Manual of Structural KinesiologyBasic Biomechanical Factors & Concepts3-1 Chapter 3 Basic...

Manual of Manual of Structural Structural KinesiologyKinesiology Basic Biomechanical Factors & ConceptsBasic Biomechanical Factors & Concepts 3-3-11

Chapter 3Chapter 3Basic Biomechanical Basic Biomechanical Factors & ConceptsFactors & Concepts

Manual of Structural KinesiologyManual of Structural KinesiologyR.T. Floyd, EdD, ATC, CSCSR.T. Floyd, EdD, ATC, CSCS


BiomechanicsBiomechanics

• BiomechanicsBiomechanics - study of the - study of the mechanics as it relates to the mechanics as it relates to the functional and anatomical analysis functional and anatomical analysis of biological systems and of biological systems and especially humansespecially humans– Necessary to study the body’s Necessary to study the body’s

mechanical characteristics & mechanical characteristics & principles to understand its principles to understand its movementsmovements



•MechanicsMechanics - study of physical - study of physical actions of forcesactions of forces

• Mechanics is divided intoMechanics is divided into– StaticsStatics – DynamicsDynamics



• Statics - study of systems that are Statics - study of systems that are in a constant state of motion, in a constant state of motion, whether at rest with no motion or whether at rest with no motion or moving at a constant velocity moving at a constant velocity without accelerationwithout acceleration– Statics involves all forces acting on Statics involves all forces acting on

the body being in balance resulting in the body being in balance resulting in the body being in equilibriumthe body being in equilibrium



• Dynamics - study of systems in Dynamics - study of systems in motion with accelerationmotion with acceleration– A system in acceleration is A system in acceleration is

unbalanced due to unequal forces unbalanced due to unequal forces acting on the bodyacting on the body



• KinematicsKinematics & & kineticskinetics– Kinematics - description of motion Kinematics - description of motion

and includes consideration of time, and includes consideration of time, displacement, velocity, acceleration, displacement, velocity, acceleration, and space factors of a system‘s and space factors of a system‘s motionmotion

– Kinetics - study of forces associated Kinetics - study of forces associated with the motion of a with the motion of a bodybody


Types of machines found in the Types of machines found in the bodybody

• Musculoskeletal system may be thought Musculoskeletal system may be thought of as a series of simple machinesof as a series of simple machines– Machines - used to increase mechanical Machines - used to increase mechanical

advantageadvantage

– Consider mechanical aspect of each Consider mechanical aspect of each component in analysis with respect to component in analysis with respect to components’ machine-like functioncomponents’ machine-like function



• Machines function in four waysMachines function in four ways– balance multiple forcesbalance multiple forces– enhance force in an attempt to reduce total enhance force in an attempt to reduce total

force needed to overcome a resistanceforce needed to overcome a resistance– enhance range of motion & speed of enhance range of motion & speed of

movement so that resistance may be movement so that resistance may be moved further or faster than applied forcemoved further or faster than applied force

– alter resulting direction of the applied forcealter resulting direction of the applied force



• Musculoskeletel system arrangement Musculoskeletel system arrangement provides for 3 types of machines in provides for 3 types of machines in producing movementproducing movement– Levers (most common)Levers (most common)– Wheel-axlesWheel-axles– PulleysPulleys


LeversLevers

• Humans moves through a system of Humans moves through a system of leverslevers

• Levers cannot be changed, but they can Levers cannot be changed, but they can be utilized more efficientlybe utilized more efficiently– lever - a rigid bar that turns about an lever - a rigid bar that turns about an axisaxis

of rotation or a fulcrumof rotation or a fulcrum– axis - point of rotation about which lever axis - point of rotation about which lever

movesmoves


LeversLevers

• Levers rotate about an axis as a result Levers rotate about an axis as a result of of forceforce (effort, (effort, E)E) being applied to being applied to cause its movement against a cause its movement against a resistanceresistance or weight or weight

• In the bodyIn the body– bones represent the barsbones represent the bars– joints are the axesjoints are the axes– muscles contract to apply forcemuscles contract to apply force


LeversLevers

• Resistance can vary from maximal to Resistance can vary from maximal to minimalminimal– May be only the bones or weight of body May be only the bones or weight of body

segment segment

• All lever systems have each of these All lever systems have each of these three components in one of three three components in one of three possible arrangementspossible arrangements


LeversLevers

• Three points determine type of lever & Three points determine type of lever & for which kind of motion it is best suitedfor which kind of motion it is best suited– Axis Axis (A)(A)- fulcrum - the point of rotation - fulcrum - the point of rotation – Point Point (F)(F) of force application (usually of force application (usually

muscle insertion)muscle insertion)– Point Point (R)(R) of resistance application (center of resistance application (center

of gravity of lever) or (location of an of gravity of lever) or (location of an external resistance)external resistance)


LeversLevers

• 11stst class lever – axis class lever – axis (A)(A) between between force force (F)(F) & resistance & resistance (R)(R)

• 22ndnd class lever – resistance class lever – resistance (R)(R) between axis between axis (A)(A) & force & force (F)(F)

• 33rdrd class lever – force class lever – force (F)(F) between axis between axis (A)(A) & resistance & resistance (R)(R)


• AFRAFR3rd3rd

| | Resistance Arm Resistance Arm ||

• ARFARF2nd2nd

| | Force Arm Force Arm ||

LeversLevers• FARFAR

1st1st

AA

FF RR

| Force ArmForce Arm || | Resistance Arm Resistance Arm ||

AA

RR

| | Resistance Arm Resistance Arm ||

FF

AA

RR

| | Force Arm Force Arm ||

FF


First-class LeversFirst-class Levers

• Produce balanced movements Produce balanced movements when axis is midway between when axis is midway between force & resistance (e.g., seesaw)force & resistance (e.g., seesaw)

