Antagonist Muscle Forces Research Articles

Effects of laser therapy and Grimaldi’s muscle shortening maneuver on spasticity in central nervous system injuries

Background an Aims: For 2003 year until today we treated hundreds of patients with Central Nervous System Injuries (CNSI), using Non-Surgical Laser Therapy (NSLT) obtaining good results in terms of sensibility and movement. In order to increase muscle strength and to further explore new emerging synergies, we have also started using a physical therapy practice based on the most current knowledge about the motor control, called Grimaldi’s Muscle Shortening Maneuver (GMSM). Spasticity is often the most disabling symptom and the current therapies are still not able to heal it at all. The goal of our study is to suggest a new way of treatment of spasticity, supporting it with objective measurements of muscle thresholds. Materials and Methods: In 2016-2017, 36 patients with traumatic or degenerative CNSI were enrolled. Lasers used were 808 nm, 10600 nm, and 1064 nm, applied with a first cycle of 20 sessions, four a day. Patients were subjected to Grimaldi’s Muscle Shortening Maneuver (MSM) twice a day, ten sessions at all, working selectively on hypertonic muscles and their antagonists. Before treatment, tonic stretch reflex thresholds (TSRTs) in Gastrocnemius Lateralis (GL) were assessed through a surface electromyography (sEMG) device paired with an electrogoniometer. Antagonist muscle force (Tibialis Anterioris) was assessed by some electronic hand-held dynamometers. For the clinical measure, we used the Modified Ashworth Scale (MAS). All tests have been performed at the baseline (before starting treatments), after one week (at the end of the last treatment) and after a month. Results: Results were considered positive if the instrumental assessment procedure showed modifications in TSRT values and subjects improved their antagonist muscle strength. Results showed modifications in TSRT values at every follow up. The average comparison between the follow-ups was always statistically significant (p .000). The increase in Tibialis Anterioris muscle strength was statistically significant as well (p .000). MAS showed some differences between followups but not all of them are statistically significant (T0-T1 p .063, T1-T2 p .001, T0-T2 p .000). Encouraging results suggest a possible correlation between laser and MSM therapies and modifications of TSRT in spastic muscles. Conclusion: Associating laser treatment and Grimaldi’s Muscle Shortening Maneuver (MSM) seems to be effective on spasticity in patients affected by traumatic or degenerative CNSI. Obviously, this kind of study design showed a lot of limits however this clinical series could be an important hint for every researcher working in the complex field of spasticity, a symptom that is poorly defined and hardly treated.

Correlation between ranges of leg walking angles and passive rest angles among leg types in stick insects

Because of scaling issues, passive muscle and joint forces become increasingly important as limb size decreases.1-3 In some small limbs, passive forces can drive swing in locomotion,4,5 and antagonist passive torques help control limb swing velocity.6 In stance, minimizing antagonist muscle and joint passive forces could save energy. These considerations predict that, for small limbs, evolution would result in the angle range over which passive forces are too small to cause limb movement (called "resting-state range" in prior insect work4 and "area of neutral equilibrium" in physics and engineering) correlating with the limb's typical working range, usually that in locomotion. We measured the most protracted and retracted thorax-femur (ThF) angles of the pro- (front), meso- (middle), and metathoracic (hind) leg during stick insect (Carausius morosus) walks. This ThF working range differed in the three leg types, being more posterior in more posterior legs. In other experiments, we manually protracted or retracted the denervated front, middle, and hind legs. Upon release, passive forces moved the leg in the opposite direction (retraction or protraction) until it reached the most protracted or most retracted edge of the ThF resting-state range. The ThF resting-state angle ranges correlated with the leg-type working range, being more posterior in more posterior legs. The most protracted ThF walking angles were more retracted than the post-protraction ThF angles, and the most retracted ThF walking angles were similar to the post-retraction ThF angles. These correlations of ThF working- and resting-state ranges could simplify motor control and save energy. These data also provide an example of evolution altering behavior by changing passive muscle and joint properties.7.

