Introduction to Kinesiology PDF

Steve Jernigan PT, PhD INTRODUCTION TO APPLIED KINESIOLOGY Outline  Terminology  Free Body Diagrams  Forces  Moments  Levers  Pulleys and Cams  Kinetics and Kinematics Purpose(s) of Kinesiology  Develop a rational evaluation  Develop a precise diagnosis  Devel...

Steve Jernigan PT, PhD INTRODUCTION TO APPLIED KINESIOLOGY Outline  Terminology  Free Body Diagrams  Forces  Moments  Levers  Pulleys and Cams  Kinetics and Kinematics Purpose(s) of Kinesiology  Develop a rational evaluation  Develop a precise diagnosis  Develop an effective treatment of disorders that affect the musculoskeletal system Terminology  Kinesiology: the study of human movement  Biomechanics: uses principles of physics to study how forces interact within a living body  Statics: bodies at rest  Dynamics: bodies in motion  Kinematics: motion, relationship between displacement, velocity and acceleration  Kinetics: motion, forces that create motion  Center of mass: body mass is equally distributed around this point  Center of pressure: center point of weight of a body Free Body Diagrams Intro  A drawing that consists of all the forces acting on a system or body in correct proportion. Identify forces Include parameters for each force Parallel forces can be added or subtracted to determine the resultant force Concurrent forces must be determined mathematically (vector component problems) Free Body Diagrams - Elbow  Forces acting on the lever = Vector 1) Magnitude 2) Direction 3) Point of application 4) Line of application  Force = Mass x Acceleration  Force units = Newtons or pounds (not mass)  Force Equilibrium – when at rest, the sum of all forces equals zero. ∑Fx = 0 ∑Fy = 0 Newton’s Laws of Force  First – Equilibrium – Inertia:  Body at rest will remain at rest unless acted upon by a resultant force.  Second – Acceleration:  Particle subjected to a resultant force will accelerate in the direction of that force and the magnitude of acceleration will be proportional to the force magnitude.  F = ma, W = mg  Third – Action/Reaction:  For every action there is an equal and opposite reaction. Types of Forces  Gravity – always vertically down Weight = Mass x gravitational acceleration  Shear – coplanar, in opposite direction  Tensile – colinear, in opposite direction  Compressive – colinear, in similar directions to push together  In the body? https://www.quora.com/What-is-shear-force Force Systems Force Systems Moment (Torque)  The application of force at a distance from the point of pivot.  Causes rotation around a stationary point (elbow axis).  Moment = Force x Distance  Force is the one that is perpendicular to the lever.  Distance is the distance from the pivot point to the point of force application.  Unit of measure is pound-foot or Newton-meter. Moment Example Moment = Force x Distance Moment (Torque)  Characteristics Has magnitude and direction No moment if force passes through the axis As moment arm increases, the magnitude increases Moment equilibrium: when at rest the sum of all moments equals zero. ∑M = 0 Free Body Diagram  Bringing it all together – Biceps Example Solve for the muscle force required to hold the weight still and the joint reaction force on the elbow(axis)… Free Body Diagram Steps  Convert figure to a free body diagram  Label all known elements (forces, mass, distance, angles, etc.)  Make necessary conversions  Use ∑M = 0 to solve for muscle force needed to maintain arm position (remember, perpendicular vector components)  Joint reaction force is the resultant of all the forces acting on the joint (muscle force, gravity, and lifted weight); sum all x and y vectors. The JRF will be equal and opposite to the sum of the x and y vectors. Equations Needed for FBD  W = mass x 9.81 m/s2 ; mass to weight  ∑M = 0; determine muscle force  Sine α = y/h To determine Vector Components  Cosine α = x/h  Tangent α = y/x To determine Joint Reaction Force  ∑Fx = 0  ∑Fy = 0  c2 = a2 + b2 LEVERS Levers  Lever – a simple machine used to increase or decrease mechanical advantage, often a rigid bar.  Components  Fulcrum or axis of rotation  Force (F), distance of force arm (df)  Resistance (R), distance of resistance arm(dr)  Mechanical advantage MA = FA/RA = df/dr The body is FULL of levers! Levers axis Types of Levers  First-class lever (FAR) Fulcrum between effort and resistance  Second-class lever (ARF) Resistance between effort and fulcrum  Third-class lever (AFR) Effort between fulcrum and resistance Lever Equilibrium  Equilibrium occurs when the forces on one side of the axis equal the forces on the other side of the axis. F (df) = R (dr) PULLEYS AND CAMS Pulleys and Cams  Pulleys May be used to change the line of pull or increase the mechanical advantage of a system. May be FIXED or MOVABLE  Cams Non-uniform ellipses used to improve the mechanical advantage of a system Allows for variable resistance throughout the ROM to match the length-tension relationship of the muscle Fixed Pulley  Axis is anchored  Pulley wheel only rotates  Provides change in direction of force application only  Mechanical advantage = 1  Example: Lateral malleolus and peroneal muscles Fixed