• Produce speed & range of motion Produce speed & range of motion when axis is close to force, when axis is close to force, (triceps in elbow extension)(triceps in elbow extension)

• Produce force motion when axis Produce force motion when axis is close to resistance (crowbar)is close to resistance (crowbar)



• Head balanced on neck in Head balanced on neck in flexing/extendingflexing/extending

• Agonist & antagonist muscle Agonist & antagonist muscle groups are contracting groups are contracting simultaneously on either side of a simultaneously on either side of a joint axisjoint axis– agonist produces force while agonist produces force while

antagonist supplies resistanceantagonist supplies resistance



• Elbow extension in triceps applying Elbow extension in triceps applying force to olecranon force to olecranon (F)(F) in extending the in extending the non-supported forearm non-supported forearm (R)(R) at the at the elbow elbow (A)(A)



• Force is applied where muscle inserts in Force is applied where muscle inserts in bone, not in belly of musclebone, not in belly of muscle– Ex. in elbow extension with shoulder fully Ex. in elbow extension with shoulder fully

flexed & arm beside the ear, the triceps flexed & arm beside the ear, the triceps applies force to the olecranon of ulna applies force to the olecranon of ulna behind the axis of elbow jointbehind the axis of elbow joint

– As the applied force exceeds the amount As the applied force exceeds the amount of forearm resistance, the elbow extendsof forearm resistance, the elbow extends



– Change example by placing the hand on Change example by placing the hand on the floor (as in a push-up) to push the body the floor (as in a push-up) to push the body away from the floor, the same muscle away from the floor, the same muscle action at this joint now changes the lever to action at this joint now changes the lever to 22ndnd class due to the axis being at the hand class due to the axis being at the hand and the resistance is body weight at the and the resistance is body weight at the elbow jointelbow joint


Second-class LeversSecond-class Levers

• Produces force movements, Produces force movements, since a large resistance can be since a large resistance can be moved by a relatively small forcemoved by a relatively small force– WheelbarrowWheelbarrow– NutcrackerNutcracker– Loosening a lug nutLoosening a lug nut– Raising the body up on the toesRaising the body up on the toes


Second-class LeversSecond-class Levers

– Plantar flexion of foot to raise the Plantar flexion of foot to raise the body up on the toes where ball (A) body up on the toes where ball (A) of the foot serves as the axis as of the foot serves as the axis as ankle plantar flexors apply force to ankle plantar flexors apply force to the calcaneus (F) to lift the the calcaneus (F) to lift the resistance of the body at the tibial resistance of the body at the tibial articulation (R) with the footarticulation (R) with the foot

• Relatively few 2Relatively few 2ndnd class levers in class levers in bodybody


Third-class LeversThird-class Levers

• Produce speed & range-of-motion Produce speed & range-of-motion movementsmovements

• Most common in human bodyMost common in human body• Requires a great deal of force to move Requires a great deal of force to move

even a small resistanceeven a small resistance– Paddling a boatPaddling a boat– Shoveling - application of lifting force to a Shoveling - application of lifting force to a

shovel handle with lower hand while upper shovel handle with lower hand while upper hand on shovel handle serves as axis of hand on shovel handle serves as axis of rotationrotation



– Biceps brachii in elbow flexionBiceps brachii in elbow flexion

Using the elbow joint (A) as the Using the elbow joint (A) as the axis, the biceps brachii applies axis, the biceps brachii applies force at its insertion on radial force at its insertion on radial tuberosity (F) to rotate forearm up, tuberosity (F) to rotate forearm up, with its center of gravity (R) serving with its center of gravity (R) serving as the point of resistance as the point of resistance applicationapplication



• Brachialis - true 3Brachialis - true 3rdrd class leverage class leverage– pulls on ulna just below elbowpulls on ulna just below elbow– pull is direct & true since ulna cannot rotatepull is direct & true since ulna cannot rotate

• Biceps brachii supinates forearm as it flexes Biceps brachii supinates forearm as it flexes so its 3so its 3rdrd class leverage applies to flexion only class leverage applies to flexion only

• Other examplesOther examples– hamstrings contracting to flex leg at knee while in a hamstrings contracting to flex leg at knee while in a

standing positionstanding position– using iliopsoas to flex thigh at hipusing iliopsoas to flex thigh at hip


Factors in use of anatomical Factors in use of anatomical leverslevers

• Anatomical leverage system can be Anatomical leverage system can be used to gain a mechanical advantage used to gain a mechanical advantage

• Improve simple or complex physical Improve simple or complex physical movementsmovements

• Some habitually use human levers Some habitually use human levers properlyproperly

• Some develop habits of improperly use Some develop habits of improperly use human levershuman levers


Torque and length of lever Torque and length of lever armsarms

• Torque Torque – (moment of force) the turning – (moment of force) the turning effect of an eccentric forceeffect of an eccentric force

• Eccentric forceEccentric force - force applied in a - force applied in a direction not in line with the center of direction not in line with the center of rotation of an object with a fixed axisrotation of an object with a fixed axis– In objects without a fixed axis it is an In objects without a fixed axis it is an

applied force that is not in line with object's applied force that is not in line with object's center of gravitycenter of gravity

• For rotation to occur an eccentric force For rotation to occur an eccentric force must be appliedmust be applied