Effect of Prophylactic Knee Bracing on Anterior Cruciate Ligament Agonist and Antagonist Muscle Forces During Perturbed Walking.

Background:Anterior cruciate ligament (ACL) injuries most commonly occur after a perturbation. Prophylactic knee braces (PKBs) are off-the-shelf braces designed to prevent and reduce the severity of knee injuries during sports, yet their effectiveness has been debated.Purpose:To identify differences in ACL agonist and antagonist muscle forces, during braced and unbraced conditions, while walking with the application of unexpected perturbations.Study Design:Controlled laboratory study.Methods:A total of 20 recreational athletes were perturbed during walking at a speed of 1.1 m/s, and motion analysis data were used to create patient-specific musculoskeletal models. Static optimization was performed to calculate the lower-limb muscle forces. Statistical parametric mapping was used to compare muscle forces between the braced and unbraced conditions during the stance phase of the perturbed cycle.Results:The brace reduced muscle forces in the quadriceps (QUADS), gastrocnemius (GAS), and soleus (SOL) but not in the hamstrings. The peak QUADS muscle force was significantly lower with the brace versus without at 49% to 60% of the stance phase (28.9 ± 12.98 vs 14.8 ± 5.06 N/kg, respectively; P < .001) and again at 99% of the stance phase (1.7 ± 0.4 vs 3.6 ± 0.13 N/kg, respectively; P = .049). The SOL muscle force peak was significantly lower with the brace versus without at 25% of the stance phase (1.9 ± 1.7 vs 4.6 ± 3.4 N/kg, respectively; P = .031) and at 39% of the stance phase (1.9 ± 1.4 vs 5.3 ± 5.6 N/kg, respectively; P = .007). In the GAS, there were no significant differences between conditions throughout the whole stance phase except between 97% and 100%, where the braced condition portrayed a smaller peak force (0.23 ± 0.13 vs 1.4 ± 1.1 N/kg for unbraced condition; P = .024).Conclusion:These findings suggested that PKBs that restrict knee hyperextension and knee valgus/varus motion can alter neuromuscular patterns, which result in a reduction of QUADS force.Clinical Relevance:Understanding the way PKBs alter muscle function and knee mechanics can provide invaluable information that will help in making decisions about their use. Further studies should investigate different types of braces and perturbations to evaluate the effectiveness of PKBs.

Anterior cruciate ligament agonist and antagonist muscle force differences between males and females during perturbed walking

Anterior cruciate ligament (ACL) injuries most commonly occur following a perturbation. Perturbations make the athlete unbalanced or at loss of control, which ultimately can lead to injury. The purpose of this study was to identify differences in ACL agonist and antagonist muscle forces, between sexes, during unexpected perturbations. Twenty recreational athletes were perturbed during walking at a speed of 1.1 m/s. Motion analysis data were used to create subject-specific musculoskeletal models and static optimization was performed to calculate muscle forces in OpenSim. Statistical parametric mapping (SPM) was used to compare muscle forces between males and females during the stance phase of the perturbed cycle. Females illustrated higher ACL antagonist muscle forces (p < 0.05) and lower ACL agonist muscle forces, compared to their male counterparts. The quadriceps (QUADs) muscle group peak was about 1.4 times higher in females (35.50 ± 8.71 N/kg) than males (22.81 ± 5.83 N/kg during 57%-62% of the stance phase (p < 0.05). Females presented a larger peak of gastrocnemius (GAS) at two instances: 12.42 ± 4.5 N/kg vs. 8.10 ± 2.83 N/kg between 70% and 75% at p < 0.05 and 2.26 ± 0.55 N/kg vs. 0.52 ± 0.09 N/kg between 95% and 100% at p < 0.05. Conversely, males illustrated higher initial hamstrings (HAMS) peak of 10.67 ± 4.15 N/kg vs. 5.38 ± 1.1 N/kg between 8% and 11%. Finally, males showed almost double the soleus (SOL) peak at 30.63 ± 8.64 N/kg vs. 17.52 ± 3.62 N/kg between 83% and 92% of the stance phase at p < 0.001. These findings suggest that females may exhibit riskier neuromuscular control in unanticipated situations, like sports.

