AT 5311 EXAM 1
Which of the following are considered a sign of inflammation?
swelling, heat, loss of function, redness, and pain
Articular cartilage functions primarily under ___________ loads. Ligaments and tendons function primarily under _______________ loads. a. Compressive. Compressive. b. Tensile. Compressive. c. Tensile. Tensile. d. Compressive. Tensile.
d. Compressive. Tensile.
Which of the following best describes the fracture healing process a. Hematoma formation, bone remodeling, callus formation b. Callus formation, hematoma formation, bone remodeling c. Bone remodeling, hematoma formation, callus formation d. Hematoma formation, callus formation, bone remodeling
d. Hematoma formation, callus formation, bone remodeling
_____________ is a measure of a tissue's ability to absorb mechanical energy a. Pressure b. Maturation c. Adaptation d. Toughness
d. Toughness
Injury
damage sustained by tissues of the body in response to physical trauma
Displacement
difference between 2 points; shortest distance from a to b - d= x2-x1
Linear velocity
displacement/time
Lever arm
distance from the axis of rotation to pt of force - to increase advantage, increase the length of lever or moment arm
Torque is the
effect of a force that tends to cause a change in the body's state of angular position or motion - rotational effect or twisting action (torsion) of a force about an axis of rotation -Also known as "moment of force" or simply "moment" Calculated as the product of force and moment arm Torque (Nm) = applied force (N) x moment arm (m) Typically, two torques in human body: -Muscular - can be propulsive (↑ rotation) or braking (↓ rotation) --> pushing off and slowing down when running; muscles try to overcome resistance -Resistive - opposes muscular torque (ex. weight of segment) --> bicep curls, weight of arm
General motion (mixed)
most common; Combines angular and linear motion - Pedaling a bike - Walking - Basketball shot Ex: the human thigh when walking. Linear motion of the thigh goes in a forward direction combined with angular motion as it rotates around the hip joint axis in alternating flexion and extension phases.
Articular cartilage injury
no blood flow Excessive joint loading may lead to 3 types of articular cartilage damage 1.Loss of cartilage matrix macromolecules, alteration of matrix, or chondrocyte injury 2.Isolated damage to the cartilage itself •Chondral fracture or flap tears 3.Injury to cartilage and underlying bone •Osteochondral fracture
Deformable-body mechanics
objects deform when loaded, related to training and injury -Ex: foot, hand
Linear acceleration
occurs when an object slows down, speeds up, or changes direction -A point spinning at constant angular velocity will not speed up or slow down, BUT because the point follows a circular path, it is constantly changing direction and thus experiencing constant linear acceleration
If slowing down in a + direction
- Velocity will be + - Change in motion = (-) - Acceleration = (-)
Injury Prevention and Rehabilitation
- Reduce impact forces - Reduce joint loading - Decrease the incidence of injury - ex: football rules updates - Equipment design improvements -Better helmets, pads, and footwear?
If speed is not changing (constant velocity) in a (-) direction
- Velocity = (-) - Change in motion = 0 - Acceleration = 0
Slowing down in a (-) direction
- Velocity = (-) - change in motion = (-) - acceleration = +
If speeding up in a (-) direction
- Velocity = (-) - change in motion = + - Acceleration = (-)
If speeding up in a + direction (velocity and acceleration)
- Velocity will be + - + change in motion - acceleration will be +
If speed is NOT changing (constant velocity) in a + direction
- Velocity will be + - 0 change in motion - Acceleration = 0
Which of the following factors can affect the quality and quantity of load-bearing connective tissues?
- immobilization - diet - physical activity - bed rest
If we want to INCREASE the moment arm, then we could
- increase the force while holding the moment arm constant - increase the moment arm while holding the force constant - increase both the force and moment arm - decrease the force while increasing the moment arm more then proportionally - decrease the moment arm while increasing the force more than proportionally
ACL surgical repairs are commonly performed using a patellar tendon or hamstring tendon graft. Considering what you know about the anatomy and physiology of these tendons and ligaments, which graft type would likely have better outcomes and why?
