Co-contraction Index Research Articles

EMG Activity of Transversus Abdominis, Multifidus and Co-Contraction Index in Different Phases Amongst Varied Level Archers: A Cross-Sectional Study

Abstract Introduction. Core muscle activity is a necessary requirement in most sports. However, its role in archers has not been studied. Therefore, this study sought to determine muscle activity of Transversus abdominis (TA) and Multifidus (MF) and co-contraction index (CCI) using surface electromyography (s EMG) during different phases of shots in archers with different levels of training. Material and Methods. It was an observational study with a cross-sectional design. Twenty-eight healthy male archers were recruited and grouped according to their level of training: Group A (Beginners (n = 9)), Group B (Trained (n = 10)), Group C (Elite (n = 9)). The muscle activation (%MVIC) for MF and TA for 10 successive archery shots (distance: 10 meters in 200 seconds) was recorded using s EMG for all the phases of the shots along with CCI. Results. Three-way ANOVA revealed a significant difference for TA activity within groups (p ≤ 0.001) and phases (p = 0.002), A significant difference for MF activity was found within groups (p ≤ 0.001). A significant difference for CCI was found between groups (p ≤ 0.001) and in the interaction between phase × shot (p = 0.001). Conclusions. The findings of the study showed that elite archers had more activity of the core muscles (TA and MF) and their CCI was found to be much higher with respect to the trained and beginner archers. Therefore, it is essential to incorporate dynamic stabilization exercises into archery training.

Kinetics, kinematics, and knee muscle activation during sit to stand transition in unilateral and bilateral knee osteoarthritis

BackgroundThe sit to stand transition (STS) is a task performed by those with knee osteoarthritis (KOA) with biomechanical modifications that may influence the lower limb load distribution. As a weight bearing task mainly performed in the sagittal plane, the presence of unilateral or bilateral KOA may lead to asymmetry during its performance. Research questionAre the biomechanical and neuromuscular aspects of the sit to stand transition (STS) different between participants with unilateral and bilateral KOA? MethodsTwenty-eight participants were allocated as follows: unilateral KOA (OAUNI; n = 12) and bilateral KOA (OABI; n = 16). All participants were evaluated by means of kinematics (Qualisys Motion Capture System, Qualisys Medical AB, SUE), kinetics (Bertec Corporation's model 4060−08 Mod., USA), and electromyography (TrignoTM Wireless System, DelSys Inc., USA) during the STS. The variables calculated were the symmetry indices of the total support moment (TSM) and ground reaction force (ISGRF and ISTSM, respectively), magnitude of the TSM, individual joint contribution to the TSM, peak trunk flexion, hip, knee, and ankle range of motion, duration in seconds, the magnitudes of activation of the extensor and flexor muscles, knee extensors: flexor co-contraction indices and isometric knee extensor peak torques. Participants also answered the WOMAC questionnaire and performed the 30-second STS test (STS30). ResultsThe OABI got up from a chair with a lower TSM magnitude in the most affected limb (p = 0.040), used greater trunk flexion amplitude (p ≤ 0.034), and presented lower isometric KET (p = 0.039) and worse self-reported pain (p = 0.011) and physical function (p = 0.015). SignificanceParticipants with unilateral and bilateral KOA differ regarding lower limb kinetics and trunk kinematics while getting up from a chair, without modification in the lower limb intersegmental coordination or symmetry regarding ground reaction force or TSM distribution.

Individuals with chronic ankle instability exhibit altered ankle kinematics and neuromuscular control compared to copers during inversion single-leg landing

ObjectivesThis study compares the ankle kinematics and muscle activities of the individuals with chronic ankle instability (CAI), coper, and control groups in normal and inversion single-leg landings. Designcross-sectional study; SettingBiomechanics laboratory. ParticipantsPhysically active adults with CAI (N = 12); and coper (N = 12) and control (N = 12) groups. Main outcome measuresThe participants performed normal and inversion single-leg landing. The muscle activity 200 ms before and after landing of the tibialis anterior, the medial gastrocnemius, and the fibularis longus (FL) were recorded. The FL latency, sagittal and frontal co-contraction indexes (CCI), ankle inversion angle at the initial contact, and the maximum inversion angle were recorded. ResultsSignificantly longer FL latency, decreased FL muscle activity, frontal CCI, and an increased maximum inversion angle at post-landing were discovered during inversion single-leg landing in the CAI group compared to the coper and control groups. However, no significant difference was observed among the CAI and coper groups during normal single-leg landing. ConclusionThese results suggest prolonged FL latency and altered ankle kinematics suggest an increased risk of recurrent lateral ankle sprains in CAI with inversion single-leg landing.

