It doesn't appear that disease severity matches up with level of stiffness for patients with osteoarthritis (OA). We aren't sure just why this is. Narrowing of the joint space from OA certainly causes joint pain and loss of motion.
Stiffness may be more a factor linked with the soft tissues. Muscle around the joint and cartilage inside the joint may be the real source of the stiffness. Research is ongoing to measure stiffness, discover its cause, and find a cure.
Body type and size may make a difference but this hasn't been proven yet. People of all sizes and shapes experience stiffness but researchers are looking for trends or patterns based on body mass index (BMI).