Passive ROM is greater than active range because the muscles surrounding the joint are relaxed.
According to the book, "Therapeutic Massage in Athletics," passive range-of-motion tests can help a therapist evaluate a joint injury to determine if a structure other than a muscle (ligament, cartilage, bursa) is involved in the injury.
Passive ROM Exercises
Therapists often use passive ROM exercises for rehab when people are not yet able to actively participate in exercise.
You can improve your range of motion through regular movement and stretching.
The British study, "Effect of Stretching Duration on Active and Passive Range of Motion in the Lower Extremity," looked at the effects of five-second versus 15-second stretches on range of motion. The study, published in the British Journal of Sports Medicine in 1999, suggested that holding stretches for 15 seconds may improve active ROM more than five-second stretches. However, the longer stretch may not significantly improve passive ROM.