Frailty identification using a sensor-based upper-extremity function test: a deep learning approach

The global increase in the older adult population highlights the need for effective frailty assessment, a condition linked to adverse health outcomes such as hospitalization and mortality. Existing frailty assessment tools, like the Fried phenotype and Rockwood score, have practical limitations, necessitating a more efficient approach. This study aims to enhance frailty prediction accuracy in older adults using a combined biomechanical and deep learning approach. We recruited 312 participants (126 non-frail, 145 pre-frail, 41 frail) and assessed frailty using the Fried index, upper-extremity function (UEF) test, and muscle force calculations. Machine learning (ML) models, including logistic regression and support vector machine (SVM), were employed alongside deep learning with long short-term memory (LSTM) networks. Results showed that incorporating muscle model parameters significantly improved frailty prediction. The LSTM model achieved the highest accuracy (74%), outperforming SVM (67%) and regression (66%), with precision and F1 scores of 81% and 75%, respectively. Notably, muscle co-contraction emerged as a critical predictor, with frail individuals exhibiting substantially higher levels. Our findings demonstrate that integrating UEF tasks with deep learning models provides superior frailty prediction, potentially offering a robust, efficient clinical tool. However, further validation with larger, more diverse populations is needed to confirm the generalizability of our results. This study underscores the potential of advanced computational techniques to improve the identification and monitoring of frailty in older adults.

Upper Leg Muscular Co-Contraction During Maximal-Speed Sprinting in Male Club Ice Hockey Athletes

BACKGROUND

Little is known about the lower extremity muscle co-contraction patterns during sprinting and its relation to running velocity (i.e., performance). Therefore, we compared lower extremity muscular activation patterns during sprinting between slower and faster collegiate club hockey athletes. We hypothesized that faster athletes would have lower EMG-assessed co-contraction index (CCI) values in the lower extremities during over-ground sprinting.

METHODS

Twenty-two males (age = 21 [1] yrs (median[IQR]); body mass = 77.1 ± 8.6 kg (mean ± SD)) completed two 20-m over-ground sprints with concomitant EMG and asynchronous force plate testing over four days in Tallahassee, Florida, USA. We split participants using median running velocity (FAST: 8.5 ± 0.3 vs. SLOW: 7.7 ± 0.3 m/s, p < 0.001).

RESULTS

Faster athletes had lower CCI between the rectus femoris and biceps femoris (group: p = 0.05), particularly during the late swing phase of the gait cycle (post hoc p = 0.02). Early swing phase duration was moderately inversely related to Hip CCI in the stance phase (ρ=-0.58, p < 0.01) and weakly related to Knee CCI in the swing phase (ρ = 0.44, p = 0.046). Finally, swing phase duration was moderately inversely related to Hip CCI in the stance phase (ρ=-0.50, p = 0.02).

CONCLUSIONS

In agreement with our hypothesis, we found lower CCI values in the upper leg musculature during maximal-speed over-ground sprinting. These data from collegiate club hockey athletes corroborate other reports in clinical populations that the coordination between the rectus femoris and biceps femoris is associated with linear over-ground sprinting velocity.

Passive shoulder occupational exoskeleton reduces shoulder muscle coactivation in repetitive arm movements

Humans naturally employ muscle coactivation to facilitate a broad range of movements, enhancing joint stability and movement accuracy. However, excessive muscle coactivation can become unfavorable or even detrimental. This phenomenon is often observed in industrial workers who endure repetitive or prolonged joint stress, particularly in areas such as the shoulders. Prolonged stress can result in soft tissue damage and the onset of work-related musculoskeletal disorders (MSDs). In recent years, there have been efforts to mitigate the emergence of work-related MSDs among industrial workers through the implementation of upper-limb occupational exoskeletons (OEs). While previous research has demonstrated their effectiveness in reducing shoulder muscle activation, particularly in static and overhead work activities, there has been a lack of studies examining the impact of upper-limb OEs on muscle coactivation during repetitive arm movements. To bridge this gap in knowledge, our study systematically assesses the influence of a passive exoskeleton's anti-gravitational support on shoulder muscle coactivation during repetitive arm movements. Results show that peak and mean coactivation levels linearly decrease with the increase of the amount of anti-gravitational support provided by the upper-limb OE, reaching approximately 51% and 54%, respectively. Conversely, the percentage of the movement cycle corresponding to the coactivation peak appears unaffected by the level of assistance. This study marks the first instance in which a passive upper-limb OE has been shown to reduce shoulder muscle coactivations, potentially paving the way for a novel methodology in their evaluation.

Toward a Better Understanding of Walking Speed in Ataxia of Charlevoix-Saguenay: a Factor Exploratory Study

Mobility limitations, including a decrease in walking speed, are major issues for people with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). Improving our understanding of factors influencing walking speed in ARSACS may inform the development of future interventions for gait rehabilitation and contribute to better clinical practices. The objective of the study was to identify the factors influencing the self-selected walking speed in adults with ARSACS. The dependent variable of this cross-sectional study was the self-selected speed and the factors (independent variables) were age, sex, balance, balance confidence, knee flexion and extension cocontraction indexes, lower limb coordination, passive range of motion of ankle dorsiflexion, knee and hip extension, and global spasticity. Multiple regression models were used to assess the relationships between walking speed and each factor individually. Six factors were significantly associated with walking speed and thus included in regression models. The models explained between 42.4 and 66.5% of the total variance of the self-selected walking speed. The factors that most influence self-selected walking speed are balance and lower limb coordination. In order of importance, the other factors that also significantly influence self-selected walking speed are ankle dorsiflexion range of motion, lower limb spasticity, knee extension range of motion, and confidence in balance. Balance and lower limb coordination should be targeted in rehabilitation interventions to maintain walking ability and functional independence as long as possible. The six factors identified should also be included in future studies to deepen our understanding of walking speed.