No difference in knee muscle activation and kinematics during treadmill walking between adolescent girls with and without asymptomatic Generalised Joint Hypermobility

BackgroundAltered knee muscle activity in children with asymptomatic Generalized Joint Hypermobility (GJH) is reported during isometric contraction, static and dynamic balance tasks and jumping, but has not been studied during gait. Therefore, the aim was to investigate group differences in knee muscle activity simultaneously with knee joint kinematics during treadmill walking between children with and without GJH.MethodsGirls 14–15 years of age with GJH (inclusion criteria: Beighton score ≥6 of 9 and positive hyperextension ≥10° (one/both knees)) and a matched control group without GJH (inclusion criteria: Beighton score ≤5 and no knee hyperextension ≥10° ) were recruited. In total 16 participants with GJH and 10 non-GJH participants were included in the study.Surface electromyography (sEMG) was measured from the quadriceps, hamstrings and gastrocnemius muscles of the dominant leg during treadmill walking. Maximal voluntary isometric contractions while sitting were used for normalisation of sEMG to % of Maximum Voluntary EMG (%MVE). Knee joint angles during treadmill walking were measured by electrogoniometer. Furthermore, co-contraction index (CCI) was calculated, and presented for muscle groups of hamstrings-quadriceps (HQ) and gastrocnemius-quadriceps (GQ). CCI of medial and lateral sides of the knee, including ratio of the medial and lateral CCI for HQ and GQ were calculated.ResultsNo group differences were found in demographics, muscle activation level, nor CCI and CCI ratios. However, participants with GJH displayed significantly decreased knee joint angle, mean (153º vs. 156º; p =0.03) and minimum (105º vs. 111º; p=0.01), during treadmill walking compared with controls.ConclusionMuscle activity during gait was not different between participants with GJH and non-GJH participants. However, participants with GJH displayed minor but statistically significant increased knee flexion during gait. Since the clinical consequences of increased knee joint flexion during gait are unknown, future studies should follow a larger cohort longitudinally during overground walking for development of clinical complications in this group.

Copers adopt an altered movement pattern compared to individuals with chronic ankle instability and control groups in unexpected single-leg landing and cutting task

Individuals with chronic ankle instability (CAI) demonstrate altered ankle kinematics during landing compared to uninjured individuals. However, if copers may have adopted unique movement strategy to prevent repeated ankle sprains is unclear. The purpose of this study compares the lower-extremity joint kinematics and muscle activities of CAI (N = 8), coper (COP) (N = 8), and control (CON) (N = 8) groups in unexpected single-leg landing and cutting. Performance time (from initial contact to toe-off), number of mistakes in the jumping direction, low-extremity joint angle are assessed. Muscle activities were recorded from the tibialis anterior, medial gastrocnemius, and peroneus longus (PL), and mean muscle activity, co-contraction index (CI), and PL latency were analyzed. Results of performance time and CI are not significant. Significantly less number of mistakes in the jumping direction and a shorter PL latency were discovered in the COP and CON compared with the CAI group (P < 0.05). The peak hip joint flexion angle is significantly smaller in the COP than in the CON (P = 0.04). In dynamic tasks requiring quick judgments of ankle inclination, the COP may be able to accurately sense the inclination of the foot. Additionally, movement strategies differed between the COP and CON groups in an unexpected single-leg landing and cutting.

Tai Chi training's effect on lower extremity muscle co-contraction during single- and dual-task gait: Cross-sectional and randomized trial studies.

