Variations in the force velocity relationship with stimulation frequency, number of pulses, and the length where the stimulation is initiated. (a) The modeled peak force versus velocity curve does not follow the hyperbolic relationship when the stimulation train is initiated at 90° of knee flexion and is terminated when either 15° of knee flexion is reached or when 50 pulses were delivered. (b) Change in force velocity curve when the stimulation train is initiated at a knee flexion angle of 60°, the optimal muscle length for this subject. (c) Shortening contractions (negative angular velocities) and lengthening contractions (positive angular velocities) were performed when the leg was moving between 90° to 15° of knee flexion and the stimulation was applied throughout the range of motion. The model accurately captures the shape during shortening and lengthening contractions. The isomeric peak force was plotted at 60° of knee flexion. (d) The plot when the leg moves through the same shortening range (90° to 15°) and lengthening range (15° to 90°) as in c, except that the maximum number of pulses were now limited to 50 and the isometric peak force was considered at 15° of knee flexion to ensure a continuity in the force-velocity curves.