Sr. No. 1. 2. 3. 4. 5. 6. 7. 8.

INDEX Sr. No.

Content

Page No.

1.

Mechanobiology

2.

Biomechanics- an overview

1-3

3.

Biomechanics of locomotion

3-5

4.

Biomechanics of vertebrate body and muscle architecture

5-7

5.

Kinetic analysis of motion

7-9

6.

Stress and Strain

8-9

7.

Gait and stride

9-10

8.

Biomechanics of articular cartilage

10-11

9.

References

1

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Mechanobiology Mechanobiology is the branch of biology which deals with the knowledge of biomechanics incorporated with the knowledge of molecular biology, genomics and cellular biology. At the center of mechanobiology is the cellular process of mechanotransduction, or the way cells sense and respond to mechanical forces. Many of the tissues in the body contain mechanosensitive cells. These include osteocytes in bone, chondrocytes in cartilage, myocytes in the heart, endothelial cells in blood vessels, epithelial cells in renal tubules, and many others. There are many clinical applications of mechanobiology, including orthodontic tooth movement, distraction osteogenesis, artery stents, artificial heart valves, as well as promising new treatments for diabetes, muscular dystrophy and osteoporosis. Another use of mechanobiology is the development of new pain killers. Many pain sensing nociceptors are in fact mechanosensors that detect local tissue deformation and send signals to the brain that are perceived as pain. Blockers of mechanotransduction in nociceptors show promise for treatment of chronic pain syndromes. Traditionally, skeletal biomechanics has focussed on how these tissues perform the structural and locomotory functions of the vertebrate skeleton. In mechanobiology the central question is how these same load-bearing tissues are produced, maintained and adapted by cells as an active response to biophysical stimuli in their environment. The detailed study will bring great benefits to tissue engineering and to the treatment and prevention of skeletal conditions such as congenital deformities, osteoporosis, osteoarthritis and bone fractures.

Biomechanics Biomechanics is the study of the movement of living things using the science of mechanics. (Hatze, 1974) Or “Biomechanics is the branch of biophysics, which deals with the mechanics of the human or animal body; especially concerned with muscles and the skeleton”. It applies mechanical principles to the study of organisms. “The field of study which makes use of the laws of physics and engineering concepts to describe motion of body segments, and the forces which act upon them during activity.” Biomechanics uses mathematical models and computer simulations to study living organisms, in addition to direct biological measurements.

Historical roots Aristotle (~400-300 BC): first biomechanis. First written account of locomotion (On the Movement of Animals) and qualitatively studied the effects of forces.

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da Vinci (1452-1519): He was an engineer and made many contributions to mechanics, mainly applied mechanics to human anatomy. Galileo Galilei (1564-1642): The father of mechanics established the scientific method. He was particularly aware of bone mechanics, wrote an unpublished work: “The Movement of Animals”. Giovanni Borelli (1608-1679): He is generally considered the father of biomechanics, wrote the 2nd book: “One the Movement of Animals” Isaac Newton (1642-1727) Revolutionized mechanics by postulating four basic laws: a. Law of gravity b. Law of inertia (1st law) c. Law of acceleration (2nd law) d. Law of action-reaction (3rd law). Newton’s 2nd law forms the basis for all kinetic analysis of animal motion and made numerous other contributions in mathematics, optics, astronomy etc. Etienne Marey (1838-1904) analyzed motion via sequential multiple exposures and motion photography, and simultaneously measured ground reaction forces.

More recent developments 

1967 – First International Seminar on Biomechanics held in Zürich.

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1973 International Society of Biomechanics founded during a conference at Penn State.

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1977 - American Society of Biomechanics founded Universities begin to offer advanced courses and degrees in biomechanics scientific journals with “biomechanics” in the title begin to appear.

