Co-contraction Ratio Research Articles

Influences of ventilation on maximal isometric force of the finger flexors

Force production may be influenced by the phase of ventilation during which force is exerted. To examine the potential influences of ventilation on variability in maximal force measurements, we recorded peak isometric forces of the finger flexors during normal breathing, forced inspiration, forced expiration, and the Valsalva maneuver in 14 healthy adult subjects. The peak force increased significantly from forced inspiration to forced expiration (about 10%). Both forced expiration and inspiration resulted in increases in the flexor/extensor cocontraction ratio, whereas the Valsalva maneuver had no significant effects on maximal force or cocontraction ratio. Thus, this study clearly demonstrates the effects of ventilation on maximal finger force-generating capability. Ventilation needs to be controlled for accurate assessments of maximal force.

Pre-Contact Co-Contraction Ratios during Drop Landings onto One or Two Legs Differ at the Ankle but Not at the Knee Joint

Pre-Contact Co-Contraction Ratios during Drop Landings onto One or Two Legs Differ at the Ankle but Not at the Knee Joint

Functional Electrical Stimulation Improves Motor Recovery of the Lower Extremity and Walking Ability of Subjects With First Acute Stroke

The effectiveness of functional electrical stimulation (FES) has been investigated in chronic hemiplegia. The present study examines whether FES, given during acute stroke, was more effective in promoting motor recovery of the lower extremity and walking ability than standard rehabilitation alone. Forty-six subjects, 70.9+/-8.0 years old and 9.2+/-4.1 days after stroke, were assigned randomly to 1 of 3 groups receiving standard rehabilitation with FES or placebo stimulation or alone (control). FES was applied 30 minutes and placebo stimulation 60 minutes, 5 days per week for 3 weeks. Outcome measurements included composite spasticity score, maximum isometric voluntary contraction of ankle dorsi-flexors and planter-flexors, and walking ability. They were recorded before treatment, weekly during the 3-week treatment, and at week 8 after stroke. No significant differences were found in the baseline measurements. After 3 weeks of treatment, there was a significant reduction in the percentage of composite spasticity score, and a significant improvement in the ankle dorsiflexion torque, accompanied by an increase in agonist electromyogram and a reduction in electromyogram cocontraction ratio in the FES group, when compared with the other 2 groups (P<0.05). All subjects in the FES group were able to walk after treatment, and 84.6% of them returned home, in comparison with the placebo (53.3%) and control (46.2%, P<0.05) groups. Fifteen sessions of FES, applied to subjects with acute stroke plus standard rehabilitation, improved their motor and walking ability to the degree that more subjects were able to return to home.

Quantitative assessment of co-contraction in cervical musculature

The co-contraction of cervical musculature is quantitatively assessed. For the modeling procedure, electromyographic (EMG) signal and anatomical data of the neck musculature were used. EMG signals were collected from eight sites of the neck bilaterally using Ag–AgCl surface electrodes from ten adult male subjects. The subjects performed voluntary isometric contractions gradually developing to maximum efforts in flexion, extension, left lateral bending and right lateral bending. The EMG-assisted optimization modeling procedure was used to estimate muscle forces. To quantify co-contraction, muscle forces were decomposed into task subset and co-contraction subset of muscle forces. To show the degree of co-contraction, ‘co-contraction ratio’ was defined as the proportion of co-contraction muscle forces to total muscle forces. The ranges of co-contraction ratio are 0.08–0.16 during extension, 0.30–0.41 during flexion, 0.27–0.32 during left lateral bending, and 0.30–0.36 during right lateral bending. In all cases, co-contraction ratios increase as external moments increase. The ratios of compressive spinal loads from the co-contraction subset of muscle forces to those from total muscle forces are similar to co-contraction ratios during the whole ramp period. This study provides data demonstrating quantitative measures of the contribution of muscle co-contraction to cervical spinal loads.

