[2] Costameres are sub-sarcolemmal protein assemblies circumferentially aligned in register with the Z-disk of peripheral myofibrils.

Therefore, it is one of the features of the sarcolemma which helps to couple the sarcomere to the extracellular connective tissue as some experiments have shown.

[9] The DGC consists of peripheral and integral proteins that physically traverse the sarcolemma and connect the ECM to the F-actin based cytoskeleton.

The lateral transmission of force by costameres helps maintain uniform sarcomere lengths in adjacent muscle cells that are under the control of different motor units and are therefore not synchronized in their active contractions; restated, if one muscle fiber is actively contracting and an adjacent one is not, the lateral force transmission helps this second fiber to shorten as well.

[9] Costameres are also involved in protecting the relatively weak and labile sarcolemma from the mechanical stresses of contraction and stretching.