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Biomechanics Biomechanics - study of the mechanicsas it relates to the functional andanatomical analysis of biologicalChapter 3Basic Biomechanical Factors &Conceptssystems and especially humans– Necessary to study the body’s mechanicalcharacteristics & principles to understandits movementsManual of Structural KinesiologyR.T. Floyd, EdD, ATC, CSCSManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-1Manual ofStructural KinesiologyBiomechanics Statics - study of systems that are in aconstant state of motion, whether at restactions of forceswith no motion or moving at a constant Mechanics is divided intovelocity without accelerationStatics– Dynamics–Basic Biomechanical Factors & Concepts– Statics involves all forces acting on thebody being in balance resulting in the bodybeing in equilibrium3-3Manual ofStructural KinesiologyBiomechanics 3-4Kinematics & kinetics– Kinematics - description of motion andincludes consideration of time,displacement, velocity, acceleration, andspace factors of a system‘s motion– Kinetics - study of forces associated withthe motion of a bodywith acceleration– A system in acceleration is unbalanceddue to unequal forces acting on the bodyBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsBiomechanics Dynamics - study of systems in motionManual ofStructural Kinesiology3-2BiomechanicsMechanics - study of physicalManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-5Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-61
Types of machines found in the bodyTypes of machines found in the body Mechanical advantage Machines function in four ways– Load/effort or load divided by effort– Ideally using a relatively small force, or effort tomove a much greater resistance– balance multiple forces– enhance force in an attempt to reduce totalforce needed to overcome a resistance– enhance range of motion & speed ofmovement so that resistance may bemoved further or faster than applied force– alter resulting direction of the applied force Musculoskeletal system may be thought of asa series of simple machines– Machines - used to increase mechanicaladvantage– Consider mechanical aspect of each component inanalysis with respect to components’ machine-likefunctionManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-7Manual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsTypes of machines found in the bodyLevers Musculoskeletel system arrangementprovides for 3 types of machines in producingmovement Humans moves through a system oflevers Levers cannot be changed, but they canbe utilized more efficiently– Levers (most common)– Wheel-axles– Pulleys– lever - a rigid bar that turns about an axisof rotation or a fulcrum– axis - point of rotation about which levermoves Machine types not found in the body– Inclined plane– Screw– WedgeManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-9Manual ofStructural KinesiologyLevers3-10 Resistance can vary from maximal tominimal– May be only the bones or weight of bodysegment All lever systems have each of thesethree components in one of threepossible arrangements– bones represent the bars– joints are the axes– muscles contract to apply forceBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsLevers Levers rotate about an axis as a resultof force (effort, E) being applied tocause its movement against aresistance or weight In the bodyManual ofStructural Kinesiology3-83-11Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-122
LeversLevers 1st class lever – axis (A) betweenforce (F) & resistance (R) 2nd class lever – resistance (R)between axis (A) & force (F) 3rd class lever – force (F)between axis (A) & resistance(R) Three points determine type of lever &for which kind of motion it is best suited– Axis (A)- fulcrum - the point of rotation– Point (F) of force application (usuallymuscle insertion) - effort– Point (R) of resistance application (centerof gravity of lever) or (location of anexternal resistance)Manual ofStructural Kinesiology3-13Basic Biomechanical Factors & ConceptsManual ofStructural KinesiologyLevers FAR1st Force ArmResistance ArmF The mechanical advantage of levers may bedetermined using the following equations:Mechanical advantage ResistanceForceorMechanical advantage Length of force armLength of resistance armR Resistance Arm Force ArmR FA AFR3rdManual ofStructural Kinesiology Force Arm Resistance ArmF RABasic Biomechanical Factors & Concepts3-15Manual ofStructural KinesiologyFirst-class LeversBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & Concepts3-16First-class Levers Produce balanced movements whenaxis is midway between force &resistance (e.g., seesaw) Produce speed & range of motionwhen axis is close to force, (tricepsin elbow extension) Produce force motion when axis isclose to resistance (crowbar)Manual ofStructural Kinesiology3-14Levers A ARF2ndBasic Biomechanical Factors & Concepts Head balanced on neck inflexing/extending Agonist & antagonist muscle groupsare contracting simultaneously oneither side of a joint axis– agonist produces force whileantagonist supplies resistance3-17Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-183
