Co-contraction Index Research Articles

Effects of concurrent physical and mental demands for a short duration static task

The purpose of this study was to quantify the effects of concurrent physical and mental demands on the upper extremity muscle activity during static exertions. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensity (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task (Stroop color word test). Muscular responses were quantified using surface electromyography (EMG) and motor performance was measured through force fluctuations. Subjective assessments were obtained through the NASA-TLX tool and the Borg CR-10 Scale. In general, a decrease in mean anterior and posterior deltoid muscle activity and co-contraction index (CCI) of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher physical exertion levels compared to the lower levels. Furthermore, the additional mental task resulted in decreased upper and lower arm muscle activity, specifically at the 45% MVC level. Motor performance improved at the middle exertion levels, but was adversely affected by the mental task at higher exertion levels. Decreased motor performance at higher loads may have been a result of decreased muscular effort to maintain the loads in a steady posture. Both mental and physical demand adversely affected the NASA-TLX ratings, however, ratings using the Borg CR-10 Scale were only sensitive to changes in physical demand. Relevance to industry Workplace tasks, such as jobs performed by healthcare workers, assembly line workers, and computer operators, have become more multidimensional in the recent years; with workers experiencing combined physical and mental demands in their daily jobs, yet their effect on muscular responses is not clearly understood. Results from this study suggest that certain physical exertion levels are more susceptible to interference by mental demands than others.

Dynamic Ankle Control in Athletes With Ankle Instability During Sports Maneuvers

Background: Ankle sprain is a common sports injury. While the effects of static constraints in stabilizing the ankle joint are relatively well understood, those of dynamic constraints are less clear and require further investigation. Purpose: This study was undertaken to evaluate the dynamic stability of the ankle joint during the landing phase of running and stop-jump maneuvers in athletes with and without chronic ankle instability (CAI). Study Design: Controlled laboratory study. Methods: Fifteen athletes with CAI and 15 age-matched athletes without CAI performed running and stop-jump landing tasks. The dynamic ankle joint stiffness, tibialis anterior (TA)/peroneus longus (PL) and TA/gastrocnemius lateralis (GL) co-contraction indices, ankle joint angle, and root-mean-square (RMS) of the TA, PL, and GL electromyographic signals were measured during each task. Results: During running, the CAI group exhibited a greater ankle inversion angle than the control group in the pre-landing phase (P = .012-.042) and a lower dynamic ankle joint stiffness in the post-landing phase (CAI: 0.109 ± 0.039 N·m/deg; control: 0.150 ± 0.068 N·m/deg; P = .048). In the stop-jump landing task, athletes with CAI had a significantly lower TA/PL co-contraction index during the pre-landing phase (CAI: 49.1 ± 19; control: 64.8 ± 16; P = .009). In addition, the CAI group exhibited a greater ankle inversion (P = .049), a lower peak eversion (P = .04), and a smaller RMS of the PL electromyographic signal in the post-landing phase (CAI: 0.73 ± 0.32; control: 0.51 ± 0.22; P = .04). Conclusion: Athletes with CAI had a relatively inverted ankle, reduced muscle co-contraction, and a lower dynamic stiffness in the ankle joint during the landing phase of sports maneuvers and this may jeopardize the stability of the ankle. Clinical Relevance: Sports training or rehabilitation programs should differentiate between the pre-landing and post-landing phases of sports maneuvers, and should educate athletes to land with an appropriate ankle position and muscle recruitment.

Comparison of Moist Heat and Magnetic Therapy on Ultrasound Changes in the Loin Area of Adult Horses

This study aimed to compare muscle activations, co-contraction indices, and the knee adduction moment between static standing yoga postures to identify appropriate exercises for knee osteoarthritis.Healthy young women (24.4 (5.4) years, 23.1 (3.7) kg/m2) participated. Primary outcome variables were electromyographic activations of the vastus lateralis, rectus femoris, vastus medialis, biceps femoris, and semitendinosus; co-contraction between the biceps femoris and rectus femoris, and vastus lateralis and vastus medialis; and knee adduction moments of both legs during six static, standing yoga postures (two squatting postures, two lunging postures, a hamstring stretch, and a single-leg balance posture). A two-factor repeated measures analysis of variance was used to identify differences in muscle amplitudes, co-contractions, and knee adduction moment between postures and legs.Quadriceps activations were highest during squat and lunge postures (p ≤ 0.001). Hamstring activations were highest during the hamstring stretch (p ≤ 0.003). Squat and lunge postures produced higher co-contraction indices than other postures (p ≤ 0.011). The wide legged squat (Goddess) and lunge with trunk upright (Warrior) produced the lowest knee adduction moments (p ≤ 0.006), while the single-leg balance posture elicited a higher knee adduction moment than all other postures (p < 0.05).Squatting and lunging postures could improve leg strength while potentially minimizing exposure to high knee adduction moments. Future work should evaluate whether these exercises are useful in people with knee osteoarthritis.