BackgroundTai Chi (TC) mind-body exercise has been shown to reduce falls and improve balance and gait, however, few studies have evaluated the role of lower extremity muscle activation patterns in the observed benefits of TC on mobility.PurposeTo perform an exploratory analysis of the association between TC training and levels of lower extremity muscle co-contraction in healthy adults during walking under single-task (ST) and cognitive dual-task (DT) conditions.MethodsSurface electromyography of the anterior tibialis and lateral gastrocnemius muscles was recorded during 90 sec trials of overground ST (walking normally) and DT (walking with verbalized serial subtractions) walking. A mean co-contraction index (CCI), across all strides, was calculated based on the percentage of total muscle activity when antagonist muscles were simultaneously activated. A hybrid study design investigated long-term effects of TC via a cross-sectional comparison of 27 TC experts and 60 age-matched TC-naïve older adults. A longitudinal comparison assessed the shorter-term effects of TC; TC-naïve participants were randomly allocated to either 6 months of TC training or to usual care.ResultsAcross all participants at baseline, greater CCI was correlated with slower gait speed under DT (β(95% CI) = -26.1(-48.6, -3.7)) but not ST (β(95% CI) = -15.4(-38.2, 7.4)) walking. Linear models adjusting for age, gender, BMI and other factors that differed at baseline indicated that TC experts exhibited lower CCI compared to TC naives under DT, but not ST conditions (ST: mean difference (95% CI) = -7.1(-15.2, 0.97); DT: mean difference (95% CI) = -10.1(-18.1, -2.4)). No differences were observed in CCI for TC-naive adults randomly assigned to 6 months of TC vs. usual care.ConclusionLower extremity muscle co-contraction may play a role in the observed benefit of longer-term TC training on gait and postural control. Longer-duration and adequately powered randomized trials are needed to evaluate the effect of TC on neuromuscular coordination and its impact on postural control.Trial registrationThe randomized trial component of this study was registered at ClinicalTrials.gov (NCT01340365).

How Well Do Commonly Used Co-contraction Indices Approximate Lower Limb Joint Stiffness Trends During Gait for Individuals Post-stroke?

Muscle co-contraction generates joint stiffness to improve stability and accuracy during limb movement but at the expense of higher energetic cost. However, quantification of joint stiffness is difficult using either experimental or computational means. In contrast, quantification of muscle co-contraction using an EMG-based Co-Contraction Index (CCI) is easier and may offer an alternative for estimating joint stiffness. This study investigated the feasibility of using two common CCIs to approximate lower limb joint stiffness trends during gait. Calibrated EMG-driven lower extremity musculoskeletal models constructed for two individuals post-stroke were used to generate the quantities required for CCI calculations and model-based estimation of joint stiffness. CCIs were calculated for various combinations of antagonist muscle pairs based on two common CCI formulations: Rudolph et al. (2000) (CCI1) and Falconer and Winter (1985) (CCI2). CCI1 measures antagonist muscle activation relative to not only total activation of agonist plus antagonist muscles but also agonist muscle activation, while CCI2 measures antagonist muscle activation relative to only total muscle activation. We computed the correlation between these two CCIs and model-based estimates of sagittal plane joint stiffness for the hip, knee, and ankle of both legs. Although we observed moderate to strong correlations between some CCI formulations and corresponding joint stiffness, these associations were highly dependent on the methodological choices made for CCI computation. Specifically, we found that: (1) CCI1 was generally more correlated with joint stiffness than was CCI2, (2) CCI calculation using EMG signals with calibrated electromechanical delay generally yielded the best correlations with joint stiffness, and (3) choice of antagonist muscle pairs significantly influenced CCI correlation with joint stiffness. By providing guidance on how methodological choices influence CCI correlation with joint stiffness trends, this study may facilitate a simpler alternate approach for studying joint stiffness during human movement.

