A three-dimensional biomechanical evaluation of quadriceps and hamstrings function using electrical stimulation

Differences between lower extremity joint running kinetics captured by marker-based and markerless systems were speed dependent

BACKGROUND

The development of computer vision technology has enabled the use of markerless movement tracking for biomechanical analysis. Recent research has reported the feasibility of markerless systems in motion analysis but has yet to fully explore their utility for capturing faster movements, such as running. Applied studies using markerless systems in clinical and sports settings are still lacking. Thus, the present study compared running biomechanics estimated by marker-based and markerless systems. Given running speed not only affects sports performance but is also associated with clinical injury prevention, diagnosis, and rehabilitation, we aimed to investigate the effects of speed on the comparison of estimated lower extremity joint moments and powers between markerless and marker-based technologies during treadmill running as a concurrent validating study.

METHODS

Kinematic data from marker-based/markerless technologies were collected, along with ground reaction force data, from 16 young adults running on an instrumented treadmill at 3 speeds: 2.24 m/s, 2.91 m/s, and 3.58 m/s (5.0 miles/h, 6.5 miles/h, and 8.0 miles/h). Sagittal plane moments and powers of the hip, knee, and ankle were calculated by inverse dynamic methods. Time series analysis and statistical parametric mapping were used to determine system differences.

RESULTS

Compared to the marker-based system, the markerless system estimated increased lower extremity joint kinetics with faster speed during the swing phase in most cases.

CONCLUSION

Despite the promising application of markerless technology in clinical settings, systematic markerless overestimation requires focused attention. Based on segment pose estimations, the centers of mass estimated by markerless technologies were farther away from the relevant distal joint centers, which led to greater joint moments and powers estimates by markerless vs. marker-based systems. The differences were amplified by running speed.

How age and surface inclination affect joint moment strategies to accelerate and decelerate individual leg joints during walking

A joint moment also causes motion at other joints of the body. This joint coupling-perspective allows more insight into two age-related phenomena during gait. First, whether increased hip kinetic output compensates for decreased ankle kinetic output during positive joint work. Second, whether preserved joint kinetic patterns during negative joint work in older age have any functional implication. Therefore, we examined how age and surface inclination affect joint moment strategies to accelerate and/or decelerate individual leg joints during walking. Healthy young (age: 22.5 ± 4.1 years, n = 18) and older (age: 76.0 ± 5.7 years, n = 22) adults walked at 1.4 m/s on a split-belt instrumented treadmill at three grades (0%, 10%, -10%). Lower-extremity moment-induced angular accelerations were calculated for the hip (0% and 10%) and knee (0% and -10%) joints. During level and uphill walking, both age groups showed comparable ankle moment-induced ipsilateral (p = 0.774) and contralateral (p = 0.047) hip accelerations, although older adults generated lower ankle moments in late stance. However, ankle moment-induced contralateral hip accelerations were smaller (p = 0.001) in an older adult subgroup (n = 13) who showed larger hip extension moments in early stance than young adults. During level and downhill walking, leg joint moment-induced knee accelerations were unaffected by age (all p > 0.05). These findings suggest that during level and uphill walking increased hip flexor mechanical output in older adults does not arise from reduced ankle moments, contrary to increased hip extensor mechanical output. Additionally, results during level and downhill walking imply that preserved eccentric knee extensor function is important in maintaining knee stabilization in older age.

