand in young and senior adults

Background

Haptic sensing with the fingers represents a unique class of manipulative actions, engaging motor, somatosensory and associative areas of the cortex while requiring only minimal forces and relatively simple movement patterns. Using transcranial magnetic stimulation (TMS), we investigated task-related changes in motor evoked potential (MEP) amplitude associated with unimanual haptic sensing in two related experiments. In Experiment I, we contrasted changes in the excitability of the hemisphere controlling the task hand in young and old adults under two trial conditions, i.e. when participants either touched a fine grating (smooth trials) or touched a coarse grating to detect its groove orientation (grating trials). In Experiment II, the same contrast between tasks was performed but with TMS applied over the hemisphere controlling the resting hand, while also addressing hemispheric (right vs. left) and age differences.

Results

In Experiment I, a main effect of trial type on MEP amplitude was detected (p = 0.001), MEPs in the task hand being ~50% larger during grating than smooth trials. No interaction with age was detected. Similar results were found for Experiment II, trial type having a large effect on MEP amplitude in the resting hand (p < 0.001) owing to selective increase in MEP size (~2.6 times greater) for grating trials. No interactions with age or side (right vs. left) were detected.

Conclusions

Collectively, these results indicate that adding a haptic component to a simple unilateral finger action can elicit robust corticomotor facilitation not only in the working hemisphere but also in the opposite hemisphere. The fact that this facilitation seems well preserved with age, when task difficulty is adjusted, has some potential clinical implications.