Passive Insufficiency is described as a muscle not lengthening enough, restricting motion.

• A. Tight structures → cannot reach position
• B. When a muscle cannot lengthen enough, restricting motion
• C. Contractures from scarring reducing available length
• D. PROM - Passive Range of Motion exercises

Answer: (B)

Passive insufficiency occurs when a muscle that crosses more than one joint cannot lengthen enough to allow full passive range of motion at the joints it crosses. Because the muscle’s fibers have a limited length, stretching it across multiple joints reaches a point where it can’t lengthen further, so movement at one or both joints is limited. A common example is the gastrocnemius, which crosses the knee and ankle; if the knee is kept extended, the muscle is shortened across one joint, leaving insufficient length to allow full ankle dorsiflexion. That’s why the description “cannot lengthen enough, restricting motion” fits this concept.

The other statements describe related but different ideas: general tightness is a broader notion of restricted ROM not specific to the two-joint length limitation; contractures from scarring are structural, irreversible shortening from tissue changes; and PROM refers to a therapeutic technique used to assess or improve ROM, not the phenomenon itself.