- might depend case by case (injury, type of sport) - ex: no injury and no sport demand, then a patellar tendon is more of a ligament and similar to ACL
Speeding up or starting Slowing down or stopping Sign of velocity and sign of acceleration the same Sign of velocity and sign of acceleration the opposite
-Angular acceleration is in the direction of angular motion -Angular acceleration is in the direction opposite of angular motion -Body is rotating faster (speeding up) -Body is rotating slower (slowing down)
List the plane associated with each anatomical axis -Anteroposterior -Transverse (or mediolateral) -Longitudinal
-Anteroposterior = frontal -Transverse (or mediolateral) = sagittal -Longitudinal = transverse
The total angular momentum of a given system remains constant in the absence of an external torque.
-Changes in body configuration produce a trade off between: •Moment of Inertia •Angular velocity Velocity can be transferred from one segment to the next within the kinetic chain -Proximal segment must decrease angular velocity so that the distal segment can accelerate à conserve angular momentum of the system.
From sports medicine perspective, MOIs involve
-Contact -Dynamic overload -Structural vulnerability -Inflexibility -Impact Rapid growth
If an object/person is moving in the negative direction, then:
-Displacement will be negative (-) -Velocity will be negative (-) •Positive acceleration = ↓ velocity •Negative acceleration = ↑ velocity
If an object/person is moving in the positive direction, then:
-Displacement will be positive (+) -Velocity will be positive (+) •Positive acceleration = ↑ velocity •Negative acceleration = ↓ velocity
List 3 motions that occur within the -Sagittal plane -Frontal plane -Transverse plane
-Sagittal plane = flexion/extension, dorsiflexion/plantarflexion, hyperextension -Frontal plane = abduction/adduction, inversion/eversion, elevation/depression -Transverse plane = internal/external rotation, pronation/supination, horizontal ad/adduction
When examining position-time, velocity-time, and acceleration-time relationships, you should consider the following:
-What direction is the object/person moving (+ or -)? -What are the corresponding velocity and acceleration for that respective direction?
Overload principle
-To hypertrophy muscle, threshold stimulus must be reached to induce adaptation in contractile proteins
List 3 potential contributory factors for injury
1) age 2) genetics 3) nutrition
Fracture healing
1. hematoma formation (0-2 wks) - blood pools 2. Soft callus formation (2-3 wks) 3. hard callus formation (3-6 wks) 4. Bone remodeling (8wks-2yrs)
Netwon's laws of motion
1. object in motion stays in motion (same w/ resting) 2. force = mass x acceleration 3. every action has equal and opposite reaction
Mechanical energy comes in two forms
1.Kinetic energy (motion) 2.Potential energy (stored) --> standing on a tall mountain •Position •Deformation
Biomechanics of Bone
2 types -Compact/cortical -Trabecular/cancellous/spongy Bones loaded multiaxially making it difficult to test each condition that it is loaded - compressive forces mostly
If ball is kicked and landed at the same height, and air resistance is negligible, the optimal angle for producing maximum horizontal displacement would be
45º
Angular Velocity
= angular displacement/time - Rate of change of angular position -How fast the body is rotating (º/s or rad/s) Mathematically: vT (instantaneous linear velocity) = ⍵r (instantaneous angular velocity and radius of rotation)
Angular Acceleration
= angular velocity/time Rate of change of angular velocity -Starts, stops, speeds up, slows down, changes axis of rotation Direction specification follows the right-hand rule
Acceleration (a)
= change in linear velocity/time Rate of change in linear velocity -Think of acceleration as a push in a direction or tendency to change velocity, not as speed or velocity Vector quantity Positive vs. negative acceleration - (+) direction = + acceleration - (-) direction = - acceleration
Velocity (linear)
= linear displacement/time -Rate of change in linear displacement; if displacement = 0, so will velocity! -Vector quantity (can be - or +) -Meters per second (m/s)
If ⍵ (angular velocity) is constant, ar (centripetal acceleration) is directly proportional to the radius of rotation
A hammer thrower using a hammer with a 1.0 m chain must exert greater centripetal force than a thrower using a 0.75 m chain if the two throwers rotate at the same angular velocity. Centripetal acceleration of hammer with 1.0 m chain is greater because it has a larger radius of rotation
Briefly describe the primary differences between a tendon and an aponerosis.