Neck muscle biomechanics and neural control

The mechanics, morphometry, and geometry of our joints, segments, and muscles are fundamental biomechanical properties intrinsic to human neural control. The goal of our study was to investigate whether the biomechanical actions of individual neck muscles predict their neural control. Specifically, we compared the moment direction and variability produced by electrical stimulation of a neck muscle (biomechanics) to the preferred activation direction and variability (neural control). Subjects sat upright with their head fixed to a six-axis load cell and their torso restrained. Indwelling wire electrodes were placed into the sternocleidomastoid (SCM), splenius capitis (SPL), and semispinalis capitis (SSC) muscles. The electrically stimulated direction was defined as the moment direction produced when a current (2-19 mA) was passed through each muscle's electrodes. Preferred activation direction was defined as the vector sum of the spatial tuning curve built from root mean squared electromyogram when subjects produced isometric moments at 7.5% and 15% of their maximum voluntary contraction (MVC) in 26 three-dimensional directions. The spatial tuning curves at 15% MVC were well defined (unimodal, P < 0.05), and their preferred directions were 23°, 39°, and 21° different from their electrically stimulated directions for the SCM, SPL, and SSC, respectively ( P < 0.05). Intrasubject variability was smaller in electrically stimulated moment directions compared with voluntary preferred directions, and intrasubject variability decreased with increased activation levels. Our findings show that the neural control of neck muscles is not based solely on optimizing individual muscle biomechanics but, as activation increases, biomechanical constraints in part dictate the activation of synergistic neck muscles. NEW & NOTEWORTHY Biomechanics are an intrinsic part of human neural control. In this study, we found that the biomechanics of individual neck muscles cannot fully predict their neural control. Consequently, physiologically based computational neck muscle controllers cannot calculate muscle activation schemes based on the isolated biomechanics of muscles. Furthermore, by measuring biomechanics we showed that the intrasubject variability of the neural control was lower for electrical vs. voluntary activation of the neck muscles.

Manipulating post-stroke gait: Exploiting aberrant kinematics

Post-stroke individuals often exhibit abnormal kinematics, including increased pelvic obliquity and hip abduction coupled with reduced knee flexion. Prior examinations suggest these behaviors are expressions of abnormal cross-planar coupling of muscle activity. However, few studies have detailed the impact of gait-retraining paradigms on three-dimensional joint kinematics. In this study, a cross-tilt walking surface was examined as a novel gait-retraining construct. We hypothesized that relative to baseline walking kinematics, exposure to cross-tilt would generate significant changes in subsequent flat-walking joint kinematics during affected limb swing. Twelve post-stroke participants walked on a motorized treadmill platform during a flat-walking condition and during a 10-degree cross-tilt with affected limb up-slope, increasing toe clearance demand. Individuals completed 15 min of cross-tilt walking with intermittent flat-walking catch trials and a final washout period (5 min). For flat-walking conditions, we examined changes in pelvic obliquity, hip abduction/adduction and knee flexion kinematics at the spatiotemporal events of swing initiation and toe-off, and the kinematic event of maximum angle during swing. Pelvic obliquity significantly reduced at swing initiation and maximum obliquity in the final catch trial and late washout. Knee flexion significantly increased at swing initiation, toe-off, and maximum flexion across catch trials and late washout. Hip abduction/adduction was not significantly influenced following cross-tilt walking. Significant decrease in the rectus femoris and medial hamstrings muscle activity across catch trials and late washout was observed. Exploiting the abnormal features of post-stroke gait during retraining yielded desirable changes in muscular and kinematic patterns post-training.

Normalized patellofemoral joint reaction force is greater in individuals with patellofemoral pain

Patellofemoral pain is a disabling, highly prevalent pathology. Altered patellofemoral contact forces are theorized to contribute to this pain. Musculoskeletal modeling has been employed to better understand the etiology of patellofemoral pain. Currently, there are no data on the effective quadriceps moment arm for individuals with patellofemoral pain, forcing researchers to apply normative values when modeling such individuals. In addition, the ratio of patellofemoral reaction force to quadriceps force is often used as a surrogate for patellofemoral joint contact force, ignoring the fact that the quadriceps efficiency can vary with pathology and intervention. Thus, the purposes of this study were to: (1) quantify the effective quadriceps moment arm in individuals with patellofemoral pain and compare this value to a control cohort and (2) develop a novel methodology for quantifying the normalized patellofemoral joint reaction force in vivo during dynamic activities. Dynamic MR data were captured as subjects with patellofemoral pain (30F/3M) cyclically flexed their knee from 10° to 40°. Data for control subjects (29F/9M) were taken from a previous study. The moment arm data acquired across a large cohort of individuals with patellofemoral pain should help advance musculoskeletal modeling. The primary finding of this study was an increased mean normalized patellofemoral reaction force of 14.9% (maximum values at a knee angle of 10°) in individuals with patellofemoral pain. Understanding changes in the normalized patellofemoral reaction force with pathology may lead to improvements in clinical decision making, and consequently treatments, by providing a more direct measure of altered patellofemoral joint forces.