• In humans, contracting muscle applies In humans, contracting muscle applies an eccentric force (not to be confused an eccentric force (not to be confused with eccentric contraction) to bone upon with eccentric contraction) to bone upon which it attaches & causes the bone to which it attaches & causes the bone to rotate about an axis at the jointrotate about an axis at the joint

• Amount of torque is determined by Amount of torque is determined by multiplying amount of force (multiplying amount of force (force force magnitudemagnitude) by ) by force armforce arm



• Force arm - perpendicular distance Force arm - perpendicular distance between location of force application & between location of force application & axis axis – a.k.a. moment arm or torque arma.k.a. moment arm or torque arm– shortest distance from axis of rotation to shortest distance from axis of rotation to

the line of action of the forcethe line of action of the force– the greater the distance of force arm, the the greater the distance of force arm, the

more torque produced by the forcemore torque produced by the force



• Often, we purposely increase force arm Often, we purposely increase force arm length in order to increase torque so length in order to increase torque so that we can more easily move a that we can more easily move a relatively large resistance (increasing relatively large resistance (increasing our leverage)our leverage)

• Resistance armResistance arm - distance between the - distance between the axis and the point of resistance axis and the point of resistance applicationapplication



• Inverse relationship between length of Inverse relationship between length of the two lever armsthe two lever arms– Between force & force armBetween force & force arm– Between resistance & resistance armBetween resistance & resistance arm– The longer the force arm, the less force The longer the force arm, the less force

required to move the lever if the resistance required to move the lever if the resistance & resistance arm remain constant& resistance arm remain constant

– Shortening the resistance arm allows a Shortening the resistance arm allows a greater resistance to be moved if force & greater resistance to be moved if force & force arm remain constantforce arm remain constant



• Proportional relationship between force Proportional relationship between force components & resistance componentscomponents & resistance components– If either of the resistance components If either of the resistance components

increase, there must be an increase in one increase, there must be an increase in one or both of force componentsor both of force components

– Greater resistance or resistance arm Greater resistance or resistance arm requires greater force or longer force armrequires greater force or longer force arm

– Greater force or force arm allows a greater Greater force or force arm allows a greater amount of resistance to be moved or a amount of resistance to be moved or a longer resistance arm to be usedlonger resistance arm to be used



• Proportional relationship between force Proportional relationship between force components & resistance componentscomponents & resistance components– if either of the resistance components if either of the resistance components

increase, there must be an increase in one increase, there must be an increase in one or both of force componentsor both of force components

• Even slight variations in the location of Even slight variations in the location of the force and resistance are important the force and resistance are important in determining the effective force of the in determining the effective force of the musclemuscle



A, If the force arm and resistance arm are equal in length, a force equal to the resistance is required to balance it, B, As the force arm becomes longer, a decreasing amount of force is required to move a relatively larger resistance,C, As the force arm becomes shorter an increasing amount of force is required to more a relatively smaller resistance



EXAMPLE: biceps brachiiEXAMPLE: biceps brachiiF x FA = R x RAF x FA = R x RA

(force) x (force arm) = (resistance) x (resistance arm)(force) x (force arm) = (resistance) x (resistance arm)F x 0.1 meters = 45 Newtons x 0.25 metersF x 0.1 meters = 45 Newtons x 0.25 meters

F = 112.5 Newton-metersF = 112.5 Newton-metersIncrease insertion by 0.05 metersIncrease insertion by 0.05 meters

F x 0.15 meters = 45 Newtons x 0.25 metersF x 0.15 meters = 45 Newtons x 0.25 metersF = 75 Newton-metersF = 75 Newton-meters

AA

FFRR

| | RA = 0.25 meters RA = 0.25 meters |||0.1 m||0.1 m|

AA

FFRR

| | RA = 0.25 meters RA = 0.25 meters || | 0.15m| 0.15m ||

A 0.05 meter A 0.05 meter increase in increase in insertion insertion makes makes

considerable considerable difference in difference in

the force the force necessary to necessary to

move the move the leverlever





F = 112.5 Newton-metersF = 112.5 Newton-metersDecrease resistance arm by 0.05 metersDecrease resistance arm by 0.05 meters

F x 0.1 meters = 45 Newtons x 0.2 metersF x 0.1 meters = 45 Newtons x 0.2 metersF = 90 Newton-metersF = 90 Newton-meters

AA

FFRR

| | RA = 0.2 metersRA = 0.2 meters |||| 0.1m0.1m ||

AA

FFRR

| | RA = 0.25 meters RA = 0.25 meters |||| 0.1m0.1m ||

A 0.05 meter A 0.05 meter reduction in reduction in resistance resistance arm can arm can

reduce the reduce the force force

necessary to necessary to move the move the

leverlever





F = 112.5 Newton-metersF = 112.5 Newton-metersDecrease resistance by 1 NewtonDecrease resistance by 1 Newton

F x 0.1 meters = 44 Newtons x 0.25 meters F x 0.1 meters = 44 Newtons x 0.25 meters F = 110 Newton-metersF = 110 Newton-meters

AA

FFRR


AA

FFRR


Reducing Reducing resistance resistance

reduces the reduces the amount of amount of

force force needed to needed to move the move the

leverlever



• Human leverage system is built for Human leverage system is built for speed & range of movement at expense speed & range of movement at expense of forceof force

• Short force arms & long resistance Short force arms & long resistance arms require great muscular strength to arms require great muscular strength to produce movementproduce movement

