REHAB 442: Advanced Kinesiology and Biomechanics INTRODUCTION - TERMS & CONCEPTS

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1 Rehab 442: Introduction - Page 1 REHAB 442: Advanced Kinesiology and Biomechanics INTRODUCTION - TERMS & CONCEPTS Readings: Norkin & Levangie, Chapters 1 & 2 or Oatis, Ch. 1 & 2 (don't get too bogged down in details and numbers); and if you're a real glutton for punishment, check out Oatis Ch 3-7 FORCE - usually defined as mass times acceleration (F=ma), or as the entity which tends to produce motion, or to halt or change direction of motion. More simply put, force can be defined as a push or pull (exerted by one object or substance on another). Forces can be external (gravity, speeding automobiles, football players) or internal (the pull of a muscle, ligamentous resistance). COMPRESSION - a loading mode in which collinear forces (forces which lie or act are acting in opposite directions to push the material together. The act of pressing together. TENSION - a loading mode in which collinear forces acting in opposite directions tend to stretch or pull an object apart. DISTRACTION - the act of pulling apart two surfaces. SHEAR - a force which acts parallel to a surface (normally a joint surface). Also known as a tangential force. TORSION - a force which tends to twist a body. STRESS - the intermolecular resistance within a body to the deforming actions of an outside force...or, the force per unit area that develops within a structure in response to externally applied forces (tensile, compressive, shear, or rotary). STRAIN - deformation, or change in dimensions of a body as a result of the application of a force

2 Rehab 442: Introduction - Page 2 VECTOR - a quantity specified by magnitude and direction. A FORCE VECTOR is a representation of a force in terms of its magnitude, line of application, direction, and point of application. MOMENT - the measure of the tendency of a force to produce rotation about a point or axis. (see TORQUE) MOMENT ARM - the shortest distance from an action line (the line through which a force acts) and the axis of motion. TORQUE - a measure of the degree to which a force causes an object to rotate about an axis. Torque, therefore, applies to rotatory motion and is the product of a force applied perpendicular to (and at one end of) a lever arm and the distance of application of the force from the axis of motion. That is, torque=force x length of moment arm. Parallel Force Systems -- LEVERS - a lever can be defined as a rigid bar revolving around a fixed point (the fulcrum, or axis of motion) and being acted on by two forces, a resistance force (a door, the ground, a pint of ale) and an effort force (muscular contraction). 1st CLASS LEVER 2nd CLASS LEVER 3rd CLASS LEVER

3 Rehab 442: Introduction - Page 3 JOINT FORCES and MOVEMENT- joint forces are those forces acting on a joint (usually described as tension, compression, shear, torsion). Joint movements may be described in terms of: OSTEOKINEMATIC MOVEMENT - movement occurring between two bones. That is, the gross movement of the long axes of the parts through anatomical planes and about apparently stationary axes. Flexion, extension, abduction, adduction, rotation, etc. ARTHROKINEMATIC MOVEMENT - movement occurring between joint surfaces. Rolling and gliding, spin, concave on convex, etc. INSTANT CENTER ANALYSIS - a technique in which the location of the axis of motion at a joint, at a specific point in time, is determined radiographically (by comparing the location of points on a part [a bone] before and after a movement). CLOSE-PACKED POSITION - the position of a joint, usually at the extreme of a movement, in which the following three conditions exist 1. the joint surfaces are maximally congruent 2. the joint capsule and major supporting ligaments become twisted, causing joint surfaces to approximate 3. the joint becomes locked so that no further movement is possible in that direction. LOOSE-PACKED POSITION - the position of a joint, usually at the midpoint of a movement, in which the conditions for close-packing do not exist. That is, everything is loose, the joint is less stable in this position.

4 Rehab 442: Introduction - Page 4 KINETIC (KINEMATIC) CHAIN - a series of rigid links or segment (bones or body parts) interconnected by a series of joints. OPEN KINETIC CHAIN - a kinetic chain in which one end of the chain is free to move in space so that motion of one segment may occur independently of the other segments. CLOSED KINETIC CHAIN - a kinetic chain in which motion of one link/part at a joint will produce motion at all of the other joints. In humans, this is basically the case when the distal end of an extremity is fixed (on the ground, or on a door handle, etc.). GRAVITY (MASS, WEIGHT, etc.) - (review these terms in the book if you are not comfortable with the difference between mass and weight) CENTER OF GRAVITY - the single point of a body about which every particle of its mass is equally distributed. If the body were suspended (or supported) at this point it would be perfectly balanced. The COG is the point at which the force of gravity may be considered to act. LINE OF GRAVITY - the action line and direction of the force of gravity (if the length of the line represents the magnitude of the force, then the LOG is a vector). Always vertical and directed toward the center of the earth. BASE OF SUPPORT - the area formed under the body by connecting with one continuous line all points in contact with the ground.

5 Rehab 442: Introduction - Page 5 GROUND REACTION FORCE - in weightbearing, the forces that act on the body as a result of its interaction with the ground. The ground reaction forces are equal and opposite (in direction) to those that the body is applying to the ground. Also known as Floor Reaction Forces. GROUND REACTION FORCE VECTOR (GRFV) - vector representation of the GRFs. CENTER OF PRESSURE - (In a weightbearing part, thus usually the foot) the center, or average location of the forces of weightbearing. It is the point of origin of the ground reaction force vector. Can be thought of as the point of application of the force of weightbearing, though this is not entirely accurate. STRENGTH - mechanical strength is the ability of an object to resist deformation (the stress at which an object/structure fails). MUSCULAR STRENGTH - the maximum amount of force developed by a muscle or muscle group, usually to resist or create a torque. Strength cannot be measured directly. Therefore in practice strength is measured indirectly by such things as amount of weight lifted, number of repetitions of a movement completed, the magnitude of torque produced. WORK - mechanical work is the product of force and displacement (W=F x S). That is, work is a force overcoming a resistance and moving an object through a distance. Physiological (or biological) work can be divided into: 1) external work, i.e., movement of external objects by contracting skeletal muscles, and 2) internal work, which comprises all other forms of biological work, including skeletal muscle activity not moving external objects. POWER - the rate of doing work (power=work/time)

6 **************************************************************** Rehab 442: Introduction - Page 6 MEASUREMENT - the process of assigning names or numbers to objects or events, in order to understand or describe them. RELIABILITY - the consistency with which a data collection instrument measures whatever it is measuring. That is, when a measurement is repeated, is the same value obtained? INTRA-RATER RELIABILITY is consistency or repeatability in the measurements made by the same person. INTER-RATER RELIABILITY is consistency or repeatability in the measurements made by the different people. VALIDITY - the extent to which an instrument measures what it is supposed to measure. MEANINGFULNESS -