Describing a type of muscle fibre that occurs in the muscle spindles in skeletal muscles. Two to twelve intrafusal fibres enclosed in a capsule are found in each muscle spindle, lying parallel to the main (extrafusal) fibres. Each intrafusal fibre consists of a noncontractile (equatorial) region connected to a contractile (polar) region at each end of the fibre. The equatorial region is connected to stretch receptors.