• Ex. biceps & triceps attachmentsEx. biceps & triceps attachments– biceps force arm is 1 to 2 inches biceps force arm is 1 to 2 inches – triceps force arm less than 1 inchtriceps force arm less than 1 inch



• Human leverage for sport skills requires Human leverage for sport skills requires several leversseveral levers– throwing a ball involves levers at shoulder, throwing a ball involves levers at shoulder,

elbow, & wrist jointselbow, & wrist joints

• The longer the lever, the more effective The longer the lever, the more effective it is in imparting velocityit is in imparting velocity– A tennis player can hit a tennis ball harder A tennis player can hit a tennis ball harder

with a straight-arm drive than with a bent with a straight-arm drive than with a bent elbow because the lever (including the elbow because the lever (including the racket) is longer & moves at a faster speedracket) is longer & moves at a faster speed



• Long levers produce more linear force Long levers produce more linear force and thus better performance in some and thus better performance in some sports such as baseball, hockey, golf, sports such as baseball, hockey, golf, field hockey, etc.field hockey, etc.



• For quickness, it is desirable to have a For quickness, it is desirable to have a short lever armshort lever arm– baseball catcher brings his hand back to baseball catcher brings his hand back to

his ear to secure a quick throwhis ear to secure a quick throw– sprinter shortens his knee lever through sprinter shortens his knee lever through

flexion that he almost catches his spikes in flexion that he almost catches his spikes in his gluteal muscleshis gluteal muscles


Wheel and axleWheel and axle

• Used primarily to enhance range of Used primarily to enhance range of motion & speed of movement in the motion & speed of movement in the musculoskeletal systemmusculoskeletal system– function essentially as a form of a leverfunction essentially as a form of a lever

• When either the wheel or axle turn, the When either the wheel or axle turn, the other must turn as wellother must turn as well– Both complete one turn at the same timeBoth complete one turn at the same time



• Center of the wheel & the axle both Center of the wheel & the axle both correspond to the fulcrumcorrespond to the fulcrum

• Both the radius of the wheel & the Both the radius of the wheel & the radius of the axle correspond to the radius of the axle correspond to the force armsforce arms


Wheel and axleWheel and axle• If the wheel radius of the is greater than If the wheel radius of the is greater than

the radius of the axle, then, due to the the radius of the axle, then, due to the longer force arm, the wheel has a longer force arm, the wheel has a mechanical advantage over the axlemechanical advantage over the axle– a relatively smaller force may be applied to a relatively smaller force may be applied to

the wheel to move a relatively greater the wheel to move a relatively greater resistance applied to the axleresistance applied to the axle

– if the radius of the wheel is 3 times the if the radius of the wheel is 3 times the radius of the axle, then the wheel has a 3 radius of the axle, then the wheel has a 3 to 1 mechanical advantage over the axleto 1 mechanical advantage over the axle



– calculate mechanical advantage of a calculate mechanical advantage of a wheel & axle by considering the wheel & axle by considering the radius of the wheel over the axleradius of the wheel over the axle

Mechanical Mechanical radius of the wheelradius of the wheel

advantage = radius of the axleadvantage = radius of the axle


Wheel and axleWheel and axle• If application of force is reversed and If application of force is reversed and

applied to the axle, then the mechanical applied to the axle, then the mechanical advantage results from the wheel turning advantage results from the wheel turning a greater distance & speeda greater distance & speed– if the radius of the wheel is 3 times the if the radius of the wheel is 3 times the

radius of the axle, then outside of the wheel radius of the axle, then outside of the wheel will turn at a speed 3 times that of the axlewill turn at a speed 3 times that of the axle

– the distance that the outside of the wheel the distance that the outside of the wheel turns will be 3 times that of the outside of the turns will be 3 times that of the outside of the axleaxle



– Calculate the mechanical advantage Calculate the mechanical advantage for this example by considering the for this example by considering the radius of the wheel over the axleradius of the wheel over the axle

Mechanical Mechanical force on the axle force on the axle

advantage = force on the wheeladvantage = force on the wheel


Wheel and axleWheel and axle• Ex. resulting in greater range of motion Ex. resulting in greater range of motion

& speed is with upper extremity in & speed is with upper extremity in internal rotators attaching to humerusinternal rotators attaching to humerus– humerus acts as the axlehumerus acts as the axle– hand & wrist are located at the outside of hand & wrist are located at the outside of

the wheel when elbow is flexed 90 degreesthe wheel when elbow is flexed 90 degrees– with minimal humerus rotation, the hand & with minimal humerus rotation, the hand &

wrist travel a great distancewrist travel a great distance– allows us significantly increase the speed allows us significantly increase the speed

at which we can throw objectsat which we can throw objects


PulleysPulleys• Single pulleys function to change Single pulleys function to change

effective direction of force applicationeffective direction of force application• Ex. lateral malleolus acting as a Ex. lateral malleolus acting as a

pulley around which tendon of pulley around which tendon of peroneus longus runsperoneus longus runs– As peroneus longus contracts, it pulls As peroneus longus contracts, it pulls

toward it belly (toward the knee)toward it belly (toward the knee)– Using the lateral malleolus as a pulley, Using the lateral malleolus as a pulley,

force is transmitted to plantar aspect of force is transmitted to plantar aspect of foot resulting in eversion/plantarflexionfoot resulting in eversion/plantarflexion


Laws of motion and physical Laws of motion and physical activitiesactivities

• Body motion is produced or started by Body motion is produced or started by some action of muscular systemsome action of muscular system

• Motion cannot occur without a forceMotion cannot occur without a force

• Muscular system is source of force in Muscular system is source of force in humanshumans

