Electromyographic patterns accompanying isokinetic exercise under varying speed and sequencing conditions

The purposes of this study were: a) to investigate electromyographic patterns accompanying isokinetic exercise under varying speed and sequencing conditions, and b) to investigate the role of antagonist coactivation under these same conditions. Five adult males performed maximal knee extensions and flexions on a modified Orthotron isokinetic dynamometer. Tests were done at four speeds (100-400°/sec) and under two counterbalanced conditions: extension followed by flexion (E/F) and flexion followed by extension (F/E). Simultaneous recordings of torque, knee joint position and agonist/antagonist EMG changes from the quadriceps and hamstring musculature were collected and analyzed. No consistent EMG pattern emerged that inferred intermittent surges of muscular activity as the primary mechanism yielding double peaked torques that characteristically occur in isokinetic exercise. Further analyses revealed relatively small co-contractions of antagonists during the various phases of movement. The findings suggest that gravity and inertia of the limb/lever system were the major factors responsible for limb deceleration and substantive antagonist co-contraction was not required for braking. If isokinetic knee flexion and extension exercises are used for conditioning or developmental purposes of healthy subjects, any distraction of the co-contracting antagonist from the recorded force of the agonist appears to be small once the activity is learned.