Faster Club Hockey Athletes Have Reduced Upper Leg Muscular Co-contraction During Maximal-Speed Sprinting

Background

Most electromyographic (EMG) data for muscular activation patterns during ambulation is limited to older adults with existing chronic disease(s) walking at slow velocities. However, we know much less about the lower extremity muscle co-contraction patterns during sprinting and its relation to running velocity (i.e., performance). Therefore, we compared lower extremity muscular activation patterns during sprinting between slower and faster collegiate club hockey athletes. We hypothesized that faster athletes would have lower EMG-assessed co-contraction index (CCI) values in the lower extremities during over-ground sprinting.

Results

Twenty-two males (age = 21[1] yrs (median[IQR]); body mass = 77.1 ± 8.6 kg (mean ± SD)) completed two 20-m over-ground sprints with concomitant EMG and asynchronous force plate testing. We split participants using median running velocity (FAST: 8.5 ± 0.3 vs. SLOW: 7.7 ± 0.3.

Conclusions

m/s, p < 0.001). Faster athletes had lower CCI between the rectus femoris and biceps femoris (group: p = 0.05), particularly during the late swing phase of the gait cycle (post hoc p = 0.02). In agreement with our hypothesis, we found lower CCI values in the upper leg musculature during maximal-speed over-ground sprinting. These data from collegiate club hockey athletes corroborate other reports in clinical populations that the coordination between the rectus femoris and biceps femoris is associated with linear over-ground sprinting velocity.

Muscle co-contraction and co-activation in cerebral palsy during gait: A scoping review

BACKGROUND

Cerebral palsy (CP) results from an injury to a developing brain. Muscle activation patterns during walking are disrupted in individuals with CP. Indeed, excessive muscle co-contraction or co-activation (MCo/MCa) is one of the characteristics of pathological gait. Although some researchers have studied MCo/MCa in individuals with CP during gait, inconsistent results limit our understanding of this literature. Increased knowledge of MCo/MCa patterns in individuals with CP may help the development of improved gait management approaches.

RESEARCH QUESTION

This review aims to summarize MCo/MCa patterns while walking in individuals with CP across the existing literature and compare them with their healthy peers.

METHODS

This study follows the Joanna Briggs Institute (JBI) guidelines and the recommendations presented in PRISMA Extension for Scoping Reviews (PRISMA-ScR). The recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for scoping Reviews statement were respected. The following databases were searched: MEDLINE (Ovid), EMBASE (Ovid), CINAHL Plus with Full Text (Ebsco), SPORTDiscus with Full Text (Ebsco), and Web of Science.

RESULTS

Among 2545 identified studies, 21 studies remained after screening. In total, 337 participants with CP and 249 healthy participants were included. Both MCo and MCa terminologies are used for describing simultaneous muscle activation; however, when it is measured by electromyography (EMG), MCa terminology should be preferred to facilitate interpretation. A wide range of MCo/MCa patterns has been found across studies using different methodologies (e.g., gait protocol, computation methods). Finally, most of the included studies confirm that MCo/MCa is increased in individuals with CP during walking compared to controls.

SIGNIFICANCE

This review identified missing concepts and common limitations in the literature which could be addressed in future research such as the association between MCo/MCa and gait deviations, and the most appropriate MCo/MCa computation method.

A computational musculoskeletal arm model for assessing muscle dysfunction in chronic obstructive pulmonary disease

Computational models have been used extensively to assess diseases and disabilities effects on musculoskeletal system dysfunction. In the current study, we developed a two degree-of-freedom subject-specific second-order task-specific arm model for characterizing upper-extremity function (UEF) to assess muscle dysfunction due to chronic obstructive pulmonary disease (COPD). Older adults (65 years or older) with and without COPD and healthy young control participants (18 to 30 years) were recruited. First, we evaluated the musculoskeletal arm model using electromyography (EMG) data. Second, we compared the computational musculoskeletal arm model parameters along with EMG-based time lag and kinematics parameters (such as elbow angular velocity) between participants. The developed model showed strong cross-correlation with EMG data for biceps (0.905, 0.915) and moderate cross-correlation for triceps (0.717, 0.672) within both fast and normal pace tasks among older adults with COPD. We also showed that parameters obtained from the musculoskeletal model were significantly different between COPD and healthy participants. On average, higher effect sizes were achieved for parameters obtained from the musculoskeletal model, especially for co-contraction measures (effect size = 1.650 ± 0.606, p < 0.001), which was the only parameter that showed significant differences between all pairwise comparisons across the three groups. These findings suggest that studying the muscle performance and co-contraction, may provide better information regarding neuromuscular deficiencies compared to kinematics data. The presented model has potential for assessing functional capacity and studying longitudinal outcomes in COPD.

