Scientists study the dynamic and static nature of the cytoskeleton using different microscopic and biochemical techniques. Mechanical properties of cytoskeletal filaments can be determined using atomic force microscopy or AFM. AFM uses nanosized tips to pull both ends of cytoskeletal filaments to determine their tensile strength. Intermediate filaments stretch up to three and a half times their standard length before breaking in two, suggesting they are more extendible than the others. Fluorescence microscopy is used to study the interactions between cytoskeleton-associated proteins and filaments. For example, kinesin motor proteins walking on microtubules can be visualized using GFP-labeled kinesin and fluorescent dye-labeled microtubules. To visualize F-actin polymerization , purified G-actin monomers are labeled with a fluorescent dye and microinjected into a live cell, where the labeled subunits polymerize into actin filaments. The fluorescence detected through the microscope further allows the localization of these filaments within the cell.