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IUPUI HPER 205 - Basic Biomechanics Concepts

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Lecture 6 Outline of Last Lecture I. Neural Control of Voluntary Movement II. CNS III. PNS IV. Neurons V. Neural Control of Voluntary Movement part 2 VI. Motor Unit VII. All or None Principle VIII. Innervation IX. Reciprocal Inhibition X. Factors Affecting Muscle Tension XI. Development XII. Muscle Length - Tension Relationship XIII. Proprioception XIV. Muscles Spindles XV. Stretch Reflex XVI. Golgi Tendon OrganOutline of Current Lecture I. Fundamentals II. Lever Systems III. Mechanical Advantage IV. The Three Levers HPER 205 1st Edition These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !V. Dimensions Used in Biomechanics VI. Newton’s Laws of Motion VII. What Causes Motion? VIII.Forces Acting on Human Body IX. Torque X. Stability and Stress Current Lecture A. Fundamentals1. Mechanics: the analysis of forces and their effects2. Sir Isaac Newton: father of mechanicsB. Lever Systems1. Three components of a levela. Axis or fulcrumb. Resistancec. Force or effortC. Mechanical Advantage1. Def: length of force arm/length of resistance arm2. A mechanical advantage greater than 1.0 allows the applied (muscle) force to be less than the resistive force to produce an equal amount of torque. A mechanical advantage of less than 1.0 is a disadvantage in the common sense of the term.D. The Three Levers 1. First Classa. A level for which the muscle force and resistance force act on opposite sides of the fulcrum (Seesaw)b. Designed for lifting/balance- axis in the middle2. Second Classa. The muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through the moment arm longer than that through which the resistive force acts. Due to its mechanical advantage, the required muscle force is smaller than the resistive forceb. Designed for lifting (Wheelbarrow)- resistance in the middle3. Third Classa. Designed for ROM (Bicep curl) (flexing knee while standing)- force in the middleb. Most human joint are 3rd classc. The muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm shorter than that through which the resistive force acts. The MA is thus less than 1.0, so the muscle force has to be greater than the resistive force to produce torque equal to that produced by the resistive force.E. Dimensions Used in Biomechanics1. Length: metersa. 1 m = 39 in2. Time: seconds3. Inertia: property of an object to resist changes in motiona. mass: measure of inertiab. 2.2 lbs = 1kg4. Force = push or pulla. measured in newtonsb. 1 lb = 4.448 NF. Newton’s Laws of Motions1. First Lawa. A body will continue at rest or in uniform motion in a straight line unless acted on by external forces2. Second Lawa. law of accelerationb. the change in motion of an object is proportional to the force exerted and is made in the direction of the forcec. F = m x a3. Third Lawa. For every action there is an equal and opposite reactionG. What Causes Motion?1. Push or pulla. muscles can only pull2. Tend to produce acceleration3. Internal/external factors and muscle and forcesH. Forces Acting on Human Body1. Gravity (weight)a. constantly accelerating us downwardb. rate of acceleration = -9.81 m/s^2c. weight = force due to gravity- mass x gravity2. Ground reaction forces a. newtons 3rd law3. Friction: horizontal component of GRF4. Fluid forces (eg. air resistance)5. Muscle forces: internal to the bodyI. Torque1. Def: the rotary effect of a forcea. Units = Nm2. To combat the effects of external forces, muscle forces are used to generate torques 3. Quantifying Torquea. T = force x distanceb. moment arm (d): the perpendicular distance between the line of action of a force and an object’s axis of rotation J. Stability and Stress1. Stabilitya. Factors increasing stability- increase body mass- increase friction- increase base of support- height of CG- horizontal position of CG in relation to base of suport2. Mechanical Stressa. ó = F/A- internal force divided by the cross sectional area of the surfaceb. Types:- compressive+ object deforms+ shortening in the direction of the force+ gravity- tensile+ stretching or elongation of the object+ lengthening in the direction of the force- shear+ transverse (parallel to surface)+ sliding (friction)-


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