Which reflex requires gamma motor neurons to set the length of the muscle?

A reflex that requires a gamma motor neurons to set the length of the muscle is the patellar stretch reflex. The patellar stretch  reflex, when they are stimulated, they can cause the muscle to contract. In this process, it can free up the upper motor neurons and other portions of the central nervous system,

Ther are many reasons.. is it a multiple choice?