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Session: MSK & Sweat sensing
Session starts: Friday 27 January, 11:30
Presentation starts: 11:30
Room: Room 530

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Eline Flux (Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences)
Babette Mooijekind (Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences)
Lynn Bar-On (Ghent University)
Edwin van Asseldonk (University of Twente)
Annemieke Buizer (Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences)
Marjolein van der Krogt (Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences)

Abstract:
Stretch hyperreflexia is often assessed passively, but can express itself differently during dynamic activities such as gait (1). Studies assessing dynamic stretch hyperreflexia typically compare muscle activity to modeled musculotendon lengthening (1, 2), while fascicle lengthening is more directly related to stretch reflex activity (3). We hypothesized that children with stretch hyperreflexia display dynamic hyperreflexia during gait, which is more pronounced when measuring fascicle lengthening compared to musculotendon lengthening. 3D-gait analysis including electromyography (EMG) was performed on fourteen children with spastic cerebral palsy (CP) and fifteen typically developing (TD) children walking on an instrumented treadmill. Medial gastrocnemius fascicle lengthening was imaged using dynamic ultrasound and musculotendon lengthening was simulated using OpenSim. Dynamic stretch hyperreflexia was identified during late swing and early stance, and defined as a sudden EMG peak preceded by a manually detected increased lengthening velocity within a reflex window of 40-120 ms. As a proxy for stretch reflex magnitude, the ratio between RMS EMG and maximum fascicle or musculotendon velocity within the reflex window was calculated, and compared between CP and TD using independent t-tests. 62.5% of CP showed clearly increased fascicle velocity preceding increased EMG activity in late swing, compared to 50% for musculotendon velocity. For early stance, this was 53.8% and 46.2% respectively. EMG/velocity ratios were significantly larger in children with CP compared to TD children, for both fascicle (91.5±57.4 vs. 28.6±14.5 for swing and 362.0±329.0 vs 96.7±135.6 for early stance, p<0.001) and musculotendon velocity (50.9±26.6 vs 15.0±8.4 for swing and 120.9±52.1 vs 29.2±16.8 for early stance, p<0.001). This difference was more pronounced when measuring musculotendon velocity instead of fascicle velocity, both in swing (240% and 220% larger ratio respectively) and in stance (315% and 275% respectively). The increased EMG/velocity ratio suggests that children with CP indeed have increased dynamic stretch reflexes during gait compared to TD, which can be more frequently attributed to fascicle lengthening. Notwithstanding, increased activity was not always preceded by a clear peak in fascicle velocity. Therefore, other triggers might be involved in causing the increased activity, such as fascicle or tendon acceleration or other tissue dynamics, which requires further research. 1. Flux, J NeuroEngineering Rehabil 18:151 (2021) 1-17 2. van der Krogt, Clin Biomech 24:5 (2009) 422-428 3. Cronin, J Electromyogr Kinesiol 21:8 (2011) 197-207