What is a myograph and how did Hermann von Helmholtz use it?

A myograph is an instrument used to measure and record the mechanical activity of muscles. It was invented by the German scientist Hermann von Helmholtz as part of his efforts to apply the laws of physics and chemistry to biological processes, effectively challenging the prevailing theory of vitalism during the 19th century.1

Helmholtz used the myograph in 1850 to conduct groundbreaking experiments on nerve impulses. At the time, many physiologists believed that nerve impulses were instantaneous or governed by a mysterious "vital force" that could not be measured. By using the myograph, Helmholtz successfully demonstrated that the nerve impulse was a measurable physical phenomenon with a finite, relatively slow speed of approximately 90 feet (27 meters) per second. This discovery provided critical evidence that physiological functions could be explained through mechanical and chemical laws rather than vitalistic forces.1