Dynamic electromyography findings of the lower leg muscles during walking in spastic cerebral palsy children with hindfoot valgus

BACKGROUND

Hindfoot valgus is one of the most prevalent foot deformities in cerebral palsy children. Investigating the muscle activation patterns of cerebral palsy children with hindfoot valgus is crucial to understand their abnormal gait different from typically developing children.

METHODS

Electromyography data of 20 cerebral palsy children with hindfoot valgus and 20 typically developing children were recorded for tibialis anterior, peroneal longus, and gastrocnemius medialis. The activation onset and offset times, normalized peak electromyography amplitude, average electromyography amplitude and integral electromyography amplitude for 20 completed cycles were averaged for data analysis. The co-activation index and activation percentage of peroneal longus were used to evaluate the co-activation level for tibialis anterior and peroneal longus muscles.

FINDINGS

Compared with typically developing children, the activation onset of tibialis anterior and the activation offset of tibialis anterior, peroneal longus, and gastrocnemius medialis were significantly delayed in cerebral palsy children; moreover, the muscle activation durations of tibialis anterior, peroneal longus, and gastrocnemius medialis were significantly longer, and the normalized average electromyography amplitude of tibialis anterior, peroneal longus and gastrocnemius medialis, and the normalized integral electromyography amplitude of tibialis anterior were significantly lower in cerebral palsy children. Furthermore, for cerebral palsy children, the co-activation index was greater, and the peroneal longus muscles activation percentage was lower in the stance phase and greater in the swing phase than that of typically developing children.

INTERPRETATION

The lower leg muscle activation patterns in cerebral palsy children were found to be abnormal.

Muscle coordination and recruitment during squat assistance using a robotic ankle-foot exoskeleton

Squatting is an intensive activity routinely performed in the workplace to lift and lower loads. The effort to perform a squat can decrease using an exoskeleton that considers individual worker's differences and assists them with a customized solution, namely, personalized assistance. Designing such an exoskeleton could be improved by understanding how the user's muscle activity changes when assistance is provided. This study investigated the change in the muscle recruitment and activation pattern when personalized assistance was provided. The personalized assistance was provided by an ankle-foot exoskeleton during squatting and we compared its effect with that of the no-device and unpowered exoskeleton conditions using previously collected data. We identified four main muscle recruitment strategies across ten participants. One of the strategies mainly used quadriceps muscles, and the activation level corresponding to the strategy was reduced under exoskeleton assistance compared to the no-device and unpowered conditions. These quadriceps dominant synergy and rectus femoris activations showed reasonable correlations (r = 0.65, 0.59) to the metabolic cost of squatting. These results indicate that the assistance helped reduce quadriceps activation, and thus, the metabolic cost of squatting. These outcomes suggest that the muscle recruitment and activation patterns could be used to design an exoskeleton and training methods.

Treatment of spasticity

Spasticity is characterized by an enhanced size and reduced threshold for activation of stretch reflexes and is associated with "positive signs" such as clonus and spasms, as well as "negative features" such as paresis and a loss of automatic postural responses. Spasticity develops over time after a lesion and can be associated with reduced speed of movement, cocontraction, abnormal synergies, and pain. Spasticity is caused by a combination of damage to descending tracts, reductions in inhibitory activity within spinal cord circuits, and adaptive changes within motoneurons. Increased tone, hypertonia, can also be caused by changes in passive stiffness due to, for example, increase in connective tissue and reduction in muscle fascicle length. Understanding the cause of hypertonia is important for determining the management strategy as nonneural, passive causes of stiffness will be more amenable to physical rather than pharmacological interventions. The management of spasticity is determined by the views and goals of the patient, family, and carers, which should be integral to the multidisciplinary assessment. An assessment, and treatment, of trigger factors such as infection and skin breakdown should be made especially in people with a recent change in tone. The choice of management strategies for an individual will vary depending on the severity of spasticity, the distribution of spasticity (i.e., whether it affects multiple muscle groups or is more prominent in one or two groups), the type of lesion, and the potential for recovery. Management options include physical therapy, oral agents; focal therapies such as botulinum injections; and peripheral nerve blocks. Intrathecal baclofen can lead to a reduction in required oral antispasticity medications. When spasticity is severe intrathecal phenol may be an option. Surgical interventions, largely used in the pediatric population, include muscle transfers and lengthening and selective dorsal root rhizotomy.

The effects of task-oriented mental practice on upper limb function and coordination in chronic stroke patients—Randomized controlled trial design

Objective

This study is a randomized experimental design study conducted to investigate the effect of task-oriented mental practice (TOMP) on upper limb function and coordination in chronic stroke patients.

Methods

A total of 34 chronic stroke patients participated in this study and were randomly divided into an experimental group (EG) of 17 patients (TOMP) and a control group (CG) of 17 patients (task-oriented training). To measure the subject’s upper extremity function and coordination, the results of Fugl-Meyer assessment (FMA) of motor function (U/E) and co-coordination ratio (CCR) values calculated from the measurements of the BTS FreeEMG 300 were used.

Results

In the comparison before and after group intervention in terms of FMA, the EG showed significant changes in all items of FMA, but the CG showed significant changes only in the shoulder items ( p < 0.05). In the comparison between groups, significant differences were observed only in the total score of FMA ( p < 0.05). In terms of the CCR value, positive changes were found in the EG in all items except for the shoulder flexion, but negative changes were observed in all items in the CG.

