Passive Joint Torque Research Articles

Shear wave ultrasound elastography of the biceps brachii can be used as a precise proxy for passive elbow torque in individuals with hemiparetic stroke.

Muscle tissue is prone to changes in composition and architecture following stroke. Changes in muscle tissue of the extremities are thought to increase resistance to muscle elongation or joint torque under passive conditions. These effects likely compound neuromuscular impairments, exacerbating movement function. Unfortunately, conventional rehabilitation is devoid of precise measures and relies on subjective assessments of passive joint torques. Shear wave ultrasound elastography, a tool to measure muscle mechanical properties, may be readily available for use in the rehabilitation setting as a precise measure, albeit at the muscle-tissue level. To support this postulation, we evaluated the criterion validity of shear wave ultrasound elastography of the biceps brachii; we investigated its relationship with a laboratory-based criterion measure for quantifying elbow joint torque in individuals with moderate to severe chronic stroke. Additionally, we evaluated construct validity, with the specific sub-type of hypothesis testing of known groups, by testing the difference between arms. Measurements were performed under passive conditions at seven positions spanning the arc of elbow joint flexion-extension in both arms of nine individuals with hemiparetic stroke. Surface electromyography was utilized for threshold-based confirmation of muscle quiescence. A moderate relationship between the shear wave velocity and elbow joint torque was identified, and both metrics were greater in the paretic arm. Data supports the progression toward a clinical application of shear wave ultrasound elastography in evaluating altered muscle mechanical properties in stroke, while acknowledging that undetectable muscle activation or hypertonicity may contribute to the measurement. Shear wave ultrasound elastography may augment the conventional method of manually testing joint mobility by providing a high-resolution precise value. Tissue-level measurement may also assist in identifying new therapeutic targets for patient-specific impairment-based interventions.

The effects of eccentric exercise on passive hamstring muscle stiffness: Comparison of shear-wave elastography and passive knee torque outcomes.

The aim of our study was to assess eccentric-exercise-induced changes in passive knee joint torque, passive knee joint stiffness and shear modulus at of the hamstring muscles. We hypothesized that eccentric exercise would elicit an increase in all outcomes. Fourteen healthy volunteers (age = 25.5±4.7 years) performed eccentric exercise protocol. Before and after 0h, 1h, 24h and 48h, we measured the shear modulus of hamstring muscles using shear-wave elastography and passive knee joint stiffness on isokinetic dynamometer. After eccentric exercise, the shear modulus of biceps femoris increased after 0h (22.4 ± 34.1 %; p = 0.021) and for semitendinosus after 0h (14.5 ± 4.9 %), 1h (16.2 ± 6.5 %) and 24h (16.6 ± 8.3 %) (p = 0.005-0.015). There were no changes for semimembranosus and no changes in passive knee joint moment measures. There were also no correlations between the two methods. Eccentric exercise increased shear modulus of hamstring muscles, while passive joint torque was not affected. This suggests that shear-wave elastography could be more sensitive than torque measures to intra-muscular changes induced by eccentric exercise.

Associations between Range of Motion and Tissue Stiffness in Young and Older People.

The purpose of this study was to investigate differences in the associations between passive ankle dorsiflexion range of motion (ROM) and stiffness of the triceps surae, sciatic nerve, and deep fascia located in the posterior leg between young and older people. Twenty young and twenty older males were recruited and were placed in a prone position with their hip and knee fully extended. Passive ankle dorsiflexion ROM was determined based on the onset of pain during passive dorsiflexion at 1°·s using an isokinetic dynamometer. Shear wave speeds (as a stiffness index) of the triceps surae, the sciatic nerve, and the deep fascia in the posterior leg were evaluated by ultrasound shear wave elastography. The shear wave speeds of the medial and lateral gastrocnemius measured at 15° dorsiflexion correlated negatively with passive ROM in young but not in older participants. The shear wave speed of the sciatic nerve measured at 15° dorsiflexion correlated negatively with passive ROM only in older participants. No association was observed between passive ROM and shear wave speed of the deep fascia in the posterior leg. For data measured at maximal dorsiflexion angle (as an index of stretch tolerance), shear wave speeds of the triceps surae and passive joint torque correlated positively with passive ROM in both groups. These results suggest that the tissues limiting passive ankle dorsiflexion ROM are muscle and nerve for young and older people, respectively, whereas stretch tolerance influences passive ROM for both groups. This implies that the relative contribution of nonmuscular tissues to joint flexibility become stronger than that of muscles with age.

