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Chapter 3 Basic Biomechanical Factors & Concepts

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Chapter 3 Basic Biomechanical Factors & Concepts Biomechanics • Biomechanics - study of the mechanics as it relates to the functional and anatomical analysis of biological Chapter 3 systems and especially humans Basic Biomechanical Factors & – Necessary to study the body’s mechanical characteristics & principles to understand Concepts its movements Manual of Structural Kinesiology R.T. Floyd, EdD, ATC, CSCS Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-1 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-2 Biomechanics Biomechanics • Mechanics - study of physical • Statics - study of systems that are in a actions of forces constant state of motion, whether at rest with no motion or moving at a constant • Mechanics is divided into velocity without acceleration – Statics – Statics involves all forces acting on the – Dynamics body being in balance resulting in the body being in equilibrium Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-3 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-4 Biomechanics Biomechanics • Dynamics - study of systems in motion • Kinematics & kinetics with acceleration – Kinematics - description of motion and – A system in acceleration is unbalanced includes consideration of time, due to unequal forces acting on the body displacement, velocity, acceleration, and space factors of a system‘s motion – Kinetics - study of forces associated with the motion of a body Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-5 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-6 1 Types of machines found in the body Types of machines found in the body • Mechanical advantage • Machines function in four ways – Load/effort or load divided by effort – balance multiple forces – Ideally using a relatively small force, or effort to move a much greater resistance – enhance force in an attempt to reduce total • Musculoskeletal system may be thought of as force needed to overcome a resistance a series of simple machines – enhance range of motion & speed of – Machines - used to increase mechanical movement so that resistance may be advantage moved further or faster than applied force – Consider mechanical aspect of each component in analysis with respect to components’ machine-like – alter resulting direction of the applied force function Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-7 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-8 Types of machines found in the body Levers • Musculoskeletel system arrangement • Humans moves through a system of provides for 3 types of machines in producing levers movement – Levers (most common) • Levers cannot be changed, but they can – Wheel-axles be utilized more efficiently – Pulleys – lever - a rigid bar that turns about an axis • Machine types not found in the body of rotation or a fulcrum – Inclined plane – Screw – axis - point of rotation about which lever – Wedge moves Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-9 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-10 Levers Levers • Levers rotate about an axis as a result • Resistance can vary from maximal to of force (effort, E) being applied to minimal cause its movement against a – May be only the bones or weight of body resistance or weight segment • In the body • All lever systems have each of these – bones represent the bars three components in one of three – joints are the axes possible arrangements – muscles contract to apply force Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-11 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-12 2 Levers Levers • Three points determine type of lever & • 1st class lever – axis (A) between for which kind of motion it is best suited force (F) & resistance (R) – Axis (A) - fulcrum - the point of rotation • 2nd class lever – resistance (R) – Point (F) of force application (usually between axis (A) & force (F) muscle insertion) - effort • 3rd class lever – force (F) – Point (R) of resistance application (center between axis (A) & resistance of gravity of lever) or (location of an (R) external resistance) Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-13 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-14 Levers Levers • FAR | Force Arm || Resistance Arm | 1st F R • The mechanical advantage of levers may be A determined using the following equations: Mechanical advantage = • ARF | Resistance Arm | | Force Arm | Resistance 2nd R F Force or A Mechanical advantage = • AFR | Force Arm | | Resistance Arm | Length of force arm 3rd Length of resistance arm F R A Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-15 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-16 First-class Levers First-class Levers • Produce balanced movements when • Head balanced on neck in axis is midway between force & flexing/extending resistance (e.g., seesaw) • Agonist & antagonist muscle groups • Produce speed & range of motion are contracting simultaneously on when axis is close to force, (triceps either side of a joint axis in elbow extension) – agonist produces force while • Produce force motion when axis is antagonist supplies resistance close to resistance (crowbar) Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-17 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-18 3 First-class Levers First-class Levers • Elbow extension in triceps applying • Force is applied where muscle inserts in force to olecranon (F) in extending the bone, not in belly of muscle non-supported forearm (R) at the – Ex. in elbow extension with shoulder fully elbow (A) flexed & arm beside the ear, the triceps applies force to the olecranon of ulna behind the axis of elbow joint – As the applied force exceeds the amount of forearm resistance, the elbow extends Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-19 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-20 First-class Levers Second-class Levers – Change example by placing the hand on • Produces force movements, since a the floor (as in a push-up) to push the body large resistance can be moved by a away from the floor, the same muscle relatively small force action at this joint now changes the lever to – Wheelbarrow 2nd class due to the axis being at the hand – Nutcracker and the resistance is body weight at the – Loosening a lug nut elbow joint – Raising the body up on the toes Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-21 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-22 Second-class Levers Third-class Levers – Plantar flexion of foot to raise the • Produce speed & range-of-motion body up on the toes where ball (A) movements of the foot serves as the axis as • Most common in human body ankle plantar flexors apply force to • Requires a great deal of force to move the calcaneus (F) to lift the even a small resistance resistance of the body at the tibial – Paddling a boat articulation (R) with the foot – Shoveling - application of lifting force to a • Relatively few 2 nd class levers in shovel handle with lower hand while upper hand on shovel handle serves as axis of body rotation Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-23 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-24 4 Third-class Levers Third-class Levers – Biceps brachii in elbow flexion • Brachialis - true 3 rd class leverage Using the elbow joint (A) as the – pulls on ulna just below elbow axis, the biceps brachii applies – pull is direct & true since ulna cannot rotate force at its insertion on radial • Biceps brachii supinates forearm as it flexes tuberosity (F) to rotate forearm so its 3 rd class leverage applies to flexion only up, with its center of gravity (R) • Other examples serving as the point of – hamstrings contracting to flex leg at knee while in a resistance application standing position – using iliopsoas to flex thigh at hip Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-25 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-26 Factors in use of anatomical levers Torque and length of lever arms • Anatomical leverage system can be • Torque – (moment of force) the turning used to gain a mechanical advantage effect of an eccentric force • Improve simple or complex physical • Eccentric force - force applied in a movements direction not in line with the center of rotation of an object with a fixed axis • Some habitually use human levers – In objects without a fixed axis it is an properly applied force that is not in line with object's • Some develop habits of improperly center of gravity using human levers • For rotation to occur an eccentric force must be applied Manual of Manual of Structural Kinesiology Basic Biomechanical Factors & Concepts 3-27 Structural Kinesiology Basic Biomechanical Factors & Concepts 3-28 Torque and length of lever arms Torque and length of lever arms • In humans, contracting muscle applies • Force arm - perpendicular distance an eccentric force (not to be confused between location of force application & with eccentric contraction) to bone upon axis which it attaches & causes the bone to – a.k.a. moment arm or torque arm rotate about an axis at the joint – shortest distance from
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