Conclusion

It was confirmed that the TOMP applied in this study can have a positive effect on upper limb function and coordination in chronic stroke patients.

Measurement and Analysis of Human Infant Crawling for Rehabilitation: A Narrative Review

When a child shows signs of potential motor developmental disorders, early diagnosis of central nervous system (CNS) impairment is beneficial. Known as the first CNS-controlled mobility for most of infants, mobility during crawling usually has been used in clinical assessments to identify motor development disorders. The current clinical scales of motor development during crawling stage are relatively subjective. Objective and quantitative measures of infant crawling afford the possibilities to identify those infants who might benefit from early intervention, as well as the evaluation of intervention progress. Thus, increasing researchers have explored objective measurements of infant crawling in typical and atypical developing infants. However, there is a lack of comprehensive review on infant-crawling measurement and analysis toward bridging the gap between research crawling analysis and potential clinical applications. In this narrative review, we provide a practical overview of the most relevant measurements in human infant crawling, including acquisition techniques, data processing methods, features extraction, and the potential value in objective assessment of motor function in infancy; meanwhile, the possibilities to develop crawling training as early intervention to promote the locomotor function for infants with locomotor delays are also discussed.

Functional mobility in walking adult population with ataxia of Charlevoix-Saguenay

BACKGROUND

This study aimed to describe lower limbs impairments, balance and activity limitations related to indoor mobility in adult walkers with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS).

RESULTS

Twenty-five participants were recruited with a mean age of 32.2 (± 10.4) years with 45.7% using a walking aid. There is a significant difference between participants with and without a walking aid in terms of lower limbs coordination, balance and mobility. Although participants who walk without a walking aid perform better than the others and they are below predictive or reference values. Despite significant mobility limitations, only mild spasticity and passive range of motion limitations were observed. However, there is a significant difference between unaffected individuals and participants with ARSACS for lower limb muscle cocontraction.

CONCLUSIONS

Results show a high level of lower limb impairments, balance and mobility limitation in adults' participants with ARSACS that are still walking, including people not using a walking aid. One of the most original finding is the presence of excessive cocontraction and a relatively mild level of spasticity in the lower limbs muscles. Results of this study better circumscribes the impairments and activities that should be the focus of intervention including rehabilitation in ARSACS.

Electromyography-informed modeling for estimating muscle activation and force alterations in Parkinson's disease

Electromyography (EMG)-driven neuromusculoskeletal modeling (NMSM) enables simulating the mechanical function of multiple muscle-tendon units as controlled by nervous system in the generation of complex movements. In the context of clinical assessment this may enable understanding biomechanical factor contributing to gait disorders such as one induced by Parkinson's disease (PD). In spite of the challenges in the development of patient-specific models, this preliminary study aimed at establishing a feasible and noninvasive experimental and modeling pipeline to be adopted in clinics to detect PD-induced gait alterations. Four different NMSM have been implemented for three healthy controls using CEINMS, an OpenSim-compatible toolbox. Models differed in the EMG-normalization methods used for calibration purposes (i.e. walking trial normalization and maximum voluntary contraction normalization) and in the set of experimental EMGs used for the musculotendon-unit mapping (i.e. 4 channels vs. 15 channels). Model accuracy assessment showed no statistically significant differences between the more complete model (non-clinically viable) and the proposed reduced one (clinically viable). The clinically viable reduced model was systematically applied on a dataset including ten PD's and thirteen healthy controls. Results showed significant differences in the neuromuscular control strategy of the PD group in term of muscle forces and joint torques. Indeed, PD patients displayed a significantly lower magnitude on force production and revealed a higher amount of force variability with the respect of the healthy controls. The estimated variables could become a measurable biomechanical outcome to assess and track both disease progression and its impact on gait in PD subjects.

Effect of Acupuncture on Muscle Endurance in the Female Shoulder Joint: A Pilot Study

Shoulder joint dysfunction is the leading cause of decreased athletic ability in athletes. Shoulder joint sports injuries affect the athletic performance of athletes. Improvements in the muscle endurance of the shoulder joint can reduce the incidence of shoulder joint dysfunction. Acupuncture has been an important part of Asian culture for a long time. In acupuncture, nerves are stimulated, inducing postactivation potentiation (PAP) in the body's motor units and enhancing muscle strength. In this research, 20 female participants with full flexion/extension and adduction/abduction ranges of motion in the shoulder joint during isokinetic exercises underwent stimulation of the following acupuncture points in the shoulder joint: Binao (LI14), Jianyu (LI15), Jianliao (SJ14), Naohui (SJ13), Yuzhong (KI26), Zhongfu (LU1), Yunmen (LU2), Xiabai (LU4), Chize (LU5), Tianfu (LU3), and Xiaoluo (SJ12). In the study, there were significant increases after acupuncture in the average maximum torque in flexion, extension, and adduction; the average work in flexion/extension and adduction/abduction; the average power in flexion/extension and adduction/abduction; the total work in flexion/extension and adduction/abduction; the total net sagittal-plane work (flexion + extension); and the total net frontal-plane work (adduction + abduction) (P < 0.05). The average maximum abduction torque did not increase significantly, potentially due to antagonistic forces of muscles. Therefore, acupuncture at acupoints around the shoulder joint can increase muscle excitability, thereby delaying muscle fatigue and increasing muscle endurance.