Muscle co-contraction of ankle joint in young adults in functional reach test at different distances

It has been reported that young people may be able to modulate simultaneous contraction depending on the task. The functional reach test (FRT) is widely used as a method to assess dynamic balance. Although there are several reports on the center of pressure (COP), there are few reports on muscle activity and no studies focus on muscle co-contraction during FRT at different distances. We aimed to clarify how the differences in reach distance affect the activity of the lower limb muscles by measuring COP and muscle activity during FRT at different distances. Eighteen healthy young adults performed FRT at different distances (maximum, 75%, and 50%) and measured COP and muscle activity of tibialis anterior (TA) and soleus (SOL). Postural control variables were calculated from the COP, and mean muscle activity and muscle co-contraction index (CI) were calculated from muscle activity. Each variable was compared between the reach distance conditions and the correlation between the variable was examined. Most COP variables were significantly higher as the reach distance increased. A significant increase in muscle activity and CI was similarly observed with increasing distance. There was no consistent correlation between COP variables and CI, but there was a positive correlation between TA muscle activity and CI. The results of the present study showed that the young people used task-specific strategies by modulating lower limb muscle contraction and varying the degree of simultaneous muscle contraction during reaching movements at different distances.

Human-Inspired Control of Dual-Arm Exoskeleton Robots With Force and Impedance Adaptation

Humans can adapt to complex environments by voluntarily adjusting the impedance parameters and interaction force. Traditional robots perform tasks independently without considering their interactions with the external environment, which leads to poor flexibility and adaptability. Comparatively, humans can adapt to complex environments by voluntarily adjusting the impedance parameters and interaction force. In order to solve the problems of human–robot security and adaptability to unknown environment, a human-inspired control with force and impedance adaptation is proposed to interact with unknown environments and exhibit this biological behavior on the developed dual-arm exoskeleton robots. First, we propose a computationally model utilizing the sampled surface electromyogram (sEMG) signals to calculate the human arm endpoint stiffness and define a co-contraction index to describe the dynamic behaviors of the muscular activities in the tasks. Then, the obtained human limb impedance stiffness parameters and the sampling position information are transferred to the slave arm of the exoskeleton as the input variables of the controller in real-time. In addition, a variable stiffness observer is used here to compensate for the errors of the calculated stiffness by sEMG signals. The experimental studies of human impedance transfer control have been conducted to show the effectiveness of the developed approach. Results of the experimental suggest that the proposed controller can achieve human motor adaptation and enable the subjects to execute a skill transfer control by a dual-arm exoskeleton robot.

Neuromuscular function in anterior cruciate ligament reconstructed patients at long-term follow-up

BackgroundThe permanence of neuromuscular adaptations following anterior cruciate ligament reconstruction is not known. The aim of this study was to compare bilateral muscle co-contraction indices, time to peak ground reaction force, and timing of muscle onset between anterior cruciate ligament reconstruction subjects 10–15 years post reconstruction with those of matched uninjured controls during a one-leg hop landing. MethodsNine healthy controls and 9 reconstruction subjects were recruited. Clinical and functional knee exams were administered. Lower limb co-contraction indices, time to peak ground reaction force, and muscle onset times were measured bilaterally. Differences in clinical and functional outcomes were assessed with unpaired t-tests, and mixed model repeated measures were used to examine effects of group, limb and interaction terms in electromyography measures. Findings89% of control knees were clinically “normal”, whereas only 33% of reconstructed knees were “normal”. Anterior cruciate ligament-reconstructed subjects tended to achieve shorter functional hop distances but demonstrated symmetrical lower limb electromyography measures that were no different from those of controls' with the exception that biceps femoris activation was delayed bilaterally prior to ground contact but was greater during the injury risk phase of landing. InterpretationWith the exception of hamstring activation, lower limb electromyography measures were largely similar between ligament-reconstructed and matched control subjects, which was in contrast to the clinical findings. This result brings into question the significance of neuromuscular function at this long-term follow-up but raises new questions regarding the role of symmetry and pre-injury risk.

Fear Priming: A Method for Examining Postural Strategies Associated With Fear of Falling.

