Therapeutic Kinesiology:Musculoskeletal Systems, Palpation, and Body Mechanics

Therapeutic Kinesiology Instructor Manual: Ch06 p.1 TK INSTRUCTOR MANUAL: CHAPTER 6 Biomechanics Chapter manuals include: Objectives Lecture Notes Suggested Classroom and Student Development Activities For other chapter-by-chapter resources, see: Key Term Quizzes Muscle Origin and Insertion Worksheets Muscle OIAs List by Chapter MyTest Test Bank For additional resources see “Teaching Tips and Tools”: 7 research-based learning principles for kinesiology courses in massage 5-step self-directed learning cycle for body mechanics courses Tools that build metacognitive skills: e.g., concept (mind) maps, grading rubrics, and self-assessments inventories OBJECTIVES Define velocity, acceleration, and deceleration. Explain how gravity affects velocity during muscular contractions. Define friction. Describe what increases and decreases friction. Define line of pull. Define the mechanical axis of a bone. Define a reverse muscle action and describe how a joint movement can reverse. List and define each of Newton’s three laws of motion. Describe a force vector in relation to a muscular contraction. List and describe three types of forces that produce movement. Define torque and describe how muscles work as force couples to produce torque. Describe the forcevelocity relationship. Describe the stressstrain curve and its relationship to tissue response under load. Define a lever and its three parts. Identify the output favored by each lever. Describe each type of the three levers and provide an example of each one. Define equilibrium and contrast the three different types of equilibrium. Describe several applications of biomechanics to effective and sound body mechanics. LECTURE NOTES BIOMECHANICS: STUDY OF MECHANICAL ASPECTS OF HUMAN MOVEMENT Concepts Statics: nonmoving systems (e.g., posture) Dynamics: moving systems (e.g., sports activities) Three main body masses: head, thorax, pelvis Line of gravity (LOG): vertical axis Center of gravity (COG): center of weight Effects of gravity on velocity Velocity: Combination of speed and direction Acceleration: Increases velocity Occurs during motion in direction of gravity Eccentric contractions Examples: walking downhill, lowering weights Deceleration: Decrease in velocity Occurs during motion against gravity Concentric contractions Examples: walking uphill, lifting weights Friction: A force between moving surfaces Too much friction prevents motion Too little friction prevents control and stability Line of pull Direction of muscular force on joint Changes as angle of joint moves Stabilizing effect when vertical Mobilizing effect when perpendicular Mechanical axis of a bone Imaginary line between center of articulating joints Depends on overall shape of bone Reverse muscle action Moving and fixed ends of muscle switch roles Also reverses the joint action Any muscle action can be reversed THREE LAWS OF MOTION Inertia: Body at rest or in linear motion tends to stay at rest or in motion unless acted upon by an external force. Inertia: A property of mass that Resists the initiation of motion Resists changes in motion Acceleration: The distance an object travels when set in motion is proportional to the force causing the movement. Greater force + stronger acceleration = farther the object travels Power: Strength plus velocity Momentum: Force applied to increase velocity Action and reaction: For every action there is an opposite and equal reaction. The greater a force, the greater its counterforce Ground reaction force (GRF): Resistance from ground FORCE Force vector: Size and direction of force Muscular force measured by Point of application: muscular attachment site Direction of force: line of muscular pull Magnitude of force: strength of contraction Types of force Linear Forces applied along same axis Either toward or away from each other Can result in gliding motion Can result in rotary motion (e.g., joint flexion) Parallel Separate, linear forces of equal magnitude Forces applied in same plane Force in either same or opposite directions Concurrent Two forces with same point of application from different directions Creates a third resultant force Torque Rotational motion around an axis Rotary counterpart of linear force Moment arm Perpendicular distance between line of pull/axis of motion Greatest at 90 degrees Force couple Two parallel forces in opposite directions (e.g., two hands turning a wheel) Force couples produce motion (e.g., muscles producing posterior pelvic tilt) Forcevelocity relationship Speed of contraction affects force it generates As muscular force increases, speed of contraction decreases (e.g., switching gears on a bike) As muscular force decreases, speed of contraction increases (e.g., slowing down touch to apply deeper pressure) Stressstrain relationship Stress: Internal resistance of tissue to deformation Strain: Change in tissue length due to deformation Stressstrain curve of a tissue: Determined by comparing length of tissue after being under stress to its original length LEVERS Simple machine that magnifies force and converts force to torque Every lever has three parts Axis (A): Fulcrum around which lever pivots Effort (E): Force that moves lever Resistance (R): Load or weight that lever moves Lever arms Effort arm (EA): Distance between effort and axis Resistance arm (RA): Distance between resistance and axis Types of levers depend on arrangement of parts First-class lever: Favors force over distance Second-class: Produces power, load in middle Third-class: Favors distance over force Levers in human body: Each body segment functions as lever arm Axis: Joints serve as fulcrums Resistance: Body's weight or external object are load Effort: Muscle contraction produces force Mechanical advantage of a lever (M Ad): Ratio between EA and RA First class: RA = EA Can also be EA > RA or RA > EA Only lever that can balance force and distance Examples: crowbar, teeter-totter Second class: EA > RA Favors force over speed and distance Example: wheelbarrow Third class: RA > EA Favors speed and distance over force Examples: brooms, bats Equilibrium Stable equilibrium All forces balance each other All forces add up to zero Unstable equilibrium Minimal force causes COG to shift Example: person balancing on physioball Neutral equilibrium (Figure 6.27c) COG remains level as object shifts position Example: rolling ball Maintaining equilibrium Important for safe body mechanics Keep COG over base of support (BOS) Keep COG close to line of gravity (LOG) When lifting Keep spine straight Contract abdominals Lower COG for greater stability by bending knees and hips Push down to come up SUGGESTED CLASSROOM AND STUDENT DEVELOPMENT ACTIVITIES PROVIDE AN OVERVIEW OF CLASS Before class, write a short, schematic overview of the class on the board, then go over it at the beginning of class. For example: Today's class covers: General terms and concepts Three laws of motion Force Levers Activities: Review, lecture, biomechanics lab, recap, and homework GOING OVER GUIDELINES EXERCISE Balancing stability with mobility (p. 148) EXPLORING TECHNIQUE EXERCISE Stress and strain in myofascial release (p. 142) PRACTICAL APPLICATIONS Have students analyze one activity of daily living, a natural movement that involves the manipulation of some implement (broom, towel, sponge, handle, etc.) and analyze it for use of levers. Have students analyze body use patterns in several types of massage strokes for ways to improve leverage. SELF-CARE EXERCISES Integrate the self-care exercises in this chapter into the lecture. This will help students make connections of abstract biomechanical principles with pattern recognition skills and practical applications to their own body mechanics. Balancing your body with reverse actions (p. 133) Overcoming on-the-job inertia (p. 134) Exercises for grounding and countersupport (p. 136) Efficient use of force in pressure applications (p. 139) Pushing and pulling with a partner (p. 146) Lifting a heavy object (p. 148) © 2013 by Education, Inc. Foster, Instructor Resources for Therapeutic Kinesiology