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Application Of Biomechanic Principles and Concepts Muscles • muscles work in pairs - flexion and extension • concentric contraction - muscle shortens • isometric - no change in length of muscle • extensors cause the return from flexion • eccentric contraction - muscle lengthens • muscle contracts to create internal force Joints • articulation of two or more bones - the point where they connect • provide a variety movements: pivot, ball & socket, hinge, saddle, ellipsoid, & condylar • flexors decrease the angle of a joint • use weights creates resistance torque at the joint • torque produced by muscles must be larger than resistance force to generate joint torque sufficient enough to produce motion Gravity • center of gravity shifts with each position • external weight adds to the body’s shift of center of gravity • the line of gravity shifts toward the barbell • gravity is the external force Stability and Balance • the larger the base of support the more stable the object • the closer the line of gravity falls at the center of the base of support - more stable • line of gravity shifts toward external weight • base of support should be widened in the direction of the force - applied or absorbed Newton’s First Law Of Motion • an object at rest will remain at rest until acted upon by an outside force • an object in motion will remain in motion until acted upon by an outside force • the external force used in fitness are the muscles Newton’s Second Law Of Motion • mass x force = acceleration • barbells are the mass and the muscles are the force in fitness • the body is the mass when running or jumping Newton’s Third Law Of Motion • for every action, there is an equal and opposite action • when ever a body exerts a force upon another body, the second body exerts an equal and opposite force upon the fi rst Application Of Force • effort is applied in the direction of the desired movement • apply force to the center of the barbell for control • push, pull and lift in a straight line in fitness to prevent injury 95 by Carolyn Thompson NASPE 1994 (C) 2007 Bonnie’s Fitware Inc. Application Of Biomechanic Principles and Concepts Force • force = mass x acceleration - force is the effect that one body has on another • force produces motion, stops motion and prevents motion • internal forces are the muscles which only pull as they work in pairs • size of the muscle will affect the amount of force possible • number of muscles used will affect force • external forces are gravity, friction and fluid resistance Types Of Motion • linear -body or object moves as a whole in a straight line • walking or jogging are linear motions-all parts moving at the same speed • rotary - movement in an arc or a circle around a fixed point • movement of leg at the hip joint is rotary motion in fitness Levers • a device to transmit energy • bones are viewed as levers • the bone is the rigid bar, the joint is the fulcrum, the muscle is the force • distance between the fulcrum and resistance = resistance arm • distance between the fulcrum and contracting muscle = force arm • longer force arm produces power, shorter force arm produces speed First Class Lever • the fulcrum (axis of rotation) is between the force application and the resistance • unusual in the body - biceps curl is a first class lever • other examples: teeter-totter, crowbar, pair of pliers, hammer removing a nail Second Class Lever • resistance is between the force and the fulcrum: wheelbarrow, rowboat, nutcracker, door • long force arm makes it easier to move something • favors force at the expense of speed and range of movement • unusual in the body - whole use of body is the push-up position Third Class Lever • force is between the fulcrum and the resistance: rackets, bats, weights, golf club • most effective lever to produce speed • most common in the body • fulcrum is the joint, force is the muscle and the resistance is the barbell, bat or club Absorption Of Force • impact of force is reduced by increasing the surface area, the time and distance over which the force is received. • flexion helps absorb force when jumping and jogging • bend knees on high impact aerobics 96 by Carolyn Thompson NASPE 1994 (C) 2007 Bonnie’s Fitware Inc.
