Kinesiology & Biomechanics
Djoko PrakosaDept. of Anatomy, Embryology &
Anthropology
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
Principles of applied mechanics
• Force = 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- Newton’s 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 Verticalprojection
To point nearBOS center
To point nearBOS 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 tissue
Tension: 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 tissue
Elastic 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 Muscle
Extensibility: 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 Muscle• Contractile component: Muscle fibers• Series of elastic component: Tendon• Parallel elastic component: Muscle membrane &
connective tissues
Mechanical Properties of Skeletal Muscle
• Length-tension relationship• Is measured isometrically and tetanically
Mechanical Properties of Skeletal Muscle
• In a muscle force generation capacity increases when the muscle is slightly stretch because of the effect of both active and passive component
• Important for two-joints muscles. E.g hamstring
Mechanical Properties of Skeletal Muscle• Stretch-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 temperature
• A 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