Downregulating Aberrant Motor Evoked Potential Synergies of the Lower Extremity Post Stroke During TMS of the Contralesional Hemisphere

BACKGROUND

Growing evidence demonstrates unique synergistic signatures in the lower limb (LL) post-stroke, with specific across-plane and across-joint representations. While the inhibitory role of the ipsilateral hemisphere in the upper limb (UL) has been widely reported, examination of the contralesional hemisphere (CON-H) in modulating LL expressions of synergies following stroke is lacking.

OBJECTIVE

We hypothesize that stimulation of lesioned and contralesional motor cortices will differentially regulate paretic LL motor outflow. We propose a novel TMS paradigm to identify synergistic motor evoked potential (MEP) patterns across multiple muscles.

METHODS

Amplitude and background activation matched adductor MEPs were elicited using single pulse TMS of L-H and CON-H (control ipsilateral) during an adductor torque matching task from 11 stroke and 10 control participants. Associated MEPs of key synergistic muscles were simultaneously observed.

RESULTS

By quantifying CON-H/L-H MEP ratios, we characterized a significant targeted inhibition of aberrant MEP coupling between ADD and VM (p = 0.0078) and VL (p = 0.047) exclusive to the stroke group (p = 0.028) that was muscle dependent (p = 0.039). We find TA inhibition in both groups following ipsilateral hemisphere stimulation (p = 0.0014; p = 0.015).

CONCLUSION

We argue that ipsilaterally mediated attenuation of abnormal synergistic activations post stroke may reflect an adaptive intracortical inhibition. The predominance of sub 3ms interhemispheric MEP latency differences implicates LL ipsilateral corticomotor projections. These findings provide insight into the association between CON-H reorganization and post-stroke LL recovery. While a prevailing view of driving L-H disinhibition for UL recovery seems expedient, presuming analogous LL neuromodulation may require further examination for rehabilitation. This study provides a step toward this goal.

Effects of spinal cord injury-induced changes in muscle activation on foot drag in a computational rat ankle model

Spinal cord injury (SCI) can lead to changes in muscle activation patterns and atrophy of affected muscles. Moderate levels of SCI are typically associated with foot drag during the swing phase of locomotion. Foot drag is often used to assess locomotor recovery, but the causes remain unclear. We hypothesized that foot drag results from inappropriate muscle coordination preventing flexion at the stance-to-swing transition. To test this hypothesis and to assess the relative contributions of neural and muscular changes on foot drag, we developed a two-dimensional, one degree of freedom ankle musculoskeletal model with gastrocnemius and tibialis anterior muscles. Anatomical data collected from sham-injured and incomplete SCI (iSCI) female Long-Evans rats as well as physiological data from the literature were used to implement an open-loop muscle dynamics model. Muscle insertion point motion was calculated with imposed ankle trajectories from kinematic analysis of treadmill walking in sham-injured and iSCI animals. Relative gastrocnemius deactivation and tibialis anterior activation onset times were varied within physiologically relevant ranges based on simplified locomotor electromyogram profiles. No-atrophy and moderate muscle atrophy as well as normal and injured muscle activation profiles were also simulated. Positive moments coinciding with the transition from stance to swing phase were defined as foot swing and negative moments as foot drag. Whereas decreases in activation delay caused by delayed gastrocnemius deactivation promote foot drag, all other changes associated with iSCI facilitate foot swing. Our results suggest that even small changes in the ability to precisely deactivate the gastrocnemius could result in foot drag after iSCI.

Rectus femoris knee muscle moment arms measured in vivo during dynamic motion with real-time magnetic resonance imaging

Moment arms represent a muscle's ability to generate a moment about a joint for a given muscle force. The goal of this study was to develop a method to measure muscle moment arms in vivo over a large range of motion using real-time magnetic resonance (MR) imaging. Rectus femoris muscle-tendon lengths and knee joint angles of healthy subjects (N = 4) were measured during dynamic knee joint flexion and extension in a large-bore magnetic resonance imaging (MRI) scanner. Muscle-tendon moment arms were determined at the knee using the tendon-excursion method by differentiating measured muscle-tendon length with respect to joint angle. Rectus femoris moment arms were averaged across a group of healthy subjects and were found to vary similarly during knee joint flexion (mean: 3.0 (SD 0.5) cm, maximum: 3.5 cm) and extension (mean: 2.8 (SD 0.4) cm, maximum: 3.6 cm). These moment arms compare favorably with previously published dynamic tendon-excursion measurements in cadaveric specimens but were relatively smaller than moment arms from center-of-rotation studies. The method presented here provides a new approach to measure muscle-tendon moment arms in vivo and has the potential to be a powerful resource for characterizing musculoskeletal geometry during dynamic joint motion.