Development of a dynamic index finger and thumb model to study impairment

Modeling of the human hand provides insight for explaining deficits and planning treatment following injury. Creation of a dynamic model, however, is complicated by the actions of multi-articular tendons and their complex interactions with other soft tissues in the hand. This study explores the creation of a musculoskeletal model, including the thumb and index finger, to explore the effects of muscle activation deficits. The OpenSim model utilizes physiological axes of rotation at all joints, passive joint torques, and appropriate moment arms. The model was validated through comparison with kinematic and kinetic experimental data. Simulated fingertip forces resulting from modeled musculotendon loading largely fell within one standard deviation of experimental ranges for most index finger and thumb muscles, although agreement in the sagittal plane was generally better than for the coronal plane. Input of experimentally obtained electromyography data produced the expected simulated finger and thumb motion. Use of the model to predict the effects of activation deficits on pinch force production revealed that the intrinsic muscles, especially first dorsal interosseous (FDI) and adductor pollicis (ADP), had a substantial impact on the resulting fingertip force. Reducing FDI activation, such as might occur following stroke, altered fingertip force direction by up to 83° for production of a dorsal fingertip force; reducing ADP activation reduced force production in the thumb by up to 62%. This validated model can provide a means for evaluating clinical interventions.

P.460 - Unraveling upper extremity performance in DMD: a biophysical model

Upper extremity (UE) activity scales are currently used as the golden standard for defining UE function in non-ambulant Duchenne muscular dystrophy (DMD) patients. These scales, however, are not able to explain the biophysical working mechanism behind changes in UE function. Therefore, we aimed to identify critical physiological outcome variables underlying reduced UE task performance in DMD. These critical variables were used to construct an explanatory biophysical model of the UE working mechanism in DMD. The most critical physiologic outcome variables related to UE task performance (Brooke scale and Performance of Upper Limb (PUL) scale) were maximal active joint angle, followed by maximal muscle torque, maximal muscle activity, echogenicity (fatty infiltration) and maximal passive range of motion. These variables explained more than 90% of the variability in UE task performance. Based on these critical variables a biophysical model was constructed. In this model we considered UE task performance to be mainly dependent on the ability to move your arms actively, which is influenced by both passive range of motion and the available joint torque. The available joint torque is dependent on muscle capacity, and should be sufficient to lift the weight of the arm against gravity and to overcome passive joint torque (stiffness). Muscle capacity is influenced by both the ability to activate the muscle and the muscle force that is generated at the joint level. This model allows us to understand the underlying cause of UE limitations. Based on this knowledge one can select appropriate interventions to improve UE function, such as arm supports to improve the reachable workspace, contracture prevention, or medication to improve muscle strength. In addition, the model could form the basis for the development of new composite outcome measures for clinical trials.

A Robot-Driven Computational Model for Estimating Passive Ankle Torque With Subject-Specific Adaptation.

Robot-assisted ankle assessment could potentially be conducted using sensor-based and model-based methods. Existing ankle rehabilitation robots usually use torquemeters and multiaxis load cells for measuring joint dynamics. These measurements are accurate, but the contribution as a result of muscles and ligaments is not taken into account. Some computational ankle models have been developed to evaluate ligament strain and joint torque. These models do not include muscles and, thus, are not suitable for an overall ankle assessment in robot-assisted therapy. This study proposed a computational ankle model for use in robot-assisted therapy with three rotational degrees of freedom, 12 muscles, and seven ligaments. This model is driven by robotics, uses three independent position variables as inputs, and outputs an overall ankle assessment. Subject-specific adaptations by geometric and strength scaling were also made to allow for a universal model. This model was evaluated using published results and experimental data from 11 participants. Results show a high accuracy in the evaluation of ligament neutral length and passive joint torque. The subject-specific adaptation performance is high, with each normalized root-mean-square deviation value less than 10%. This model could be used for ankle assessment, especially in evaluating passive ankle torque, for a specific individual. The characteristic that is unique to this model is the use of three independent position variables that can be measured in real time as inputs, which makes it advantageous over other models when combined with robot-assisted therapy.