Surface Electromyography Normalization Affects the Interpretation of Muscle Activity and Coactivation in Children With Cerebral Palsy During Walking

Investigating muscle activity and coactivation with surface electromyography (sEMG) gives insight into pathological muscle function during activities like walking in people with neuromuscular impairments, such as children with cerebral palsy (CP). There is large variation in the amount of coactivation reported during walking in children with CP, possibly due to the inconsistent handling of sEMG and in calculating the coactivation index. The aim of this study was to evaluate how different approaches of handling sEMG may affect the interpretation of muscle activity and coactivation, by looking at both absolute and normalized sEMG. Twenty-three ambulatory children with CP and 11 typically developing (TD) children participated. We conducted a three-dimensional gait analysis (3DGA) with concurrent sEMG measurements of tibialis anterior, soleus, gastrocnemius medialis, rectus femoris, and hamstring medialis. They walked barefoot at a self-selected, comfortable speed back and forth a 7-m walkway. The gait cycle extracted from the 3DGA was divided into six phases, and for each phase, root mean square sEMG amplitude was calculated (sEMG-RMS-abs), and also normalized to peak amplitude of the linear envelope (50-ms running RMS window) during the gait cycle (sEMG-RMS-norm). The coactivation index was calculated using sEMG-RMS-abs and sEMG-RMS-norm values and by using two different indices. Differences between TD children's legs and the affected legs of children with CP were tested with a mixed model. The between-subject muscle activity variability was more evenly distributed using sEMG-RMS-norm; however, potential physiological variability was eliminated as a result of normalization. Differences between groups in one gait phase using sEMG-RMS-abs showed opposite differences in another phase using sEMG-RMS-norm for three of the five muscles investigated. The CP group showed an increased coactivation index in two out of three muscle pairs using sEMG-RMS-abs and in all three muscle pairs using sEMG-RMS-norm. These results were independent of index calculation method. Moreover, the increased coactivation indices could be explained by either reduced agonist activity or increased antagonist activity. Thus, differences in muscle activity and coactivation index between the groups change after normalization. However, because we do not know the truth, we cannot conclude whether to normalize and recommend incorporating both.

Oxygen Cost During Walking in Individuals With Stroke: Hemiparesis Versus Cerebellar Ataxia

Background. Understanding the factors that limit mobility in stroke patients is fundamental for proposing appropriate rehabilitation strategies. A high oxygen cost during walking (Cw) has a strong impact on the community ambulation of hemiparetic patients. The Cw in poststroke cerebellar ataxia is poorly evaluated, unlike hemiparetic gait. Objective. To compare the oxygen cost/self-selected walking speed (S) relationship in stroke individuals with cerebellar ataxia or hemiparetic gait. Methods. Thirty-three subjects were included (14 cerebellar stroke, 19 hemispheric stroke), with stroke confirmed by brain imaging and able to walk without human assistance. We measured Cw using the Metamax3B. The relationship between Cw and self-selected walking speed was modelled by logistic regression and then compared between the cerebellar and hemispheric groups. Results. No significant difference was found between the 2 groups for all characteristics of the population, except motor impairments, spasticity, and ataxia (P < .01). We identified 2 separate Cw/S relationships with different logistic regression equations for the 2 groups. Faster than 0.4 m s⁻¹, Cw was 30.6% to 39.9% higher in patients with cerebellar stroke in comparison with hemispheric stroke individuals. The Cw was correlated with ataxia (r = 0.88; P < .001) in the cerebellar group, whereas there was a correlation with motor impairments (r = −0.61; P < .01), spasticity (r = 0.59; P < .01), and ataxia (r = 0.81; P < .01) in hemispheric stroke individuals. Conclusion. The Cw in poststroke cerebellar ataxia is significantly higher compared with hemiparetic patients at an equivalent walking speed. The impact on community walking needs to be explored in stroke survivors with cerebellar stroke.

The effects of cognitive load and optical flow on antagonist leg muscle coactivation during walking for young and older adults

The purpose of this study was to compare how healthy aging interacts with environments that challenge cognitive load and optical flow to affect antagonist leg muscle coactivation during walking. We measured leg muscle activity in sixteen older adults (70.4 ± 4.2 years) and twelve young adults (23.6 ± 3.9 years) walking on a treadmill at their preferred speed while watching a speed-matched virtual hallway. Cognitive load was challenged using a dual-task to interfere with available attentional resources. Optical flow was challenged using perturbations designed to create a perception of lateral imbalance. We found antagonist coactivation increased with aging, independent of condition. We also found that, compared to unperturbed walking, only in the presence of optical flow perturbations did the older adults increase their antagonist coactivation. Antagonist coactivation in the young adults was not affected by either condition. Our findings provide evidence that antagonist leg muscle coactivation in healthy older adults is more sensitive to walking environments that challenge optical flow than environments that challenge cognitive load. As increased antagonist coactivation may indicate compromised balance, these findings may be relevant in the design of living environments to reduce falls risk.

