They proposed that there was a rubber-like shortening of myosin filaments brought about by altering the state of ionization of the myosin. Hasselbach showed that the thick filaments contain the protein myosin. Progress was then rapid so that at a historic Cold Spring Harbor Symposium in 1972 the outline of the molecular mechanism of muscle contraction could be enunciated. For each cycle of activity one ATP would be hydrolyzed. To understand the chemical events which drive muscle one needs to know the protein structures involved at atomic resolution.
Muscle is made of massive arrays of macromolecules.
A great deal of technology has been invested in this problem, which has also driven technology. Some early insight was provided by light microscopy. However, the first radical new insight came from electron microscopy. More recently, the structures of the component molecules have been determined x-ray crystallography at atomic resolution. An understanding of muscle contraction is an important example of the success of protein crystallography, in particular when used in conjunction with high resolution electron microscopy.