First-class LeversFirst-class Levers Elbow extension in triceps applyingforce to olecranon (F) in extending thenon-supported forearm (R) at theelbow (A)Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts Force is applied where muscle inserts inbone, not in belly of muscle– Ex. in elbow extension with shoulder fullyflexed & arm beside the ear, the tricepsapplies force to the olecranon of ulnabehind the axis of elbow joint– As the applied force exceeds the amountof forearm resistance, the elbow extends3-19Manual ofStructural KinesiologyFirst-class LeversBasic Biomechanical Factors & Concepts Produces force movements, since alarge resistance can be moved by arelatively small g a lug nutRaising the body up on the toesManual ofStructural KinesiologySecond-class Levers3-22 Produce speed & range-of-motionmovements Most common in human body Requires a great deal of force to moveeven a small resistance– Paddling a boat– Shoveling - application of lifting force to ashovel handle with lower hand while upperhand on shovel handle serves as axis ofrotation Relatively few 2nd class levers inbodyBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsThird-class Levers– Plantar flexion of foot to raise thebody up on the toes where ball (A)of the foot serves as the axis asankle plantar flexors apply force tothe calcaneus (F) to lift theresistance of the body at the tibialarticulation (R) with the footManual ofStructural Kinesiology3-20Second-class Levers– Change example by placing the hand onthe floor (as in a push-up) to push the bodyaway from the floor, the same muscleaction at this joint now changes the lever to2nd class due to the axis being at the handand the resistance is body weight at theelbow jointManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-23Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-244
Third-class LeversThird-class Levers Brachialis - true 3rd class leverage– Biceps brachii in elbow flexionUsing the elbow joint (A) as theaxis, the biceps brachii appliesforce at its insertion on radialtuberosity (F) to rotate forearmup, with its center of gravity (R)serving as the point ofresistance applicationManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts– pulls on ulna just below elbow– pull is direct & true since ulna cannot rotate Biceps brachii supinates forearm as it flexesso its 3rd class leverage applies to flexion only Other examples– hamstrings contracting to flex leg at knee while in astanding position– using iliopsoas to flex thigh at hip3-25Factors in use of anatomical leversBasic Biomechanical Factors & Concepts– In objects without a fixed axis it is anapplied force that is not in line with object'scenter of gravity For rotation to occur an eccentric forcemust be applied3-27Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-28Torque and length of lever arms In humans, contracting muscle appliesan eccentric force (not to be confusedwith eccentric contraction) to bone uponwhich it attaches & causes the bone torotate about an axis at the joint Amount of torque is determined bymultiplying amount of force (forcemagnitude) by force armBasic Biomechanical Factors & Concepts3-26 Torque – (moment of force) the turningeffect of an eccentric force Eccentric force - force applied in adirection not in line with the center ofrotation of an object with a fixed axisTorque and length of lever armsManual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsTorque and length of lever arms Anatomical leverage system can beused to gain a mechanical advantage Improve simple or complex physicalmovements Some habitually use human leversproperly Some develop habits of improperlyusing human leversManual ofStructural KinesiologyManual ofStructural Kinesiology Force arm - perpendicular distancebetween location of force application &axis– a.k.a. moment arm or torque arm– shortest distance from axis of rotation tothe line of action of the force– the greater the distance of force arm, themore torque produced by the force3-29Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-305