Age-related changes in optimality and motor variability: an example of multifinger redundant tasks

We used two methods, analytical inverse optimization (ANIO) and uncontrolled manifold (UCM) analysis of synergies, to explore age-related changes in finger coordination during accurate force and moment of force production tasks. The two methods address two aspects of the control of redundant systems: Finding an optimal solution (an optimal sharing pattern) and using variable solutions across trials (covarying finger forces) that are equally able to solve the task. Young and elderly subjects produced accurate combinations of total force and moment by pressing with the four fingers of the dominant hand on individual force sensors. In session-1, single trials covered a broad range of force-moment combinations. Principal component (PC) analysis showed that the first two PCs explained about 90% and 75% of finger force variance for the young and elderly groups, respectively. The magnitudes of the loading coefficients in the PCs suggested that the young subjects used mechanical advantage to produce moment while elderly subjects did not (confirmed by analysis of moments produced by individual digits). A co-contraction index was computed reflecting the magnitude of moment produced by fingers acting against the required direction of the total moment. This index was significantly higher in the young group. The ANIO approach yielded a quadratic cost function with linear terms. In the elderly group, the contribution of the forces produced by the middle and ring fingers to the cost function value was much smaller than in the young group. The angle between the plane of experimental observations and the plane of optimal solutions (D-angle), was very small (about 1.5°) in the young group and significantly larger (about 5°) in the elderly group. In session-2, four force-moment combinations were used with multiple trials at each. Covariation among finger forces (multifinger synergies) stabilizing total force, total moment, and both was seen in both groups with larger synergy indices in the young group. Multiple regression analysis has shown that, at higher force magnitudes, the synergy indices defined with the UCM method were significantly related to the percent of variance accounted by the first two PCs and to the D-angle computed using the ANIO method. We interpret the results as pointing at a transition with age from synergic control to element-based control (back-to-elements hypothesis). Optimization and analysis of synergies are complementary approaches that focus on two aspects of multidigit coordination, sharing and covariation, respectively.

Study of lower extremity muscle function in stroke patients by velocity-encoded phase-contrast magnetic resonance imaging

To compare the difference of muscle dynamic characteristics for the ankle dorsiflexors and plantarflexors between stroke patients at the chronic stage and healthy controls so as to provide a new method of assessing the in vivo muscle function in patients with hemiplegia. From May 2008 to May 2009, 26 stroke patients and 21 age-and gender-matched normal controls were recruited. All subjects were positioned on a scanner table and requested to perform the voluntary movement of ankle flexion-extension. The velocity encoded phase contrast magnetic resonance imaging (VE-PC MRI) provided the images of tibialis anterior muscle (TA), medial head of gastrocnemius muscle (MG) and soleus muscle (SOL) during a movement cycle. By measuring the calf muscle contraction velocity, the balance function was assessed by Berg balance scale (BBS). The correlation between scores of BBS and the mean maximum velocity were compared and analyzed. The peak velocity of TA (1 - 8 phase, 8.900 - 21.120 mm/s vs 12.99 - 34.50 mm/s), MG (12-19phase, 13.60 - 13.28 mm/s vs 25.85 - 18.38 mm/s) and SOL (12 - 16 phase, 18.63 - 33.62 mm/s vs 27.68 - 47.22 mm/s) was lower in the affected side than that in the controls during ankle extension (P < 0.05); During ankle dorsiflexion, the co-contraction index of SOL/TA (2 - 9 phase, 0.81 - 0.82 vs 0.27 - 0.44) and the co-contraction index of GM/TA (2 - 9 phase, 0.73 - 0.58 vs 0.10 - 0.11) was markedly higher in the affected side than the controls. The patient score of BBS was negatively correlated with the mean velocity of TA (r = -0.69, P = 0.001) and GM (r = -0.47, P = 0.01) in the affected side. There was correlation between TA (r = -0.60, P = 0.001) and GM (r = -0.49, P = 0.01) in the unaffected side. During the movement of active ankle flexion-extension, the velocities of TA, SOL and MG are lower in the affected side. The co-contraction index is markedly higher in the affected side during ankle dorsiflexion. This in turn leads to a decline of balance function in patients. VE-PC MRI can provide quantitative in vivo measurements of lower extremity muscle function in stroke patients.