A tendon is a white, collageous fiber which contain flexible bands that connect muscles to bones, while aponerosis is more of a fibrous, ribbon like sturcture where the fibers run in a single line/direction.
Within Frontal Plane, Around Anteroposterior Axis
Abduction and adduction Radial deviation or ulnar deviation (wrist) Inversion or eversion (ankle) Elevation or depression (scapula) Lateral flexion to the left or lateral flexion to the right
Absolute vs. Relative Angle
Absolute Angle: Angle of the trunk is calculated with respect to the vertical plane Relative Angle: Angle of the trunk is calculated with respect to the knee, hip, and torso
Classes of Levers
All lever systems will have an axis (A), resistance (R), and force (F) in three different arrangements. Function to do one or more of the following: -Balance 2 or more forces -Change direction of the applied force -Favor speed and range of motion -Favor force production.
Angular motion (rotation)
All points on the body move through the same angle - moving around an axis Can either be a: Whole-body rotation - Giant swing, pirouette, somersault Segment rotation - Flexion, extension, adduction, abduction, etc.
Relationship Between Linear and Angular Velocity
All points undergo same average angular velocity because they all take same time to undergo respective angular displacement Points farther from an axis of rotation travel greater linear distance than points closer to an axis of rotation at the same time -Farther = greater distance (and greater displacement) Therefore, points farther from an axis of rotation travel at a greater linear speed (and greater instantaneous linear velocity) than points closer to an axis of rotation
Adaptive capabilities of the MSK tissues are as important as to understanding injury as is tissue biomechanical function
All tissues can adapt to their environment to a greater or lesser extent Dramatic changes and adaptations happen in: -Bone -Cartilage -Tendon -Ligament -Muscle Adaptations are a result of many factors -Activity -Inactivity -Immobilization -Diet
Osteoarthritis
Also known as degenerative joint disease (DJD) Etiology -Primary - idiopathic -Secondary - result from trauma or metabolic disorder (typically in sports)
Characteristics of EMG Signal
Amplitude: - Dependent on motor unit recruitment and rate - Measured in Volts (V) Frequency: -Describes the amplitude of the frequencies contained in signal -Measured in Hertz (1 Hz = 1/s)
Projectile Motion
An object in the air is acted on only by forces of gravity and air resistance -No self-propelled force capability Consider vertical (gravity) and horizontal (distance) kinematics separately - ex: vertical - can't change direction once in the air - ex: horizontal - once a ball is released, can't change the direction
Using impulse to decrease momentum
An object may have a fast initial velocity and we want to decrease this velocity to a slow or zero final velocity. - slow down gradually •Examples: catching a ball, landing from a jump,
Kinetic Energy
An object's capacity to do work because of its motion KE = 1/2mv2 Where: -m = mass (kg) v = velocity (m/s)
Anatomical Axes
Anteroposterior (AP) axis --> inside to outside -Imaginary line running from anterior to posterior •Perpendicular to a frontal plane Transverse axis --> left to right (medial/lateral) -Imaginary line running from left to right •Perpendicular to a sagittal plane Longitudinal axis --> up and down -Imaginary line running superior to inferior •Perpendicular to a transverse axis A segment moves within a plane and rotates around an axis -Plane of motion and axis of rotation are perpendicular
Noise
Any portion or aspect of the output signal which is undesirable and may possibly mask the true signal of interest Can be from: -Electrical disturbances inside the device -Lights or telephone poles -Movement of the wires or equipment Accounting for noise by - Adequately set up the environment - Take the differential - Apply filters We want to maximize the signal to noise ratio
Second Class Lever
Arrangement - A/R/F Function - favors force production because of the force arm will always be > than resistance arm. Least common in the body but most efficient because longest moment arm - ex: ankle - Force applied by gastroc & soleus complex (force), forefoot is the axis, and resistance from the leg.