Evaluation of lower limb cross planar kinetic connectivity signatures post-stroke

Following stroke, aberrant three dimensional multijoint gait impairments emerge that present in kinematic asymmetries such as circumduction. A precise pattern of cross-planar coordination may underlie abnormal hemiparetic gait as several studies have underscored distinctive neural couplings between medio-lateral control and sagittal plane progression during walking. Here we investigate potential neuromechanical constraints governing abnormal multijoint coordination post-stroke. 15 chronic monohemispheric stroke patients and 10 healthy subjects were recruited. Coupled torque production patterns were assessed using a volitional isometric torque generation task where subjects matched torque targets for a primary joint in 4 directions while receiving visual feedback of the magnitude and direction of the torque. Secondary torques at other lower limb joints were recorded without subject feedback. We find that common features of cross-planar connectivity in stroke subjects include statistically significant frontal to sagittal plane kinetic coupling that overlay a common sagittal plane coupling in healthy subjects. Such coupling is independent of proximal or distal joint control and limb biomechanics. Principal component analysis of the stroke aggregate kinetic signature reveals unique abnormal frontal plane coupling features that explain a larger percentage of the total torque coupling variance. This study supports the idea that coupled cross-planar kinetic outflow between the lower limb joints uniquely emerges during pathological control of frontal plane degrees of freedom resulting in a generalized extension of the limb. It remains to be seen if a pattern of lower limb motor outflow that is centrally mediated contributes to abnormal hemiparetic gait.

Selective activation of the human tibial and common peroneal nerves with a flat interface nerve electrode

OBJECTIVE

Electrical stimulation has been shown effective in restoring basic lower extremity motor function in individuals with paralysis. We tested the hypothesis that a flat interface nerve electrode (FINE) placed around the human tibial or common peroneal nerve above the knee can selectively activate each of the most important muscles these nerves innervate for use in a neuroprosthesis to control ankle motion.

APPROACH

During intraoperative trials involving three subjects, an eight-contact FINE was placed around the tibial and/or common peroneal nerve, proximal to the popliteal fossa. The FINE's ability to selectively recruit muscles innervated by these nerves was assessed. Data were used to estimate the potential to restore active plantarflexion or dorsiflexion while balancing inversion and eversion using a biomechanical simulation.

MAIN RESULTS

With minimal spillover to non-targets, at least three of the four targets in the tibial nerve, including two of the three muscles constituting the triceps surae, were independently and selectively recruited in all subjects. As acceptable levels of spillover increased, recruitment of the target muscles increased. Selective activation of muscles innervated by the peroneal nerve was more challenging.

SIGNIFICANCE

Estimated joint moments suggest that plantarflexion sufficient for propulsion during stance phase of gait and dorsiflexion sufficient to prevent foot drop during swing can be achieved, accompanied by a small but tolerable inversion or eversion moment.

Empirical assessment of dynamic hamstring function during human walking

The hamstrings are often associated with the development of crouch gait, a fatiguing form of walking characterized by excessive hip flexion, knee flexion and ankle dorsiflexion during stance. However, recent studies have called into question whether abnormally active hamstrings induce the limb to move into a crouch posture. The purpose of this study was to directly measure the influence of the hamstrings on limb posture during stance. Nineteen healthy young adults walked on an instrumented treadmill at their preferred speed. A 90 ms pulse train was used to stimulate the medial hamstrings during either terminal swing or loading response of random gait cycles. Induced motion was defined as the difference in joint angle trajectories between stimulated and non-stimulated strides. A dynamic musculoskeletal simulation of normal gait was generated and similarly perturbed by increasing hamstring excitation. The experiments show that hamstring stimulation induced a significant increase in posterior pelvic tilt, knee flexion and ankle dorsiflexion during stance, while having relatively less influence on the hip angular trajectory. The induced motion patterns were similar whether the hamstrings were stimulated during late swing or early stance, and were generally consistent with the direction of induced motion predicted by gait simulation models. Hence, we conclude that overactive hamstrings have the potential to induce the limb to move toward a crouch gait posture.

