Muscle architecture and EMG activity changes during isotonic and isokinetic eccentric exercises

International audienceThe present study aimed to compare musclearchitecture and electromyographic activity during isotonic(IT) and isokinetic (IK) knee extensors eccentric contractions.Seventeen subjects were assigned in test and reproducibilitygroups. During test session, subjects performedtwo IT and two IK sets of eccentric contractions of kneeextensor muscles. Torque, angular velocity, VL architectureand EMG activity of agonist (vastus lateralis, VL;vastus medialis; rectus femoris) and antagonist (semitendinosus;biceps femoris, BF) muscles were simultaneouslyrecorded and averaged on a 5 window. Torque–angle andangular velocity–angle relationships exhibited differencesin mechanical load between the IT and IK modes. Changesin muscle architecture were similar in both modes, sinceVL fascicles length increased and fascicle angle decreased,resulting in a decrease in muscle thickness during eccentriccontraction. Agonist activity and BF co-activity levels werehigher in IT mode than in IK mode at short muscle lengths,whereas agonist activity was higher in IK mode than in ITmode at long muscle lengths. Differences in mechanicalload between both modes induced specific neuromuscularresponses in terms of agonist activity and antagonist coactivity.These results suggest that specific neural adaptationsmay occur after IT or IK eccentric training. Thishypothesis needs to be tested in order to gain new insightsconcerning the most effective eccentric protocols based onwhether the objective is sportive or clinical