First class lever
Arrangement - F/A/R Function - balance 2 forces, change direction of applied force, & favors speed/ROM. ex: Cervical Spine and Cranium - Force is applied by neck extensors, vertebrae is axis, weight of head is the resistance.
Third Class Lever
Arrangement - R/F/A Function - favor speed and range of motion. Most common in the body. (all other joints) - Force is applied by muscle, axis is joint center, and resistance is distal segment.
Type 2A fiber
Faster contraction, somewhat fatigue resistant
Analyzing Projectile Motion
Because of the uniform nature of gravity (vertical acceleration is constant), there is: -Linear change in vertical velocity -Time it takes to reach the apex (e.g. peak height) will be equal to the time it takes for the object to fall to the same height it was released from -At the apex, vertical velocity will be zero. -Vertical velocity at release = Vertical velocity at impact given it is released and lands at the same height Common Physics example -A bullet that is dropped at the same instant that another is fired horizontally will strike level ground at the same time
What Is Biomechanics?
Bio = living or biological systems Mechanics = analysis of forces and their effects (kinematics, kinetic, etc)
Viscoelasticity
Bone exhibits strain-rate sensitivity, creep behavior, hysteresis, and fatigue. Bone can withstand high stresses when loaded once, but as the number of loads increase, the bone's ability to withstand the stress decreases. If damage is NOT excessive, remodeling occurs to resorb material around damaged area and new bone is deposited If damage IS excessive, remodeling can't keep up with repair and fractures can occur
Instantaneous angular velocity
Calculated angular velocity at a specific instant when and object or rigid body is rotating
Average angular velocity
Calculated angular velocity for the object or rigid body through a certain angular displacement - average time from beginning to end
Center of Gravity and Stability
Capacity of a body to return to equilibrium when displaced -Not easily moved or thrown off balance Factors -Height of center of gravity -Size of the base of support -Weight of the object -Lower, wider, heavier = more stable
If vT (tangential velocity) is constant, ar is inversely proportional to the radius to the radius of rotation
Centripetal acceleration (ar) is greater when running on inside lane compared to outside lane of a track at same linear speed because tangential linear velocity is the same, but radius of rotation is larger in outside lane
Angular Displacement
Change in orientation of a rigid body in reference to some axis (amt of angle) -Angle between the final and initial angular positions -Angular displacement = △⍬ = ⍬f − ⍬I Specify the direction of angular displacement -Clockwise (−) or counterclockwise (+) -Note: must specify viewing position as clarification •Right-hand rule! (imagine clock)
Coefficient of Restitution (e)
Coefficient of restitution: the ratio between the relative post-collision velocity (RVpost) of two bodies and their relative pre-collision velocity (RVpre) -e = RVpost / Rvpre The range for e is between 0 and 1 -1 = little energy lost -0 = all energy lost Imagine bouncing a ball -If ball is hard rubber, the e would likely be closer to 1 -If ball is deflated, the e would likely be closer to 0 The material properties of the colliding bodies will determine where on the collision continuum each impact falls
Ligament injury
Commonly injured due to repetition, overuse, quick movements throughout joint ROM (excessing tensile loading) resulting in ligamentous sprain Characterized according to severity - Mild - Moderate - Severe
Biomechanics of Compact Bone
Compact Bone -As load increases on the bone, the load and deformation increase in a relatively linear fashion (Hooke's Law) -Elastic limit - transition from elastic behavior to plastic -Plastic deformation - smaller and smaller increases in load will produce greater and greater increases in deformation -If bone shape is known, material properties can be calculated
Tendon injury
Connective structure of tendon includes 3 zones -Body of tendon -Connections of tendon to bone -Connections of tendon to muscle Tendon injury may be result of direct insult (laceration from sharp object) or indirect insult (excessive tensile loading - strain) Characterized according to severity -Mild -Moderate -Severe -May result in spontaneous tendon rupture
Kinetics
Deals with the forces that cause or tend to cause changes in motion: pushes and pulls, turning effect of a force, loading of an object
Kinematics
Description of motion WITHOUT regard to the forces involved : How far? How fast? What direction? - ex: bicep curl (how quickly did it flex)
Net Joint Torque
Determines the net effect of the applied force (e.g. muscular force) and resistance (e.g. weight) applied to a system. -Positive net torque = increase rotation in the direction of torque produced. -Negative net torque = decrease or controls rotation in the direction of the resistance. Computed as the sum of muscular and resistive torque applied to a system.