Muscle force production and functional performance in spastic cerebral palsy: Relationship of cocontraction

Damiano DL, Martellotta TL, Sullivan DJ, Granata KP, Abel MF. Muscle force production and functional performance in spastic cerebral palsy: relationship of cocontraction. Arch Phys Med Rehabil 2000;81:895-900. Objective: To determine cocontraction's relation to strength and motor function in children with spastic cerebral palsy (CP). Design: Prospective evaluation with a convenience sample of 10 subjects. Setting: Pediatric rehabilitation center at a tertiary care hospital. Patients: Ten ambulatory children with spastic CP, mean age 5 to 14yrs. Main Outcome Measures: A single comprehensive assessment of hamstring and quadriceps muscle strength; gait analysis while monitoring electromyographic (EMG) activity in those muscles; administration of the Gross Motor Function Measure (GMFM); heart-rate monitoring during quiet rest versus gait to compute an energy expenditure index (EEI). Cocontraction ratios and magnitudes were determined for the gait and strength testing trials using the EMG data. Results: Cocontraction ratios during strength tests correlated directly with those during free gait. Cocontraction magnitude and total EMG magnitude had an inverse relationship to EEI; children with more muscle activity in the agonist and antagonist tended to be more energy efficient. Knee extensor muscle strength correlated positively with the GMFM and gait velocity. Neither cocontraction ratio nor magnitude during gait was related to strength. Conclusions: Children with CP used a similar muscle activation strategy across two different motor tasks. Strength and cocontraction were uniquely related to different aspects of motor function. Further research is needed to quantify more precisely cocontraction and force to EMG relations in this population. © 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Task-Dependent Viscoelasticity of Human Multijoint Arm and Its Spatial Characteristics for Interaction with Environments

Human arm viscoelasticity is important in stabilizing posture, movement, and in interacting with objects. Viscoelastic spatial characteristics are usually indexed by the size, shape, and orientation of a hand stiffness ellipse. It is well known that arm posture is a dominant factor in determining the properties of the stiffness ellipse. However, it is still unclear how much joint stiffness can change under different conditions, and the effects of that change on the spatial characteristics of hand stiffness are poorly examined. To investigate the dexterous control mechanisms of the human arm, we studied the controllability and spatial characteristics of viscoelastic properties of human multijoint arm during different cocontractions and force interactions in various directions and amplitudes in a horizontal plane. We found that different cocontraction ratios between shoulder and elbow joints can produce changes in the shape and orientation of the stiffness ellipse, especially at proximal hand positions. During force regulation tasks we found that shoulder and elbow single-joint stiffness was each roughly proportional to the torque of its own joint, and cross-joint stiffness was correlated with elbow torque. Similar tendencies were also found in the viscosity-torque relationships. As a result of the joint stiffness changes, the orientation and shape of the stiffness ellipses varied during force regulation tasks as well. Based on these observations, we consider why we can change the ellipse characteristics especially in the proximal posture. The present results suggest that humans control directional characteristics of hand stiffness by changing joint stiffness to achieve various interactions with objects.

Relief of hemiparetic spasticity by TENS is associated with improvement in reflex and voluntary motor functions

Our previous studies showed that a single 45 min application of transcutaneous electrical nerve stimulation (TENS) prolonged soleus H and stretch reflex latencies in hemiparetic subjects. In addition, 9 daily 30 min TENS applications enhanced vibratory inhibition of the H reflex and tended to decrease hyperactive stretch reflexes. These findings suggested that longer-term TENS may be effective in reducing hemiparetic spasticity. Our present objectives were 2-fold: to determine whether longer-term repetitive TENS stimulation would lead to a reduction in clinical spasticity in hemiparetic subjects, and whether such a reduction could be associated with a decrease in stretch reflex excitability and an improvement in voluntary motor function. We compared the effects of 15 daily 60 min TENS treatments over a 3 week period, with those of placebo stimulation applied to the common peroneal nerve of the affected leg in similar groups of spastic hemiparetic subjects. Our test battery consisted of 5 measurements which assessed (1) clinical spasticity scores, (2) maximal H reflex to M response ratios, (3) vibratory inhibition of H reflex, (4) stretch reflexes, and (5) maximal voluntary isometric plantarflexion and dorsiflexion, in standing. In contrast to placebo stimulation which produced no significant effects, repeated applications of TENS over time decreased clinical spasticity ( P < 0.05), and increased vibratory inhibition of the soleus H reflex ( P = 0.02) after 2 weeks. These changes occurred with a substantial improvement in voluntary dorsiflexing force up to 820%, but not plantarflexing force. They were followed by a reduction in the magnitude of stretch reflexes ( P = 0.05) in the spastic ankle plantarflexor, concomitant with a decrease in the EMG co-contraction ratios after a further week of stimulation. Our results thus indicated that repeated applications of TENS can reduce clinical spasticity and improve control of reflex and motor functions in hemiparetic subjects. Furthermore, the underlying mechanisms may be due partly to an enhancement in presynaptic inhibition of the spastic plantarflexor, and partly to a possible “disinhibition” of descending voluntary commands to the paretic dorsiflexor motoneurons.