Final answer:
Passive insufficiency is the inability of a muscle to fully lengthen across all the joints it crosses in Manual Muscle Testing (MMT). It happens when the muscle is already stretched or at a mechanical disadvantage.
Step-by-step explanation:
Passive insufficiency is a concept in Manual Muscle Testing (MMT) that refers to the inability of a muscle to lengthen fully across all the joints it crosses. It occurs when the muscle is already stretched or at a mechanical disadvantage due to the positions of the joints.
For example, the hamstrings are a group of muscles that cross both the hip and knee joints. When the hip is flexed and the knee is extended, the hamstrings are already in a lengthened position. In this case, the hamstrings would have passive insufficiency because they cannot lengthen further to allow full flexion at the knee.