Radiation dose to the tongue and velopharynx predicts acoustic-articulatory changes after chemo-IMRT treatment for advanced head and neck cancer

The aim of this study was to investigate to what extent changes in speech after C-IMRT treatment are related to mean doses to the tongue and velopharynx (VP). In 34 patients with advanced hypopharyngeal, nasopharyngeal, or oropharyngeal cancer, changes in speech from pretreatment to 10 weeks and 1 year posttreatment were correlated with mean doses to the base of tongue (BOT), oral cavity (OC) and tonsillar fossa/soft palate (VP). Differences in anteroposterior tongue position, dorsoventral degree of tongue to palate or pharynx constriction, grooving, strength, nasality, and laryngeal rise, were assessed by acoustic changes in three speech sounds that depend on a (post-) alveolar closure or narrowing (/t/, /s/, /z/), three with a tongue to palate/pharyngeal narrowing (/l/, /r/, /u/), and in vowel /a/ at comfortable and highest pitch. Acoustically assessed changes in tongue positioning, shape, velopharyngeal constriction, and laryngeal elevation were significantly related to mean doses to the tongue and velopharynx. The mean dose to BOT predicted changes in anteroposterior tongue positioning from pre- to 10-weeks posttreatment. From pretreatment to 1-year, mean doses to BOT, OC, and VP were related to changes in grooving, strength, laryngeal height, nasality, palatalization, and degree of pharyngeal constriction. Changes in speech are related to mean doses to the base of tongue and velopharynx. The outcome indicates that strength, motility, and the balance between agonist and antagonist muscle forces change significantly after radiotherapy.

Assessment of lower leg muscle force distribution during isometric ankle dorsi and plantar flexion in patients with diabetes: a preliminary study

AimThe aim of this study was to evaluate the differences in ankle muscle strength using hand-held dynamometry and to assess difference in the isometric muscle force distribution between the people with diabetes and control participants. MethodsThe maximal muscle strength of ankle plantarflexion, dorsiflexion, eversion, inversion, lesser toes flexors and extensors, hallux flexors, and extensors was assessed in 20 people with diabetes and 20 healthy participants using hand-held dynamometry. The maximal isometric ankle plantarflexion and dorsiflexion were imported to OpenSim software to calculate 12 individual muscle (8 plantarflexors and 4 dorsiflexors) forces acting on ankle joint. ResultsA significant reduction in ankle strength for all measured actions and a significant decrease in muscle force for each of the 12 muscles during dorsi and plantar flexion were observed. Furthermore, the ratios of agonist to antagonist muscle force for 6 of the muscles were significantly different between the control group and the group with diabetes. ConclusionsIt is likely that the muscles for which the agonist/antagonist muscle force ratio was significantly different for the healthy people and the people with diabetes could be more affected by diabetes.

EMG Activation Patterns Associated with High Frequency, Long-Duration Intracortical Microstimulation of Primary Motor Cortex

The delivery of high-frequency, long-duration intracortical microstimulation (HFLD-ICMS) to primary motor cortex (M1) in primates produces hand movements to a common final end-point regardless of the starting hand position (Graziano et al., 2002). We have confirmed this general conclusion. We further investigated the extent to which the (1) temporal pattern, (2) magnitude, and (3) latency of electromyographic (EMG) activation associated with HFLD-ICMS-evoked movements are dependent on task conditions, including limb posture. HFLD-ICMS was applied to layer V sites in M1 cortex. EMG activation with HFLD-ICMS was evaluated while two male rhesus macaques performed a number of tasks in which the starting position of the hand could be varied throughout the workspace. HFLD-ICMS-evoked EMG activity was largely stable across all parameters tested independent of starting hand position. The most common temporal pattern of HFLD-ICMS-evoked EMG activity (58% of responses) was a sharp rise to a plateau. The plateau level was maintained essentially constant for the entire duration of the stimulus train. The plateau pattern is qualitatively different from the largely bell-shaped patterns typical of EMG activity associated with natural goal directed movements (Brown and Cooke, 1990; Hoffman and Strick, 1999). HFLD-ICMS produces relatively fixed parameters of muscle activation independent of limb position. We conclude that joint movement associated with HFLD-ICMS occurs as a function of the length-tension properties of stimulus-activated muscles until an equilibrium between agonist and antagonist muscle force is achieved.

