Chp 8 Biomechanics – Flashcards
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Biomechanics
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- Study of the actions of forces - Term first used 1970's - Includes both internal forces produced by muscles and external forces that act on the body - Biomechanics human movement is one sub discipline of exercise science
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What does biomechanics do
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- Examines the internal and external forces acting on the human body and the effects produced by these forces. - Aids in technique analysis and the development of innovative equipment designs. - Draws on knowledge from sports medicine, physical therapy, kinesiology, and biomechanical engineering.
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Quantitative Analysis
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Involves measurement of variables that are thought to optimize or maximize performance (the use of #)
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Qualitative Analysis
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Involves obtaining visual or aural information to asses performance (nonnumeric description of quality)
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Quantitative Analysis Example
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- Pattern of forces using a force platform - Sequence of muscle activity using electromyography (EMG) - Three-dimensional (3D) movements of each body -segment using high speed cinematography - PT - range of motion (recovery)
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Qualitative Analysis involves
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- A framework within which skilled performance can be observed - A checklist to use when identifying errors
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Qualitative Analysis Example
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Description of a squat
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Kinematics
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The form, pattern, or sequencing of movement with respect to time
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Kinetics
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Study of actions of forces
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Kinematic Variables used to describe motion
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- time - displacement - velocity - acceleration - Vector quantities have both size and direction - These variables are used to describe both linear and angular motion
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Time
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temporal characteristics of a performance, either of the total skill or its phases
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Displacement
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length and direction of the path an athlete takes from start to finish
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Velocity
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displacement per unit of time
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Acceleration
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rate of change of velocity
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Linear Displacement
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Change in linear position Example: Skating in hockey (across)
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Angular Displacement
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Change in the angular position or orientation of a line segment Example: Curl with arm
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Linear Velocity
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rate of change in linear position
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Angular Velocity
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- Angular displacement per unit of time - Skilled performers move body segments at high rate of angular velocity
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Angular Acceleration
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angular velocity per unit of time
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Biomechanics- Kinematics
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Biomechanics use quantitative kinematics to research differences between skilled performers and non-athletes
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Biomechanics- Kinematics examples
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- Runners stride length & frequency - Swimmer's stroke rate & length - Track events velocity of takeoff - High jumpers vertical displacement - Basketball angle of projection, angle of release - Throwing events aerodynamics of flight path - Swinging (bat, racquet) timing, project speed and angle
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Biomechanics- Kinematics that involve non-athletes (most)
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- Infant through maternity developmental stages - Adapted P.E. kinematic patterns with motor disorders - Therapeutic uses to aid in recovery of injuries/surgeries
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Kinetics
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Focuses on the various forces that are associated with a movement Examples: - Force - Internal forces - External forces
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Force
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Is any action, a push or pull, which tends to cause an object to change its state of motion by experiencing an acceleration
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Internal Forces
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Generated by muscles pulling via their tendons on bones, and to bone-on-bone forces exerted across joint surfaces
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External Forces
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Acting from without, such as the force of gravity or the force from any body contact with the ground, environment, sport equipment, or opponent
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Preliminary Steps for Analyzing Human Motion
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1. Identify the system to be studied, which is to separate the object of interest from its surroundings. 2. Identify the frame of reference in which the movement takes place. 3. Identify the type of motion that is occurring, the body planes in which movement takes place (sagittal, frontal, or transverse). Identify the axes of rotation about which rotational motion occurs (sagittal, frontal, or vertical).
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Types of motion
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- Linear - Angular
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Linear Motion
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- caused by forces which act through a body's center of mass - results when the forces are applied through the center of mass Example: pushing heavy desk
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Angular Motion
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- caused by forces that do not go through the center of mass - results when the forces are applied away from the center of mass Example: tackled in football
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Biomechanics-Kinetics
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- Force rarely acts in isolation - Net force - Net force zero - Net force present
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Net Force
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- Overall effect of many forces acting on a body - Vector sum of all the acting forces
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Net force zero
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acting forces balanced in magnitude and direction
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Net force present
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body moves in the direction of the net force with acceleration
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Mass
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the measure of how much matter an object has
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Inertia
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the reluctance of an object to change its state of motion from rest to moving, to moving faster, or to slowing down back to rest
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Moment of inertia
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a function of the mass of a rotating object and how its mass is distributed about its axis of rotation
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Center of mass
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- Located at the balance point of a body; a point found in or about a body where the mass could be concentrated - Generally, 15 cm above the crotch, or approximately 55% of standing height in females and 57% in males
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Newton's 3 laws of motion
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- Describe the relationship between all the external forces acting on the human body at any time and the resulting motion of the total body. - Sir Isaac Newton developed these laws to explain why things move the way they do.
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Newton's 1st law: inertia
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- An object will not change its state of motion (it will continue to be at rest or moving with constant velocity), unless acted upon by a net, external force. Example: because of their large mass, football linemen are difficult to move out of the way
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Newton's 2nd law: acceleration
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- A force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body's mass - The greater the amount of force applied, the greater - - Speed: F=ma
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Newton's 3rd law: action-reaction
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- For every action, there is an equal and opposite reaction -In terms of forces: - When one body exerts a force on a second, the second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body
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Friction
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- Friction is a force that acts at the interface of surfaces in contact in the direction opposite the direction of motion or impending motion - Factors influencing the value of friction µ - Relative roughness and hardness of the surfaces - Type of molecular interaction between surfaces Gloves, wax, etc...
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Fluid Dynamics
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All athletic events take place in a fluid environment, whether in water (swimming), in air (cycling), or in a combination of both (water polo).
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Flow velocity
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the motion of the fluid flowing past an object or the motion of the object through the fluid.
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Archimedes Principle
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- The magnitude of the buoyant force is equal to the weight of the fluid displaced by the body - If magnitude of weight is greater than buoyant force, the body sinks, moving downward in the direction of the net force
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Fluid Mechanics
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- Buoyancy is studied in relation to floatation of human body in water - Difference in floatability is function of body density - Density of bone and muscle is greater than the density of fat
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Determination of fluid mechanics
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Orientation of the body as it floats in water is determined by the relative position of the totally body center of gravity relative to the total body center of volume
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Drag (fluid mechanics)
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- Generally a resistance force
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Resistance force
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A force that slows the motion of a body moving through a fluid
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Theoretical square law
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- The magnitude of the drag force increases approx with the square of velocity - Effect seen with high velocity sports: cycling, speed skating, downhill skiing, bobsled, luge
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3 types of drag
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- Skin friction/surface drag - Form drag/profile drag - Wave drag
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Skin Friction
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resistance derived from friction btw adjacent layers of fluid near body moving through a fluid. (tight fitting clothing for athletes)
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Form Drag
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resistance created by a pressure differential btw the lead & rear ends of a body moving through a fluid
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Wave drag
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resistance created by the generation of waves at the interface btw two fluids, such as air & water
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Body Balance and Stability Control
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- Balance is a very important factor in athletic performance - Generally depends upon the location of the center of mass and how stable that center of mass is - The stick figure model is useful
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Balance
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- Process whereby the body's state of equilibrium is controlled for a given purpose. - The base of support and location of the center of mass is manipulated. - If the line of gravity passes through some part of the body's base of support, the body will be balanced.
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Equilibrium
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The state of a system that is not experiencing any change in its direction or speed - Static - Dynamic
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Static Equilibrium
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System is at rest
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Dynamic Equilibrium
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System is moving with constant velocity
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Stability
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- A measure of the difficulty with which equilibrium can be disturbed. - A net external force is required to overcome the static equilibrium of a sprint start. - There is a trade-off between maximizing stability and acquiring speed off a mark.