Frontal plane (coronal plane)
Divides body into anterior and posterior parts
Sagittal plane
Divides body into right and left parts - flexion/extension
Transverse plane (horizontal plane)
Divides body into superior and inferior parts
Analyzing Ground Reaction Forces
During most human movement, especially gait, we can examine propulsive and breaking forces. Propulsive Force - a force that is causing a body to speed up. -If the direction is positive, it will be positive -If the direction is negative, it will be negative Breaking Force - a force that is causing a body to slow down. -If the direction is positive, it will be negative -If the direction is negative, it will be positive
Factors influencing the EMG signal
EMG amplitude affected by numerous factors not related to neural activity -Muscle mechanics: •Length, velocity, architecture, etc. -Skin impedance: •Hair, oils, dead skin cells impede flow of electrons at electrode-electrolyte interface -Electrode site preparation: •Shave, abrade, isopropyl alcohol •May not necessary with newer electrode and amplifier designs -Especially true with onsite electrode pre-amplification -Tissue characteristics: •The electrical conductivity varies with tissue type, thickness, physiological changes and temperature. Physiological cross talk: -Phenomenon whereby myoelectric activity is registered simultaneously from multiple muscle by the same electrode. -Neighboring muscles may produce a significant amount of EMG that is detected by the local electrode site. Geometry between muscle belly & electrode site: -Any change of distance between signal origin and detection site will alter the EMG reading. Electrode placement: -NOT on or near the tendon of the muscle -NOT at the outside edges of the muscle -Palpation for area of greatest muscle bulk -Recording electrodes must lie in parallel with muscle fibers
How can we compare between people or timepoints?
EMG signals are user dependent in nature - May be different at different times of day or between days in the same person Normalization is used to account for the variance within the individual or between individuals Done by using the quiet resting measure or the maximal isometric voluntary contraction - Normalized coefficient = (mean RMS value of test contraction)/(mean RMS value of reference value)
Strain energy
Energy due to deformation SE = ½k△x2 Where: -k = stiffness constant of the material (N/m) -△x = deformation (change in length) of the object (m)
Gravitational PE
Energy due to position PE = mgh Where: -mg = mass or weight (N) -h = elevation (height) above reference point (m) (ground or some other surface)
Tissue Types
Epithelial: thin, sheet like tissue -Examples: lining of intestines, organs, skin Nervous: develops from ectoderm; basic unit is a neuron -Example: brain, spinal cord, CNS, PNS, nerve endings Muscle: derived from mesoderm -Types: skeletal, cardiac, smooth Connective: also derived from mesoderm; has extracellular substances -Example: tendons, ligaments, bones, adipose
Linear Kinetics
Examines relationship between a body's resistance to change and its linear state of motion and the effect of applied forces Include: - Mass: quantity of matter in a body --> weight -Inertia: resistance to being moved linearly and is the property of matter by which it remains at rest or in uniform motion --> laying on the couch and need to get the remote -Force (N): mechanical action or effect applied to the body that tends to produce acceleration --> muscles create force Consider Newton's Laws of Motion
Angular Kinetics
Examines the relationship between a body's resistance to a change in its angular state of motion and the effect of applied torques Includes: -Moment of force (torque) --> rotation of force -Moment of inertia --> resistance to change
Using impulse to increase momentum
Exerting a large force against the object for as long a time as possible - want to overhand vs flicking wrist when throwing •Examples: throwing, jumping, spiking a volleyball
T/F: An acute muscle strain typically results from direct compression forces being applied to the muscle.