• TwoTwo types of motiontypes of motion– linear motionlinear motion– angular motionangular motion



• Linear motion (translatory motion) - Linear motion (translatory motion) - motion along a linemotion along a line– rectilinearrectilinear motion - motion along a straight motion - motion along a straight

lineline– curvilinearcurvilinear motion - motion along a curved motion - motion along a curved

line line

• Linear displacementLinear displacement - distance that a - distance that a system moves in a straight linesystem moves in a straight line



• Angular motion (rotary motion) - rotation Angular motion (rotary motion) - rotation around an axisaround an axis– In the body, the axis of rotation is provided In the body, the axis of rotation is provided

by the various jointsby the various joints

• Angular displacementAngular displacement - change in - change in location of a rotating bodylocation of a rotating body

• Linear & angular are relatedLinear & angular are related– angular motion of the joints produces the angular motion of the joints produces the

linear motion of walkinglinear motion of walking



• Sports ex. - cumulative angular motion Sports ex. - cumulative angular motion of the joints imparts linear motion to a of the joints imparts linear motion to a thrown object (ball, shot) or to an object thrown object (ball, shot) or to an object struck with an instrument (bat, racket)struck with an instrument (bat, racket)

• DisplacementDisplacement - the actual distance that - the actual distance that the object has been displaced from its the object has been displaced from its original point of referenceoriginal point of reference



• DistanceDistance - actual sum length of - actual sum length of measurement traveledmeasurement traveled– object may have traveled a distance of 10 object may have traveled a distance of 10

meters along a linear path in two or more meters along a linear path in two or more directions but only be displaced from its directions but only be displaced from its original reference point by 6 meters original reference point by 6 meters

• Newton's laws of motion have many Newton's laws of motion have many applications to physical education applications to physical education activities and sportsactivities and sports


Law of InertiaLaw of Inertia

• A body in motion tends to remain in A body in motion tends to remain in motion at the same speed in a motion at the same speed in a straight line unless acted on by a straight line unless acted on by a force; a body at rest tends to remain force; a body at rest tends to remain at rest unless acted on by a forceat rest unless acted on by a force

• Muscles produce force to start, stop, Muscles produce force to start, stop, accelerate, decelerate & change the accelerate, decelerate & change the direction of motiondirection of motion



• InertiaInertia - resistance to action or change - resistance to action or change– In human movement, inertia refers to In human movement, inertia refers to

resistance to acceleration or decelerationresistance to acceleration or deceleration– tendency for the current state of motion to tendency for the current state of motion to

be maintained, regardless of whether the be maintained, regardless of whether the body segment is moving at a particular body segment is moving at a particular velocity or is motionlessvelocity or is motionless

– the reluctance to change status; only force the reluctance to change status; only force can change statuscan change status



• The greater the mass of an object the greater The greater the mass of an object the greater its inertiaits inertia– the greater the mass, the more force needed to the greater the mass, the more force needed to

significantly change an object’s inertiasignificantly change an object’s inertia

• ExamplesExamples– Sprinter in starting blocks must apply considerable Sprinter in starting blocks must apply considerable

force to overcome his resting inertiaforce to overcome his resting inertia– Runner on an indoor track must apply considerable Runner on an indoor track must apply considerable

force to overcome moving inertia & stop before force to overcome moving inertia & stop before hitting the wallhitting the wall

– Thrown or struck balls require force to stop themThrown or struck balls require force to stop them



• Force is required to change inertiaForce is required to change inertia– Any activity carried out at a steady Any activity carried out at a steady

pace in a consistent direction will pace in a consistent direction will conserve energyconserve energy

– Any irregularly paced or directed Any irregularly paced or directed activity will be very costly to energy activity will be very costly to energy reservesreserves

– Ex. handball & basketball are so Ex. handball & basketball are so much more fatiguing than jogging or much more fatiguing than jogging or dancingdancing


Law of AccelerationLaw of Acceleration

• A change in the acceleration of a A change in the acceleration of a body occurs in the same direction as body occurs in the same direction as the force that caused it. The change the force that caused it. The change in acceleration is directly in acceleration is directly proportional to the force causing it proportional to the force causing it and inversely proportional to the and inversely proportional to the mass of the body.mass of the body.



• AccelerationAcceleration - the rate of change in - the rate of change in velocityvelocity– To attain speed in moving the body, a To attain speed in moving the body, a

strong muscular force is generally strong muscular force is generally necessarynecessary

• Mass - the amount of matter in the bodyMass - the amount of matter in the body– affects the speed & acceleration in physical affects the speed & acceleration in physical

movementsmovements



• A much greater force is required from the A much greater force is required from the muscles to accelerate a 230-pound man than muscles to accelerate a 230-pound man than than to accelerate a 130-pound man to the than to accelerate a 130-pound man to the same running speedsame running speed

• A baseball maybe accelerated faster than a A baseball maybe accelerated faster than a shot because of the difference in weightshot because of the difference in weight

• The force required to run at half speed is less The force required to run at half speed is less than the force required to run at top speedthan the force required to run at top speed

• To impart speed to a ball or an object, the To impart speed to a ball or an object, the body part holding the object must be rapidly body part holding the object must be rapidly acceleratedaccelerated


Law of ReactionLaw of Reaction

• For every action there is an opposite and For every action there is an opposite and equal reaction.equal reaction.– As we place force on a surface by walking As we place force on a surface by walking

over it, the surface provides an equal over it, the surface provides an equal resistance back in the opposite direction to resistance back in the opposite direction to the soles of our feetthe soles of our feet