Applications  Biomechanics helps us understand • •

Limitations on the size of organisms Energy efficiency

 In studying a wide range of the inner workings of a cell to the movement and development of limbs.  Physiological behavior of living tissues can be studied so researchers are able to advance the field of tissue engineering, as well as develop improved treatments for a wide array of pathologies.  Biomechanics of horse can be used as a testing tool for soundness of hoof and legs.  Another important area of research in biomechanics is automobile safety design. Most people have seen films of crash-test dummies. 3

 Horse breeders can take advantage of it by using it for producing better racing thorough bred horses.  In surgical correction of fracture cases, mechanical strength of bone is taken under consideration for applying internal fixation tools for example bone plates etc.  Biomechanics of equine foot has played a vital role in dealing with hoof disorders and bringing out new techniques.

Tools of biomechanics  Observation of gait and locomotion  Direct measurements  Motion capture  3D Videography and motion photography  kinematics analysis

Locomotion Act of changing place or position is called movement. The study of movement is called kinesiology. Locomotion is the act of moving from place to place. Or Any movements that result in progression from one place to another, is locomotion.

Classification of locomotion Locomotion is classified as:-

Appendicular It is accomplished by special appendages which oscillate in order to produce movement.

Axial It is achieved by changing the body shape. In this bodies undulate, pulse, or undergo peristaltic waves.

Patterns of locomotion  Protozoan They move with ciliary or flagellar appendages & pseudopods 4

 Swimming in different animals is result of hydraulic propulsion and undulation  Terrestrial arthropods and vertebrates jointed appendages, the legs  Crawling in Snakes and other limbless vertebrates muscular thrusts against the substrate  Flight forward thrust of wings

Locomotion in Amoeba Pseudopodia are used by many cells, such as Amoeba, Chaos (Pelomyxa) and human leukocytes (white blood cells). These are not structures as such but rather are associated with actin near the moving edge. Formation and functioning of a pseudopod by an amoeboid cell.

Locomotion in water Buoyancy reduces the influence of gravity. The primary force retarding forward movement is frictional drag. Swimming uses the body or its appendages to push against the water. Buoyancy reduces the influence of gravity. • The primary force retarding forward movement is frictional drag. • Swimming uses the body or its appendages to push against the water.

Locomotion in air Flight has evolved in Insects, birds, bats etc.  Propulsion is achieved by pushing down against the air with wings.  Raising and lowering wings is achieved by alternate contraction of extensor muscles and flexor muscles. The primary flight muscles of birds, the pectoralis and supracoracoideus, are designed for work and power output, with large stress and strain. The tail contributes to lift and drag; it is also integral to maneuvering and stability. Flying of insects  Aerodynamic force (F) is responsible for flight of insects. 

Here we can appreciate some upstroke and down stroke forces acting upon with the help of wings.

Locomotion on land Mollusks slide along a path of mucus.

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Vertebrates and arthropods have a raised body and move forward by pushing the ground with a series of jointed appendages.Vertebrates have four limbs, while arthropods have six or more. Both arthropods and vertebrates achieve faster gaits by overlapping leg movements. Basic walking pattern of all tetrapod vertebrates LH – LF – RH – RF. Most snakes employ serpentine locomotion. Snakes use muscle contractions along their bodies to move. Scales, which catches on an uneven surface. If the ground is very smooth they have trouble moving at all.

Vertebrate biomechanics Vertebrates have an efficient complex system of bones, muscles, tendons which enables them to move in a desired way. Bones are designed to provide adequate strength with minimal material (minimal mass or weight). Such an economy of bone mass/weight offers evolutionary advantages; viz., faster reaction capability; reduced metabolic requirements.