ボールバウンシング課題の速度増加局面における動作特性の変容

The present study aimed to examine the difference in upper limb movement characteristics between basketball players and novices during the speed-increase phase in a basketball bouncing task. Two-dimensional video analysis and electromyography were used to clarify the motor control with increase in bouncing speed. The participants were 9 college basketball players and 6 novice subjects. The basketball players had approximately 10 years of experience in playing basketball and were now in training for approximately 5 days per week in their college basketball team. The novices had learned how to play basketball in their physical education class, but the ball bouncing movement was not a familiar task for them. The subjects were instructed to synchronize their movement with an external audio signal (100 bpm), and to change the bouncing speed as quickly as possible when a LED signal was lighted. During the bouncing task, two-dimensional body kinematics (joint angular displacements) were measured using a high-speed camera at 100 frames/s. Electromyographic changes were measured by surface electromyograms (EMGs) obtained at the shoulder, elbow, and wrist muscles; the co-contraction index (CI) was calculated on the basis of the activities of the flexor and extensor muscles of each joint. We found that the amplitude of angular displacement in the elbow and wrist joints was greater in the basketball players than in the novices. In each group, EMG activities, especially those of the elbow and wrist muscles, showed different changes with increased bouncing speed. In the speed-increase phase, the wrist muscles CI in the basketball players was less than that in the novices. The results of this study indicate that basketball players bounce the ball with a greater range of motion and less joint stiffness. In contrast, novices have a more restricted range of motion and higher co-contraction in the speed-increase phase. Thus it appears that basketball players can control a ball with a longer ball contact time and lower co-contraction, and can produce a more effective bouncing movement in the speed-increase phase.

Lower Extremity Muscle Activation Changes Following a Standard 6-week Neuromuscular Training Program

Sex-dimorphic neuromuscular control patterns evident during landings are proposed to increase female anterior cruciate ligament (ACL) injury risk compared to males. Training programs aimed at modifying these high-risk patterns have been demonstrated to be an effective intervention for reducing ACL injury rates. It is unclear, however, how such programs lead explicitly to fewer ACL injuries. We propose that females adopt control strategies following training that more effectively counter potentially hazardous impact-induced external loads. PURPOSE: To examine the effects of a 6-week neuromuscular training program (NTP) on lower extremity muscle activation during a single-leg land and cut task. METHODS: Twenty three (12 trained, 11 control) recreational female athletes had lower extremity muscle electromyography (EMG) data quantified during 10 single-leg land-and-cut trials before (Base), immediately (Post 0), and six weeks (Post 6) after a six-week NTP. Surface EMG electrodes were secured over the muscle bellies of the medial (MH) and lateral hamstrings (LH), vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), and medial (MG) and lateral gastrocnemius (LG) of the dominant limb. The average RMS amplitudes were calculated for each muscle during two jump landing phases; 100 ms prior to ground contact (Pre) and ground contact to 50% of stance (Re). Pre and Re co-contraction indices were also quantified for thigh muscle pairs (VL-LH and VM-MH). Subject based means of the dependent variables were submitted to two-way repeated measures (time) ANOVAs to test for the main and interaction effects of time and group. RESULTS: Subjects demonstrated significantly (p < 0.05) greater Pre and Re LH and MH muscle activation, Re LG muscle activation, and Pre and Re VL-LH and VM-MH co-contraction at both Post 0 and Post 6 time points. Increases in Pre VM (p = 0.014) and Re MG (p = 0.006) activation were only noted at the Post 6 follow-up. CONCLUSION: Lower extremity muscle activation increased during dynamic single-leg landings following a 6-week NTP. Specifically, females increased hamstring and gastrocnemius activation magnitudes, and relative activation of the hamstrings to quadriceps, which may reduce ACL injury risk. Importantly, these beneficial adaptations may even be retained six weeks following training.