Torque and length of lever armsTorque and length of lever arms Inverse relationship between length ofthe two lever arms Often, we purposely increase force armlength in order to increase torque sothat we can more easily move arelatively large resistance (increasingour leverage) Resistance arm - distance between theaxis and the point of resistanceapplicationManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts– Between force & force arm– Between resistance & resistance arm– The longer the force arm, the less forcerequired to move the lever if the resistance& resistance arm remain constant– Shortening the resistance arm allows agreater resistance to be moved if force &force arm remain constant3-31Torque and length of lever arms3-33Torque and length of lever armsManual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & Concepts3-34Torque and length of lever armsSecond class leversA, Placing the resistance halfwaybetween the axis & the point of forceapplication provides a MA of 2;B, Moving the resistance closer tothe axis increases the MA, butdecreases the distance that theresistance is moved;C, the closer the resistance ispositioned to the point of forceapplication the less of a MA, but thegreater the distance it is movedFirst class leversA, If the force arm & resistance armare equal in length, a force equal tothe resistance is required to balance it;B, As the force arm becomes longer, adecreasing amount of force is requiredto move a relatively larger resistance;C, As the force arm becomes shorter,an increasing amount of force isrequired to move a relatively smallerresistanceManual ofStructural Kinesiology3-32 Even slight variationsin the location of theforce and resistanceare important indetermining theeffective force of themuscle– If either of the resistance componentsincrease, there must be an increase in oneor both of force components– Greater resistance or resistance armrequires greater force or longer force arm– Greater force or force arm allows a greateramount of resistance to be moved or alonger resistance arm to be usedBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsTorque and length of lever arms Proportional relationship between forcecomponents & resistance componentsManual ofStructural KinesiologyManual ofStructural Kinesiology3-35Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-366
Torque and length of lever armsTorque and length of lever armsA 0.05 meterincrease ininsertionresults in asubstantialreduction inthe forcenecessary tomove theresistanceThird class leversA, a force greater than the resistance,regardless of the point of forceapplication, is required due to theresistance arm always being longer;B, Moving the point of force applicationcloser to the axis increases the rangeof motion & speed;C, Moving the point of force applicationcloser to the resistance decreases theforce neededEXAMPLE: biceps curlF x FA R x RA(force) x (force arm) (resistance) x (resistance arm)F x 0.1 meters 45 newtons x 0.25 metersF 112.5 newtonsIncrease insertion by 0.05 metersF x 0.15 meters 45 newtons x 0.25 metersF x 0.15 meters 11.25 newton-metersF 75 newtonsRA 0.25 meters 0.1 m FRRA 0.25 meters 0.15m FRAManual ofStructural Kinesiology3-37Basic Biomechanical Factors & ConceptsManual ofStructural KinesiologyTorque and length of lever armsA 0.05 meterreduction inresistancearm canreduce theforcenecessary tomove theresistance 0.1m FRRA 0.2 meters 0.1m AManual ofStructural KinesiologyReducingresistancereduces theamount offorceneeded tomove theleverEXAMPLE: biceps curlF x FA R x RA(force) x (force arm) (resistance) x (resistance arm)F x 0.1 meters 45 newtons x 0.25 metersF 112.5 newtonsDecrease resistance by 1 NewtonF x 0.1 meters 44 newtons x 0.25 meterF x 0.1 meters 11 newton-metersF 110 newtonsRA 0.25 meters FR 0.1 m FRABasic Biomechanical Factors & Concepts3-38Torque and length of lever armsEXAMPLE: biceps curlF x FA R x RA(force) x (force arm) (resistance) x (resistance arm)F x 0.1 meters 45 newtons x 0.25 metersF 112.5 newtonsDecrease resistance arm by 0.05 metersF x 0.1 meters 45 newtons x 0.2 metersF x 0.1 meters 9 newton-metersF 90 newtonsRA 0.25 meters ABasic Biomechanical Factors & Concepts RA 0.25 metersManual ofStructural KinesiologyFRA3-39 0.1 m ABasic Biomechanical Factors & ConceptsTorque and length of lever armsTorque and length of lever arms Human leverage system is built forspeed & range of movement at expenseof force Short force arms & long resistance armsrequire great muscular strength toproduce movement Ex. biceps & triceps attachments Human leverage for sport skills requiresseveral levers– throwing a ball involves levers at shoulder,elbow & wrist joints The longer the lever, the more effectiveit is in imparting velocity– A tennis player can hit a tennis ball harderwith a straight-arm drive than with a bentelbow because the lever (including theracket) is longer & moves at a faster speed– biceps force arm is 1 to 2 inches– triceps force arm less than 1 inchManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-403-41Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-427
