<P> Leonardo da Vinci studied anatomy in the context of mechanics . He analyzed muscle forces as acting along lines connecting origins and insertions, and studied joint function . Da Vinci tended to mimic some animal features in his machines . For example, he studied the flight of birds to find means by which humans could fly; and because horses were the principal source of mechanical power in that time, he studied their muscular systems to design machines that would better benefit from the forces applied by this animal . </P> <P> Galileo Galilei was interested in the strength of bones and suggested that bones are hollow because this affords maximum strength with minimum weight . He noted that animals' bone masses increased disproportionately to their size . Consequently, bones must also increase disproportionately in girth rather than mere size . This is because the bending strength of a tubular structure (such as a bone) is much more efficient relative to its weight . Mason suggests that this insight was one of the first grasps of the principles of biological optimization . </P> <P> In the 16th century, Descartes suggested a philosophic system whereby all living systems, including the human body (but not the soul), are simply machines ruled by the same mechanical laws, an idea that did much to promote and sustain biomechanical study . Giovanni Alfonso Borelli embraced this idea and studied walking, running, jumping, the flight of birds, the swimming of fish, and even the piston action of the heart within a mechanical framework . He could determine the position of the human center of gravity, calculate and measured inspired and expired air volumes, and showed that inspiration is muscle - driven and expiration is due to tissue elasticity . Borelli was the first to understand that the levers of the musculoskeletal system magnify motion rather than force, so that muscles must produce much larger forces than those resisting the motion . Influenced by the work of Galileo, whom he personally knew, he had an intuitive understanding of static equilibrium in various joints of the human body well before Newton published the laws of motion . </P> <P> In the 19th century Étienne - Jules Marey used cinematography to scientifically investigate locomotion . He opened the field of modern' motion analysis' by being the first to correlate ground reaction forces with movement . In Germany, the brothers Ernst Heinrich Weber and Wilhelm Eduard Weber hypothesized a great deal about human gait, but it was Christian Wilhelm Braune who significantly advanced the science using recent advances in engineering mechanics . During the same period, the engineering mechanics of materials began to flourish in France and Germany under the demands of the industrial revolution . This led to the rebirth of bone biomechanics when the railroad engineer Karl Culmann and the anatomist Hermann von Meyer compared the stress patterns in a human femur with those in a similarly shaped crane . Inspired by this finding Julius Wolff proposed the famous Wolff's law of bone remodeling . </P>

How do principles of engineering apply to heart structure and function
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