6533b7dcfe1ef96bd1272844

RESEARCH PRODUCT

Coactivation at the ankle joint is not sufficient to estimate agonist and antagonist mechanical contribution

subject

description

The aim of this study was to assess, via an elec- tromyographic (EMG) biofeedback method, the mechanical con- tribution of both agonist and antagonist muscles during maximal voluntary contraction (MVC). We compared this original method with the MVC-EMGmax ratio and the torque/EMG relationship method, both of which are commonly used to estimate antago- nist torque. The plantarflexion (PF) and dorsiflexion (DF) MVCs were measured simultaneously with EMG activity of triceps surae (TS) and tibialis anterior in 15 young adults (mean age 23 years). Antagonist torques obtained from the torque/EMG relationship and EMG biofeedback methods appeared to be similar. TS antagonist torque had a major mechanical impact on DF MVC (� 42%). EMG coactivation is significantly different than normalized antagonist torque. TS antagonist torque is not negligible when maximal DF is assessed, and the EMG bio- feedback method is a simple method to estimate antagonist tor- que. Muscle Nerve 41: 511-518, 2010 The external torque maximally exerted at a joint is generally considered to be representative of the force production capacity of skeletal muscles. This torque, generated during a maximal voluntary con- traction (MVC), corresponds to the algebraic sum of agonist and antagonist torques, 1 and it is affected by the activation of both agonist and an- tagonist muscles. 2 Indeed, coactivation is a simulta- neous activation of both agonist and antagonist muscle groups around a joint. This coactivation appears to be necessary for: (i) the stabilization of the concerned joint 3-5 ; (ii) the homogeneous dis- tribution of the pressures exerted within the articu- lar capsule 6,7 ; and (iii) the prevention of relative bone displacements. 8