Measurement of intraarticular wrist joint biomechanics with a force controlled system

Pathologies of the wrist, such as fractures or instabilities, can lead to alterations in joint biomechanics. Accurate treatment of these pathologies is a frequent challenge for the surgeon. For biomechanical investigations, a test-setup that applies physiological loading of the wrist joint is necessary. A force controlled test-bench with agonistic and antagonistic muscle forces was built to move six fresh frozen human upper extremities through flexion and extension of the wrist joint. Tendon forces, range of motion, intraarticular contact area and contact pressure of the lunate and scaphoid facet as well as tendon excursion were investigated and compared with the current literature. During wrist motion the extensors exerted double the force of the flexors. Capsulotomy and sensor insertion decreased the range of motion from 63.4° (SD 14.1) to 45.9° (SD 23.7). The ratio of force transmitted through the radius and ulna was 77:23 and pressure distribution between the scaphoid and lunate facet showed a 70:30 relationship. The obtained data indicate a good agreement with the available literature. Therefore, the force controlled test-bench in combination with intraarticular radiocarpal measurements can be used to investigate the influence of wrist pathologies on joint biomechanics.

A hybrid static optimisation method to estimate muscle forces during muscle co-activation

The general static optimisation (GSO) process is one of various muscle force estimation methods due to its low computational requirements. However, it can show biased muscle force estimation under muscle co-contraction. In the present study, we introduced a novel hybrid static optimisation (HSO) method to estimate reasonable muscle forces during muscle co-activation movements using more specific equality constraints, i.e. agonist and antagonist muscle moments predicted from a new correlation coefficient approach. The new method was evaluated for heel-rise movements. We found that the proposed method improved the potential of antagonist muscle force estimation in comparison to the GSO solutions. The proposed HSO method could be applied in biomechanics and rehabilitation, for example.

Role of the nervous system in sarcopenia and muscle atrophy with aging: strength training as a countermeasure

Aging is characterized by loss of spinal motor neurons (MNs) due to apoptosis, reduced insulin-like growth factor I signaling, elevated amounts of circulating cytokines, and increased cell oxidative stress. The age-related loss of spinal MNs is paralleled by a reduction in muscle fiber number and size (sarcopenia), resulting in impaired mechanical muscle performance that in turn leads to a reduced functional capacity during everyday tasks. Concurrently, maximum muscle strength, power, and rate of force development are decreased with aging, even in highly trained master athletes. The impairment in muscle mechanical function is accompanied and partly caused by an age-related loss in neuromuscular function that comprise changes in maximal MN firing frequency, agonist muscle activation, antagonist muscle coactivation, force steadiness, and spinal inhibitory circuitry. Strength training appears to elicit effective countermeasures in elderly individuals even at a very old age (>80 years) by evoking muscle hypertrophy along with substantial changes in neuromuscular function, respectively. Notably, the training-induced changes in muscle mass and nervous system function leads to an improved functional capacity during activities of daily living.