Electromyography Exposes Heterogeneity in Muscle Co-Contraction following Stroke

Walking after stroke is often described as requiring excessive muscle co-contraction, yet, evidence that co-contraction is a ubiquitous motor control strategy for this population remains inconclusive. Co-contraction, the simultaneous activation of agonist and antagonist muscles, can be assessed with electromyography (EMG) but is often described qualitatively. Here, our goal is to determine if co-contraction is associated with gait impairments following stroke. Fifteen individuals with chronic stroke and nine healthy controls walked on an instrumented treadmill at self-selected speed. Surface EMGs were collected from the medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) of each leg. EMG envelope amplitudes were assessed in three ways: (1) no normalization, (2) normalization to the maximum value across the gait cycle, or (3) normalization to maximal M-wave. Three co-contraction indices were calculated across each agonist/antagonist muscle pair (MG/TA and SOL/TA) to assess the effect of using various metrics to quantify co-contraction. Two factor ANOVAs were used to compare effects of group and normalization for each metric. Co-contraction during the terminal stance (TSt) phase of gait is not different between healthy controls and the paretic leg of individuals post-stroke, regardless of the metric used to quantify co-contraction. Interestingly, co-contraction was similar between M-max and non-normalized EMG; however, normalization does not impact the ability to resolve group differences. While a modest correlation is revealed between the amount of TSt co-contraction and walking speed, the relationship is not sufficiently strong to motivate further exploration of a causal link between co-contraction and walking function after stroke. Co-contraction does not appear to be a common strategy employed by individuals after stroke. We recommend exploration of alternative EMG analysis approaches in an effort to learn more about the causal mechanisms of gait impairment following stroke.

Applying a pelvic corrective force induces forced use of the paretic leg and improves paretic leg EMG activities of individuals post-stroke during treadmill walking

OBJECTIVE

To determine whether applying a mediolateral corrective force to the pelvis during treadmill walking would enhance muscle activity of the paretic leg and improve gait symmetry in individuals with post-stroke hemiparesis.

METHODS

Fifteen subjects with post-stroke hemiparesis participated in this study. A customized cable-driven robotic system based over a treadmill generated a mediolateral corrective force to the pelvis toward the paretic side during early stance phase. Three different amounts of corrective force were applied. Electromyographic (EMG) activity of the paretic leg, spatiotemporal gait parameters and pelvis lateral displacement were collected.

RESULTS

Significant increases in integrated EMG of hip abductor, medial hamstrings, soleus, rectus femoris, vastus medialis and tibialis anterior were observed when pelvic corrective force was applied, with pelvic corrective force at 9% of body weight inducing greater muscle activity than 3% or 6% of body weight. Pelvis lateral displacement was more symmetric with pelvic corrective force at 9% of body weight.

CONCLUSIONS

Applying a mediolateral pelvic corrective force toward the paretic side may enhance muscle activity of the paretic leg and improve pelvis displacement symmetry in individuals post-stroke.

SIGNIFICANCE

Forceful weight shift to the paretic side could potentially force additional use of the paretic leg and improve the walking pattern.

Recent perspectives of cerebral palsy in children

The movement and posture disorder of cerebral palsy (CP) is presumed to mainly be a consequence of the motor disorder, but accompanying disturbances with sensations and perception have also been suggested to influence motor function. The heterogeneous condition of CP is caused by an injury to the immature brain affecting movement and posture development. The attainment of standing and walking can be difficult and an assistive device to accomplish the tasks may be required for some children with CP. In this review, we enlightened the role of possible sensory and perceptual disturbances for standing difficulties in children with CP.

Effects of knee action phase and fatigue on Rectus Femoris and Biceps Femoris co-activation during the eggbeater kick

The purpose of this study was to investigate the effect of knee extension/flexion and fatigue on muscle co-activation of the Rectus Femoris (RF) and Biceps Femoris (BF) during the eggbeater kick. Ten national level male water polo players executed eggbeater kicks at maximum effort for the duration of the test. The eggbeater kick cycle was divided into four phases (FLX1, FLX2, EXT1, EXT2). Surface electromyographs were recorded from RF and BF. EMG activity normalized to the maximum voluntary isometric contraction, muscle co-activation (CCI) and angular velocity (AV) of the right and left knee were calculated. Highest levels of RCCI and LCCI were observed during final phase of flexion (FLX2) and initial phase of extension (EXT1) (p<0.05). FLX2 and final phase of extension (EXT2) revealed the highest AV during the cycle. A decrease in CCI was observed with fatigue for FLX2 while AV was reduced for all phases. During the cycle RF and BF act as agonist/antagonist to accelerate and decelerate knee flexion/extension. The high AV and low CCI levels observed for EXT2 might increase joint instability and consequent risk of injury. This knowledge provides a better understanding of the mechanisms involved in stabilizing and controlling the knee during underwater movement.

The effect of task-oriented training on the muscle activation of the upper extremity in chronic stroke patients

[Purpose] The aim of this study was to determine the effects of task-oriented training on upper extremity muscle activation in daily activities performed by chronic stoke patients. [Subjects and Methods] In this research, task-oriented training was conducted by 2 chronic hemiplegic stroke patients. Task-oriented training was conducted 5 times a week, 30 minutes per day, for 2 weeks. Evaluation was conducted 3 times before and after the intervention. The Change of muscle activation in the upper extremity was measured using a BTS FreeEMG 300. [Results] The subjects’ root mean square values for agonistic muscles for the reaching activity increased after the intervention. All subjects’ co-coordination ratios decreased after the intervention in all movements of reaching activity. [Conclusion] Through this research, task-oriented training was proven to be effective in improving the muscle activation of the upper extremity in chronic hemiplegic stroke patients.