Fear of falling influences postural strategies used for balance, and is key in the maintenance of independent living and quality of life as adults age. However, there is a distinct need for methodology that aims to specifically address and prime fear under dynamic conditions, and to better determine the role of fear in movement preparation. This preliminary study investigated how fear priming influences fear of falling in young and older individuals, and assessed how changes in fear of falling map to movement behavior. Young (21.5 ± 1.7 years, n = 10) and older (58.1 ± 2.2 years) participants matched for height, weight, and sex were repeatedly exposed to four different and incrementally challenging laboratory-based slipping perturbations during a self-initiated, goal-directed step and reach task. Both younger and older cohorts showed similar heightened perceptions in fear of falling after fear priming, and changes in peak joint excursions including reduced ankle flexion, and increased lumbar flexion after fear priming. Age-related changes were only evident in total mediolateral center of mass displacement, with younger participants showing greater displacement after fear priming. Despite clear differences in preparatory muscle onsets relative to reach onset seen in older participants, muscle timings or co-contraction indices were not significantly different. Methods utilizing repeated exposure to varying increases of a slip-based postural challenge can successfully prime fear of falling in individuals, regardless of age.

Effects of Optimization Technique on Simulated Muscle Activations and Forces.

Two optimization techniques, static optimization (SO) and computed muscle control (CMC), are often used in OpenSim to estimate the muscle activations and forces responsible for movement. Although differences between SO and CMC muscle function have been reported, the accuracy of each technique and the combined effect of optimization and model choice on simulated muscle function is unclear. The purpose of this study was to quantitatively compare the SO and CMC estimates of muscle activations and forces during gait with the experimental data in the Gait2392 and Full Body Running models. In OpenSim (version 3.1), muscle function during gait was estimated using SO and CMC in 6 subjects in each model and validated against experimental muscle activations and joint torques. Experimental and simulated activation agreement was sensitive to optimization technique for the soleus and tibialis anterior. Knee extension torque error was greater with CMC than SO. Muscle forces, activations, and co-contraction indices tended to be higher with CMC and more sensitive to model choice. CMC's inclusion of passive muscle forces, muscle activation-contraction dynamics, and a proportional-derivative controller to track kinematics contributes to these differences. Model and optimization technique choices should be validated using experimental activations collected simultaneously with the data used to generate the simulation.

A Proposal for Lower-Extremity Rehabilitation Based on Preliminary Observation on the Abnormal Co-contraction Patterns of Ankle Muscles in Post-stroke Patients

Purpose: This study was aimed to investigate the differences in the co-contraction index of ankle muscles’ activities and proposed the rehabilitation methods in terms of special physical education based on the clinical findings. Methods: A total of ten participants (5 stroke patients and 5 normal adults) were participated in this study. Their two ankle muscles (tibialis anterior and gastrocnemius muscles) were measured by electromyography (EMG) during the gait cycle and then, the muscle activities were calculated as a co-contraction index (CCI). Finally, the indexes between stroke patients and normal adults were compared. Results: As a result, CCI during the stance phase in the gait cycle was significantly higher in stroke patients than normal adults (p=.047). In addition, each group showed a significant difference in CCI between the stance and swing phase through within-group analysis (p=.043). Conclusion: In this study, stroke patients showed a higher CCI during the gait cycle, especially, in the stance phase. In conclusion, when considering the higher CCI would provide double-sidedness; 1) a demerit is the higher CCI would decrease in the mobility of ankle joint, whereas, 2) a merit is to increase in the stability of the ankle joint to protect fall-down, I proposed that as a lower-extremity rehabilitation method, sports activity, and aerobic exercise, using an online virtual reality technology will be necessary to ensure the safety of sports game as well as the enjoyment to maximize the quality of post-stroke life. Therefore, professionals in the field of special physical education should actively enlarge their education and development skills to the field of new biotechnology.

Rhythmic Auditory Stimulation as an Adjuvant Therapy Improved Post-stroke Motor Functions of the Upper Extremity: A Randomized Controlled Pilot Study.

