What term refers to the inability of muscles to shorten simultaneously at two joints due to excessive shortening?

The term that pertains to the inability of muscles to shorten simultaneously at two joints due to excessive shortening is known as active insufficiency. This occurs when a muscle is contracted to the extent that it cannot generate enough force to effectively perform a task across both joints it crosses. For example, when the hamstrings are fully flexed at the knee and hip, they lack the ability to produce adequate force to flex the knee or extend the hip because they are overly shortened.

Active insufficiency specifically refers to the diminished capacity of a muscle to produce force when it is already in a shortened position, thus limiting its functional capabilities across multiple joints. This is different from passive insufficiency, which describes when a muscle cannot lengthen sufficiently to allow optimal movement at two joints. The other options do not represent this specific concept; muscle fatigue refers to a decline in muscle performance due to prolonged activity, and joint laxity refers to the looseness of the joint itself rather than the functional capability of the muscle. Understanding active insufficiency is crucial when evaluating muscle function and planning rehabilitation exercises.