Shear wave elastography of passive skeletal muscle stiffness: Influences of sex and age throughout adulthood

BackgroundNumerous structural and compositional changes – related not only to age, but also activity level and sex – may affect skeletal muscle stiffness across the adult age-span. Measurement techniques available thus far have largely limited passive stiffness evaluations to those of entire joints and muscle–tendon units. Shear wave elastography is an increasingly popular ultrasound technique for evaluating the mechanical properties of skeletal muscle tissue. The purpose of this study was to quantify the passive stiffness, or shear modulus, of the biceps brachii throughout adulthood in flexed and extended elbow positions. We hypothesized that shear modulus would be higher in males relative to females, and with advanced age in both sexes. MethodsShear wave elastography quantified biceps brachii stiffness at 90° elbow flexion and full extension in a large sample of adults between 21 and 94years old (n=133; 47 males). FindingsRegression analysis found sex and age were significant parameters for older adults (>60years) in full extension. As expected, shear modulus values increased with advancing age; however, shear modulus values for females tended to be higher than those for males. InterpretationThis study begins to establish normative trends for skeletal muscle shear modulus throughout adulthood. Specifically, this work establishes for the first time that the higher passive joint torque often found in males relative to females likely relates to parameters other than muscle shear modulus. Indeed, perhaps increases in skeletal muscle passive stiffness, though potentially altering the length–tension curve, serve a protective role — maintaining the tendon–muscle–tendon length–tension curve within a functional range.

Myofascial force transmission between the latissimus dorsi and gluteus maximus muscles: An in vivo experiment

There are extensive connections between the latissimus dorsi (LD) and gluteus maximus (GMax) muscles and the thoracolumbar fascia (TLF), which suggests a possible pathway for myofascial force transmission. The present study was designed to provide empirical evidence of myofascial force transmission from LD to contralateral GMax through TFL in vivo. To accomplish this goal, we evaluated whether active or passive tensioning of the LD results in increased passive tension of the contralateral GMax, indexed by changes in the hip resting position (RP) or passive stiffness. The hip RP was defined as the angular position in which the passive joint torque equals zero, and passive hip stiffness was calculated as the change in passive torque per change in joint angle. Thirty-seven subjects underwent an assessment of their passive hip torque against medial rotation by means of an isokinetic dynamometer. These measures were carried out under three test conditions: (1) control, (2) passive LD tensioning and (3) active LD tensioning. Electromyography was used to monitor the activity of the hip muscles and the LD under all conditions. Repeated measures analyses of variance demonstrated that passive LD tensioning shifted the hip RP towards lateral rotation (p=0.009) but did not change the passive hip stiffness (p>0.05). Active LD tensioning shifted the hip RP towards lateral rotation (p<0.001) and increased the passive hip stiffness (p≤0.004). The results demonstrated that manipulation of the LD tension modified the passive hip variables, providing evidence of myofascial force transmission in vivo.

Estimating in vivo passive forces of the index finger muscles: Exploring model parameters

We compared predicted passive finger joint torques from a biomechanical model that includes the exponential passive muscle force–length relationship documented in the literature with finger joint torques estimated from measures in ten adult volunteers. The estimated finger joint torques were calculated from measured right index fingertip force, joint postures, and anthropometry across 18 finger and wrist postures with the forearm muscles relaxed. The biomechanical model predicting passive finger joint torques included three extrinsic and three intrinsic finger muscles. The values for the predicted passive joint torques were much larger than the values calculated from the fingertip force and posture measures with an average RMS error of 7.6 N cm. Sensitivity analysis indicated that the predicted joint torques were most sensitive to passive force–length model parameters compared to anthropometric and postural parameters. Using Monte Carlo simulation, we determined a new set of values for the passive force–length model parameters that reduced the differences between the joint torques calculated from the two methods to an average RMS value of 0.5 N cm, a 94% average improvement of error from the torques predicted using the existing data. These new parameter values did vary across individuals; however, using an average set for the parameter values across subjects still reduced the average RMS difference to 0.8 N cm. These new parameters may improve dynamic modeling of the finger during sub-maximal force activities and are based on in vivo data rather than traditional in vitro data.

