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BiomechanicsBiomechanics is the analysis of the mechanics of living organisms. The analysis can be carried forth on multiple levels, from the molecular, wherein molecular biomaterials, such as collagen, are considered, to the macroscopic level. Simple applications of Newtonian Mechanics may supply correct approximations on each level, but precise details are better cast in the form of Continuum Mechanics. Some simple examples of biomechanics include the investigation of the forces that act on limbs, the aerodynamics of bird and insect flight, the hydrodynamics of swimming in fish and locomotion in general across all forms of life, from individual cells to whole organisms. The biomechanics of human beings is a core part of kinesiology. Physics (most notably thermodynamics and continuum mechanics) and mechanical engineering (fluid mechanics, solid mechanics) play a strong role in the science and study of biomechanics. By applying the laws and concepts of physics, biomechanical mechanisms and structures can be simulated and studied. Relevant mathematical tools include matrix mechanics, linear algebra, differential equations, and the basic calculus. Biomaterials are crucial to biomechanics. A simple example: if the human skin were composed of a protein other than collagen, then many of its mechanical properties, such as elastic modulus, would be different. Chemistry and molecular biology explain how biomaterials work. Example: the binding of myosin to actin is based on the biochemical reaction where and ATP move the troponin and tropomyosin to allow for the crossbridges to bind to the activation sites on the actin. Applications Biomechanisms include all higher-class forms of life. The study of biomechanics can range from the inner workings of a cell to the movement and development of limbs and bones. Biomechanists can use knowledge and properties of organisms to explain many aspects of life, including speculation on the exinct life, such as dinosaurs. Continuum Mechanics The tensors standard to this subset of mechanics are crucial to representing many quantities in biomechanics. In practice, however, the full tensor form of, say, a rank 4 stiffness matrix is never used. Instead, simplifications, such as isotropy and transverse isotropy reduce the independent components. Biomechanics of Circulation Blood flow is governed by the Navier-Stokes equations. Blood is assumed incompressible. Biomechanics of the bones Bones are anisotropic, but are, to a good approximation, transversely isotropic. The stress-strain relations of bones can be modeled using Hooke's Law, where they are off by a constant known as the stiffness constant or Young's modulus or the elastic modulus. The elastic modulus, a rank 4 tensor depends on the isotropy of the bone. Biomechanics of the Muscle There are three main types of muscles: - Skeletal Muscle (striated) sustained "tetanic" condition (overlapping twitches)
- Cardiac Muscle (striated) beats (refractory period between twitches)
- Smooth Muscle (smooooottth). . . involuntary, dude. The stomach and most of the digestive tract is composed of smooth muscle. And yes, it is quite smooth.
Skeletal Muscle Biomechanics Skeletal Muscle is usually studied when its contractile force is in tetanus, which is produced from the high frequency stimuli. Skeletal muscle twitches may overlap, unlike cardiac muscle, allowing for wave summation upon successive frequency-based twitching. At a sufficiently high frequency, tetanus occurs, and the contracticle force appears constant through time despite stimulus that should cause more twitching. Hill's Model is the most popular model used to study muscle. Viscoelasticity Viscoelasticity is very evident in soft tissue, where there is energy dissipation between loading and unloading in the stress-strain curves. Soft tissue can be preconditioned, by repetitive loading and unloading, to the extent where its load-unload curve is the same. Nonlinear Theories Hooke's law is linear, but the biology being studied might involve nonlinear properties. See also References - Fung, Y.C. "Biomechanics: Mechanical Properties of Living Tissue" (2nd ed.). New York: Springer. ISBN 0-387-97947-6.
- Humphrey, Jay D. "Cardiovascular Solid Mechanics: Cells, Tissues, and Organs." New York: Springer. ISBN 0-387-95168-7.
- Vogel, Steven. (2003). Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. ISBN 0691112975
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