– Our feet push down & back, while the Our feet push down & back, while the surface pushes up & forwardsurface pushes up & forward

• Force of the surface reacting to the force Force of the surface reacting to the force we place on it is we place on it is ground reaction forceground reaction force



• We provide the action force while We provide the action force while the surface provides the reaction the surface provides the reaction forceforce– easier to run on a hard track than easier to run on a hard track than

on a sandy beach due to the on a sandy beach due to the difference in the ground reaction difference in the ground reaction forces of the two surfacesforces of the two surfaces

– track resists the runner's propulsion track resists the runner's propulsion force, and the reaction drives the force, and the reaction drives the runner aheadrunner ahead



– sand dissipates the runner's force reducing sand dissipates the runner's force reducing the reaction force with the apparent loss in the reaction force with the apparent loss in forward force & speedforward force & speed

– sprinter applies a force in excess of 300 sprinter applies a force in excess of 300 pounds on his starting blocks, which resist pounds on his starting blocks, which resist with an equal forcewith an equal force

– in flight, movement of one part of the body in flight, movement of one part of the body produces a reaction in another part produces a reaction in another part because there is no resistive surface to because there is no resistive surface to supply a reaction forcesupply a reaction force


FrictionFriction

• FrictionFriction - force that results from the - force that results from the resistance between surfaces of two resistance between surfaces of two objects from moving upon one anotherobjects from moving upon one another– Depending increased or decreased friction Depending increased or decreased friction

may be desiredmay be desired– To run, we depend upon friction forces To run, we depend upon friction forces

between our feet & the ground so that we between our feet & the ground so that we may exert force against the ground & may exert force against the ground & propel ourselves forwardpropel ourselves forward


FrictionFriction

– With slick ground or shoe surface With slick ground or shoe surface friction is reduced & we are more friction is reduced & we are more likely to sliplikely to slip

– In skating, we desire decreased In skating, we desire decreased friction so that we may slide across friction so that we may slide across the ice with less resistancethe ice with less resistance


FrictionFriction

• Static friction or kinetic frictionStatic friction or kinetic friction– Static frictionStatic friction - the amount of friction - the amount of friction

between two objects that have not yet between two objects that have not yet begun to movebegun to move

– Kinetic friction Kinetic friction - friction occurring between - friction occurring between two objects that are sliding upon one two objects that are sliding upon one anotheranother


FrictionFriction

• Static friction is always greater than Static friction is always greater than kinetic frictionkinetic friction– It is always more difficult to initiate dragging It is always more difficult to initiate dragging

an object across a surface than to continue an object across a surface than to continue draggingdragging

– Static friction may be increased by Static friction may be increased by increasing the normal or perpendicular increasing the normal or perpendicular forces pressing the two objects together forces pressing the two objects together such as in adding more weight to one such as in adding more weight to one object sitting on the other objectobject sitting on the other object


FrictionFriction

• To determine the amount of friction To determine the amount of friction forces consider both forces pressing the forces consider both forces pressing the two objects together & the two objects together & the coefficient of coefficient of frictionfriction – depends upon the hardness & roughness of depends upon the hardness & roughness of

the surface texturesthe surface textures

• Coefficient of friction - ratio between Coefficient of friction - ratio between force needed to overcome the friction force needed to overcome the friction over the force holding the surfaces over the force holding the surfaces togethertogether


FrictionFriction

• Rolling frictionRolling friction - resistance to an object - resistance to an object rolling across a surface such as a ball rolling across a surface such as a ball rolling across a court or a tire rolling rolling across a court or a tire rolling across the groundacross the ground– Rolling friction is always much less that Rolling friction is always much less that

static or kinetic frictionstatic or kinetic friction


Balance, equilibrium, & stabilityBalance, equilibrium, & stability

• BalanceBalance - ability to control equilibrium, - ability to control equilibrium, either static or dynamiceither static or dynamic

• EquilibriumEquilibrium - state of zero acceleration - state of zero acceleration where there is no change in the speed where there is no change in the speed or direction of the bodyor direction of the body– static or dynamicstatic or dynamic

• Static equilibrium - Static equilibrium - body is at rest or body is at rest or completely motionlesscompletely motionless



• Dynamic equilibriumDynamic equilibrium - all applied & - all applied & inertial forces acting on the moving body inertial forces acting on the moving body are in balance, resulting in movement are in balance, resulting in movement with unchanging speed or directionwith unchanging speed or direction

• To control equilibrium & achieve To control equilibrium & achieve balance, balance, stabilitystability needs to be maximized needs to be maximized

• Stability is the resistance to a Stability is the resistance to a – change in the body's accelerationchange in the body's acceleration– disturbance of the body's equilibriumdisturbance of the body's equilibrium



• Stability is enhanced by determining Stability is enhanced by determining body's body's center of gravitycenter of gravity & appropriately & appropriately changing itchanging it

• Center of gravity - point at which all of Center of gravity - point at which all of body's mass & weight are equally body's mass & weight are equally balanced or equally distributed in all balanced or equally distributed in all directionsdirections

• Balance - important in resting & moving Balance - important in resting & moving bodiesbodies



• Generally, balance is desiredGenerally, balance is desired• Some circumstances exist where Some circumstances exist where

movement is improved when the body movement is improved when the body tends to be unbalancedtends to be unbalanced

