Peripheral regulation of stiffness during arm movements by coactivation of the antagonist muscles

Quantifying muscle coactivation in individuals with incomplete spinal cord injury using wavelets

BACKGROUND

Individuals with incomplete spinal cord injury often have decreased gait function and coactivation of antagonistic muscle pairs. Common ways of quantifying coactivation using electromyographic signals do not consider frequency information in the signal. As electromyographic signals from different motor unit types have different frequency components and muscle fiber type can change in individuals with spinal cord injury, it may be beneficial to consider frequency components. The aims were to demonstrate the utility of using a method which considers temporal and frequency components of the electromyographical signal to quantify coactivation in lower extremity muscles in individuals with incomplete spinal cord injury through 1) comparison with able-bodied individuals and 2) comparison before and after body weight supported treadmill training.

METHODS

Frequency decomposition techniques were applied to electromyographical signals to consider the temporal and frequency components of the electromyographical signals to quantify coactivation over a range of frequencies.

RESULTS

Our main findings show that correlation coefficients between total EMG intensities of rectus femoris-biceps femoris and medial gastrocnemius-tibialis anterior were significantly different between able-bodied individuals and those with incomplete spinal cord injury (p = 0006, p = 0.01). The correlation spectra of medial gastrocnemius-tibialis anterior of the spinal cord injury group were substantially different than those the able-bodied group, while the EMG normalcy score was significantly different (p = 0.002). We also found that there was a change in coactivation of ankle muscles after body weight supported treadmill training.

INTERPRETATION

Our findings indicate that there may be frequency specific differences in muscle coactivation between able-bodied individuals and those with incomplete spinal cord injury. Changes in coactivation were also observed before and after body weight supported treadmill training. These differences may reflect the changes in recruitment patterns of different motor unit types.

Global lower limb muscle coactivation during walking at different speeds: Relationship between spatio-temporal, kinematic, kinetic, and energetic parameters

Muscle coactivation is the mechanism that regulates the simultaneous activity of antagonist muscles around the same joint. During walking, muscle joint coactivation varies within the gait cycle according to the functional role of the lower limb joints. In the present study, we used a time-varying multi-muscle coactivation function (TMCf) with the aim of investigating the coactivation of 12 lower limb muscles and its relationship with the gait cycle, gait speed (low, self-selected, and fast), ground reaction force, gait variability, and mechanical energy consumption, and recovery in a sample of 20 healthy subjects. Results show that the TMCf is speed dependent and highly repeatable within and between subjects, similar to the vertical force profile, and negatively correlated with energy recovery and positively correlated with both energy consumption and balance-related gait parameters. These findings suggest that the global lower limb coactivation behavior could be a useful measure of the motor control strategy, limb stiffness, postural stability, energy efficiency optimization, and several aspects in pathological conditions.

Increased lower limb muscle coactivation reduces gait performance and increases metabolic cost in patients with hereditary spastic paraparesis

BACKGROUND

The aim of this study was to investigate the lower limb muscle coactivation and its relationship with muscles spasticity, gait performance, and metabolic cost in patients with hereditary spastic paraparesis.

METHODS

Kinematic, kinetic, electromyographic and energetic parameters of 23 patients and 23 controls were evaluated by computerized gait analysis system. We computed ankle and knee antagonist muscle coactivation indexes throughout the gait cycle and during the subphases of gait. Energy consumption and energy recovery were measured as well. In addition to the correlation analysis between coactivation indexes and clinical variables, correlations between coactivation indexes and time-distance, kinematic, kinetic, and energetic parameters were estimated.

FINDINGS

Increased coactivity indexes of both knee and ankle muscles throughout the gait cycle and during the subphases of gait were observed in patients compared with controls. Energetic parameters were significantly higher in patients than in controls. Both knee and ankle muscle coactivation indexes were positively correlated with knee and ankle spasticity (Ashworth score), respectively. Knee and ankle muscle coactivation indexes were both positively correlated with energy consumption and both negatively correlated with energy recovery.

INTERPRETATION

Positive correlations between the Ashworth score and lower limb muscle coactivation suggest that abnormal lower limb muscle coactivation in patients with hereditary spastic paraparesis reflects a primary deficit linked to lower limb spasticity. Furthermore, these abnormalities influence the energetic mechanisms during walking. Identifying excessive muscle coactivation may be helpful in individuating the rehabilitative treatments and designing specific orthosis to restrain spasticity.