The Relationship Between Passive Ankle Plantar Flexion Joint Torque and Gastrocnemius Muscle and Achilles Tendon Stiffness: Implications for Flexibility

Experimental laboratory study. We tested the hypothesis that the muscle fibers and the connective tendinous structures, combined in series, provide the resistance to passive joint movement at the ankle. We also determined the relative association between passive joint torque and each of these 2 elements. The reason for individual variation in joint flexibility or tightness is not clearly understood, but the influence of musculotendinous stiffness has been inferred. Each of the subjects (6 women and 6 men) was seated with the right knee extended and right ankle positioned at a 30 degrees , 20 degrees , 10 degrees , 0 degrees , -10 degrees , -20 degrees , and -30 degrees (0, neutral position, positive values reflecting plantar flexion) angle while passive plantar flexion torque was measured. The distal muscle-tendon junction of the medial gastrocnemius was visualized by ultrasonography, and its positional change was defined as muscle belly length change. The whole muscle-tendon unit length change was estimated from joint angle changes, from which Achilles tendon length change was estimated. Both the muscle belly and tendon were significantly elongated as the ankle was dorsiflexed (at 0 degrees the mean +/- SD muscle belly elongation was 10.3% +/- 1.8 %, and the tendon elongation was 2.8% +/- 1.2 %, of the initial length at 30 degrees of ankle plantar flexion), from which stiffness indices were determined both for muscle belly and tendon. The passive torque at 0 degrees , -10 degrees , -20 degrees , and -30 degrees was significantly correlated with the stiffness indices of the Achilles tendon (at 0 degrees , r2 = 0.70 and 0.62 for overall and specific stiffness, respectively; P<.05). A tendon stiffness index, separately obtained from tendon lengthening during maximal isometric contraction, was also correlated with passive ankle plantar flexion torque at 0 degrees , -10 degrees , -20 degrees , and -30 degrees (at 0 degrees , r2 = 0.76; P<.05). The specific stiffness index of the muscle belly was correlated (r2 = 0.47, P<.05) with the passive ankle plantar flexion torque at 0 degrees , but its overall stiffness index was not (r2 = 0.32, P>.05). Results suggest that extensibility of the muscle-tendon unit of the Achilles tendon for the most part is related to passive ankle plantar flexion joint torque.

Human motor compensations for thixotropy‐dependent changes in muscular resting tension after moderate joint movements

This study on healthy subjects explores history-dependent changes in the resting tension of relaxed wrist muscles after moderate joint excursions and the motor control consequences of these changes during voluntary wrist joint position maintenance. Integrated surface electromyogram (IEMG) was recorded from wrist extensor/flexor muscles. Angular position and torque were recorded from the wrist joint. Changes in wrist flexor muscle resting tension were sensed by a force transducer pressed against the tendons. Consecutive stepwise changes (7.5 degrees ) in wrist joint position (within the dorsiflexed range) were either imposed on relaxed subjects or actively performed while the subjects under visual guidance tried to mimic the passive movements. In relaxed subjects, passive joint torque resistance at a given steady dorsiflexed position either gradually declined or rose depending on the direction of the previous transition movements. In corresponding voluntary contraction experiments, the IEMG amplitude from position holding wrist extensors was found to vary in a similar way as the passive torque resistance. Further, there was a strong correlation between history-dependent changes in extensor IEMG amplitude and stress alterations exhibited by the relaxed antagonist flexors. The above described, slowly subsiding post-movement mechanical and motor adaptations were accelerated by brief forceful cocontractions of the forearm muscles. Moderate stepwise changes in joint position are sufficient to induce history-dependent after-effects in passive muscular resting tension, after-effects which during voluntary position holding are effectively compensated for by the motor control system.

Extrinsic flexor muscles generate concurrent flexion of all three finger joints

The role of the forearm (extrinsic) finger flexor muscles in initiating rotation of the metacarpophalangeal (MCP) joint and in coordinating flexion at the MCP, the proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints remains a matter of some debate. To address the biomechanical feasibility of the extrinsic flexors performing these actions, a computer simulation of the index finger was created. The model consisted of a planar open-link chain comprised of three revolute joints and four links, driven by the change in length of the flexor muscles. Passive joint characteristics, included in the model, were obtained from system identification experiments involving the application of angular perturbations to the joint of interest. Simulation results reveal that in the absence of passive joint torque, shortening of the extrinsic flexors results in PIP flexion (80°), but DIP (8°) and MCP (7°) joint extension. The inclusion of normal physiological levels of passive joint torque, however, results in simultaneous flexion of all three joints (63° for DIP, 75° for PIP, and 43° for MCP). Applicability of the simulation results was confirmed by recording finger motion produced by electrical stimulation of the extrinsic flexor muscles for the index finger. These findings support the view that the extrinsic flexor muscles can initiate MCP flexion, and produce simultaneous motion at the MCP, PIP, and DIP joints.