Biomechanics: Principles


Biomechanics is the application of engineering and physics to biology. All biological functions are subject to and constrained by the laws of physics. An understanding of basic physical principles allows one to understand many aspects of animal function, and the relationships between form and function. Of particular importance is the study of how animals generate movement.

Keywords: force; energy; muscle; bone; kinematics; kinetics; scale

Figure 1.

Lever–load systems. (a) Torque is the product of the magnitude of a force, F, and the perpendicular distance, r, between the line of action of the force and the centre of rotation (COR). (b) A first‐order lever–load system; (c) a second‐order lever–load system; (d) a third‐order lever–load system.

Figure 2.

Principal stresses and strains that develop in response to (a) axial loading, (b) shear and (c) torsion. Axial loading causes tension (ε1) and compression (ε2) at orientations perpendicular to each other. Shearing leads to parallel but noncollinear forces in the same plane, computed as x/y or tan ϕ. Torsion occurs when an element is twisted around an axis, generating tension, compression and shearing stresses. In torsion, cross‐sectional stresses, τ, that occur in response to an applied torque, T, are proportional to Tr/J where r is the radius and J is the polar moment of inertia (the sum of Ix + Iy).

Figure 3.

(a) A load–deformation curve, which characterizes the mechanical property of brittle, stiff and compliant materials. Y is the yield point, after which plastic deformation occurs; F is the fracture point, at which the material breaks. The Young modulus of elasticity is the slope of the curve (y/x). (b) Stress–strain curve for an elastic material during loading and unloading. The shaded area represents the energy lost (usually as heat).


Further Reading

Alexander R McN (1984) Elastic Mechanisms in Animal Movement. Cambridge, UK: Cambridge University Press.

Alexander R McN (1992) Exploring biomechanics: animals in motion. San Francisco: WH Freeman.

Currey J (1986) The Mechanical Adaptations of Bone. Princeton: Princeton University Press.

Heglund NC and Cavagna GA (1987) Mechanical work, oxygen consumption and efficiency in isolated frog and rat striated muscle. American Journal of Physiology 253: C22–C29.

LeVeau BF (1992) Williams and Lissner's Biomechanics of Human Motion, 3rd edn. Philadelphia: WB Saunders.

McMahon T and Bonner JT (1983) On size and life. San Francisco: WH Freeman.

Schmidt‐Nielsen K (1984) Scaling. Cambridge, UK: Cambridge University Press.

Vogel S (1988) Life's Devices: The Physical World of Plants and Animals. Princeton: Princeton University Press.

Wainright SA (1988) Axis and Circumference. Cambridge, MA: Harvard University Press.

Wainright SA, Biggs WD, Curry JD and Gosline JM (1976) Mechanical Design in Organisms. Princeton: Princeton University Press.

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Lieberman, Daniel E(Apr 2001) Biomechanics: Principles. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001859]