Does joint impedance improve dynamic leg simulations with explicit and implicit solvers?

The nervous system predicts and executes complex motion of body segments actuated by the coordinated action of muscles. When a stroke or other traumatic injury disrupts neural processing, the impeded behavior has not only kinematic but also kinetic attributes that require interpretation. Biomechanical models could allow medical specialists to observe these dynamic variables and instantaneously diagnose mobility issues that may otherwise remain unnoticed. However, the real-time and subject-specific dynamic computations necessitate the optimization these simulations. In this study, we explored the effects of intrinsic viscoelasticity, choice of numerical integration method, and decrease in sampling frequency on the accuracy and stability of the simulation. The bipedal model with 17 rotational degrees of freedom (DOF)-describing hip, knee, ankle, and standing foot contact-was instrumented with viscoelastic elements with a resting length in the middle of the DOF range of motion. The accumulation of numerical errors was evaluated in dynamic simulations using swing-phase experimental kinematics. The relationship between viscoelasticity, sampling rates, and the integrator type was evaluated. The optimal selection of these three factors resulted in an accurate reconstruction of joint kinematics (err < 1%) and kinetics (err < 5%) with increased simulation time steps. Notably, joint viscoelasticity reduced the integration errors of explicit methods and had minimal to no additional benefit for implicit methods. Gained insights have the potential to improve diagnostic tools and accurize real-time feedback simulations used in the functional recovery of neuromuscular diseases and intuitive control of modern prosthetic solutions.

Does joint impedance improve dynamic leg simulations with explicit and implicit solvers?

The nervous system predicts and executes complex motion of body segments actuated by the coordinated action of muscles. When a stroke or other traumatic injury disrupts neural processing, the impeded behavior has not only kinematic but also kinetic attributes that require interpretation. Biomechanical models could allow medical specialists to observe these dynamic variables and instantaneously diagnose mobility issues that may otherwise remain unnoticed. However, the real-time and subject-specific dynamic computations necessitate the optimization these simulations. In this study, we explored the effects of intrinsic viscoelasticity, choice of numerical integration method, and decrease in sampling frequency on the accuracy and stability of the simulation. The bipedal model with 17 rotational degrees of freedom (DOF)-describing hip, knee, ankle, and standing foot contact-was instrumented with viscoelastic elements with a resting length in the middle of the DOF range of motion. The accumulation of numerical errors was evaluated in dynamic simulations using swing-phase experimental kinematics. The relationship between viscoelasticity, sampling rates, and the integrator type was evaluated. The optimal selection of these three factors resulted in an accurate reconstruction of joint kinematics (err < 1%) and kinetics (err < 5%) with increased simulation time steps. Notably, joint viscoelasticity reduced the integration errors of explicit methods and had minimal to no additional benefit for implicit methods . Gained insights have the potential to improve diagnostic tools and accurize real-time feedback simulations used in the functional recovery of neuromuscular diseases and intuitive control of modern prosthetic solutions.

Compensatory Strategies Due to Knee Flexion Constraint during Gait of Non-Disabled Adults.

Constraining knee flexion of non-disabled individuals could further our understanding regarding the importance of knee joint during gait, which is a common disturbance in individuals with gait impairment. In this study we investigated whether a mechanical constraint of knee flexion in non-disabled adults would lead to compensatory strategies. Eleven non-disabled male adults walked without and with an orthosis that permitted full extension and limited knee flexion up to either 45° or 30°. We analyzed the temporal organization of lower limb kinematics and electromyograms of the rectus femoris, vastus medialis and lateralis, tibialis anterior, semitendinosus, biceps femoris, and gastrocnemius medialis and lateralis. Non-disabled adults compensated for the reduced knee flexion by increasing hip and ankle joint excursions and ankle flexor activation amplitude. Also, these adults shortened pre-swing and lengthened swing duration in the constrained limb and increased the activity of bifunctional hip extensor and knee flexor muscles in the constrained limb in relation to the unconstrained limb. The use of an orthosis that limited knee flexion in non-disabled adults leaded to compensatory strategies in the temporal organization of joint excursions and muscle activations in the constrained limb. The compensatory effects were correlated with the extent of knee flexion constraint.

Effects of limited knee flexion movement in intra-limb gait coordination.