Torque and length of lever armsTorque and length of lever arms Long levers producemore linear force andthus better performancein some sports such asbaseball, hockey, golf,field hockey, etc.Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts For quickness, it is desirable to have ashort lever arm– baseball catcher brings his hand back tohis ear to secure a quick throw– sprinter shortens his knee lever throughflexion that he almost catches his spikes inhis gluteal muscles3-43Manual ofStructural KinesiologyWheels and axlesBasic Biomechanical Factors & Concepts3-44Wheels and axles Used primarily to enhance range ofmotion & speed of movement in themusculoskeletal system Center of the wheel & the axle bothcorrespond to the fulcrum Both the radius of the wheel & theradius of the axle correspond to theforce arms– function essentially as a form of a lever When either the wheel or axle turn, theother must turn as well– Both complete one turn at the same timeManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-45Manual ofStructural KinesiologyWheels and axles– calculate mechanical advantage of awheel & axle by considering theradius of the wheel over the axle– a relatively smaller force may be applied tothe wheel to move a relatively greaterresistance applied to the axle– if the radius of the wheel is 5 times theradius of the axle, then the wheel has a 5to 1 mechanical advantage over the axleBasic Biomechanical Factors & Concepts3-46Wheels and axles If the wheel radius is greater than theradius of the axle, then, due to thelonger force arm, the wheel has amechanical advantage over the axleManual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsMechanicaladvantage3-47Manual ofStructural Kinesiology radius of the wheelradius of the axleBasic Biomechanical Factors & Concepts3-488
Wheels and axlesWheels and axles If application of force is reversed andapplied to the axle, then the mechanicaladvantage results from the wheelturning a greater distance & speed– Calculate the mechanical advantagefor this example by considering theradius of the wheel over the axle– if the radius of the wheel is 5 times theradius of the axle, then outside of thewheel will turn at a speed 5 times that ofthe axle– the distance that the outside of the wheelturns will be 5 times that of the outside ofthe axleManual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsMechanicaladvantage 3-49Manual ofStructural KinesiologyWheels and axles– Mechanical advantage 1 Pulleys may be combined toform compound pulleys toincrease mechanical advantage– Each additional rope increasesmechanical advantage by 13-51PulleysBasic Biomechanical Factors & Concepts3-52 Body motion is produced or started bysome action of muscular system Motion cannot occur without a force Muscular system is source of force inhumans Two types of motion– As peroneus longus contracts, itpulls toward it belly (toward theknee)– Using the lateral malleolus as apulley, force is transmitted to plantaraspect of foot resulting ineversion/plantarflexionBasic Biomechanical Factors & ConceptsManual ofStructural KinesiologyLaws of motion and physical activities Ex. lateral malleolus acting as apulley around which tendon ofperoneus longus runsManual ofStructural Kinesiology3-50 Single pulleys function tochange effective direction offorce application– humerus acts as the axle– hand & wrist are located at the outside of the wheelwhen elbow is flexed 90 degrees– with minimal humerus rotation, the hand & wristtravel a great distance– allows us significantly increase the speed at whichwe can throw objectsBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsPulleys Ex. resulting in greater range ofmotion & speed is with upperextremity in internal rotatorsattaching to humerusManual ofStructural Kinesiologyradius of the axleradius of the wheel– linear motion– angular motion3-53Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-549
Laws of motion and physical activities Linear motion (translatory motion) motion along a line Angular motion (rotary motion) - rotationaround an axis– rectilinear motion - motion along a straightline– curvilinear motion - motion along a curvedline– In the body, the axis of rotation is providedby the various joints Linear & angular motion are related– angular motion of the joints produces thelinear motion of walking Linear displacement - distance that asystem moves in a straight lineManual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsLaws of motion and physical activities3-55Laws of motion and physical activities Sports ex. - cumulative angular motionof the joints imparts linear motion to athrown object (ball, shot) or to an objectstruck with an instrument (bat, racket)Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-56Laws of motion and physical activities Displacement - actual distance that theobject has been displaced from itsoriginal point of reference Distance - actual sum length ofmeasurement traveled– object may have traveled a distance of 10meters along a linear path in two or moredirections but only be displaced from itsoriginal reference point by 6 metersManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-57Laws of motion and physical activities Angular displacement - change inlocation of a rotating body Linear displacement - distance that asystem moves in a straight line Speed - how fast an object is moving ordistance that an object moves in aspecific amount of time Velocity - includes the direction &describes the rate of displacementManual ofStructural KinesiologyBasic Biomechanical Factors & ConceptsManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-58Laws of motion and physical activities Newton's laws of motion have manyapplications to physical educationactivities and sports3-59Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-6010
