Altering length and velocity feedback during a neuro-musculoskeletal simulation of normal gait contributes to hemiparetic gait characteristics

Abstract

BackgroundSpasticity is an important complication after stroke, especially in the anti-gravity muscles, i.e. lower limb extensors. However the contribution of hyperexcitable muscle spindle reflex loops to gait impairments after stroke is often disputed. In this study a neuro-musculoskeletal model was developed to investigate the contribution of an increased length and velocity feedback and altered reflex modulation patterns to hemiparetic gait deficits.MethodsA musculoskeletal model was extended with a muscle spindle model providing real-time length and velocity feedback of gastrocnemius, soleus, vasti and rectus femoris during a forward dynamic simulation (neural control model). By using a healthy subject’s base muscle excitations, in combination with increased feedback gains and altered reflex modulation patterns, the effect on kinematics was simulated. A foot-ground contact model was added to account for the interaction effect between the changed kinematics and the ground. The qualitative effect i.e. the directional effect and the specific gait phases where the effect is present, on the joint kinematics was then compared with hemiparetic gait deviations reported in the literature.ResultsOur results show that increased feedback in combination with altered reflex modulation patterns of soleus, vasti and rectus femoris muscle can contribute to excessive ankle plantarflexion/inadequate dorsiflexion, knee hyperextension/inadequate flexion and increased hip extension/inadequate flexion during dedicated gait cycle phases. Increased feedback of gastrocnemius can also contribute to excessive plantarflexion/inadequate dorsiflexion, however in combination with excessive knee and hip flexion. Increased length/velocity feedback can therefore contribute to two types of gait deviations, which are both in accordance with previously reported gait deviations in hemiparetic patients. Furthermore altered modulation patterns, in particular the reduced suppression of the muscle spindle feedback during swing, can contribute largely to an increased plantarflexion and knee extension during the swing phase and consequently to hampered toe clearance.ConclusionsOur results support the idea that hyperexcitability of length and velocity feedback pathways, especially in combination with altered reflex modulation patterns, can contribute to deviations in hemiparetic gait. Surprisingly, our results showed only subtle temporal differences between length and velocity feedback. Therefore, we cannot attribute the effects seen in kinematics to one specific type of feedback.

Muscular weakness represents the main limiting factor of walk, functional independence and quality of life of myelopathy patients associated to HTLV-1

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Involvement of PARP1 in the regulation of alternative splicing

“…Although the roles of nucleosomes positioned at promoters have been widely studied in transcriptional regulation, the roles of nucleosomes in splicing regulation are less well understood [ 11 , 12 ]. The positioning of nucleosomes at exons [ 13 , 14 ] is dependent on several factors including the intrinsic DNA sequence [ 15 , 16 ], DNA methylation levels [ 17 , 18 ] and histone modifications [ 19 ]. Indeed, nucleosomes regulate RNA polymerase elongation kinetics, thus aiding in the recognition of weak splice sites [ 7 , 17 ].…”

Rectus femoris transfer surgery affects balance recovery in children with cerebral palsy: A computer simulation study

“…First, the balance recovery simulations used foot-ground contact modeling that depends upon parameters such as geometry, stiffness and dissipation [23]. The same contact model parameters were used in each simulation [16], so observed differences are not the result of foot-ground differences.…”

“…In addition, we penalized changes in hip, knee and ankle joint angles in the cost function to reduce variability in the resulting motions. Spasticity was simulated by multiplying the non-spastic position and velocity gains by a factor (1.1) to increase the sensitivity of the controller [23].…”