Electromyography and economy of walking in chronic heart failure and heart transplant patients

Background Patients with chronic heart failure frequently report intolerance to exercise and present with changes in walk pattern, but information about heart transplant patients is lacking. Alterations of the gait pattern are related to interaction changes between the metabolism, neurological system and the mechanical demands of the locomotor task. The aim of this study was to investigate the electromyographic cost, coactivation and cost of transport of walking of chronic heart failure and heart transplant patients. Design This research was of an exploratory, cross-sectional design. Methods Twelve chronic heart failure patients, twelve healthy controls and five heart transplant patients participated in the study. Electromyographic data and oxygen uptake were collected simultaneously at five walking speeds. Results In the experimental groups, the electromyographic cost, percentage of coactivation in the leg and cost of transport were higher than in controls. The electromyographic cost was in line with the cost of transport. The minimum electromyographic cost matched with the self-selected walking speed in controls, while in chronic heart failure and heart transplant patients, it was reached at speeds higher than the self-selected walking speed. Conclusion The largest postural isometric activation and antagonist activation resulted in the highest metabolic demand. These findings are of great clinical relevance because they support the concept that interventions in order to improve the muscle performance in these patients can increase the self-selected walking speed and therefore the metabolic economy of walking.

Gait Patterns in Patients with Hereditary Spastic Paraparesis

Background

Spastic gait is a key feature in patients with hereditary spastic paraparesis, but the gait characterization and the relationship between the gait impairment and clinical characteristics have not been investigated.

Objectives

To describe the gait patterns in hereditary spastic paraparesis and to identify subgroups of patients according to specific kinematic features of walking.

Methods

We evaluated fifty patients by computerized gait analysis and compared them to healthy participants. We computed time-distance parameters of walking and the range of angular motion at hip, knee, and ankle joints, and at the trunk and pelvis. Lower limb joint moments and muscle co-activation values were also evaluated.

Results

We identified three distinct subgroups of patients based on the range of motion values. Subgroup one was characterized by reduced hip, knee, and ankle joint range of motion. These patients were the most severely affected from a clinical standpoint, had the highest spasticity, and walked at the slowest speed. Subgroup three was characterized by an increased hip joint range of motion, but knee and ankle joint range of motion values close to control values. These patients were the most mildly affected and had the highest walking speed. Finally, subgroup two showed reduced knee and ankle joint range of motion, and hip range of motion values close to control values. Disease severity and gait speed in subgroup two were between those of subgroups one and three.

Conclusions

We identified three distinctive gait patterns in patients with hereditary spastic paraparesis that correlated robustly with clinical data. Distinguishing specific features in the gait patterns of these patients may help tailor pharmacological and rehabilitative treatments and may help evaluate therapeutic effects over time.

Lower limb antagonist muscle co-activation and its relationship with gait parameters in cerebellar ataxia

Increased antagonist muscle co-activation, seen in motor-impaired individuals, is an attempt by the neuromuscular system to provide mechanical stability by stiffening joints. The aim of this study was to investigate the co-activation pattern of the antagonist muscles of the ankle and knee joints during walking in patients with cerebellar ataxia, a neurological disease that strongly affects stability. Kinematic and electromyographic parameters of gait were recorded in 17 patients and 17 controls. Ankle and knee antagonist muscle co-activation indexes were measured throughout the gait cycle and during the sub-phases of gait. The indexes of ataxic patients were compared with those of controls and correlated with clinical and gait variables. Patients showed increased co-activity indexes of both ankle and knee muscles during the gait cycle as well as during the gait sub-phases. Both knee and ankle muscle co-activation indexes were positively correlated with disease severity, while ankle muscle co-activation was also positively correlated with stance and swing duration variability. Significant negative correlations were observed between the number of self-reported falls per year and knee muscle co-activation. The increased co-activation observed in these cerebellar ataxia patients may represent a compensatory strategy serving to reduce gait instability. Indeed, this mechanism allows patients to reduce the occurrence of falls. The need for this strategy, which results in excessive muscle co-contraction, increased metabolic costs and cartilage degeneration processes, could conceivably be overcome through the use of supportive braces specially designed to provide greater joint stability.

Coactivation in arm and shoulder muscles during voluntary fixation of a single joint

The objective of this study was to determine the organization of coactivation in the arm and shoulder muscles. Normal human subjects made alternate movements of a joint in the horizontal plane, either adduction-abduction of the second finger and shoulder, ulnar-radial deviation of the wrist, or extension-flexion of the elbow, during which they fixed a focal joint while decreasing the movement amplitude and increasing the fixation strength. They varied the fixation strength at four different levels up to the maximum. The focal-joint angle, and surface electromyograms (EMGs) from the intrinsic hand, antebrachial, upper-arm, and shoulder muscles were recorded. EMGs in the phase of fixation were quantified by integration after rectification. The degree of coactivation among the muscles was evaluated by calculating correlation coefficients across the integrated EMGs. There were correlations in the integrated EMGs among focal-joint muscles (FJMs), and also between one of the FJMs and the muscles distal and/or proximal to the FJMs: in the finger fixation between the hand and antebrachial muscles, in the wrist fixation between the antebrachial and hand/upper-arm muscles, in the elbow fixation between the upper-arm and antebrachial/shoulder muscles, and in the shoulder fixation between the shoulder and upper-arm muscles. Moderate or slight correlations were seen in muscles more distant from FJMs. Our results indicate that the longitudinal distance from FJMs in the shoulder and arm muscles is an important factor in determining levels of coactivation. This is discussed in relation to the fact that neighboring muscles share joints with FJMs.