Antagonist muscle co-activation of limbs in human infant crawling: A pilot study

Muscle Co-activation (MCo) is the simultaneous muscular activation of agonist and antagonist muscle groups, which provides adequate joint stability, movement accuracy during movement. Infant crawling is an important stage of motor function development that manifests non-synchronization growth and development of upper and lower limbs due to the well-known gross motor development principle of head to toe. However, the effect of MCo level for agonist and antagonist muscle groups on motor function development of limbs has not been previously reported. In this paper, sEMG signals were collected from triceps brachii (TB) and biceps brachii (BB), quadriceps femoris (QF) and hamstrings (HS) of limbs when fourteen infants were crawling at their self-selected speed. Antagonist muscle co-activation was evaluated by measuring two common indexes (co-activation index and Pearson's correlation coefficient).A significant difference was observed between upper limbs and lower limbs, but the relationship between MCo and speed of crawling was poor. This study is an opening for further investigation including a longitudinal study and compare against infant with CNS disorders.

The effect of bilateral trainings on upper extremities muscle activation on level of motor function in stroke patients

[Purpose] This study was conducted in order to compare muscle activation level on the affected and unaffected limb according to the recovery level of upper limb between bilateral activity with hands clasped and bilateral activity with pilates ring. [Subjects and Methods] Twenty inpatient who have had a stroke were recruited. Subjects were divided into two groups by the Fugl-Meyer Assessment of Motor Function score of moderately recovered group and well recovered group. The muscles activation of upper extremity and Co-Contraction Ratio (CCR) were analyzed. [Results] In the muscles activation of the well group, trapezius, anterior deltoid, and triceps muscles of affected side and biceps muscles of both sides were significantly higher when activity with pilates ring than activity with hands clasped. CCR of both side in the well group was significantly decreased during activity with pilates ring and in the moderate group, CCR of affected side was significantly decreased during activity with pilates ring. [Conclusion] Bilateral activity with a pilates ring is more effective than activity with hands clasped for the facilitation of muscle activation and coordination in stroke patients.

Quantifying thigh muscle co-activation during isometric knee extension contractions: within- and between-session reliability

Muscle co-activation around the knee is important during ambulation and balance. The wide range of methodological approaches for the quantification of co-activation index (CI) makes comparisons across studies and populations difficult. The present study determined within- and between-session reliability of different methodological approaches for the quantification of the CI of the knee extensor and flexor muscles during maximum voluntary isometric contractions (MVICs). Eight healthy volunteers participated in two repeated testing sessions. A series of knee extension MVICs of the dominant leg with concomitant torque and electromyographic (EMG) recordings were captured. CI was calculated utilizing different analytical approaches. Intraclass correlation coefficient (ICC) showed that within-session measures displayed higher reliability (ICC>0.861) and lower variability (Coefficient of variation; CV<21.8%) than between-session measures (ICC<0.645; CV>24.2%). A selection of a 500ms or larger window of RMS EMG activity around the PT delivered more reliable and less variable results than other approaches. Our findings suggest that the CI can provide a reliable measure for comparisons among conditions and is best utilized for within-session experimental designs.

Reducing Abnormal Muscle Coactivation After Stroke Using a Myoelectric-Computer Interface: A Pilot Study

Background A significant factor in impaired movement caused by stroke is the inability to activate muscles independently. Although the pathophysiology behind this abnormal coactivation is not clear, reducing the coactivation could improve overall arm function. A myoelectric computer interface (MCI), which maps electromyographic signals to cursor movement, could be used as a treatment to help retrain muscle activation patterns. Objective To investigate the use of MCI training to reduce abnormal muscle coactivation in chronic stroke survivors. Methods A total of 5 healthy participants and 5 stroke survivors with hemiparesis participated in multiple sessions of MCI training. The level of arm impairment in stroke survivors was assessed using the upper-extremity portion of the Fugl-Meyer Motor Assessment (FMA-UE). Participants performed isometric activations of up to 5 muscles. Activation of each muscle was mapped to different directions of cursor movement. The MCI specifically targeted 1 pair of muscles in each participant for reduction of coactivation. Results Both healthy participants and stroke survivors learned to reduce abnormal coactivation of the targeted muscles with MCI training. Out of 5 stroke survivors, 3 exhibited objective reduction in arm impairment as well (improvement in FMA-UE of 3 points in each of these patients). Conclusions These results suggest that the MCI was an effective tool in directly retraining muscle activation patterns following stroke.

Lower limb co-contraction during walking in subjects with stroke: A systematic review

PURPOSE

The aim of this paper was to identify and synthesise existing evidence on lower limb muscle co-contraction (MCo) during walking in subjects with stroke.

METHODS

An electronic literature search on Web of Science, PubMed and B-on was conducted. Studies from 1999 to 2012 which analysed lower limb MCo during walking in subjects with stroke, were included.