Effect of knee flexion angle on ground reaction forces, knee moments and muscle co-contraction during an impact-like deceleration landing: Implications for the non-contact mechanism of ACL injury

Investigating landing kinetics and neuromuscular control strategies during rapid deceleration movements is a prerequisite to understanding the non-contact mechanism of ACL injury. The purpose of this study was to quantify the effect of knee flexion angle on ground reaction forces, net knee joint moments, muscle co-contraction and lower extremity muscles during an impact-like, deceleration task. Ground reaction forces and knee joint moments were determined from video and force plate records of 10 healthy male subjects performing rapid deceleration single leg landings from a 10.5 cm height with different degrees of knee flexion at landing. Muscle co-contraction was based on muscle moments calculated from an EMG-to-moment processing model. Ground reaction forces and co-contraction indices decreased while knee extensor moments increased significantly with increased degrees of knee flexion at landing (all p < 0.005). Higher ground reaction forces when landing in an extended knee position suggests they are a contributing factor in non-contact ACL injuries. Increased knee extensor moments and less co-contraction with flexed knee landings suggest that quadriceps overload may not be the primary cause of non-contact ACL injuries. The results bring into question the counterbalancing role of the hamstrings during dynamic movements. The soleus may be a valuable synergist stabilizing the tibia against anterior translation at landing. Movement strategies that lessen the propagation of reaction forces up the kinetic chain may help prevent non-contact ACL injuries. The relative interaction of all involved thigh and lower leg muscles, not just the quadriceps and hamstrings should be considered when interpreting non-contact ACL injury mechanisms.

Effects of Physical and Mental Demands on Muscle Activity of the Upper Extremity

Workplace tasks that involve multidimensional demands, such as physical and cognitive workloads, may increase the injury risks posed on workers. To aid in designing ergonomic guidelines for workplace safety, it is thus important to understand the interactive nature of these combined demands. The goal of this study was to investigate the effects of said multidimensional demands on the muscles of the upper extremity. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensities (5%, 25%, 45%, 65%, and 75% maximum voluntary contraction (MVC)) in the presence and absence of a mental task. Mean shoulder muscle activity and co-contraction indices (CCI) of the upper extremity were measured using electromyographic signals. Force fluctuations were measured using a force transducer to evaluate joint steadiness. In general, shoulder muscle activity (mean activity and CCIs) increased with increasing levels of physical exertions. A decrease in mean anterior and posterior deltoid muscle activity and CCI of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher levels of physical workload compared to the lower levels. Force fluctuations were lowest at 25% MVC, and highest at 85% MVC. Mental workload significantly increased force fluctuations at 85% MVC, which may have been a result of decreased muscle output to maintain the loads in a steady posture. Overall, results from this study suggest that certain task demands are more susceptible to interference by mental workload than others. It will provide a better understanding of combined exposure levels in occupational settings and serve as a guideline to determine task demands for different occupational settings.

A Comparison Between Electromyography-Driven Robot and Passive Motion Device on Wrist Rehabilitation for Chronic Stroke

Background. The effect of using robots to improve motor recovery has received increased attention, even though the most effective protocol remains a topic of study. Objective . The objective was to compare the training effects of treatments on the wrist joint of subjects with chronic stroke with an interactive rehabilitation robot and a robot with continuous passive motion. Methods. This study was a single-blinded randomized controlled trial with a 3-month follow-up. Twenty-seven hemiplegic subjects with chronic stroke were randomly assigned to receive 20-session wrist training with a continuous electromyography (EMG)-driven robot (interactive group, n = 15) and a passive motion device (passive group, n = 12), completed within 7 consecutive weeks. Training effects were evaluated with clinical scores by pretraining and posttraining tests (Fugl-Meyer Assessment [FMA] and Modified Ashworth Score [MAS]) and with session-by-session EMG parameters (EMG activation level and co-contraction index). Results. Significant improvements in FMA scores (shoulder/elbow and wrist/hand) were found in the interactive group (P < .05). Significant decreases in the MAS were observed in the wrist and elbow joints for the interactive group and in the wrist joint for the passive group (P < .05). These MAS changes were associated with the decrease in EMG activation level of the flexor carpi radialis and the biceps brachii for the interactive group (P < .05). The muscle coordination on wrist and elbow joints was improved in the interactive groups in the EMG co-contraction indexes across the training sessions (P < .05). Conclusions. The interactive treatment improved muscle coordination and reduced spasticity after the training for both the wrist and elbow joints, which persisted for 3 months. The passive mode training mainly reduced the spasticity in the wrist flexor.

