Applying Stretch to Evoke Hyperreflexia in Spasticity Testing: Velocity vs. Acceleration

\ua9 Copyright \ua9 2021 Sloot, Weide, van der Krogt, Desloovere, Harlaar, Buizer and Bar-On. In neurological diseases, muscles often become hyper-resistant to stretch due to hyperreflexia, an exaggerated stretch reflex response that is considered to primarily depend on the muscle\u27s stretch velocity. However, there is still limited understanding of how different biomechanical triggers applied during clinical tests evoke these reflex responses. We examined the effect of imposing a rotation with increasing velocity vs. increasing acceleration on triceps surae muscle repsonse in children with spastic paresis (SP) and compared the responses to those measured in typically developing (TD) children. A motor-operated ankle manipulator was used to apply different bell-shaped movement profiles, with three levels of maximum velocity (70, 110, and 150\ub0/s) and three levels of maximum acceleration (500, 750, and 1,000\ub0/s2). For each profile and both groups, we evaluated the amount of evoked triceps surae muscle activation. In SP, we evaluated two additional characteristics: the intensity of the response (peak EMG burst) and the time from movement initiation to onset of the EMG burst. As expected, the amount of evoked muscle activation was larger in SP compared to TD (all muscles: p < 0.001) and only sensitive to biomechanical triggers in SP. Further investigation of the responses in SP showed that peak EMG bursts increased in profiles with higher peak velocity (lateral gastrocnemius: p = 0.04), which was emphasized by fair correlations with increased velocity at EMG burst onset (all muscles: r > 0.33–0.36, p ≤ 0.008), but showed no significant effect for acceleration. However, the EMG burst was evoked faster with higher peak acceleration (all muscles p < 0.001) whereas it was delayed in profiles with higher peak velocity (medial gastrocnemius and soleus: p < 0.006). We conclude that while exaggerated response intensity (peak EMG burst) seems linked to stretch velocity, higher accelerations seem to evoke faster responses (time to EMG burst onset) in triceps surae muscles in SP. Understanding and controlling for the distinct effects of different biological triggers, including velocity, acceleration but also length and force of the applied movement, will contribute to the development of more precise clinical measurement tools. This is especially important when aiming to understand the role of hyperreflexia during functional movements where the biomechanical inputs are multiple and changing

Dynamic spasticity of plantar flexor muscles in cerebral palsy gait

Objective: To quantify dynamic spasticity, i.e. the coupling between muscle-tendon stretch velocity and muscle activity during gait, of the gastrocnemius and soleus muscles in children with spastic cerebral palsy. Design: Prospective, cross-sectional study. Subjects: Seventeen ambulatory children with cerebral palsy with spastic calf muscles, and H matched typically developing children. Methods: The children walked at 3 different speeds. Threedimensional kinematic and electromyographic data were collected. Muscle-tendon velocities of the gastrocnemius medialis and soleus were calculated using musculoskeletal modelling. Results: In typically developing children, muscles were stretched fast in swing without subsequent muscle activity, while spastic muscles were stretched more slowly for the same walking speed, followed by an increase in muscle activity. The mean ratio between peak activity and peak stretch velocity in swing was approximately 4 times higher in spastic muscles, and increased with walking speed. In stance, the stretch of muscles in typically developing children was followed by an increase in muscle activity. Spastic muscles were stretched fast in loading response, but since muscle activity was already built up in swing, no clear dynamic spasticity effect was present. Conclusion: Spastic calf muscles showed increased coupling between muscle-tendon stretch velocity and muscle activity, especially during the swing phase of gait. © 2010 Foundation of Rehabilitation Information

Personalisation of Plantarflexor Musculotendon Model Parameters in Children with Cerebral Palsy.

Neuromusculoskeletal models can be used to evaluate aberrant muscle function in cerebral palsy (CP), for example by estimating muscle and joint contact forces during gait. However, to be accurate, models should include representative musculotendon parameters. We aimed to estimate personalised parameters that capture the mechanical behaviour of the plantarflexors in children with CP and typically developing (TD) children. Ankle angle (using motion capture), torque (using a load-cell), and medial gastrocnemius fascicle lengths (using ultrasound) were measured during slow passive ankle dorsiflexion rotation for thirteen children with spastic CP and thirteen TD children. Per subject, the measured rotation was input to a scaled OpenSim model to simulate the torque and fascicle length output. Musculotendon model parameters were personalised by the best match between simulated and experimental torque-angle and fascicle length-angle curves according to a least-squares fit. Personalised tendon slack lengths were significantly longer and optimal fibre lengths significantly shorter in CP than model defaults and than in TD. Personalised tendon compliance was substantially higher in both groups compared to the model default. The presented method to personalise musculotendon parameters will likely yield more accurate simulations of subject-specific muscle mechanics, to help us understand the effects of altered musculotendon properties in CP

Medial gastrocnemius muscle and tendon interaction during gait in typically developing children and children with cerebral palsy