Contents of locomotor system Tendons Generally regular connective tissue. Provide musculo-skeletal connections for Muscle to bone Muscle to muscle Bone to bone Can have various shapes when found in the form of sheath- “aponeuroses”. Ligaments connect bone-to-bone or reinforce joints. made up of Yellow Fibrous C.T. Joints or Articulations They form connections between two or more bones. Usually, but not always allow for movement. Formed from various connective tissues • Fibrous • Cartilaginous • Synovial (most complex--typical limb joints)

Architecture of mammalian body The mammalian body is well represented by a bow and string appearance. The bow is formed by thoraco-lumbar vertebrae, their articulations and accompanying ligaments and muscles. The string consists of abdominal muscles, especially straight muscles which reaches from thorax to pelvis. The bow and string are indirectly attached by thoracic skeleton cranially and pelvis skeleton caudally. The mammalian body is well represented by a bow and string appearance. The bow is formed by thoracolumbar vertebrae, their articulations and accompanying ligaments and muscles. The string consists of 6

abdominal muscles, especially straight muscles which reaches from thorax to pelvis. The bow and string are indirectly attached by thoracic skeleton cranially and pelvis skeleton caudally. Contraction of abdominal muscles will cause flexion of bow. Contraction of epiaxial (dorsal trunk muscles like multifidous, longissimus dorsii) muscles will cause straightening of bow.Viscera of abdomen attached to spine also tends to straighten the bow.

Muscle architecture: Multiple muscles and multiple parts or heads (head = a separate belly and origin) exist to distribute (as opposed to concentrate) stresses on bones and to provide movement diversity. Fascicle & fiber arrangement: Parallel arrangement, e.g., strap or spindle arrangement, fibers/fascicles arranged parallel to the tendon of insertion. This results in a greater range of shortening and thus yields greater movement velocity (distance per time). Pennate arrangement = fibers/fascicles arranged at an angle to the direction in which the tendon moves. This results in a greater area of muscle fibers along axes of contraction and produces more strength (at the expense of a reduced range of contraction). Note: The amount of force that a muscle can generate is proportional to the area of muscle fibers, i.e., number of contractile protein molecules, multiplied by the cosine of the muscle-tendon angle.

Three types of pennate arrangement are: — unipennate, e.g., ulnar & radial heads of the deep digital flexor muscle; — bipennate, e.g., infraspinatus muscle; — multipennate, e.g., humeral head of the deep digital flexor muscle.

• •

Natural movements involve many muscles working simultaneously or one after the other. When two muscles act together they are called synergistic and when they work against each other they are called antagonists. 7

• • • • • •

During movement one part is fixed point (because of its attachment to the trunk) and the other is moving point ( smaller and lighter than fixed point). The function of a muscle can be derived by its origin, placement and insertion and the point of rotation. Most of the natural movements viz. breathing, walking, trotting, galloping are all rhythmic cycle of contraction and relaxation of antagonistic muscle groups. Even during relaxation every muscle is under a certain amount of minimal pressure, the muscle tonus. It is caused by stimuli from muscle spindles. During anaesthesia hypotonus is achieved (a reduced muscle tone). In order to start the movement, both the muscle tonus of antagonising muscle(s) and the gravitational force must be overcome.

During movement following two types of muscle contraction are seen: Isotonic-muscle tension is constant and length is changed.  Isometric-muscle length is constant but tone is changed. Muscles attaching close to the joint with their velocity advantage are termed “high gear” muscles and those with a more distal attachment resulting in a mechanical advantage are termed “low gear” muscles.

Kinetic analysis of motion • • •

Biomechanical principles can be applied to a system of bodies at rest, termed statics, or to a system of bodies in motion, termed dynamics. In such systems, bodies may be pushed or pulled by actions termed forces. Such forces always act in harmony; i.e., if one body is pushing on another body, the second one is pushing back on the first body equally hard (Newton’s third law, the law of reaction).

Newton’s first law is the law of inertia: a body remains at rest or in constant velocity motion until acted upon by an external unbalanced force. Newton’s second law is the law of acceleration: the acceleration of a body is proportional to the unbalanced force acting upon it and inversely proportional to the mass of the body. Mathematically this law is expressed as:F = ma where F = force; m = mass; a = acceleration.

