Kinesiology & BiomechanicsDjoko PrakosaDept. of Anatomy, Embryology & Anthropology

Musculoskeletal Biomechanics

Significance: Kinesiology Occupational ergonomics Medical rehabilitation --> Occupational therapy Orthopedics Rehabilitation engineering Bioinstrumentation

Terminology Arthrokinematics = small amplitude motions of bones at joint surface roll= points on the surface of one bone contact points at the same interval of the other boneGlide= only one point on the moving surface contacts various points on the opposing joint surfacespin= rotational movement around the mechanical axis --> specific movements of joint surfaces. Normal movement is necessary to ensure long-term joint integrity Joint surfaces move with respect to one another by simultaneously rolling, gliding and spinning

Arthrokinematics

If the moving joint surface rolls on its partners without simultaneously gliding the surfaces would separated (gap or subluxate) in some place and impinge in others

Relation shape between bony shapes at joint surface and the surfaces movements --> rules of concavity and convexity

Rules of Concavity and Convexity Each joint involves two bony surfaces, one convex the other concave - When the concave surface is fixed and the convex surface moves on it --> the convex surface rolls and glides in opposite directions - When the convex surface is fixed and the concave surface moves on it --> the concave surface rolls and glides in the same direction

Concepts and Terminology

Principles of applied mechanics - vector addition - vector product - resolving vector into components - forces - moments - Newtons law of motion

Principles of applied mechanicsForce = mechanical disturbances or load

Moments = the tendency of the force (F) to turn the bones about the joint. M = F * L L = moment arm

Principles of applied mechanics- Newtons law of motion 1st law: A body tends to remain in its inertial state of rest or motion unless and until acted upon by an external disturbing force. 2nd law: Acceleration of a body is directionally proportional to the net force acting on the body and inversely proportional to its mass. - 3rd law:For every action, there is always an equal and opposite reaction.

Mass & Center of MassMass = a physical quantity of matter composing a body = a property of matter that causes it to have weight in a gravitational field F = ma W = mg

Center of Mass (COM) = the point where the entire weight of the body is concentrated = the point in a body about which all the parts exactly balance each other - Whole body mass - Segmental mass

Mass and Center of Mass

STABILITY

MOBILITY

mass

large

small

COG position

low

high

BOS size

large

small

COG Vertical projection

To point near BOS center

To point near BOS boundary

Levers

= rigid bar that pivots about a fixed point (axis or fulcrum), when a force applied to it.

Force is applied by muscles at some point along the lever to move the body part (resistance/load).

The relationship of fulcrum to force to resistance distinguishes the different classes of levers.

Levers

First Class Lever

Second Class Lever

Third Class Lever

First-class lever

- the axis (fulcrum) is located between the force and the resistance/load

- the longer the lever arm is, the less force is required to overcome the resistance.

- example: the forearm moving from a position of flexion into extension at the elbow through contraction of the triceps brachii muscles

Second-class lever

- the resistance/load is between the axis and the force

- example: opening the mouth against resistance

Third-class lever

- the force is between the axis and the resistance

- allow muscle to be inserted near the joint and thereby produce increased speed of movement although at a sacrifice a force.

- example: flexion of the elbow joint through contraction of the biceps brachii muscle.

Joint Functionprovide movementosteokinematic = describe how each bony joint partner moves relative to each otherarthrokinematic = specific movements that occur at the articulating joint surfaces To evaluate joint movement --> relate osteokinema-tic to arthrokinematic --> determines the movement of the mechanical axis of the moving bone relative to the stationary joint surface. Mechanical axis of a joint = line passing through the moving bone, oriented perpendicular to the center of the stationary joint surface

Joint MotionMotion = a continuous change in position of an object

The axis around which movement takes place and the plane through which movement occurs define specific motions or resultant positions. Coronal axis -> flexion, extension Sagittal axis --> abduction, adduction, lateral flexion Longitud. axis -> internal/external rotation

