Eighteen adults performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100% maximal voluntary contraction (%MVC) at leg flexion angles of 25, 50, and 75°. The results indicated that isometric torque production increased as leg flexion angle increased (75°>50°>25°). For each muscle tested (rectus femoris, vastus lateralis, and vastus medialis), the EMG amplitude increased up to 100%MVC at each leg flexion angle (25, 50, and 75°). The MMG amplitude for each muscle, however, increased up to 100%MVC at 25 and 50° of leg flexion, but plateaued from 75 to 100%MVC at 75° of leg flexion. We hypothesize that the varied patterns for the MMG amplitude–isometric torque relationships were due to leg flexion angle differences in: (1) muscle stiffness, (2) intramuscular fluid pressure, or (3) motor unit firing frequency.