Exploration Of Muscle Activity Patterns During Deep Water Running

Deep water running (DWR) simulates running while submerged in the water up to neck level and unable to touch the bottom of the pool. It is not known which aspects of DWR are critical to provide a cross-training stimulus for on land running. We sought to understand the coordination between select lower extremity muscles. PURPOSE: To compare the magnitude of co-contraction between select muscles during DWR and treadmill running (TMR). METHODS: Subjects (n=7, 26.3±4.3 yrs, 158±9.9 cm, 61±6.6 kg) were instrumented to record electromyography (EMG) of the Rectus Femoris (RF), Biceps Femoris (BF), Gastrocnemius (GA), and Tibialis Anterior (TA). Subjects first completed three exercise conditions during DWR at Rating of Perceived Exertion (RPE) levels of 11 (fairly light), 13 (somewhat hard), and 15 (hard). Subjects then completed the same RPE levels during TMR. EMG data were recorded (1500 Hz) and a 25-s data set extracted for analysis. EMG data were smoothed (500 Hz), zero-offset removed, rectified and normalized to maximal voluntary contraction. A co-contraction index (CCI) was calculated for RF-BF and GA-TA muscle combinations using the formula: CCI(i) = (M1(i)/M2(i) × (M1(i) + M2(i)))/2 for i=0-25s, M1 is the lower and M2 the higher EMG at each time. Average CCI for RF-TF and GA-TA was calculated across the 25-s data set and compared across Mode (DWR, TMR) and RPE (11, 13, 15) using a 2 x 3 repeated measures ANOVA. Planned comparisons were conducted using paired t-tests to compare CCI between DWR and TMR at each RPE level. RESULTS: RF-BF CCI was influenced by the interaction of Mode and RPE (p=0.036) whereas GA-TA CCI only tended to be different between modes (p=0.069). It was determined that RF-BF CCI was lower (p<0.05) during DWR then TMR at RPE 11 (DWR 1.94±0.64%, TMR 7.65±6.1%) and RPE 13 (DWR 2.76±1.4%, TMR 7.49±5.2%) but not at RPE 15 (DWR 4.46±2.34, TMR 9.59±7.4%, p>0.05). GA-TA CCI was lower (p<0.05) during DWR than TMR at RPE 11 (DWR 1.65±1.2%, TMR 8.89±3.7%) and RPE 13 (DWR 1.99±2.2%, TMR 8.61±3.7%) and tended to be lower at RPE 15 (DWR 3.20±3.8%, TMR 8.07±6.43, p=0.08). CONCLUSION: There was less co-contraction for flexor/extensor pairs of muscles during DWR then TMR at lower intensities. It appears that higher intensity DWR is needed to achieve similar co-contraction magnitudes of lower intensity TMR.

Association of Quadriceps and Hamstrings Cocontraction Patterns With Knee Joint Loading

Sex differences in neuromuscular control of the lower extremity have been identified as a potential cause for the greater incidence of anterior cruciate ligament (ACL) injuries in female athletes compared with male athletes. Women tend to land in greater knee valgus with higher abduction loads than men. Because knee abduction loads increase ACL strain, the inability to minimize these loads may lead to ACL failure. To investigate the activation patterns of the quadriceps and hamstrings muscles with respect to the peak knee abduction moment. Cross-sectional study. Neuromuscular research laboratory. Twenty-one recreationally active adults (11 women, 10 men). Volunteers performed 3 trials of a 100-cm forward hop. During the hop task, we recorded surface electromyographic data from the medial and lateral hamstrings and quadriceps and recorded lower extremity kinematics and kinetics. Lateral and medial quadriceps-to-hamstrings (QratioH) cocontraction indices, the ratio of medial-to-lateral QratioH cocontraction, normalized root mean square electromyographic data for medial and lateral quadriceps and hamstrings, and peak knee abduction moment were calculated and used in data analyses. Overall cocontraction was lower in women than in men, whereas activation was lower in the medial than in the lateral musculature in both sexes (P < .05). The medial QratioH cocontraction index (R(2) = 0.792) accounted for a significant portion of the variance in the peak knee abduction moment in women (P = .001). Women demonstrated less activation in the vastus medialis than in the vastus lateralis (P = .49) and less activation in the medial hamstrings than in the lateral hamstrings (P = .01). Medial-to-lateral QratioH cocontraction appears to be unbalanced in women, which may limit their ability to resist abduction loads. Because higher abduction loads increase strain on the ACL, restoring medial-to-lateral QratioH cocontraction balance in women may help reduce ACL injury risk.