Quantifying individual muscle contribution to three-dimensional reaching tasks

We investigated the individual muscle contribution to arm motion to better understand the complex muscular coordination underlying three-dimensional (3D) reaching tasks of the upper limb (UL). The individual contributions of biceps, triceps, deltoid anterior, medius, posterior and pectoralis major to the control of specific degrees of freedom (DOFs) were examined: using a scaled musculoskeletal model, the muscle excitations that reproduce the kinematics were calculated using computed muscle control and a forward simulation was generated. During consequent perturbation analyses, the muscle excitation of selected muscles was instantaneously increased and the resulting effect on the specific DOF was studied to quantify the muscle contribution. The calculated muscle contributions were compared to the responses elicited during electrical stimulation experiments. Innovative in our findings is that muscle action during reaching clearly depended on the reaching trajectory in 3D space. For the majority of the muscles, the magnitude of muscle action changed and even reversed when reaching to different heights and widths. Furthermore, muscle effects on non spanned joints were reported. Using a musculoskeletal model and forward simulation techniques, we demonstrate individual position-dependent muscle contributions to 3D joint kinematics of the UL.

Effect of running speed on lower limb joint kinetics

PURPOSE

Knowledge regarding the biomechanical function of the lower limb muscle groups across a range of running speeds is important in improving the existing understanding of human high performance as well as in aiding in the identification of factors that might be related to injury. The purpose of this study was to evaluate the effect of running speed on lower limb joint kinetics.

METHODS

Kinematic and ground reaction force data were collected from eight participants (five males and three females) during steady-state running on an indoor synthetic track at four discrete speeds: 3.50±0.04, 5.02±0.10, 6.97±0.09, and 8.95±0.70 m·s. A standard inverse-dynamics approach was used to compute three-dimensional torques at the hip, knee, and ankle joints, from which net powers and work were also calculated. A total of 33 torque, power, and work variables were extracted from the data set, and their magnitudes were statistically analyzed for significant speed effects.

RESULTS

The torques developed about the lower limb joints during running displayed identifiable profiles in all three anatomical planes. The sagittal-plane torques, net powers, and work done at the hip and knee during terminal swing demonstrated the largest increases in absolute magnitude with faster running. In contrast, the work done at the knee joint during stance was unaffected by increasing running speed, whereas the work done at the ankle joint during stance increased when running speed changed from 3.50 to 5.02 m·s, but it appeared to plateau thereafter.

CONCLUSIONS

Of all the major lower limb muscle groups, the hip extensor and knee flexor muscles during terminal swing demonstrated the most dramatic increase in biomechanical load when running speed progressed toward maximal sprinting.

Electrical stimulation of the rectus femoris during pre-swing diminishes hip and knee flexion during the swing phase of normal gait

Individuals who have suffered cerebral insults often exhibit stiff-knee gait, a condition characterized by reduced knee flexion during swing. We investigated the effect that an increment in normal rectus femoris (RF) activity can have on hip and knee joint angles during swing, as a first step to determining this muscle's involvement in stiff-knee gait. For this, we developed a protocol that electrically stimulated the RF during pre-swing or after toe-off in randomly selected strides of treadmill walking, consistent with the timing of RF activity during normal gait. Seven healthy young adults participated in the study. Pre-swing stimulation induced a significant (p < 0.05) reduction in peak knee flexion (avg 7.5°) in all subjects, with an accompanying decrease in hip flexion in four of the subjects. RF stimulation after toe-off diminished peak knee flexion in three subjects and reduced hip flexion in four subjects. When compared to muscle-actuated gait simulations that were similarly perturbed, the induced motion measures were generally consistent in direction but exhibited greater variability across strides and subjects. We conclude that excess RF activity during pre-swing has the potential to contribute to stiff-knee gait, and that clinical treatment should consider the "counter-intuitive" function that the RF has in extending the hip.

