Everything about Biomechanics totally explained
'Biomechanics' is the application of mechanical principles on living organisms. This includes research and analysis of the
mechanics of living
organisms and the application of engineering principles to and from biological systems. This research and analysis can be carried forth on multiple levels, from the
molecular, wherein
biomaterials such as
collagen and elastin are considered, all the way up to the tissue and organ level. Some simple applications of
Newtonian mechanics can supply correct approximations on each level, but precise details demand the use of
continuum mechanics.
Giovanni Alfonso Borelli wrote the first book on biomechanics,
De Motu Animalium, or
On the Movement of Animals. He not only saw animals' bodies as mechanical systems, but pursued questions such as the physiological difference between imagining performing an action and actually doing it. Some simple examples of biomechanics research include the investigation of the forces that act on limbs, the
aerodynamics of
bird and
insect flight, the
hydrodynamics of
swimming in
fish, the anchorage and mechanical support provided by tree roots, 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.
Applied mechanics, most notably
thermodynamics and
continuum mechanics, and
mechanical engineering disciplines such as
fluid mechanics and
solid mechanics, play prominent roles in the study of biomechanics. By applying the laws and concepts of physics, biomechanical mechanisms and structures can be simulated and studied.
It has been shown that applied
loads and
deformations can affect the properties of living tissue. There is much research in the field of growth and remodeling as a response to applied loads. For example, the effects of elevated
blood pressure on the mechanics of the
arterial wall, the behavior of
cardiomyocytes within a heart with a cardiac
infarct, and
bone growth in response to exercise, and the acclimative growth of plants in response to wind movement, have been widely regarded as instances in which living tissue is remodelled as a direct consequence of applied loads.
Relevant mathematical tools include
linear algebra,
differential equations,
vector and
tensor calculus, numerics and computational techniques such as the
finite element method.
The study of
biomaterials is of crucial importance to biomechanics. For example, the various tissues within the body, such as skin, bone, and arteries each possess unique material properties. The passive mechanical response of a particular tissue can be attributed to characteristics of the various
proteins, such as
elastin and
collagen, living cells, ground substances such as
proteoglycans, and the orientations of fibers within the tissue. For example, if human
skin were largely composed of a protein other than
collagen, many of its mechanical properties, such as its
elastic modulus, would be different.
Chemistry,
molecular biology, and
cell biology have much to offer in the way of explaining the active and passive properties of living tissues. For example, in
muscle contractions, the binding of
myosin to
actin is based on a
biochemical reaction involving calcium ions and
ATP.
Applications
The study of biomechanics ranges from the inner workings of a
cell to the movement and development of
limbs, to the mechanical properties of
soft tissue, and
bones. As we develop a greater understanding of the physiological behavior of living tissues, researchers are able to advance the field of
tissue engineering, as well as develop improved treatments for a wide array of
pathologies.
Biomechanics as a
sports science, kinesiology, applies the laws of mechanics and physics to human performance in order to gain a greater understanding of performance in athletic events through modeling, simulation, and measurement.
Continuum mechanics
It is often appropriate to model living tissues as
continuous media. For example, at the tissue level, the arterial wall can be modeled as a
continuum. This assumption breaks down when the
length scales of interest approach the order of the micro structural details of the material. The basic postulates of continuum mechanics are conservation of
linear and
angular momentum,
conservation of mass,
conservation of energy, and the
entropy inequality. Solids are usually modeled using "reference" or "
Lagrangian" coordinates, whereas fluids are often modeled using "spatial" or "
Eulerian" coordinates. Using these postulates and some assumptions regarding the particular problem at hand, a set of equilibrium equations can be established. The
kinematics and
constitutive relations are also needed to model a continuum
Second and fourth order tensors are crucial in representing many quantities in electromechanical. In practice, however, the full tensor form of a fourth-order constitutive matrix is rarely used. Instead, simplifications such as
isotropy,
transverse isotropy, and
incompressibility reduce the number of independent components. Commonly-used second-order tensors include the
Cauchy stress tensor, the second
Piola-Kirchhoff stress tensor, the
deformation gradient tensor, and the
Green strain tensor. A reader of the mechanic's literature would be well-advised to note precisely the definitions of the various tensors which are being used in a particular work.
Biomechanics of circulation
Under most circumstances,
blood flow can be modeled by the
Navier-Stokes equations. Whole blood can often be assumed to be an incompressible
Newtonian fluid. However, this assumption fails when considering flows within arterioles. At this scale, the effects of individual red blood cells becomes significant, and whole blood can no longer be modeled as a continuum. When the diameter of the blood vessel is slightly larger than the diameter of the red blood cell the Fahraeus–Lindqvist effect occurs and there's a decrease in wall shear stress. However, as the diameter of the blood vessel decreases further, the red blood cells have to squeeze through the vessel and often can only pass in single file. In this case, the inverse Fahraeus–Lindqvist effect occurs and the wall shear stress increases.
Biomechanics of the bones
Bones are
anisotropic but are approximately
transversely isotropic. In other words, bones are stronger along one axis than across that axis, and are approximately the same strength no matter how they're rotated around that axis.