This study aimed to investigate intra-limb coordination in non-disabled individuals walking with and without a constrained knee and in individuals with stroke. We hypothesized that a constrained knee would modify the intra-limb coordination of non-disabled individuals and that non-disabled individuals walking with a constrained knee would present coordination patterns similar to those presented by individuals with stroke. Twelve individuals with chronic stroke (age: 54.1 ± 9.9 years) and 12 age- and sex-matched individuals (age: 54.8 ± 9.2 years) with no known gait impairment (non-disabled individuals) participated in this study. Non-disabled individuals walked with and without an orthosis on one of their knees, limiting flexion to 40°, which was the average maximum knee flexion presented by the participants with stroke. Lower limb coordination was assessed on the basis of vector coding for the thigh-shank and shank-foot couplings during stance and swing periods of gait. Constrained knee flexion in non-disabled individuals mainly affected the thigh-shank coupling but not the shank-foot coupling of the constrained limb. There was reduced anti-phase coordination during the stance and swing periods and a marked increase in in-phase coordination during the swing period. Non-disabled individuals presented most changes toward the coordination pattern presented by individuals with stroke, except for the thigh-phase mode during the swing period, which was lower than that in individuals with stroke. Reduced knee flexion movement caused similar alterations in the intra-limb coordination pattern in non-disabled individuals compared to those observed in individuals with stroke. Therefore, diminished knee flexion movement, which is presented by individuals with stroke, can be considered a key disturbance that leads to impairment in lower extremity intra-limb coordination.

Enfoques del ejercicio terapéutico sobre la espasticidad en miembro inferior post-Enfermedad Cerebro Vascular: revisión sistemática / Approaches of therapeutic exercise over lower limb spasticity after stroke: a systematic review

RESUMEN Introducción: En la enfermedad cerebro vascular uno de los principales problemas es la espasticidad, que compromete el control postural, la funcionalidad y la calidad de vida. Para lograr la mayor recuperación funcional, se han utilizado los enfoques neuromusculares del ejercicio terapéutico (Ej: Rood, Bobath, Brunnstrom y la Facilitación Neuromuscular Propioceptiva), sin embargo, existe controversia sobre la eficacia de estas intervenciones. Objetivo: Realizar un análisis crítico de la evidencia científica disponible sobre el efecto de los enfoques tradicionales en la espasticidad de los miembros inferiores en personas post-Enfermedad Cerebro Vascular. Métodos: Se incluyeron ensayos clínicos controlados de las bases de datos PUBMED, MEDLINE, PEDro, CINAHL, SCIENCEDIRECT y SCOPUS. La calidad metodológica de los artículos incluidos se evaluó por medio de la escala PeDro. Resultados: Once estudios cumplieron con los criterios de inclusión, obteniendo una calidad metodológica de intermedia a alta. Entre las limitaciones de los estudios revisados se destacan principalmente la ausencia del cálculo del tamaño de muestra, de enmascaramiento de los evaluadores, pérdida de participantes, muestras heterogéneas, carencia de protocolos estandarizados y diversidad de variables evaluadas. Conclusión: El tratamiento fisioterapéutico para disminuir la espasticidad puede ser efectivo aplicado entre tres y cinco días por semana, durante 40 minutos. Sin embargo, estos resultados están soportados en estudios con limitaciones metodológicas y dificultades en su comparación. Por ello, se requieren nuevos estudios para evaluar la eficacia de dichos enfoques, con el fin implementar intervenciones fisioterapéuticas basadas en la mejor evidencia, que contribuyan en una mejor calidad de vida de esta población.

ABSTRACT Introduction: Spasticity due to a stroke is one of the major changes that leads to sensorimotor deficits, causing postural control and functional capability deficits. In order to achieve the best possible functional recovery, several neuromuscular therapeutic exercise approaches have been employed (eg Rood, Bobath, Brunnstrom and proprioceptive neuromuscular facilitation), but still there are many doubts about the effectiveness of these interventions. Purpose: To perform a critical analysis of the available scientific evidence on the effect of the traditional approaches in spasticity recovery of the lower limbs in post-stroke individuals. Methods: Randomized controlled Trials available in PubMed, MEDLINE, PEDro, CINAHL, and Scopus data SCIENCEDIRECT bases were included in this study. The methodological quality of included articles was evaluated by the PEDro scale. Results: Eleven studies were included, obtaining a methodological quality of intermediate to high. The main observed limitations of the analyzed studies were: the absence of sample size estimation, the lack of blind evaluators, loss of participants, heterogeneous samples, lack of standardized protocols and diversity of employed variables. Conclusions: Based upon the results, it can be suggested that spasticity reduction can be effective applying from three to five days interventions per week, lasting 40 minutes. However, such suggestions are supported by studies with methodological limitations and employing different procedures that prevent a direct comparison among the studies. Therefore new studies are required to evaluate the effectiveness of such approaches, to implement physiotherapy interventions based on the scientific evidences that would further contribute to a better quality of life of post-stroke individuals.