Preswing knee flexion assistance is coupled with hip abduction in people with stiff-knee gait after stroke

BACKGROUND AND PURPOSE

Stiff-knee gait is defined as reduced knee flexion during the swing phase. It is accompanied by frontal plane compensatory movements (eg, circumduction and hip hiking) typically thought to result from reduced toe clearance. As such, we examined if knee flexion assistance before foot-off would reduce exaggerated frontal plane movements in people with stiff-knee gait after stroke.

METHODS

We used a robotic knee orthosis to assist knee flexion torque during the preswing phase in 9 chronic stroke subjects with stiff-knee gait on a treadmill and compared peak knee flexion, hip abduction, and pelvic obliquity angles with 5 nondisabled control subjects.

RESULTS

Maximum knee flexion angle significantly increased in both groups, but instead of reducing gait compensations, hip abduction significantly increased during assistance in stroke subjects by 2.5 degrees , whereas no change was observed in nondisabled control subjects. No change in pelvic obliquity was observed in either group.

CONCLUSIONS

Hip abduction increased when stroke subjects received assistive knee flexion torque at foot-off. These findings are in direct contrast to the traditional belief that pelvic obliquity combined with hip abduction is a compensatory mechanism to facilitate foot clearance during swing. Because no evidence suggested a voluntary mechanism for this behavior, we argue that these results were most likely a reflection of an altered motor template occurring after stroke.

Muscle contributions to support and progression during single-limb stance in crouch gait

Pathological movement patterns like crouch gait are characterized by abnormal kinematics and muscle activations that alter how muscles support the body weight during walking. Individual muscles are often the target of interventions to improve crouch gait, yet the roles of individual muscles during crouch gait remain unknown. The goal of this study was to examine how muscles contribute to mass center accelerations and joint angular accelerations during single-limb stance in crouch gait, and compare these contributions to unimpaired gait. Subject-specific dynamic simulations were created for ten children who walked in a mild crouch gait and had no previous surgeries. The simulations were analyzed to determine the acceleration of the mass center and angular accelerations of the hip, knee, and ankle generated by individual muscles. The results of this analysis indicate that children walking in crouch gait have less passive skeletal support of body weight and utilize substantially higher muscle forces to walk than unimpaired individuals. Crouch gait relies on the same muscles as unimpaired gait to accelerate the mass center upward, including the soleus, vasti, gastrocnemius, gluteus medius, rectus femoris, and gluteus maximus. However, during crouch gait, these muscles are active throughout single-limb stance, in contrast to the modulation of muscle forces seen during single-limb stance in an unimpaired gait. Subjects walking in crouch gait rely more on proximal muscles, including the gluteus medius and hamstrings, to accelerate the mass center forward during single-limb stance than subjects with an unimpaired gait.

Dynamic in vivo quadriceps lines-of-action

Tissue stresses and quadriceps forces are crucial factors when considering knee joint biomechanics. However, it is difficult to obtain direct, in vivo, measurements of these quantities. The primary purpose of this study was to provide the first complete description of quadriceps geometry (force directions and moment arms) of individual quadriceps components using in vivo, 3D data collected during volitional knee extension. A secondary purpose was to determine if 3D quadriceps geometry is altered in patients with patellofemoral pain and maltracking. After obtaining informed consent, cine-phase contrast (PC) MRI sets (x,y,z velocity and anatomic images) were acquired from 25 asymptomatic knees and 15 knees with patellofemoral pain during active knee extension. Using a sagittal-oblique and two coronal-oblique imaging planes, the origins and insertions of each quadriceps line-of-action were identified and tracked throughout the motion by integrating the cine-PC velocity data. The force direction and relative moment (RM) were calculated for each line-of-action. All quadriceps lines-of-action were oriented primarily in the superior direction. There were no significant differences in quadriceps geometry between asymptomatic and subjects with patellofemoral pain. However, patellofemoral kinematics were significantly different between the two populations. This study will improve the ability of musculoskeletal models to closely match in vivo human performance by providing accurate 3D quadriceps geometry and associated patellofemoral kinematics during dynamic knee motion. Furthermore, determination that quadriceps geometry is not altered in patellofemoral pain supports the use of generalized a knee model based on asymptomatic quadriceps architecture.