The first single-molecule experiments were patch clamp experiments performed in the 1970s, but these were limited to studying ion channels. Today, systems investigated using single-molecule techniques include the movement of myosin on actin filaments in muscle tissue and the spectroscopic details of individual local environments in solids. Biological polymers' conformations have been measured using atomic force microscopy (AFM). Using force spectroscopy, single molecules (or pairs of interacting molecules), usually polymers, can be mechanically stretched and their elastic response recorded in real time.