How is passive insufficiency defined?

Passive insufficiency refers to the condition where a muscle cannot stretch enough to allow the full range of motion at the joints that it crosses. This occurs when a muscle is lengthened across multiple joints and reaches its limit of elongation, preventing further stretching. Option C accurately describes this phenomenon, as it indicates that a muscle is unable to lengthen any further, thus limiting the motion available at the joints it acts upon.

This concept often comes into play in clinical settings when assessing flexibility and range of motion. For instance, consider a two-joint muscle like the hamstrings; if the hip is flexed while the knee is extended, the hamstrings will not be able to stretch fully across both joints, leading to passive insufficiency. Understanding this concept is crucial for physical therapy practices, as it can influence treatment planning and exercise prescription.