Transient analysis of trunk response in sudden release loading using kinematics-driven finite element model

Background Sudden trunk perturbations occur in various occupational and sport activities. Despite numerous measurement studies, no comprehensive modeling simulations have yet been attempted to investigate trunk biodynamics under sudden loading/unloading. Methods Dynamic kinematics-driven approach was used to evaluate the temporal variation of trunk muscle forces, internal loads and stability before and after a sudden release of a posterior horizontal load. Measured post-disturbance trunk kinematics, as input, and muscle electromyography (EMG) activities, for qualitative validation, were considered. Findings Computed agonist and antagonist muscle forces before and after release agreed well with reported EMG activities and demonstrated basic response characteristics such as activation latency and reflex activation. The trunk was found quite stable before release and in early post-release period. Larger applied load substantially increased trunk kinematics, muscle forces and spinal loads. Interpretation Excessive spinal loads due to large muscle forces in sudden loading conditions is a risk factor as the central nervous system attempts to reflexively control the sudden disturbances, a situation that further deteriorates under larger perturbations and longer latency periods. Predictions indicate the potential of the kinematics-driven model in ergonomics as well as training and rehabilitation programs.

Mechanical efficiency of limb swing during walking and running in guinea fowl (Numida meleagris)

Understanding the mechanical determinants of the energy cost of limb swing is crucial for refining our models of locomotor energetics, as well as improving treatments for those suffering from impaired limb-swing mechanics. In this study, we use guinea fowl (Numida meleagris) as a model to explore whether mechanical work at the joints explains limb-swing energy use by combining inverse dynamic modeling and muscle-specific energetics from blood flow measurements. We found that the overall efficiencies of the limb swing increased markedly from walking (3%) to fast running (17%) and are well below the usually accepted maximum efficiency of muscle, except at the fastest speeds recorded. The estimated efficiency of a single muscle used during ankle flexion (tibialis cranialis) parallels that of the total limb-swing efficiency (3% walking, 15% fast running). Taken together, these findings do not support the hypothesis that joint work is the major determinant of limb-swing energy use across the animal's speed range and warn against making simple predictions of energy use based on joint mechanical work. To understand limb-swing energy use, mechanical functions other than accelerating the limb segments need to be explored, including isometric force production and muscle work arising from active and passive antagonist muscle forces.

Application of an Entropy-Assisted Optimization Model in Prediction of Agonist and Antagonist Muscle Forces

Many existing optimization based biomechanical models fail to predict antagonist muscle activity. Some optimization models predict such a cocontraction, but either lack a compelling physiological basis or are computationally formidable. The current study takes advantage of the flexible definition of entropy as a scientific measure, and utilizes it in the objective function of an optimization formulation to construct a new optimization model for predicting agonist and antagonist muscle forces. In this model, the objective function of a nonlinear program consists of a weighted sum of two components: a linear or nonlinear term favoring agonist muscle exertions (reciprocal inhibition), and the entropy term enforcing cocontraction. The concept of the current optimization model is based on recent findings in neurophysiology that there exist two separate central nervous systems for generation of two motor patterns: agonist contraction and agonist-antagonist cocontraction.

Effect of stretching on agonist–antagonist muscle activity and muscle force output during single and multiple joint isometric contractions

Eight moderately active male subjects where tested for peak force in an isometric knee extension test and peak force and rate of force development in an isometric squat test. Both tests where performed at a 100 degrees knee angle and average integrated electromyography (IEMG) was measured from the vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) muscles. Subjects performed the two conditions, stretching (S) or control (C) in a randomized order. Subjects where tested for baseline strength measures in both the isometric knee extension and isometric squat and then either stretched or sat quietly for 10 min. Following S or C subjects where then tested at six time points. Following S peak force in the isometric knee extension was significantly (P < or = 0.05) less than C at 1, 2, 8 and 16 min post. No significant difference in peak force was found between S and C in the isometric squat. However, following S the rate of force development in the isometric squat was significantly less than C at immediately post. No significant differences where observed in IEMG of the VM or VL between S and C in either the isometric knee extension or isometric squat. However, IEMG significantly decreased in the BF at 1 min post after S in comparison with C in both the isometric knee extension and isometric squat. Stretching appears to decrease muscle force output in a single joint isometric contraction and rate of force development in a multiple joint isometric contraction. Possible changes in agonist-antagonist muscle activity patterns need to be further examined.