Medial knee joint loading increases in those who respond to hyaluronan injection for medial knee osteoarthritis

Knee osteoarthritis (OA) is a cause of decline in function and the medial compartment is often affected. Intraarticular injection of hyaluronic acid (HA) is indicated as a symptom modifying treatment with at least 6 months passing between consecutive injection series. The effects of HA injection on gait variables have not been extensively examined. Therefore, our objective was to investigate the effects of HA injection on gait in people with medial knee OA. Twenty-seven subjects were included; each was tested prior to treatment (baseline), no later than 3 weeks following the last injection (post-HA), and again 5 months after treatment ended (follow-up). Responder criteria were defined to identify responders and non-responders. Subjects underwent 3D gait analysis, muscle activity was sampled, and co-contraction indices were calculated. Responders experienced increased peak knee adduction moments post-HA, whereas non-responders did not. Improved self-report scores were associated with increased knee adduction moments and increased medial co-contraction. Pain relief may result in higher loading onto the already vulnerable medial compartment due to changes in lower limb mechanics and muscle activation patterns. Eventually this may result in a more rapid progression of joint deterioration.

Changes in lower limb co-contraction and stiffness by toddlers with Down syndrome and toddlers with typical development during the acquisition of independent gait

During gait acquisition, children learn to use their changing resources to meet the requirements of the task. Compared to typically developing toddlers (TD), toddlers with Down syndrome (DS) have functionally different musculoskeletal characteristics, such as hypotonia, and joint and ligament laxity, that could produce a reduced passive stiffness. The interplay between this inherently lower passive stiffness and the demands of walking may result in different strategies during gait acquisition. This study compared normalized global stiffness and lower limb’s co-contraction indices (CCI) used by toddlers with TD ( n = 12) and with DS ( n = 12), during the early stages of gait acquisition. Stiffness and CCI were normalized by gravitational torque ( m L g) in both phases of gait (stance, swing). Five longitudinal evaluations were conducted from the onset of locomotion until three months post-acquisition. All children were video taped and had electromyographic (EMG) recordings from muscle pairs of one leg, which were used to calculate CCI of hip, knee, ankle, and total leg CCI. Body and lower limb stiffness were calculated according to a hybrid pendulum resonance equation. Results from ANOVAs revealed no group differences on stiffness or on CCI’s during stance but children with DS showed greater CCI during swing. Despite the structural musculoskeletal differences between toddlers with TD and with DS, the similarities observed in their processes of gait development suggest functional equivalences.

Quantitative evaluation of motor functional recovery process in chronic stroke patients during robot-assisted wrist training

This study was to investigate the motor functional recovery process in chronic stroke during robot-assisted wrist training. Fifteen subjects with chronic upper extremity paresis after stroke attended a 20-session wrist tracking training using an interactive rehabilitation robot. Electromyographic (EMG) parameters, i.e., EMG activation levels of four muscles: biceps brachii (BIC), triceps brachii (TRI, lateral head), flexor carpiradialis (FCR), and extensor carpiradialis (ECR) and their co-contraction indexes (CI) were used to monitor the neuromuscular changes during the training course. The EMG activation levels of the FCR (11.1% of decrease from the initial), BIC (17.1% of decrease from the initial), and ECR (29.4% of decrease from the initial) muscles decreased significantly during the training ( P < 0.05). Such decrease was associated with decreased Modified Ashworth Scores for both the wrist and elbow joints ( P < 0.05). Significant decrease ( P < 0.05) was also found in CIs of muscle pairs, BIC&TRI (21% of decrease from the initial), FCR&BIC (11.3% of decrease from the initial), ECR&BIC (49.3% of decrease from the initial). The decreased CIs related to the BIC muscle were mainly caused by the reduction in the BIC EMG activation level, suggesting a better isolation of the wrist movements from the elbow motions. The decreased CI of ECR& FCR in the later training sessions ( P < 0.05) was due to the reduced co-contraction phase of the antagonist muscle pair in the tracking tasks. Significant improvements ( P < 0.05) were also found in motor outcomes related to the shoulder/elbow and wrist/hand scores assessed by the Fugl–Meyer assessment before and after the training. According to the evolution of the EMG parameters along the training course, further motor improvements could be obtained by providing more training sessions, since the decreases of the EMG parameters did not reach a steady state before the end of the training. The results in this study provided an objective and quantitative EMG measure to describe the motor recovery process during poststroke robot-assisted wrist for the further understanding on the neuromuscular mechanism associated with the recovery.

