British biologist Hugh Huxley (1924–2013) and English physiologist and biophysicist Andrew Huxley (1917–2012; the scientists were unrelated) researched theories regarding muscle contraction. Hugh Huxley was initially a nuclear physicist who entered the field of biology at the end of World War II. He used both X-ray diffraction and electron microscopy to study muscle contraction. Andrew Huxley obtained data similar to Hugh’s, indicating that the contractile proteins thought to be present in muscles are not contractile at all, but rather slide past each other to shorten a muscle. This theory is called the “sliding filament theory of muscle contraction.”