Non axis --> translational = linear = in a straight line

Joint mobilityInstataneous axis of rotation (IAR)Helical axis of motion (HAM) --> Most movement occur around and through several axes simultaneously

- (dis)traction: separation of 2 articular surfaces along longitudinal axis of distal segment- compression: meeting 2 articular surfaces along the longitudinal axis of distal segment

Joint Position- Resting or Neutral or loose-packed position --> capsule most relaxed and greatest amount of play is possible. play = accessory movement essential for normal functioning of joint injured joint seeks this position to allow swelling

- Close-packed position --> joint capsule and ligament are maximally tighten maximal contact between joint surfaces --> stable & difficult to move or separate

Close-packed position of some joint Interphalangeal &metacarpophalangeal Maximal extensionIntercarpal joints Max dorsoflexionRadioulnar joints 50 supinationhumeroulnar extensi in supinationhumeroradial flexion in supinationglenohumeral abduct & ext rotationHip Max extension, int rotation, abductKnee Max extension & ext rotationSpine Maximal extension

Mechanical forces acting on connective tissueTension: occurs when structure is stretch longitudinaly

Compression: when a load produces forces that push the material together, creating a deforming stress

Shear: creates resistance to sliding --> causes the structure to deform internally in an angular manner

Torque: a load produces by parallel forces in opposite directions about the long axis of a structure

Properties of connective tissueElastic qualities = springlike behavior, with the elongation produced by the tensile loading being recovered after a load is removed --> temporary elongationViscous qualities = putty-like behavior; the linear deformation produced by tensile stress remains even after the stress is removed --> permanent elongation

Viscoelastic

Basic Behavior of Skeletal MuscleExtensibility: the ability to be stretched or to increase in length Elasticity: the ability to return to the original length after a stretch Irritability: the ability to respond to a a stimulus Ability to develop tension: the ability to decrease in length Increase in tension does not imply decrease in muscle length.

Mechanical Model of a MuscleContractile component: Muscle fibersSeries of elastic component: TendonParallel elastic component: Muscle membrane & connective tissues

Mechanical Properties of Skeletal MuscleLength-tension relationshipIs measured isometrically and tetanically

Mechanical Properties of Skeletal MuscleIn a muscle force generation capacity increases when the muscle is slightly stretch because of the effect of both active and passive componentImportant for two-joints muscles. E.g hamstring

Mechanical Properties of Skeletal MuscleStretch-shortening cycles When a muscle is stretched just prior to contraction, the resulting contraction is more forceful than in the absence of the pre-stretch. possible contributors to forceful tension development elastic recoil effect of the series elastic component of the actively stretched muscle stretch reflex of the forced lengthening muscle example: wind-up during baseball pitching

Mechanical Properties of Skeletal Muscle

Force/load = 0 muscle contract concentrically with max speed. With increasing load, muscle shorten more slowly. When load = muscle max force muscle fails to shorten (isometric). When load increase further muscle lengthen eccentrically more rapid with greater load

Effect of temperatureA rise in muscle temperature increase in conduction velocity across sarcolemma, increase freq. of stimulation increase muscle force. increase enzyme activity increasing efficiency of muscle contraction. Increase elasticity of collagen enhances extensibility muscle tendon unit increase muscle force

Structural Organization of Skeletal Muscle

muscle fiber motor unit fiber types fiber architecture parallel fiber arrangement: parallel to the longitudinal axis of the muscle, e.g. sartorius, masseter, biceps brachii, etc. pennate fiber arrangement: at an angle to the longitudinal axis of the muscle, e.g. rectus femoris, deltoid, etc.

The greater the angle of pennation, the smaller the amount of effective force transmitted to the tendon The angle of the pennation increases as tension progressively increases in the muscle fibers

*13. Neuromuscular System And Kinesiology Block 1.1, Sept 23, 2008 Week 4 International ProgrammeDr. dr. Djoko Prakosa, PA