All life forms on earth, including humans, are constantly subjected to the universal force of gravitation, and thus to forces from within and surrounding the body. Through the study of the interaction of these forces and their effects, the form, function and motion of our bodies can be examined and the resulting knowledge applied to promote quality of life. Under gravity and other loads, and controlled by the nervous system, human movement is achieved through a complex and highly coordinated mechanical interaction between bones, muscles, ligaments and joints within the musculoskeletal system. Any injury to, or lesion in, any of the individual elements of the musculoskeletal system will change the mechanical interaction and cause degradation, instability or disability of movement. On the other hand, proper modification, manipulation and control of the mechanical environment can help prevent injury, correct abnormality, and speed healing and rehabilitation
It started with the development of mechanics that were concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effect of the bodies on their environment. More than 3000 years ago Babylonian astronomers studied the problem of planetary positions. The Renaissance astronomer Nicolaus Copernicus (1473–1543) published his heliocentric theory in 1543, which was in contrast to the widely accepted geocentric system model popular during the 13th–17th centuries that had been proposed by Aristotle (384–322 BC) and Claudius Ptolemy (90–c.168). During the early modern period (1453–1789), renowned scientists, including Galileo, Kepler and Newton, laid the foundation of classical mechanics. Galileo Galilei (1564–1642) worked theoretically and experimentally on the motions of bodies, particularly of falling bodies. Johannes Kepler (1571–1630) empirically discovered his laws of planetary motion which gave an approximate description of the motion of planets around the sun and provided one of the foundations for Isaac Newton’s theory of universal gravitation. In 1687 Isaac Newton (1643–1727) used the newly developed mathematics of calculus to give a detailed mathematical explanation of mechanics and published his classic Philosophiae Naturalis Principia Mathematica. In this three-volume publication he formulated the law of universal gravitation and the three laws of motion which can be applied to the motion of planets in the heavens and all forms of movements on earth