The range of motion of knee extension covering almost all in a population is 155 degrees to -10. A normal range of motion for a therapy exam is 140 - 0 degrees. Range of motion of an engineered Pendulum strength training machine is somewhat different as the machine takes into consideration the hip and seat angle, seat thickness, shin pad density, load, training population and ergonomics.
An important exercise consideration if experiencing knee discomfort is training on the seated leg extension from 90 to the 45 degree mark (of the 140 degree movement) causes the least amount of patellofemoral stress. Pain inhibits function and this 45 degree zone often allows an athlete to do a short range of limited or pain free movement to re-strengthen the quadriceps and eventually restore a full pain free range.
Returning to Full Range of Motion on the Pendulum Leg Extension