Botulinum toxin for the management of muscle overactivity and spasticity after stroke.

Stroke is a major cause of disability involving the arm and leg. This disability results from the upper motoneuron syndrome (UMN) evident after stroke. It is commonly associated with spasticity and muscle overactivity, which can lead to abnormal limb posturing that interferes with active and passive function. The origin of limb deformity in patients with UMN is based on the concept of unbalanced agonist and antagonist muscle forces acting across joints. In the past decade, botulinum toxin A (BTX-A) a new medication that modifies muscle force and, hence, can treat muscle imbalance, has become available and has renewed interest in the management of muscle overactivity and spasticity after stroke. A reduction in muscle tone, painful spasms, and improved functionality can be obtained. Research and clinical reports support the concept that chemodenervation with BTX-A is an excellent intervention for treating focal muscle overactivity and spasticity secondary to stroke. Many muscles differing in size, shape, and location have been injected, and clinical effectiveness is particularly notable in elbow flexors, ankle plantar flexors, and smaller limb muscles, such as intrinsics of the hand and wrist. Smaller muscles are readily accessible for injection and require smaller amounts of toxin.

きっ抗筋の遠心性収縮を伴う疑似閉鎖性運動連鎖筋力増強法について 電気刺激による筋力増強法

The present invention relates generally to an apparatus for exercising human muscles. It uses the electrically stimulated antagonist muscle force to resist the voluntary contracting agonist muscle. This method induas both eccentric contraction of antagonist muscle and concentric contraction of agonist muscle, which has been referred to as “closedkinetic-chain exercise”. It allows a person to receive closed-kinetic-chanin exercise at a comfortable posture and prevents osteoporosis.This study was performed to determine the electrical stimulated antagonist muscle force as a resistance of the voluntary contracting agonist muscle. Maximum electrically stimulated muscle force indicated 26% to voluntary muscle force with knee flexion, and the force ratio of antagonist muscle to agonist muscle varies according to the combination of muscles and knee joint angle.

An EMG technique for measuring spinal loading during asymmetric lifting

Objective. To compare two methods of calibrating the erector spinae electromyographic signal against moment generation in order to predict extensor moments during asymmetric lifting tasks, and to compare the predicted moments with those obtained using a linked-segment model. Methods. Eight men lifted loads of 6.7 and 15.7 kg at two speeds, in varying amounts of trunk rotation. For each lift, the following were recorded at 60 Hz; the rectified and averaged surface electromyographic signal, bilaterally at T10 and L3, lumbar curvature using the 3-Space Isotrak, movement of body segments using a 4-camera Vicon system, and ground reaction forces using a Kistler force-plate. Electromyographic (EMG) and Isotrak data were used to calculate lumbosacral extensor moments using the electromyographic model, whereas movement analysis data and ground reaction forces were used to estimate net moments using the linked-segment model. For the electromyographic technique, predictions of extensor moment were based on two different sets of EMG-extensor moment calibrations: one performed in pure sagittal flexion and the other in flexion combined with 45° of trunk rotation. Results. Extensor moments predicted by the electromyographic technique increased significantly with load and speed of lifting but were not influenced by the method of calibration. These moments were 7–40% greater than the net moments obtained with the linked-segment model, the difference increasing with load and speed. Conclusions. The calibration method does not influence extensor moments predicted by the electromyographic technique in asymmetric lifting, suggesting that simple, sagittal-plane calibrations are adequate for this purpose. Differences in predicted moments between the electromyographic technique and linked-segment model may be partly due to different anthropometric assumptions and different amounts of smoothing and filtering in the two models, and partly due to antagonistic muscle forces, the effects of which cannot be measured by linked-segment models. Relevance Asymmetric lifting is a significant risk factor for occupationally-related low back pain. Improved techniques for measuring spinal loading during such complex lifting tasks may help to identify work practices which place the spine at risk of injury.