• General factors applicable to enhancing General factors applicable to enhancing equilibrium, maximizing stability, & equilibrium, maximizing stability, & ultimately achieving balance:ultimately achieving balance:1.1. A person has balance when the center of A person has balance when the center of

gravity falls within the base of supportgravity falls within the base of support



2.2. A person has balance in the direct A person has balance in the direct proportion to the size of the baseproportion to the size of the baseThe larger the base of support, the more The larger the base of support, the more balancebalance

3.3. A person has balance depending on the A person has balance depending on the weight (mass)weight (mass)The greater the weight, the more balanceThe greater the weight, the more balance

4. A person has balance, depending on the 4. A person has balance, depending on the height of the center of gravityheight of the center of gravityThe lower the center of gravity, the more The lower the center of gravity, the more balancebalance



5. A person has balance, depending on where 5. A person has balance, depending on where the center of gravity is in relation to the base the center of gravity is in relation to the base of supportof supportBalance is less if the center of gravity is near Balance is less if the center of gravity is near the edge of the basethe edge of the baseWhen anticipating an oncoming force, When anticipating an oncoming force, stability may be improved by placing the stability may be improved by placing the center of gravity nearer the side of the base center of gravity nearer the side of the base of support expected to receive the forceof support expected to receive the force



6. In anticipation of an oncoming force, 6. In anticipation of an oncoming force, stability may be increased by enlarging the stability may be increased by enlarging the size of the base of support in the direction of size of the base of support in the direction of the anticipated force.the anticipated force.

7. Equilibrium may be enhanced by increasing 7. Equilibrium may be enhanced by increasing the friction between the body & the surfaces the friction between the body & the surfaces it contactsit contacts

8. Rotation about an axis aids balance8. Rotation about an axis aids balanceA moving bike is easier to balance than a A moving bike is easier to balance than a stationary bikestationary bike



9. Kinesthetic physiological functions 9. Kinesthetic physiological functions contribute to balancecontribute to balanceThe semicircular canals of the inner ear, The semicircular canals of the inner ear, vision, touch (pressure), & kinesthetic sense vision, touch (pressure), & kinesthetic sense all provide balance information to the all provide balance information to the performerperformerBalance and its components of equilibrium Balance and its components of equilibrium and stability are essential in all movements and stability are essential in all movements and are all affected by the constant force of and are all affected by the constant force of gravity as well as by inertia gravity as well as by inertia



• In walking a person throws the body in In walking a person throws the body in and out of balance with each stepand out of balance with each step

• In rapid running movements where In rapid running movements where moving inertia is high, the center of moving inertia is high, the center of gravity has to be lowered to maintain gravity has to be lowered to maintain balance when stopping or changing balance when stopping or changing directiondirection

• In jumping activities the center of gravity In jumping activities the center of gravity needs to be raised as high as possibleneeds to be raised as high as possible


ForceForce

• Muscles are the main source of force that Muscles are the main source of force that produces or changes movement of a produces or changes movement of a body segment, the entire body, or some body segment, the entire body, or some object thrown, struck, or stoppedobject thrown, struck, or stopped

• Strong muscles are able to produce more Strong muscles are able to produce more force than weak musclesforce than weak muscles– both maximum and sustained exertion over both maximum and sustained exertion over

a period of timea period of time


ForceForce

• ForcesForces either push or pull on an object in either push or pull on an object in an attempt to affect motion or shapean attempt to affect motion or shape

• Without forces acting on an object there Without forces acting on an object there would be no motionwould be no motion

• Force - product of mass times Force - product of mass times accelerationacceleration

• Mass - amount of matter in a bodyMass - amount of matter in a body


ForceForce

• The weight of a body segment or the The weight of a body segment or the entire body X the speed of acceleration entire body X the speed of acceleration determines the forcedetermines the force– Important in footballImportant in football– Also important in activities using only a part Also important in activities using only a part

of the bodyof the body– In throwing a ball, the force applied to the In throwing a ball, the force applied to the

ball is equal to the weight of the arm times ball is equal to the weight of the arm times the speed of acceleration of the armthe speed of acceleration of the arm

– Leverage factors are also importantLeverage factors are also important


ForceForce

Force = mass x accelerationForce = mass x accelerationF = M x AF = M x A

• Momentum (Momentum (quantity of motion) - equal to quantity of motion) - equal to mass times velocitymass times velocity

• The greater the momentum, the greater The greater the momentum, the greater the resistance to change in the inertia or the resistance to change in the inertia or state of motionstate of motion


ForceForce

• Many activities, particularly upper Many activities, particularly upper extremity, require a summation of forces extremity, require a summation of forces from the beginning of movement in the from the beginning of movement in the lower segment of the body to the twisting lower segment of the body to the twisting of the trunk and movement at the of the trunk and movement at the shoulder, elbow, and wrist jointsshoulder, elbow, and wrist joints

• Ex. golf drive, shot-putting, discus and Ex. golf drive, shot-putting, discus and javelin throwingjavelin throwing


Mechanical loading basicsMechanical loading basics

• Significant mechanical loads are Significant mechanical loads are generated & absorbed by the tissues of generated & absorbed by the tissues of the bodythe body

• Internal or external forces may causing Internal or external forces may causing these loadsthese loads

• Only muscles can actively generate Only muscles can actively generate internal force, but tension in tendons, internal force, but tension in tendons, connective tissues, ligaments, and joints connective tissues, ligaments, and joints capsules may generate passive internal capsules may generate passive internal forcesforces



• External forces are produced from External forces are produced from outside the body & originate from gravity, outside the body & originate from gravity, inertia, or direct contactinertia, or direct contact

• All tissues, in varying degrees, resist All tissues, in varying degrees, resist changes in their shapechanges in their shape