Coactivation during gait as an adaptive behavior after stroke

The aims of the present study were to quantify the impairment in ankle coactivation on the paretic and non-paretic sides of subjects with hemiparesis and to examine the relationship of ankle coactivation with postural instability, motor deficit of the paretic lower extremity and locomotor performance. Electromyography of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles were recorded bilaterally during gait in 30 subjects (62.1+/-9.9 years) who had suffered a recent stroke (<6 months) as well as on one side of 17 healthy controls (59.3+/-9.1 years) walking at very slow speed. Ankle muscle coactivation was calculated by dividing the time of overlap between MG and TA signals (threshold of 20 microV) by the duration of the gait phases of interest: stance, swing, first and second double support sub-phases and single support sub-phase. The time spent in single support and the peak plantarflexor moment of force on the paretic side were used to measure, respectively, postural stability and dynamic strength of the paretic plantarflexors. The subjects with hemiparesis demonstrated less coactivation on the paretic side during the single support sub-phase (p<0.01) and more coactivation during first and second double support sub-phases on the non-paretic side (p<0.001) compared to control values. The patients with coactivation patterns that differed the most from controls were the patients with the more severe impairments and disabilities. While the reduced coactivation on the paretic side may contribute to poor postural stability and poor locomotor performance, the presence of excessive coactivation on the non-paretic side when both limbs were in ground contact may be an adaptation to help maintain postural stability during gait.

Reciprocal activation and coactivation in antagonistic muscles during rapid goal-directed movements

Seven normal subjects performed elbow extensions as rapidly as possible from an initial position to a visually defined target at 36 degrees in amplitude. In electromyograms, the reciprocal activation of the agonist and then antagonist bursts was always followed by simultaneous activation of the antagonistic muscles, i.e., coactivation. Instructions added to perform extensions "as rapidly as possible" changed coactivation; the command to "strongly fix the upper arm at the target" increased coactivation, whereas "relax immediately after the start of movement" made coactivation almost disappear. However, basic features of reciprocal activation remained the same. Other instructions given also changed coactivation on initiation and termination, while reciprocal activation was relatively unaltered. When subjects were encouraged to "relax immediately after the start of movement, but fix the upper arm quickly after attaining the target," coactivation initiated shortly after reaching the target (< 200 ms). Following the instruction to "relax the upper arm quickly after attaining the target," coactivation terminated rapidly after reaching the target (< 280 ms). The results show that instructions serve to change amplitude and timing of coactivation while keeping reciprocal activation relatively unaltered, suggesting that coactivation is controlled independently of reciprocal activation during rapid goal-directed movements.

Control of goal-oriented, rapid arm movements by individuals with diabetes mellitus

Diabetic subjects completed a series of rapid, goal-directed arm movements under two conditions of unexpected external loading. Evaluation of electromyographic (EMG) patterns revealed that cocontraction and triphasic activity were predominantly associated with inertial and spring loading, respectively. During inertial load responses some EMG patterns indicated a modified cocontraction pattern. Response accuracy was unaffected by type of load but movement time was greater for the inertial load condition.

Peripheral control of the antagonist muscle during unexpectedly loaded arm movements

Ten subjects completed a series of goal-directed arm flexion movements unexpectedly perturbed by three different types of mechanical load. Examination of electromyograph (EMG) waveforms and kinematic information collected during randomly distributed test trials facilitated investigation into the interaction between loading conditions and the response-associated EMG innervation patterns. Results of the EMG waveform analysis revealed that inertial and spring loads produced cocontraction and triphasic activation patterns, respectively. Unexpected application of a stretched-spring load, which produced a change in initial torque values without changing the rate of loading, also resulted in the use of a triphasic activation pattern. These different EMG patterns were observed while movement displacement for all three loads fell within the limits of the target area.

Feedback control of limb stiffness and scaled phase invariance properties of skilled high-speed arm flexion movements of a loaded manipulator

In this and a previous experiment it has been observed that subjects produce innervation patterns (EMG) that are load specific, i.e., they produce concentration patterns for movements made with inertial loads and triphasic patterns for movements made with elastic loads. The protocol of these experiments prevented any adaptive responses to the load changes, therefore, it was assumed that pattern matching to load type was a real time updating response of the peripheral feedback systems. This updating response was assumed to be a mechanism for fine tuning the muscle torque by regulation of the mechanical impedance (stiffness) of the limb. Using a standard equation of motion, it was shown that the velocity is equal to the ratio of the muscle torque to the mechanical impedance. Substitution of this ratio for the ordinate of the scaled phase diagrams was then suggested as a real time updating mechanism to account for the scaled phase invariance recorded in this experiment and in the experiment reported by Ruitenbeek, J.C., Biol. Cybernetics 51 (1984) 11-20.