Active Insufficiency occurs when a muscle cannot contract fully across both joints it crosses.

• A. When a muscle cannot lengthen enough
• B. When a muscle cannot contract fully across both joints it crosses
• C. Movement tied to daily activities
• D. Functional Excursion

Answer: (B)

Active insufficiency happens when a multi-joint muscle is shortened across the joints it crosses so much that it cannot contract effectively to move those joints. The statement captures this idea exactly: the muscle cannot contract fully because it’s shortened across both joints it crosses.

Think of the biceps brachii, which crosses the shoulder and elbow. If the shoulder is flexed, the muscle is already shortened across the shoulder; trying to flex the elbow afterward requires further shortening across both joints, which the muscle can’t achieve, so elbow flexion is limited. A similar idea applies to the hamstrings across the hip and knee—when both joints are in positions that shorten the hamstrings, contraction across both joints is limited.

In contrast, other phrases refer to different concepts. Saying a muscle cannot lengthen enough points to passive insufficiency (limiting ROM when the muscle is stretched across joints), not its ability to contract. The other options don’t describe this contraction limitation across two joints.