Force
Sir Isaac Newton described the motion of all objects using the concepts of inertia and force, and in doing so he found they obey certain conservation laws. In 1687, Newton published his thesis "Philosophiæ Naturalis Principia Mathematica". In this work Newton set out three laws of motion that to this day are the way forces are described in physics.
Biomechanics
The next major bio-mechanic, Giovanni Alfonso Borelli, was the first to understand that “the levers of the musculature system magnify motion rather than force, so that muscles must produce much larger forces than those resisting the motion”. Using the works of Galileo and building off from them, Borelli figured out the forces required for equilibrium in various joints of the human body. He even discovered the human center of gravity and air volume as well as  muscle elasticity. His work is often considered the most important in the history of bio-mechanics because he made so many new discoveries that opened the way for the future generations to continue his work and studies.