• Tissue deformation may result from Tissue deformation may result from external forces, but can result from external forces, but can result from internally generated forcesinternally generated forces



• Internal forces canInternal forces can– fracture bonesfracture bones– dislocate jointsdislocate joints– disrupt muscles & connective tissuesdisrupt muscles & connective tissues

• To prevent injury or damage from tissue To prevent injury or damage from tissue deformation the body must be used to deformation the body must be used to absorb energy from both internal & absorb energy from both internal & external forcesexternal forces



• It is advantageous to absorb force over It is advantageous to absorb force over larger aspects of our body rather than larger aspects of our body rather than smaller and to spread the absorption rate smaller and to spread the absorption rate over a greater period of timeover a greater period of time

• Stronger & healthier tissues are more Stronger & healthier tissues are more likely to withstand excessive mechanical likely to withstand excessive mechanical loading & the resultant excessive tissue loading & the resultant excessive tissue deformationdeformation



• Excessive tissue deformation due to Excessive tissue deformation due to mechanical loading may result frommechanical loading may result from– Tension (stretching or strain)Tension (stretching or strain)– CompressionCompression– ShearShear– BendingBending– Torsion (twisting)Torsion (twisting)


ThrowingThrowing

• In the performance of various sport skills In the performance of various sport skills such as throwing, many applications of such as throwing, many applications of the laws of leverage, motion, and the laws of leverage, motion, and balance may be found balance may be found

• In throwing, the angular motion of the In throwing, the angular motion of the levers (bones) of the body (trunk, levers (bones) of the body (trunk, shoulder, elbow, and wrist) is used to shoulder, elbow, and wrist) is used to give linear motion to the ball when it is give linear motion to the ball when it is releasedreleased


ThrowingThrowing

• In throwing, the individual's inertia & the In throwing, the individual's inertia & the ball's inertia must be overcome by the ball's inertia must be overcome by the application of forceapplication of force (Law of inertia) (Law of inertia)

• Muscles of the body provide the force to Muscles of the body provide the force to move the body parts & the ball move the body parts & the ball

• Law of accelerationLaw of acceleration is in effect with the is in effect with the muscular force necessary to accelerate muscular force necessary to accelerate the arm, wrist, & handthe arm, wrist, & hand


ThrowingThrowing

• The greater the force (mass X The greater the force (mass X acceleration) that a person can produce, acceleration) that a person can produce, the faster the arm will move, and thus the the faster the arm will move, and thus the greater the speed that will be imparted to greater the speed that will be imparted to the ballthe ball

• The reaction of the feet against the The reaction of the feet against the surface on which the subject stands surface on which the subject stands applies the applies the law of reactionlaw of reaction


ThrowingThrowing

• The longer the lever, the greater the The longer the lever, the greater the speed that can be imparted to thespeed that can be imparted to the ball ball– The body from the feet to the fingers can be The body from the feet to the fingers can be

considered as one long leverconsidered as one long lever– The longer the lever, from natural body The longer the lever, from natural body

length or the body movements to the length or the body movements to the extended backward position, the greater will extended backward position, the greater will be the arc through which it accelerates and be the arc through which it accelerates and thus the greater the speed imparted to the thus the greater the speed imparted to the thrown objectthrown object


ThrowingThrowing

• Short levers are advantageous in taking less Short levers are advantageous in taking less total time to release the balltotal time to release the ball

• Balance or equilibrium is a factor in throwing Balance or equilibrium is a factor in throwing when the body is rotated posteriorly in the when the body is rotated posteriorly in the beginning of the throwbeginning of the throw– the body is moved nearly out of balance to the rear,the body is moved nearly out of balance to the rear,– balance changes again with the forward movementbalance changes again with the forward movement– balance is reestablished with the follow-through balance is reestablished with the follow-through

when the feet are spread and the knees & trunk are when the feet are spread and the knees & trunk are flexed to lower the center of gravity flexed to lower the center of gravity


Web SitesWeb SitesBiomechanics World Wide

www.per.ualberta.ca/biomechanics– This site enables the reader to search the biomechanics

journals for recent information regarding mechanism of injury.Biomechanics: The Magazine of Body Movement and Medicine

http://www.biomech.com/International Society of Biomechanics

www.isbweb.org/– Software, data, information, resources, yellow pages,

conferences.University of Arkansas Medical School Gross Anatomy for

Medical Students http://anatomy.uams.edu/htmlpages/anatomyhtml/gross.html– Dissections, anatomy tables, atlas images, links, etc

http://www.per.ualberta.ca/biomechanics

http://www.biomech.com/



http://www.isbweb.org/



http://anatomy.uams.edu/htmlpages/anatomyhtml/gross.html










Web SitesWeb SitesSports Coach-Levers

www.brianmac.demon.co.uk/levers.htm– A basic review of levers with excellent links to the study of

muscle training and functionPhysics Concepts- Simple Machines

www.ceeo.tufts.edu/curriculum/classroom/simple_machines.htm– An overview of physics concepts involved in the study of

biomechanics.Design and Technology-Mechanism

http://fp.keystage3dt.f9.co.uk/mechanisms.htm– A graphical overview with animations detailing the

mechanisms of changing an input force and movement into an output force and movement.

http://www.brianmac.demon.co.uk/levers.htm






http://www.ceeo.tufts.edu/curriculum/classroom/simple_machines.htm






http://fp.keystage3dt.f9.co.uk/mechanisms.htm






Manual of Structural KinesiologyBasic Biomechanical Factors & Concepts3-1 Chapter 3 Basic...

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