Pulleys Mechanical Advantage = 1 Mechanical Advantage = Force Arm / Resistance Arm Movable Pulleys  Axis is the attachment point for force, but is not fixed  Pulley wheel rotates AND translates  Provides a change in direction of force  Each movable pulley provides a mechanical advantage of 2 1 pulley, requires 1/2 the force 2 pulleys, requires 1/4 the force 3 pulleys, requires 1/6 the force Example of Movable Pulley Pulley Problem  Convert mass to force  10 kg x 9.81 = 98.10 Newtons  Count number of movable pulleys to determine the mechanical advantage  MA with 2 movable pulleys = 4 or ¼ force required  MA = FA/RA = 4/1  F x FA = R x RA  F x 4 = 98.10 N x 1  F = 24.5 N Cam Example Note the difference in the length of the resistance arm distance and the force arm distance with the different pulley positions. Cam Problem  Convert mass to force 30 kg x 9.81 = 294.3 N  MA = FA/RA = 3  F X FA = R X RA  F X 3 = 294.3 N X 1  F = 98.1 N KINEMATICS AND KINETICS Kinematics  The study of movement related to displacement, velocity and acceleration Position - An object’s location in space Displacement - distance and direction Velocity - time rate of change in displacement or (change in distance)/(change in time) Acceleration - time rate of change in velocity or (change in velocity)/(change in time) Examples of Kinematics An object moves from position 1 to position 2, etc. From this graph, we can determine: Position Displacement (distance moved in meters, direction = vertical) = 1.5 m Velocity (Pos 1 to Pos 2 = 0.75 meters/second) 1.5m / 2sec = 0.75 m/sec Examples of Kinematics While running… Displacement of thigh angle 1 Radian ~ 57 degrees Total excursion ~ 1.50 radians or ~ 85 degrees Starts at stance, moves into hip extension briefly, then hip flexion, then hip extension Velocity Magnitude = speed of thigh movement Pos/Neg = direction of movement Note velocity of zero = change in direction of thigh movement Acceleration Positive acceleration = increasing speed, until reach peak velocity, then decelerates Negative acceleration = decreasing speed Examples of Kinematics Krista Sanchez – KU Bioengineering Picture taken from: Mascal, Landel, and Powers. Management of Patellofemoral Pain Targeting Hip, Pelvis, and Trunk Muscle Function: 2 Case Reports. Journal of Orthopedic and Sports Physical Therapy, Vol. 33, No. 11. November, 2003. Kinetics  Movement in terms of forces Forces applied at an instant in time ○ Can calculate Linear Force  ∑Fx = m(ax), ∑Fy = m(ay)  Similar to the Free Body Diagrams. When there is no motion, these equal 0 (equilibrium). ○ Can calculate Rotational Force  ∑M = Inertia(acceleration) Impulse - force applied over a period of time Work - force applied over a distance Kinetics – Inverse Dynamics Inverse Dynamics – used to determine joint forces Obtaining kinematic data using a video analysis system and force plate allows for this. Similar to free body diagrams – joint reaction force Examples Force Plate – Ground Reaction Forces Impulse = force applied over time. Center of pressure = point of application of the ground reaction force. Kinetics – Work  Work – force applied over a distance Measured in Joules ~ Nm Kinetics – Power  Power – work divided by time Speed is the key Measured in Watts or Joules/second Kinetics - Pressure  Pressure – force applied within an area Kinetics - Friction  Friction – the resistance created as a result of two bodies being in contact with one another. These forces are not calculated in free body diagrams, we assume they are “frictionless”. Taken from (8/15/2022): https://blogs.bmj.com/bjsm/2017/03/21/ankle-sprains-lower-limb-injury-can-identify-risk/ Instrumentation  Force Plate = rigid platform (known dimensions) Force transducer Amplifier http://www.amti.biz/fps-guide.aspx, Accessed 8-19-13 Instrumentation  Inclinometer – measure angles  Instrumentation  Dynamometer – measures force http://compasshealthcaresupply.com/en/ dynamometers/64-microfet2-digital-manual-muscle- dynamometer-with-software.html, accessed 8-19-13 http://www.bpp2.com/ physical_therapy_products/02- http://www.orthopedicrehabinc.com/Services/Computerized-Isokinetic- measurement-010201.html, accessed 8- Strengthening/a~4945--c~347490/article.html, accessed 8-19-13 19-13 Instrumentation  Accelerometer – used to measure acceleration  Can determine the angle (tilt) of a device (due to gravity)  Can determine the movement of a device (dynamic forces)  Examples  Pedometer, Wii  Golf and bat swing measurement  Airbag deployment on vehicles  Smart phones  Computer shut-off to protect hard drives http://wiiphysics.site88.net/, accessed 8-19-13 Instrumentation Lecture (in Module 2)  Electroinclinometer  Isokinetic dynamometer  EMG (Skeletal Muscle lecture)  This lecture will include videos and discussion. The So What...  Understand normal human movement and the forces that generate those movements.  Understand kinematics and kinetics associated with injury.  Understand the influence of disease on movement (e.g., Parkinson’s, Muscular Dystrophy, Stroke, etc.).  Develop strategies to facilitate normal movement and/or design equipment to compensate for deviations from normal, if needed.