Law of InertiaLaw of Inertia A body in motion tends to remain inmotion at the same speed in astraight line unless acted on by aforce; a body at rest tends to remainat rest unless acted on by a force Muscles produce force to start, stop,accelerate, decelerate & change thedirection of motionManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts Inertia - resistance to action or change– In human movement, inertia refers toresistance to acceleration or deceleration– tendency for the current state of motion tobe maintained, regardless of whether thebody segment is moving at a particularvelocity or is motionless– the reluctance to change status; only forcecan change status3-61Manual ofStructural KinesiologyLaw of Inertia Force is required to change inertia– Any activity carried out at a steadypace in a consistent direction willconserve energy– Any irregularly paced or directedactivity will be very costly to energyreserves– Ex. handball & basketball are somuch more fatiguing than jogging ordancing– the greater the mass, the more force needed tosignificantly change an object’s inertia Examples– Sprinter in starting blocks must apply considerableforce to overcome his resting inertia– Runner on an indoor track must apply considerableforce to overcome moving inertia & stop beforehitting the wall– Thrown or struck balls require force to stop themBasic Biomechanical Factors & Concepts3-63Manual ofStructural KinesiologyLaw of AccelerationBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & Concepts3-64Law of Acceleration A change in the acceleration of abody occurs in the same direction asthe force that caused it. The changein acceleration is directlyproportional to the force causing itand inversely proportional to themass of the body.Manual ofStructural Kinesiology3-62Law of Inertia The greater an object’s mass, the greater itsinertiaManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts Acceleration - the rate of change invelocity– To attain speed in moving the body, astrong muscular force is generallynecessary Mass - the amount of matter in the body– affects the speed & acceleration in physicalmovements3-65Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-6611
Law of AccelerationLaw of Reaction A much greater force is required from themuscles to accelerate a 230-pound man thanthan to accelerate a 130-pound man to thesame running speed A baseball maybe accelerated faster than ashot because of the difference in weight The force required to run at half speed is lessthan the force required to run at top speed To impart speed to a ball or an object, thebody part holding the object must be rapidlyaccelerated For every action there is an opposite andequal reaction.– As we place force on a surface by walkingover it, the surface provides an equalresistance back in the opposite direction tothe soles of our feet– Our feet push down & back, while thesurface pushes up & forwardManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts Force of the surface reacting to the forcewe place on it is ground reaction force3-67Manual ofStructural KinesiologyLaw of Reaction– sand dissipates the runner's force reducingthe reaction force with the apparent loss inforward force & speed– sprinter applies a force in excess of 300pounds on his starting blocks, which resistwith an equal force– in flight, movement of one part of thebody produces a reaction in anotherpart because there is no resistivesurface to supply a reaction force– easier to run on a hard track thanon a sandy beach due to thedifference in the ground reactionforces of the two surfaces– track resists the runner'spropulsion force, and the reactiondrives the runner aheadBasic Biomechanical Factors & Concepts3-69Manual ofStructural KinesiologyFriction3-70– With slick ground or shoe surfacefriction is reduced & we are morelikely to slip– In skating, we desire decreasedfriction so that we may slide acrossthe ice with less resistance– Depending increased or decreased frictionmay be desired– To run, we depend upon friction forcesbetween our feet & the ground so that wemay exert force against the ground &propel ourselves forwardBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsFriction Friction - force that results from theresistance between surfaces of twoobjects from moving upon one anotherManual ofStructural Kinesiology3-68Law of Reaction We provide the action forcewhile the surface provides thereaction forceManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-71Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-7212
