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What Should We Know By Now? Why Kinesiology is important to your field (specifically) Basic Kinesiology Terms: qualitative/quantitative, kinetics/kinematics, scalar/vector quantities, force/weight mass/matter, distance/displacement, velocity/speed volume, static/dynamic, mechanics, efficiency/effectiveness All bones in body (name, location, function, basic structure) Properties of bones, articulations, muscles Factors: influencing bone development, joint mobility/stability, force production Planes, axes, joint motions, range of motion (ROM) Muscle fiber types, GTO’s, SEC, Muscle spindles, Motor Neurons, Motor Units Skills be able to view a picture/motions and determine joint involvement, motion, degrees of movement, plane/axis Chapter 3 Basic Biomechanical Factors & Concepts We will now view the body as if it were a machine. “Mechanics” “Biomechanics” Mechanics in the Body Musculoskeletal system may be thought of as a series of simple machines used to increase mechanical advantage Machines function in four ways o balance multiple forces (see saw) o alter resulting direction of the applied force (pulley) o enhance force in an attempt to reduce force needed to overcome a resistance (wheel barrow) o enhance range of motion & speed of movement so that resistance may be moved further &/or faster than applied force (shovel) primarily how the human body functions 3 Types of Levers (p. 72) First-Class Levers o Produce balanced movements when axis is midway between force & resistance (e.g., seesaw) o Mechanical advantage in speed & range of motion when axis is close to force (scissors vs metal cutters) o Mechanical advantage in force production when axis is close to resistance (crowbar) o First-Class Levers in the Body Head balanced on neck in flexing/extending Elbow extension in triceps applying force to olecranon (F) in extending the forearm (R) at the elbow (A) Second-Class Levers o Mechanical advantage in force production, since a large resistance can be moved by a relatively small force (FA is always > RA) o Wheelbarrow, Nutcracker, Loosening a lug nut Second-Class Levers in the Body o Plantar flexion of foot to raise body on toes where ball (A) of foot serves as axis, ankle plantar flexors apply force to calcaneus (F) to lift resistance of body at the tibial articulation (R) with foot o Relatively few 2nd class levers in body Third-Class Levers o Most common in human body o Mechanical advantage in speed & range-of-motion movements o o o o (RA is always > FA) Requires a great deal of force to move even a small resistance Paddling a boat Shoveling - application of lifting force to a shovel handle with lower hand while upper hand on shovel handle serves as axis of rotation o Biceps brachii in elbow flexion using elbow joint (A) as axis, biceps brachii applies force at its insertion on radial bone (F) to rotate forearm up, with its center of gravity (R) serving as point of resistance application Factors Influencing Force Transferred to Objects Kicking, throwing, striking Length of Lever & Torque In body muscle forces pull bones around axis & create “torque” Torque – a rotary force (force that moves around an axis) o force x force arm Weight of ball creates torque o resistance x resistance arm o wt. of ball x distance ball is from axis o To lift ball, torque created when muscle contracts must > torque created from gravity pulling on ball How Limb Length Affects Torque Resistance (ball) = 5 lbs; Resistance Arm = 12 inches; Torque = 60 units To hold ball still I need: Torque = 60 units if Force Arm = 2 inches; Force = ? F x FA = torque; 30 lbs How Limb Length Affects Torque Resistance (ball) = 5 lbs; Resistance Arm = 18 inches; Torque = 90 units To hold ball still I need: Torque = 90 units Force Arm = 2 inches; Force = ?; 45 lbs Same applies to bats and rackets Longer limbs create “mechanical disadvantage in force production” How Limb Length Affects Speed of Motion However, objects held in longer limbs travel a greater distance in a given time period & so can move with higher velocities or speeds Tennis player can hit a tennis ball harder with a straight-arm drive than with a bent elbow because the lever (including the racket) is longer & moves at a faster speed baseball pitcher, golf, football punter, etc. kids leg lengths in running running speed (cycling rate) While they will need more force to move limb, they have a “mechanical advantage in speed and ROM” Effect of Angle of Attachment on Force If small angle, most of the tension will produce a force pulling along the bone will tend to stabilize joint stabilizing component Closer to 90 angle will have a much larger rotary component of force Muscle angles change throughout ROM and affects the ability to move objects For each muscle, some angles provide mechanical advantage, other angles provide less on an advantage Nautilus’s “cam” 1970’s Arthur Jones created resistance machines to try to follow strength curves called the “cam” variable resistance Systems in Motion follow Newton’s Laws Law of Inertia (1st Law) A system in motion tends to remain in motion at the same speed in a straight line unless acted on by a force system at rest tends to remain at rest unless acted on by a force Muscles produce force to start, stop, accelerate, decelerate & change the direction of motion Inertia - resistance to action or change (resistance to acceleration or deceleration) reluctance to change status; only force can change status > mass of an object > its inertia greater mass, more force needed to change an object’s inertia Law of Inertia Examples Sprinter in starting blocks must apply considerable force to overcome his resting inertia Runner on an indoor track must apply considerable force to overcome moving inertia & stop before hitting the wall Thrown or struck balls require force to stop them; Force is required to change inertia Any activity carried out at a steady pace in a consistent direction will conserve energy Any irregularly paced or directed activity will be very costly to energy reserves Ex. handball & basketball are so much more fatiguing than jogging; a distance runner speeding up and slowing down Law of Acceleration (2nd Law) in acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body: A= F/M or F = MA Acceleration - the rate of change in velocity () To attain speed in moving the body, a strong muscular force is generally necessary (Vf – Vi)/time Mass - the amount of matter in the body affects the speed & acceleration in physical movements Application: athletes acceleration abilities Law of Reaction (3rd Law) For every action there is an opposite & equal reaction As we place force on a surface by walking over it, the surface provides an equal resistance back in the opposite direction to the soles of our feet Our feet push down & back, while the surface pushes up & forward Force of the surface reacting to the force we place on it is ground reaction force Application: Pose Method of Running; skateboarding, running on sand Homework review websites on page 84; complete review, laboratory, and worksheet exercises pages 84-86 complete reading of chapter; re-organize notes, create note cards etc. write down questions of material you are struggling with to ask next class find a way to apply information to your life