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Influence of Effort Intensity and Gastrocnemius Stretch on Co-Contraction and Torque Production in the Healthy and Paretic Ankle

Abstract : Objective Spastic co-contraction is a misdirected supraspinal command in spastic paresis. We quantified the influence of effort and gastrocnemius stretch on plantar flexor co-contraction and torque during dorsiflexion efforts in hemiparetic and healthy subjects. Methods Eighteen healthy and 18 hemiparetic subjects produced "light", "medium" and "maximal" isometric dorsi- and plantar flexion efforts in two gastrocnemius positions, stretched (knee extended) and slack (knee flexed), ankle at 90°. Measuring ankle torque and soleus and medial gastrocnemius surface EMG, we calculated the co-contraction index (CCI) as the ratio of the EMG root mean square (RMS) from the muscle acting as antagonist over its RMS when acting as agonist in a maximal effort, in each knee position.Results Co-contraction was abnormally high in hemiparetic subjects at all effort levels, e.g. for soleus in the knee extended position (CCISO 0.37 ± 0.08 in hemiparesis vs 0.18 ± 0.02 in healthy subjects, p < 0.05). In hemiparetic subjects knee extended, dorsiflexion torque, (i) was reversed or canceled in 26% trials; and (ii) correlated negatively with plantar flexor CCI. Significance Major dynamometric impact of co-contraction with stretched position of the cocontracting muscle may justify muscle length modifications (e.g. through aggressive stretch programs) to improve function in spastic paresis.
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Submitted on : Tuesday, February 14, 2017 - 12:24:07 PM
Last modification on : Thursday, August 20, 2020 - 3:05:03 AM

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Maria Vinti, Annabelle Couillandre, Jérome Hausselle, Nicolas Bayle, Aldo Primerano, et al.. Influence of Effort Intensity and Gastrocnemius Stretch on Co-Contraction and Torque Production in the Healthy and Paretic Ankle. Clinical Neurophysiology, Elsevier, 2013, 124 (3), pp.528-535. ⟨10.1016/j.clinph.2012.08.010⟩. ⟨hal-01467311⟩

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