Co-contraction in RA patients with a mobile bearing total knee prosthesis during a step-up task

It was hypothesized that rheumatoid arthritis (RA) patients with a total knee prosthesis that allows axial rotation of the bearing (MB) will show more co-contraction to stabilize the knee joint during a step-up task than RA patients with a fixed bearing total knee prosthesis (FB) where this rotational freedom is absent while having the same articular geometry. Surface EMG, kinematics and kinetics about the knee were recorded during a step-up task of a MB group (n = 5), a FB group (n = 4) and a control group (n = 8). Surface EMG levels of thigh muscles were calibrated to either knee flexion or extension moments by means of isokinetic contractions on a dynamometer. During the step-up task co-contraction indices were determined from an EMG-force model. Controls showed a higher active ROM during the step-up task than the patient group, 96° versus 88° (P = 0.007). In the control group higher average muscle extension, flexion and net moments during single limb support phase were observed than in the patient group. During the 20–60% interval of the single limb support, MB patients showed a significant higher level of flexor activity, resulting in a lower net joint moment, however co-contraction levels were not different. Compared to the control group arthroplasty patients showed a 40% higher level of co-contraction during this interval (P = 0.009). Control subjects used higher extension moments, resulting in a higher net joint moment. Visual analysis revealed a timing difference between the MB and FB group. The FB group seems to co-contract approximately 20% later compared to the MB group. RA patients after total knee arthroplasty show a lower net knee joint moment and a higher co-contraction than controls indicating avoidance of net joint load and an active stabilization of the knee joint. MB and FB patients showed no difference in co-contraction levels, although timing in FB is closer to controls than MB subjects. Since visual analysis revealed a timing difference between the MB and FB group, this may express compensation by coordination. Rehabilitation programs for RA patients should include besides muscle strength training, elements of muscle-coordination training.

Knee Motion and Muscle Activity Before and After ACL Rupture

PURPOSE: to describe knee kinematics and muscle activity before and after an anterior cruciate ligament (ACL) rupture METHODS: A 37 year old male high level athlete was evaluated in the motion analysis lab after tearing his right ACL. Kinematic and EMG data were collected for both limbs during gait. 22.5 months after surgery he ruptured his left ACL. Kinematic and EMG data were collected again for both limbs. Variables of interest were knee flexion angles at peak knee flexion and muscle co-contraction values. Kinematic data were collected with a eight camera 3-D motion analysis system. Muscle activity was recorded using a 16 channel EMG system. EMG data were recorded for the medial and lateral hamstrings (MH and LH), vastus medialis and vastus lateralis (VM and VL), and medial and lateral gastrocnemius (MG and LG). Co-contraction indices were derived for each muscle pair (VMMH, VMMG, VLLH and VLLG) during weight acceptance and during mid-stance. Using descriptive tests, we compared kinematic and EMG data on the left leg prior to injury to data collected after left ACL rupture. RESULTS: During weight acceptance, co-contraction values for the quadricepshamstrings pairs increased (VL/LH: 62%; VM/MH: 38%), while the values for the quadriceps-gastrocnemius pairs decreased (VL/LG: 62%; VM/MG: 78%) after the ACL rupture. The peak knee flexion angle increased by 4.1 degrees after the left ACL rupture. All co-contraction values increased during mid-stance after the ACL rupture (VL/LH: 372%; VL/LG: 5%; VM/MH: 200%; VM/MG: 198%). CONCLUSIONS: Our hypotheses were partially supported as greater co-contraction values were seen after ACL rupture in the quadriceps:hamstrings pairs throughout gait and quadriceps:gastroc pairs during mid-stance. However the decreased co-contraction in the quadriceps:gastroc pairs and increase in the peak knee flexion angle were not expected. The increase in the quadriceps-hamstring co-contraction and decrease in the quadricepsgastrocnemius co-contraction may allow the quadriceps to pull more forcefully on the tibia as the hamstrings help to stabilize the tibia posteriorly while the gastrocs decrease their posterior force on the femur. During mid-stance, the large increase in the amount of cocontractions may reduce the risk of hyperextension as the knee moves into extension. NIH & FPT funding

Influence of additional load on the moments of the agonist and antagonist muscle groups at the knee joint during closed chain exercise