Vector analysis of force A vector quantity has a certain direction along with mass unlike a scalar quantity. A force can be characterized by three factors: magnitude, direction, and point of application. Force has a certain direction and provides acceleration in the same direction. F=ma F=force, m=mass, a=acceleration produced Suppose a force F is working on a body (mass=m) at an angle, from the horizontal. We can take components of it and acquire some results. The total force F, thus can be written as F= Fcosα + Fsinα According to Newton 8

Fsinα will combat with N=mg Here g= gravitational constant. When the force applied on this body will lose equilibrium, the body will start moving in the direction where an acceleration is produced by resultant dominant force. Force also produces torque. When two parallel unequal forces, F1 & F2 are applied to a body, the resultant can be defined asR= F1 + F2 F1 X a = F2 X b When two opposite unequal forces, F are applied to a body, the resultant can be defined as-this system is called couple. It will produce moment, torque = F . d

Equilibrium of hinge joint F is the muscular force created by parallel fibred muscle. W is the gravitational force. R is the resultant force of W and F. For equilibrium R should pass through centre of rotation of joint H. Force provides a moment to the joints known as torque. Torque = F X r Here ‘F’ is magnitude of force and ‘r’ is perpendicular distance from the direction line of force.

Stress How hard a load works to change the shape of a material is measured by mechanical stress. Mechanical stress is defined as the force per unit area within a material ( = F/A). Mechanical stress is similar to the concept of pressure and has the same units (N/m2). Mechanical stress is not vector quantity, but an even more complex quantity called a tensor. Normal stress, σn = N/a Shear stress, ζ = H/a Here a is surface cross section area The bending moment Mb = N X d It will cause compressive stress at the right side and tensile stress at the left side.

Strain The measure of the deformation of a material created by a load is called strain.This deformation is usually expressed as a ratio of the normal or resting length (L0) of the material. Strain can be calculated as a change in length divided by normal length. Strain : (L – L0)/ L0. 9

Gait Gait is the pattern of movement of the limbs of terrestrial animals, during locomotion. There is variety of gaits based upon 1. 2. 3. 4. 5.

Species of animal Speed of animal Ground Energetic efficiency of animal Miscellaneous

Different gaits in horse In horses different gaits are:Walk Four-beat gait.  Speed averages about 4 miles per hour (6.4 km/h). Trot –  Two-beat gait.  Two legs diagonally opposite from each other move forward together.  Speed averages about 8 miles per hour (13 km/h). Canter – 10

 Controlled, three-beat gait.  A bit faster than the average trot, but slower than the gallop.  The average speed of a canter is between 16-27 km/h (10-17 mph). Gallop –  Very much like the canter.  It is faster, more ground-covering, and the three-beat canter changes to a four-beat gait.  It is the fastest gait of the horse, averaging about 25 to 30 miles per hour (40 to 48 km/h). Run/pace –  

Lateral two-beat gait. The two legs on the same side of the horse move forward together.

Stride Stride is the distance from initial contact of one foot to the following initial contact of the same foot. It is the length of step, taken during a run or jog. A stride is usually the distance traveled by one right leg and one left leg step so this is two steps. However a stride confusingly can also mean the same as a step! This means the distance from where you lift one foot off the ground to where you put it down again. (Heglund et al, 1974) The stride frequency, at which animals of different size change from one gait to another (walk, trot, gallop) changes in a regular manner with body mass. The speed at the transition from trot to gallop can be used as an equivalent speed for comparing animals of different size. This transition point occurs at lower speeds and higher stride frequencies in smaller animals. Plotting stride frequency at the trotgallop transition point as a function of body mass in logarithmic coordinates yields a straight line. Stride length is the distance between successive points of initial contact of the same foot. Right and left stride lengths are normally equal.