RESULTS

Eight articles met the inclusion criteria: 3 studied MCo in acute stage of stroke, 3 in the chronic stage and 2 at both stages. Seven were observational and 1 had a pretest-posttest interventional design. The methodological quality was "fair to good" to "high" quality (only 1 study). Different methodologies to assess walking and quantify MCo were used. There is some controversy in MCo results, however subjects with stroke tended towards longer MCo in both lower limbs in both the acute and chronic stages, when compared with healthy controls. A higher level of post-stroke walking ability (speed; level of independence) was correlated with longer thigh MCo in the non-affected limb. One study demonstrated significant improvements in walking ability over time without significant changes in MCo patterns.

CONCLUSIONS

Subjects with stroke commonly present longer MCo during walking, probably in an attempt to improve walking ability. However, to ensure recommendations for clinical practice, further research with standardized methodologies is needed.

Co-contraction patterns of trans-tibial amputee ankle and knee musculature during gait

Background

Myoelectric control of upper extremity powered prostheses has been used clinically for many years, however this approach has not been fully developed for lower extremity prosthetic devices. With the advent of powered lower extremity prosthetic components, the potential role of myoelectric control systems is of increasing importance. An understanding of muscle activation patterns and their relationship to functional ambulation is a vital step in the future development of myoelectric control. Unusual knee muscle co-contractions have been reported in both limbs of trans-tibial amputees. It is currently unknown what differences exist in co-contraction between trans-tibial amputees and controls. This study compares the activation and co-contraction patterns of the ankle and knee musculature of trans-tibial amputees (intact and residual limbs), and able-bodied control subjects during three speeds of gait. It was hypothesized that residual limbs would have greater ankle muscle co-contraction than intact and able-bodied control limbs and that knee muscle co-contraction would be different among all limbs. Lastly it was hypothesized that the extent of muscle co-contraction would increase with walking speed.

Methods

Nine unilateral traumatic trans-tibial amputees and five matched controls participated. Surface electromyography recorded activation from the Tibialis Anterior, Medial Gastrocnemius, Vastus Lateralis and Biceps Femoris of the residual, intact and control limbs. A series of filters were applied to the signal to obtain a linear envelope of the activation patterns. A co-contraction area (ratio of the integrated agonist and antagonist activity) was calculated during specific phases of gait.

Results

Co-contraction of the ankle muscles was greater in the residual limb than in the intact and control limbs during all phases of gait. Knee muscle co-contraction was greater in the residual limb than in the control limb during all phases of gait.

Conclusion

Co-contractions may represent a limb stiffening strategy to enhance stability during phases of initial foot-contact and single limb support. These strategies may be functionally necessary for amputee gait; however, the presence of co-contractions could confound future development of myoelectric controls and should thus be accounted for.

Demonstration of the use of the ICF framework in detailing complex functional deficits after major burn

Burns can result in long term impairments, activity limitations and participation restrictions in a patients' life. The focus of current surgeries and therapy is to improve body functions and structures. However, often this does not translate to an improvement in activity and participation for the patient. Improvement in activity and participation is the ultimate goal of all therapy to enhance patient's quality of life. The incorporation of assessment measures at all levels of the International Classification of Functioning, Disability and Health (ICF) can assist in a holistic, patient centred approach to identify the complex impairments that impact on activity and participation, with a view to appropriately targeting future therapeutic interventions. This paper presents an example case of how implementing measures at all levels of the ICF can improve our understanding of a patient's body functions and structures, activity and participation. A number of the outcome measures utilised in this study are novel in the burns population, such that video footage supplements the methodology where relevant.

Co-activation: its association with weakness and specific neurological pathology

BACKGROUND

Net agonist muscle strength is in part determined by the degree of antagonist co-activation. The level of co-activation might vary in different neurological disorders causing weakness or might vary with agonist strength.

AIM

This study investigated whether antagonist co-activation changed a) with the degree of muscle weakness and b) with the nature of the neurological lesion causing weakness.

METHODS

Measures of isometric quadriceps and hamstrings strength were obtained. Antagonist (hamstring) co-activation during knee extension was calculated as a ratio of hamstrings over quadriceps activity both during an isometric and during a functional sit to stand (STS) task (using kinematics) in groups of patients with extrapyramidal (n = 15), upper motor neuron (UMN) (n = 12), lower motor neuron (LMN) with (n = 18) or without (n = 12) sensory loss, primary muscle or neuromuscular junction disorder (n = 17) and in healthy matched controls (n = 32). Independent t-tests or Mann Witney U tests were used to compare between the groups. Correlations between variables were also investigated.

RESULTS

In healthy subjects mean (SD) co-activation of hamstrings during isometric knee extension was 11.8 (6.2)% and during STS was 20.5 (12.9)%. In patients, co-activation ranged from 7 to 17% during isometric knee extension and 15 to 25% during STS. Only the extrapyramidal group had lower co-activation levels than healthy matched controls (p < 0.05). Agonist isometric muscle strength and co-activation correlated only in muscle disease (r = (-)0.6, p < 0.05) and during STS in UMN disorders (r = (-)0.7, p < 0.5).

CONCLUSION

It is concluded that antagonist co-activation does not systematically vary with the site of neurological pathology when compared to healthy matched controls or, in most patient groups, with strength. The lower co-activation levels found in the extrapyramidal group require confirmation and further investigation. Co-activation may be relevant to individuals with muscle weakness. Within patient serial studies in the presence of changing muscle strength may help to understand these relationships more clearly.