The present study investigated the influence of additional loads on the knee net joint moment, flexor and extensor muscle group moments, and cocontraction index during a closed chain exercise. Loads of 8, 28, or 48 kg (i.e., respectively, 11.1 ± 1.5%, 38.8 ± 5.3%, and 66.4 ± 9.0% of body mass) were added to subjects during dynamic half squats. The flexor and extensor muscular moments and the amount of cocontraction were estimated at the knee joint using an EMG-and-optimization model that includes kinematics, ground reaction, and EMG measurements as inputs. In general, our results showed a significant influence of the Load factor on the net knee joint moment, the extensor muscular moment, and the flexor muscle group moment (all Anova p < .05). Hence we confirmed an increase in muscle moments with increasing load and moreover, we also showed an original “more than proportional” evolution of the flexor and extensor muscle group moments relative to the knee net joint moment. An influence of the Phase (i.e., descent vs. ascent) factor was also seen, revealing different activation strategies from the central nervous system depending on the mode of contraction of the agonist muscle group. The results of the present work could find applications in clinical fields, especially for rehabilitation protocols.

A Mechanical Theory for the Effectiveness of Bracing for Medial Compartment Osteoarthritis of the Knee

Evidence that knee braces used for the treatment of osteoarthritis mediate pain relief and improve function by unloading the joint (increasing the joint separation) remains inconclusive. Alternatively, valgus-producing braces may mediate pain relief by mechanically stabilizing the joint and reducing muscle cocontractions and joint compression. In this study, therefore, we sought to examine the degree to which so-called unloader braces control knee instability and influence muscle cocontractions during gait. Sixteen subjects with radiographic evidence of knee malalignment and medial compartment osteoarthritis were recruited and fitted with a custom Generation II Unloader brace. Gait analysis was performed without use of the brace and with the brace in neutral alignment and in 4 degrees of valgus alignment. A two-week washout period separated the brace conditions. Muscle cocontraction indices were derived for agonist and antagonist muscle pairings. Pain, instability, and functional status were obtained with use of self-reported questionnaires, and the results were compared. The scores for pain, function, and stability were worst when the knee was unsupported (the baseline and washout conditions). At baseline, nine of the sixteen patients reported knee instability and five of the nine complained that it affected their activities of daily living. Poor knee stability was found to be correlated with low ratings for the activities of daily living, quality of life, and global knee function and with increased pain and symptoms. Knee function and stability scored best with the brace in the neutral setting compared with the brace in the valgus setting. The cocontraction of the vastus lateralis-lateral hamstrings was significantly reduced from baseline in both the neutral (p = 0.014) and valgus conditions (p = 0.023), and the cocontraction of the vastus medialis-medial hamstrings was significantly reduced with the valgus setting (p = 0.068), as a result of bracing. Patients with greater varus alignment had greater decreases in vastus lateralis-lateral hamstring muscle cocontraction. When knees with medial compartment osteoarthritis are braced, neutral alignment performs as well as or better than valgus alignment in reducing pain, disability, muscle cocontraction, and knee adduction excursions. Pain relief may result from diminished muscle cocontractions rather than from so-called medial compartment unloading.

Modulation of Prelanding Lower-Limb Muscle Responses in Athletes with Multiple Ankle Sprains

The objective of this study was to investigate modulation in prelanding muscle responses and its associated impact force on landing from unexpected and self-initiated drops in male basketball players with a history of bilateral multiple ankle sprains (BMAS). Prelanding EMG responses were recorded in four lower-limb muscles, together with the impact force on landing, while 20 healthy and 19 basketball players with BMAS performed unexpected, self-initiated drops from a height of 30 cm. Group differences were detected after self-initiated but not unexpected drops. Two main changes in prelanding EMG responses were observed in the injured basketball players during the self-initiated drops. First, tibialis anterior (TA) was activated significantly earlier in the injured group, whereas left tensor fascia latae appeared closer to the moment of landing (P < 0.025) than in the healthy players. Second, cocontraction indexes between left TA and peroneus longus, and left TA and medial gastrocnemius, were significantly greater in the injured than in the healthy players (P < 0.025). On landing, higher magnitude-of-impact forces were observed in the injured players on the right leg (by 23%, P = 0.012). In basketball players with BMAS, modulation of prelanding muscle response latencies occurred in injured (ankle) and uninjured (hip) joints during self-initiated but not unexpected drops. Greater cocontraction index between the left ankle muscle pairs in preparation for landing from self-initiated drops, and a significantly higher magnitude of impact force in the right leg on landing, were observed in the injured players.