A new in vivo technique for 3-dimensional analysis of the translation of femoral condyles and the menisci responding to antagonistic muscle forces

The aim of our study was to develop a 3-D MR-based technique for the analysis of meniscal and femoral translations during flexion of the knee, and under the influence of antagonistic muscle forces in healthy subjects. In an open MR system, 5 knees were examined at 30 degrees and 90 degrees flexion using a T1-weighted 3-D gradient echo sequence. A force of 30 Newtons, first in the extending and then in the flexing direction, was applied to the distal lower leg. After three-dimensional reconstruction, the minimal distances between the centre of the tibial plateau and the posterior edge of the menisci and femoral condyles were determined. At 30 degrees flexion, the minimum distance for the meniscus was larger medially than laterally (23.2 +/- 1.8 mm vs. 16.2 +/- 3.3 mm), and this also applied to the condyles (25.1 +/- 1.5 vs. 19.0 +/- 3.0 mm). During flexion to 90 degrees, a posterior translation of 0.5 +/- 0.2 mm was observed for the lateral, and of 3.4 +/- 1.2 mm for the medial, meniscus. The condyles demonstrated a different posterior translation (lateral 2.2 +/- 0.56 mm; medial 1.8 +/- 1.9 mm). No obvious differences were found between extension and flexion muscle activity for the different positions of the knee. In the present study, a new 3-D technique is presented for the analysis of the femoral and meniscal translation at various positions of the knee, and under muscle activity. The results suggest different translation for the menisci and condyles.

Prediction of antagonistic muscle forces using inverse dynamic optimization during flexion/extension of the knee.

This paper examined the feasibility of using different optimization criteria in inverse dynamic optimization to predict antagonistic muscle forces and joint reaction forces during isokinetic flexion/extension and isometric extension exercises of the knee. Both quadriceps and hamstrings muscle groups were included in this study. The knee joint motion included flexion/extension, varus/valgus, and internal/external rotations. Four linear, nonlinear, and physiological optimization criteria were utilized in the optimization procedure. All optimization criteria adopted in this paper were shown to be able to predict antagonistic muscle contraction during flexion and extension of the knee. The predicted muscle forces were compared in temporal patterns with EMG activities (averaged data measured from five subjects). Joint reaction forces were predicted to be similar using all optimization criteria. In comparison with previous studies, these results suggested that the kinematic information involved in the inverse dynamic optimization plays an important role in prediction of the recruitment of antagonistic muscles rather than the selection of a particular optimization criterion. Therefore, it might be concluded that a properly formulated inverse dynamic optimization procedure should describe the knee joint rotation in three orthogonal planes.

The effects of the antagonist muscle force on intersegmental loading during isokinetic efforts of the knee extensors

Hamstrings activation when acting as antagonists is considered very important for knee joint stability. However, the effect of hamstring antagonist activity on knee joint loading in vivo is not clear. Therefore, the purpose of this study was to examine the differences in antagonistic muscle force and their effect on agonist muscle and intersegmental forces during isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum isokinetic eccentric and concentric efforts of the knee extensors at 30° s −1. The muscular and tibiofemoral joint forces were then estimated using a two-dimensional model with and without including the antagonist muscle forces. The antagonist moment was predicted using an IEMG-moment model. The predicted antagonist force reached a maximum of 2.55 times body weight (BW) and 1.16 BW under concentric and eccentric conditions respectively. Paired t-tests indicated that these were significantly different ( p<0.05). A one-way analysis of variance indicated that when antagonist forces are included in the calculations the patella tendon, compressive and posterior shear joint forces are significantly higher compared to those calculated without including the antagonist forces. The anterior shear force was not affected by antagonist activity. The antagonists produce considerable force throughout the range of motion and affect the joint forces exerted at the knee joint. Further, it appears that the antagonist effect depends on the type of muscle action examined as it is higher during concentric compared to eccentric efforts of the knee extensors.