The stress-strain relations of bones can be modeled using
Hooke's law, in which they're related by
elastic moduli, for example
Young's modulus,
Poisson's ratio or the
Lamé parameters. The constitutive matrix, a fourth order
tensor, depends on the isotropy of the bone.
»
Biomechanics of the muscle
There are three main types of muscles:
- Skeletal muscle (striated): Unlike cardiac muscle, skeletal muscle can develop a sustained condition known as tetany through high frequency stimulation, resulting in overlapping twitches and a phenomenon known as wave summation. At a sufficiently high frequency, tetany occurs, and the contracticle force appears constant through time. This allows skeletal muscle to develop a wide variety of forces. This muscle type can be voluntary controlled. Hill's Model is the most popular model used to study muscle.
- Cardiac muscle (striated): Cardiomyocytes are a highly specialized cell type. These involuntarily contracted cells are located in the heart wall and operate in concert to develop synchronized beats. This is attributable to a refractory period between twitches.
- Smooth muscle (smooth - lacking striations): The stomach, vasculature, and most of the digestive tract are largely composed of smooth muscle. This muscle type is involuntary and is controlled by the enteric nervous system.
Biomechanics of soft tissues
Soft
tissues such as
tendon,
ligament and
cartilage are combinations of matrix proteins and fluid. In each of these tissues the main strength bearing element is collagen, although the amount and type of collagen varies according to the function each tissue must perform. Elastin is also a major load-bearing constituent within skin, the vasculature, and connective tissues.
The function of tendons is to connect muscle with bone and is subjected to tensile loads. Tendons must be strong to facilitate movement of the body while at the same time remaining compliant to prevent damage to the muscle tissues. Ligaments connect bone to bone and therefore are stiffer than tendons but are relatively close in their tensile strength. Cartilage, on the other hand, is primarily loaded in compression and acts as a cushion in the joints to distribute loads between bones. The compressive strength of collagen is derived mainly from collagen as in tendons and ligaments, however because collagen is comparable to a "wet noodle" it must be supported by cross-links of glycosaminoglycans that also attract water and create a nearly incompressible tissue capable of supporting compressive loads.
Recently, research is growing on the biomechanics of other types of soft tissues such as skin and internal organs.
This interest is spurred by the need for realism in the development of medical
simulation.
Viscoelasticity
Viscoelasticity is readily evident in many soft tissues, where there's energy dissipation, or hysteresis, between the loading and unloading of the tissue during mechanical tests. Some soft tissues can be
preconditioned by repetitive cyclic loading to the extent where the
stress-strain curves for the loading and unloading portions of the tests nearly overlap. The most commonly used model for viscoelasticity is the Quasilinear Viscoelasticity theory (QLV).
Nonlinear theories
Hooke's law is linear, but many, if not most problems in biomechanics, involve highly nonlinear behavior, particularly for soft tissues. Proteins such as collagen and elastin, for example, exhibit such a behavior. Some common material models include the Neo-Hookean behavior, often used for modeling elastin, and the famous Fung-elastic exponential model. Non linear phenomena in the biomechanics of soft tissue arise not only from the material properties but also from the very large strains (100% and more) that are characteristic of many problems in soft tissues.
BioMechanics In Sport
Biomechanics is the science concerned with the internal and external forces acting on the human body and the effects produced by these forces. At the highest levels of sports in which techniques play a major role, improvement comes so often from careful attention to detail that no coach can afford to leave these details to chance or guesswork. For such coaches knowledge of biomechanics might be regarded as essential.
Speed and Velocity
Hi my name is sam.
Speed and velocity describe the rate at which a body moves from one location to another. These two terms are often thought, incorrectly, to be the same. Average speed of a body is obtained by dividing the distance by the time taken where as the average Velocity is obtained by dividing the displacement by the time taken for example consider a swimmer in a 50m race in a 25m length pool who completes the race in 60 seconds - distance is 50m and displacement is 0m (swimmer is back where they started) so speed is 50/60= 0.83m/s and velocity is 0/60=0 m/s
Example
Let us consider the horizontal and vertical components of velocity of the shot in Figure 1. Figure 2 indicates the angle of release of the shot at 35° and the velocity at release as 12 m/sec.
· Vertical component Vv = 12 x sin 35° = 6.88 m/sec
· Horizontal component Vh = 12 x cos 35° = 9.82 m/sec
Let us now consider the distance the shot will travel horizontally (its displacement).
Range (R) = ((v² × sinØ × cosØ) + (v × cosØ × sqrt((v × sinØ)² + 2gh))) ÷ g
Where v = 12, Ø = 35, h = 2m (height of the shot above the ground at release) and g = 9.81
· R = ((12² × sin35 × cos35) + (12 × cos35 × sqrt((12 × sin35)² + 2x9.81x2))) ÷ 9.81
· R = 16.22m
The time of flight of the shot can be determined from the equation (2 × v × sinØ) ÷ g
· Time of flight = (2 x 12 x sin 35) ÷ 9.81 = 1.4 seconds
Further Information
Get more info on 'Biomechanics'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://biomechanics.totallyexplained.com">Biomechanics Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