FrictionFriction Static friction is always greater thankinetic friction Static friction or kinetic friction– Static friction - the amount offriction between two objects thathave not yet begun to move– Kinetic friction - friction occurringbetween two objects that aresliding upon one anotherManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts– It is always more difficult to initiate draggingan object across a surface than to continuedragging– Static friction may be increased byincreasing the normal or perpendicularforces pressing the two objects togethersuch as in adding more weight to oneobject sitting on the other object3-73Manual ofStructural KinesiologyFriction Rolling friction - resistance to an objectrolling across a surface such as a ballrolling across a court or a tire rollingacross the ground– depends upon the hardness & roughness ofthe surface textures– Rolling friction is always much less thanstatic or kinetic friction Coefficient of friction - ratio betweenforce needed to overcome the frictionover the force holding the surfacestogetherBasic Biomechanical Factors & Concepts3-75Balance, equilibrium, & stabilityBasic Biomechanical Factors & Concepts3-76 Dynamic equilibrium - all applied &inertial forces acting on the moving bodyare in balance, resulting in movementwith unchanging speed or direction To control equilibrium & achievebalance, stability needs to be maximized Stability is the resistance to a– static or dynamic Static equilibrium - body is at rest orcompletely motionlessBasic Biomechanical Factors & ConceptsManual ofStructural KinesiologyBalance, equilibrium, & stability Balance - ability to control equilibrium,either static or dynamic Equilibrium - state of zero accelerationwhere there is no change in the speedor direction of the bodyManual ofStructural Kinesiology3-74Friction To determine the amount of frictionforces consider both forces pressing thetwo objects together & the coefficient offrictionManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts– change in the body's acceleration– disturbance of the body's equilibrium3-77Manual ofStructural KinesiologyBasic Biomechanical Factors & Concepts3-7813
Balance, equilibrium, & stabilityBalance, equilibrium, & stability Stability is enhanced by determiningbody's center of gravity & appropriatelychanging it Center of gravity - point at which all ofbody's mass & weight are equallybalanced or equally distributed in alldirections Balance - important in resting & movingbodiesManual ofStructural KinesiologyBasic Biomechanical Factors & Concepts Generally, balance is desired Some circumstances exist wheremovement is improved when the bodytends to be unbalance3-79Balance, equilibrium, & stability The larger the base of support, the more balance3. A person has balance depending on theweight (mass) The greater the weight, the more balance4. A person has balance, depending on theheight of the center of gravity The lower the center of gravity, the more balance3-81Balance, equilibrium, & stabilityBasic Biomechanical Factors & Concepts3-826. In anticipation of an oncoming force,stability may be increased by enlarging thesize of the base of support in the direction ofthe anticipated force7. Equilibrium may be enhanced by increasingthe friction between the body & the surfacesit contacts8. Rotation about an axis aids balanceA moving bike is easier to balance than astationary bike Balance is less if the center of gravity is near theedge of the base When anticipating an oncoming force, stabilitymay be improved by placing the center of gravitynearer the side of the base of support expectedto receive the forceBasic Biomechanical Factors & ConceptsManual ofStructural KinesiologyBalance, equilibrium, & stability5. A person has balance, depending on wherethe center of gravity is in relation to the baseof supportManual ofStructural Kinesiology3-802. A person has balance in the directproportion to the size of the base1. A person has balancewhen the center of gravityfalls within the base ofsupportBasic Biomechanical Factors & ConceptsBasic Biomechanical Factors & ConceptsBalance, equilibrium, & stability General factorsapplicable to enhancingequilibrium, maximizingstability, & ultimatelyachieving balance:Manual ofStructural KinesiologyManual ofStructural Kinesiology3-83Manual ofStructural KinesiologyBasic Bio
Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-20 First-class Levers Force is applied where muscle inserts in bone, not in belly of muscle – Ex. in elbow extension with shoulder fully flexed & arm beside the ear, the triceps applies forc