Classification of animals according to their foot posture during walk plantigrades are ones who walk with the podials and metatarsals flat on the ground. Primates are examples of plantigrade species; in humans, the podials and metatarsals constitute the sole of the foot. Other plantigrade species examples include (but are not limited to) raccoons, opossums, bears, kangaroo,weasels, mice, pandas, rats, hyraxes, skunks and hedgehogs. A digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds (what many assume to be bird knees are actually ankles), cats, dogs, and most other mammals, but not humans, bears, and a few others (cf. plantigrade, unguligrade). They are generally quicker and move more quietly than other mammals. Ungulates (meaning roughly "being pawed" or "hoofed animal") are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. Commonly known examples of ungulates living today are the horse, zebra, donkey, cattle/bison, 11

rhinoceros, camel, hippopotamus, goat, pig, sheep, giraffe, okapi, moose, deer, tapir, antelope, and gazelle.

Biomechanics of articular cartilage Articular cartilage provides an efficient load bearing surface for synovial joints that is capable of functioning for the lifetime of an individual. The mechanical behavior of this tissue depends on the interaction of its fluid and solid components. Numerous factors can impair the function of cartilage and lead to osteoarthrosis and a painful and nonfunctional joint. In a typical synovial joint, the ends of opposing bones are covered with a thin layer of articular Cartilage. Normal articular cartilage is white, and its surface is smooth and glistening. Cartilage is aneural, and in normal mature animals, it does not have a blood supply. The entire joint is enclosed in a fibroustissue capsule, the inner surface of which is lined with the synovial membrane that secretes a fluid known as synovial fluid. A relatively small amount of fluid is present in anormal joint: less than 1 mL, which is less than one fifth of a teaspoon. Synovial fluid isclear to yellowish and is stringy. Overall, synovial fluid resembles egg white, and it is this resemblance that gives these joints their name, synovia, meaning “with egg.” Cartilage clearly performs a mechanical function. It provides a bearing surface with low friction and wear, and because of its compliance, it helps to distribute the

Articular cartilage is a living material composed of a relatively small number of cells known as chondrocytes surrounded by a multicomponent matrix composed primarily of proteoglycans and collagen. Proteoglycans consist of a protein core to which glycosaminoglycans (chondroitin sulfate and keratan sulfate) are attached to form a bottlebrush-like structure. Compressive loads on the cartilage surface tend to “cramp” these bristles and move negative charges closer together. loads between opposing bones in a synovial joint. If cartilage were a stiff material like bone, the contact stresses at a joint would be much higher, since the area of contact would be much smaller.

References Baudex, D.M. in Getty, R. (1975). Sisson and Grossman's the Anatomy of the Domestic Animals. W.B. Saunders Comp. Philadelphia. pp. 48-84 Konig, H.E and Liebich, H.G. (2006). Veterinary anatomy of Domestic Animals. 3rd Edn, Schattauer, Stuttgart, Germany. 12

Huston, R.L. (2009). Principles of Biomechanics, R.L. CRC Press, Taylor & Francis Group, Boca Raton London New York. Knudson, D. (2007) Fundamentals of Biomechanics, 2nd Edn., Springer Science+Business Media, LLC. Hatze, H. (1974). The meaning of the term: “Biomechanics.” Journal of Biomechanics, 7:189– 190. Fletcher, T.F. and Clarkson, C.E. (2008) General Anatomy & Carnivore Anatomy -Lecture Notes. pp:6,12-15 Freivalds, A. (2004). Biomechanics of the Upper Limbs: Mechanics, Modeling, and Musculoskeletal Injuries, CRC Press, Boca Raton London New York Washington, D.C. pp:21-22 Tobalske, B.W. (2007). Biomechanics of bird flight. Journal of Experimental Biology. 210:3135-3146 Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and W.H. Freeman. http://en.wikipedia.org/wiki/File:Lift-force-en.svg http://en.wikipedia.org/wiki/Bird_flight#Basic_mechanics_of_bird_flight www.DennisKunkel.com

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