essential concepts, part 3

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Muscles Produce Movement:

Muscles Produce Movement Essential Concepts, Part 3 Functional Anatomy and Kinesiology

Muscle Action:

Muscle Action 3 Types of Muscle Contraction Isometric Force is produced while muscle maintains a constant length Concentric Force produced as the muscle shortens Acceleration Eccentric Force produced while muscle is being elongated Deceleration

Muscle Action:

Muscle Action Muscle’s Action at a joint ability to cause torque in a particular direction Flexion, extension, abduction, adduction Primary action of muscle based on its anatomical position

Muscle Action:

Muscle Action Agonist Muscle (or group of muscles) most directly related to a particular movement. Antagonist Muscle (or muscle group) considered to have opposite action of agonist. Synergists Pair of muscles that cooperate during active movement.

Generating Forces:

Generating Forces Body uses muscles to generate tremendous forces Use basic principles of simple machines to improve efficiency of force production (i.e. levers) Lever Used to increase mechanical advantage A rigid bar that can rotate about a fixed point when a force is applied to overcome resistance. Fixed point Axis or fulcrum Force Muscle Resistance Weight of limb, gravity, cuff weights, manual resistance


Levers Force arm Distance between line of force and axis Resistance arm Distance between line of resistance and axis Position of axis in relation to force and resistance determines type of lever AXIS Resistance arm Force Arm F R

Types of Levers:

Types of Levers First-Class Lever Axis of rotation positioned between force and resistance Best used for balance See-saw Head (gravity) and neck extensor muscles Second-Class Lever Axis of rotation located at one end, resistance in the middle, force at other end. Best used for power Wheelbarrow Toe raise F (muscle) R (gravity) R (body wt) F (muscle)

Types of Levers:

Types of Levers Third-Class Lever Axis of rotation at one end, force in middle, resistance at other end External weight always has greater leverage than muscle force. Best used for ROM Most common lever used by musculoskeletal system Elbow flexors holding barbell F R

Mechanical Advantage:

Mechanical Advantage Ratio between force arm and resistance arm Determined by dividing force arm by resistance arm (F arm / R arm ) 1 st class lever, MA =,<, or >1 2 nd class levers, MA >1 3 rd class levers, MA < 1 Levers with MA >1 (2 nd class) Require less muscle force to overcome resistance 3 rd class levers (MA < 1) Muscle must produce force much greater than opposing, external force

Mechanical Advantage:

Mechanical Advantage Majority of muscles function with MA much <1 ( mechanical disadvantage ) Muscles attach to bone close to axis of rotation for joint F arm small External forces considerably distal to joint R arm large Skeletal muscles must produce forces several times larger than external loads that oppose them

Mechanical Advantage:

Mechanical Advantage Muscle force produces compression or shear forces on joint surfaces Periarticular tissues (cartilage, bursa, fat pads) dissipate/absorb forces Joint degeneration may occur in absence of protection (osteoarthritis secondary to decreased articular cartilage)

Mechanical Advantage:

Mechanical Advantage Rule of Simple Machines What is gained in force, is lost in distance To move object using less force, force arm must move greater distance Using more force, force arm will move smaller distance Pulleys another method of affecting mechanical advantage Used to change direction of a force, or increase or decrease force magnitude

The End:

The End

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