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An electromyographic study was conducted using three superficial quadriceps muscles in a knee extension progressive resistance exercise from 90 degrees to 180 degrees with a weighted boot. Continuous recordings were taken on five females and five males in the preexercise position with the knee at 90 degrees, during the exercise, and in the post-exercise position. It was found that the greatest muscle action potentials were produced by the rectus femoris and that the vastus lateralis and vastus medialis exhibited similar action potentials throughout the exercise. All subjects demonstrated increased muscle action potentials within the exercise bout as the gravitational torque increased and between exercise bouts with additional weight increments. No amplitude in muscle action potentials were recorded from the muscles during the pre-exercise and post-exercise positions in which the leg was hanging freely with suspension weights up to 24.13 kilograms attached. This finding suggested viscoclastic connective tissues were supporting the downward gravitational force with the knee at 90 degrees.