1. Introduction Efficient gait is dependent on optimal interaction between muscles and tendons [1]. Pathological changes in the extensibility of the MG muscle fascicles, whole muscle-belly and Achilles tendon have been reported in children with spastic cerebral palsy (CP) [2]. Studying the relative length of these tissues during gait can improve our understanding of their dynamics and, inferably, the control strategies used in CP. In-vivo dynamic ultrasound imaging has been used to visualise the interaction between the MG muscle and tendon during 3D gait analysis. However, most studies combined ultrasound imaging of one variable (either fascicles or muscle-belly and tendon) with some form of musculoskeletal modelling to extrapolate the other variables, resulting in incomplete and variable findings [3–5]. 2. Research question How do MG muscle fascicles, belly, and Achilles tendon interact during gait in children with cerebral palsy (CP) and typically developing (TD) children? 3. Methods 3D gait analysis was carried out in six children with CP (11 ± 3 years, GMFCS I, uni/bilateral: 4/2) and six TD children (12 ± 4 years) as they walked at a comfortable walking speed (average CP: 0.5 m/s, TD: 1.0 m/s) on a treadmill. An ultrasound probe (Telemed SmartUS, 60 mm) was attached to the non-preferred (TD) or most-affected (CP) leg using a custom-made probe holder (Probefix Dynamic, USONO), whose position was tracked by motion analysis. Images were collected during walking first with the probe on the mid muscle-belly, imaging fascicles and secondly with the probe on the most distal muscle tendon junction (MTJ) to estimate both muscle-belly and tendon lengthchanges. Muscle-tendon unit (MTU) length-change represented combined muscle and tendon behaviour. Fascicle, MTU, muscle-belly and tendon length patterns were averaged over time-normalised gait cycles, and expressed relative to their lengths at initial contact [4]. Due to the small and heterogeneous sample, results are presented in a descriptive way. 4. Results Gait kinematic and kinetic data showed that the children with CP had mild gait deviations (1C-F). Children with CP showed reduced length-changes of all tissues compared to TD (Fig. 1A and B). In TD children, the tendon contributed more to MTU length-changes than muscle, as opposed to more equal contributions in CP. In TD children, the muscle-belly behaviour did not reflect the fascicle behaviour whereas in CP, muscle-belly and fascicle length patterns were similar. 5. Discussion Our initial findings of pathological tendon and muscle dynamics during CP gait are in line with a previous study imaging the MTJ [3], but less so with studies relying on modelling to estimate tendon length [4,5]. The similar length pattern between muscle-belly and fascicle in CP may indicate a stiff extracellular matrix. We highlight the importance of collecting experimental data from all three tissues in order to understand the pathology. This feasibility study needs to be confirmed once larger samples are collected

Predicting Gait Patterns of Children With Spasticity by Simulating Hyperreflexia

Spasticity is a common impairment within pediatric neuromusculoskeletal disorders. How spasticity contributes to gait deviations is important for treatment selection. Our aim was to evaluate the pathophysiological mechanisms underlying gait deviations seen in children with spasticity, using predictive simulations. A cluster analysis was performed to extract distinct gait patterns from experimental gait data of 17 children with spasticity to be used as comparative validation data. A forward dynamic simulation framework was employed to predict gait with either velocity- or force-based hyperreflexia. This framework entailed a generic musculoskeletal model controlled by reflexes and supraspinal drive, governed by a multiobjective cost function. Hyperreflexia values were optimized to enable the simulated gait to best match experimental gait patterns. Three experimental gait patterns were extracted: (1) increased knee flexion, (2) increased ankle plantar flexion, and (3) increased knee flexion and ankle plantar flexion when compared with typical gait. Overall, velocity-based hyperreflexia outperformed force-based hyperreflexia. The first gait pattern could mostly be explained by rectus femoris and hamstrings velocity-based hyperreflexia, the second by gastrocnemius velocity-based hyperreflexia, and the third by gastrocnemius, soleus, and hamstrings velocity-based hyperreflexia. This study shows how velocity-based hyperreflexia from specific muscles contributes to different spastic gait patterns, which may help in providing targeted treatment

The relationship between energy cost of walking, ankle push-off and walking speed in persons with multiple sclerosis

Background: The energy cost of walking (ECw) is an important indicator of walking dysfunction in persons with multiple sclerosis (PwMS). However, its underlying causes and its relation with ankle push-off and walking speed are not well understood. Research question: What is the contribution of ankle push-off and walking speed to increased ECw in PwMS? Methods: Ten PwMS with walking limitations and 10 individually gender- and age-matched healthy controls (HC) were included. All participants performed two 6-min walking trials on a treadmill at comfortable walking speed (CWS of PwMS) and fast walking speed (FWS, 130 % of CWS of PwMS). Kinetics and metabolic cost were evaluated. Generalized estimating equations were performed to investigate effects of group and walking speed, and their interaction. Spearman correlations were conducted to examine whether ECw was related to ankle push-off in PwMS, controlling for differences in walking speed in PwMS. Results: ECw at matched walking speed was significantly higher in PwMS compared to HC. Kinetic parameters were not different between the most impaired leg in PwMS and HC at matched walking speed, but asymmetry between both legs of PwMS was observed. At FWS, ECw reduced and ankle push-off increased similarly in both groups. ECw was inversely related to peak ankle power of the most impaired leg in PwMS at CWS. Significance: Slow walking speed is one factor that contributes to increased ECw in PwMS. Furthermore, PwMS who had a higher ECw showed a lower peak ankle power, independent of walking speed. This indicates that ankle push-off could be a contributor to increased ECw