ObjectivesTo explore whether rhythmic auditory stimulation (RAS) could improve motor functions of post-stroke hemiparetic upper extremity.DesignA prospective, randomized controlled, assessor-blinded pilot study.MethodsThirty stroke patients were randomly distributed into the RAS group (n = 15) and the control group (n = 15). Both groups received regular therapies. The RAS group received additional 30 min of RAS training, while the control group received additional 30 min of regular therapies for 5 days per week for 4 weeks. The Fugl-Meyer Assessment—Upper Extremity (FMA-UE), Wolf Motor Function Test (WMFT), and Barthel Index (BI) were used. The co-activation interval and co-contraction index were calculated from surface electromyography (sEMG) recordings on the affected biceps and triceps during elbow flexion and extension. Assessments were performed before and after the treatments.ResultsSignificant improvements in motor functions were observed within both groups (p < 0.05 in the FMA-UE, WMFT, and BI, respectively), as well as between groups after the treatments (higher scores in the RAS group, all p < 0.05 except for p = 0.052 in the FMA-UE; group × time interaction, all p < 0.05). Statistical significance was found in the co-activation interval between groups after the treatments (lower in the RAS group; p = 0.022 during elbow extension; p = 0.001 during elbow flexion; group × time interaction, p < 0.05 only during elbow extension). No statistical significance was found in the co-contraction index between groups; an inversed pattern of changes was observed between groups supported by relatively higher increments in the triceps recruitments to the biceps.ConclusionUsing RAS in task-oriented exercises was effective in moderating co-contraction, facilitating task-oriented movements of the hemiparetic upper extremity, and improving ADLs among those who had emerging isolated joint movements. The effects were evident on sEMG possibly by adjusting the balance of recruitments between the agonist and the antagonist.Clinical Trial RegistrationThe study was registered at the Chinese Clinical Trial Registry (No. 1900026665).

Immediate effects of using insoles with various wedges on activation and co-contraction indices of selected trunk muscles during load lifting

Trunk muscles play an important role during load lifting and contract to control trunk stability. The aim of present study was to investigate immediate effects of using various insole wedges on activation and co-contraction indices of selected trunk muscles during load lifting. Thirty able-bodied males completed load lifting task using nine various insole wedges. The results showed these significant differences: for normalized mean amplitude of RA muscle between posterior and anterior-medial wedges and for QL muscle between posterior and lateral wedges, for normalized peak amplitude of RA muscle between posterior and anterior-medial wedges, for median frequency of LES muscle between anterior-medial and anterior-lateral wedges, and for co-contraction of RA/TES, RA/LES and RA/MU between posterior and anterior-medial wedges (P = 0.001). These findings should be considered during designation of shoe or insole for work environments. Future studies need to assess other biomechanical aspects of using various insole wedges during work-related tasks.

The Effects of Augmented Somatosensory Feedback on Postural Sway and Muscle Co-contraction in Different Sensory Conditions

Background: Augmented somatosensory feedback stimulates the mechanoreceptor to deliver information on bodily position, improving the postural control. The various types of such feedback include ankle-foot orthoses (AFOs) and vibration. The optimal feedback to mitigate postural sway remains unclear, as does the effect of augmented somatosensory feedback on muscle co-contraction. Objects: We compared postural sway and ankle muscle co-contraction without feedback (control) and with either of two forms of somatosensory feedback (AFOs and vibration). Methods: We recruited 15 healthy subjects and tested them under three feedback conditions (control, AFOs, vibration) with two sensory conditions (eyes open, or eyes closed and the head tilted back), in random order. Postural sway was measured using a force platform; the mean sway area of the 95% confidence ellipse (AREA) and the mean velocity of the center-of-pressure displacement (VEL) were assessed. Co-contraction of the tibialis anterior and gastrocnemius muscles was measured using electromyography and converted into a cocontraction index (CI). Results: We found significant main effects of the three feedback states on postural sway (AREA, VEL) and the CI. The two sensory conditions exerted significant main effects on postural sway (AREA and VEL). AFOs reduced postural sway to a level significantly lower than that of the control (p = 0.014, p < 0.001) or that afforded by vibration (p = 0.024, p < 0.001). In terms of CI amelioration, the AFOs condition was significantly better than the control (p = 0.004). Vibration did not significantly improve either postural sway or the CI compared to the control condition. There was no significant interaction effect between the three feedback conditions and the two sensory conditions. Conclusion: Lower-extremity devices such as AFOs enhance somatosensory perception, improving postural control and decreasing the CI during static standing.

