Kinesiology

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 & ConceptsManual of Structural KinesiologyManual of Structural Kinesiology

R.T. Floyd, Ed.D, ATC, CSCSR.T. Floyd, Ed.D, ATC, CSCS

Copyright © The McGraw-Hill Companies, Inc. Reprinted by permission.


BiomechanicsBiomechanics

• BiomechanicsBiomechanics - study of body - study of body mechanics, as it relates to the mechanics, as it relates to the functional and anatomical analysis functional and anatomical analysis of biological systems and especially of biological systems and especially humanshumans

– Necessary to study the body’s Necessary to study the body’s mechanical characteristics & principles mechanical characteristics & principles to understand its movementsto understand its movements



•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

– KinematicsKinematics - description of motion and - description of motion and includes consideration of time, includes consideration of time, displacement, velocity, acceleration, displacement, velocity, acceleration, and space factors of a system‘s motionand space factors of a system‘s motion

– KineticsKinetics - study of forces associated - 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 move through a system of Humans move through a system of leverslevers– leverlever - a rigid bar that turns about an - a rigid bar that turns about an axisaxis

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

movesmoves

• Levers cannot be changed, but they can Levers cannot be changed, but they can be utilized more efficientlybe utilized more efficiently


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 movementsProduce balanced movements when when axis is midway between force & axis is midway between force & resistance (e.g., seesaw – postural resistance (e.g., seesaw – postural mm, atlanto-occipital jt.)mm, atlanto-occipital jt.)

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

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


Second-Class LeversSecond-Class Levers

• Produces force movementsProduces 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-motionProduce 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

• TorqueTorque – (moment of force) the turning effect – (moment of force) the turning effect of an eccentric forceof an eccentric force

• Eccentric forceEccentric force - force applied in a direction - force applied in a direction not in line with the center of rotation of an not in line with the center of rotation of an object with a fixed axisobject 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 must For rotation to occur an eccentric force must be appliedbe applied



• In humans, a contracting muscle applies In humans, a 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 armForce arm - perpendicular distance - 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– 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 increase, if either of the resistance components increase,

there must be an increase in one or both of force there must be an increase in one or both of force componentscomponents

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



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

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

• 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, elbow, throwing a ball involves levers at shoulder, elbow,

& wrist joints& wrist joints

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

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

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