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

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

Individuals with mild-to-moderate hip osteoarthritis walk with lower hip joint contact forces despite higher levels of muscle co-contraction compared to healthy individuals

To compare hip joint contact forces (HJCF), hip muscle forces, and hip muscle co-contraction levels between individuals with mild-to-moderate hip osteoarthritis (OA) and healthy controls during walking. Eighteen participants with mild-to-moderate hip OA and 23 healthy controls walked at a self-selected speed while motion capture and electromyographic data were synchronously collected. HJCF were computed using a calibrated electromyography-informed neuromusculoskeletal model. Hip joint contact forces, muscle forces, and co-contraction indices for flexor/extensor and adductor/abductor muscle groups were compared between groups using independent sample t-tests (P<0.05). There was no between-group difference in self-selected walking speed. On average, participants with hip OA walked with 11% lower first peak (mean difference 235 [95% confidence interval (CI) 57-413] N) and 22% lower second peak (mean difference 574 [95%CI 304-844] N) HJCF compared to controls. Hip muscle forces were also significantly lower in the hip OA compared to control group at first (mean difference 224 [95%CI 66-382] N) and second (mean difference 782 [95%CI 399-1164] N) peak HJCF. Participants with hip OA exhibited higher levels of hip muscle co-contraction in both flexor/extensor and adductor/abductor muscle groups. Consistent with existing literature, hip joint angles (extension, adduction) and external moments (flexion, extension, adduction) were lower in hip OA compared to controls. Lower HJCF were detected in mild-to-moderate hip OA, primarily due to lower hip muscle force production, and despite higher levels of hip muscle co-contraction. Findings suggest that lower loading of the hip joint during walking is a feature of mild-to-moderate hip OA, which could have implications for the pathogenesis of hip OA and/or disease progression.

Military-Type Workload and Footwear Alter Lower Extremity Muscle Activity During Unilateral Static Balance: Implications for Tactical Athletic Footwear Design.

Maintaining upright standing balance is critical for military personal. The impact of military footwear and occupation-related fatigue on muscle activity during balance performance has been previously documented. However, the current literature has not provided a muscle activation profile of the lower extremity during challenging conditions such as unilateral balance trials. Twenty-two recreationally active male participants (age: 22.2 ± 2.7 years; height: 177 ± 6.8 cm; mass: 79.8 ± 9.7 kg) donned two styles of military footwear (minimalist and standard) and performed a military style workload. Unilateral static balance was accessed before (PRE) and after (POST) the workload as surface electromyography was recorded on the right lower extremity. This study found that the minimalist footwear increased muscle activation prior to the workload compared to the standard footwear (co-contraction index mean difference: 0.149), whereas the standard footwear increased muscle activity after the workload (co-contraction index mean difference: 0.097). These findings suggest that footwear design characteristics affect lower extremity muscle activity differently depending on the workload condition. These findings intend to aid in the design of military footwear to maximize balance performance in a military population.

Impact of the EMG normalization method on muscle activation and the antagonist-agonist co-contraction index during active elbow extension: Practical implications for post-stroke subjects

Electromyographic (EMG) raw signals are sensitive to intrinsic and extrinsic factors. Consequently, EMG normalization is required to draw proper interpretations of standardized data. Specific recommendations are needed regarding a relevant EMG normalization method for participants who show atypical EMG patterns, such as post-stroke subjects. This study compared three EMG normalization methods (“isometric MVC”, “isokinetic MVC”, “isokinetic MVC kinematic-related”) on muscle activations and the antagonist-agonist co-contraction index. Fifteen post-stroke subjects and fifteen healthy controls performed active elbow extensions, followed by isometric and isokinetic maximum voluntary contractions (MVC). Muscle activations were obtained by normalizing EMG envelopes during active movement using a reference value determined for each EMG normalization method. The results showed no significant difference between the three EMG normalization methods in post-stroke subjects on muscle activation and the antagonist-agonist co-contraction index. We highlighted that the antagonist-agonist co-contraction index could underestimate the antagonist co-contraction in the presence of atypical EMG patterns. Based on its practicality and feasibility, we recommend the use of isometric MVC as a relevant procedure for EMG normalization in post-stroke subjects. We suggest combined analysis of the antagonist-agonist co-contraction index and agonist and antagonist activations to properly investigate antagonist co-contraction in the presence of atypical EMG patterns during movement.