False
T/F: Cranial bones form firbous matricies that ossify directly which is called endochondral ossification.
False
T/F: Exercise and physical activity can stimulate bone remodeling, but how exercise impacts the skeleton is complex. True or false: Bone mineral density in lower legs of runners is decreased in a group that runs 15-20 miles per week and is increased in a group that covers 60-75 miles per week.
False
T/F: The principle of conservation of energy indicates how much of a system's energy is conserved and how much is gained or lost during a given time period. If we apply this concept to injury, we would state that the more energy conserved, the less potential for injury.
False
Type 2B fiber
Faster contraction, most fatigable
Greater femoral diaphysis diameter allows us to carry substantially greater loads
Femur carries greater load than phalanges Bone shape and geometry is important -Consider moment of inertia and how it influence structural properties of bone during bending •Table 4.1 Ultimate tensile stress for long bone limbs in humans ages 20-39 is approximately 100-150 MPa -Femur has highest ultimate compressive stress value -Fibula, radius, and ulna have lowest ultimate compressive stress value Applying a compressive load along the long axis has greater elastic modulus and strength than if you applied the load at a right angle -How do we see this in daily life? - axially load = bone is strong - x-axis = force has less places to go
Within Sagittal Plane, Around Mediolateral Axis
Flexion or extension Hyperextension -Extension beyond the anatomical position Dorsiflexion or plantarflexion
Angles above 45º result in shorter horizontal displacement
Flight time from vertical velocity cannot overcome loss in horizontal velocity
Moment of Inertia - Human Body
For any one axis of rotation, only one moment of inertia is associated with that axis. -A rigid object has many different moments of inertia because it may have many axes of rotation. Human's moment of inertia about any axis is variable -Human body is not a rigid object -Limbs move relative to each other -Movements may change the distribution of mass about the axis of rotation -Allows manipulation of moment of inertia.
Components of a Lever System
Fulcrum - Axis of rotation of the system. - Rotation will occur around the fulcrum. Force Applied - Amount of force applied to the lever. - Used to rotate some resistance around the fulcrum. Resistance - Weight - what you try to move. - Amount applied to the level system that opposes force applied.
Tendon & Ligament Biomechanics
Function under tensile loads Ultimate tensile stresses between 50-100 MPa and is related to CSA of specific tendon or ligament - Achilles and patellar tendon have high ultimate load If tensile load is applied very quickly, ligament is more likely to fail If tensile load is applied very slowly, attachment site of ligament to bone more likely to fail (avulsion fracture)
Articular Cartilage Biomechanics
Functions primarily under compressive loads As tensile load is applied, fibers straighten out and become taut and may begin to tear or fail if load increases further Creep = deformation of a tissue as a constant load is applied - this is a good thing - tissue can increase in length - can maintain load and length, and then plateau Cyclical loading and unloading of cartilage allows for dynamic flow of fluids in and out of the tissue and may be beneficial for the matrix and cell health -How can we apply this concept to osteoarthritis treatment? --> good to stress articular cartilage and increase flow of fluids Can be compromised by too little or too much loading
Compartment & Entrapment Conditions
Fundamental mechanical relation between mass and volume play a role -Increased density in confined space increases pressure exerted on boundaries and materials within the space Pressure on nerves = tingling, numbness, pain Pressure on blood vessels = decreased arterial or capillary perfusion or restricted venous return - decreased blood flow = discoloration
Skeletal Muscle Biomechanics
Fundamental properties of muscle linked to -Force -Length -Velocity Tetany = steady skeletal muscle contraction caused by rapid arrival of signals from the nerves Force developed in muscle is proportional to number of cross-bridges in parallel Rate at which force develops is proportional to the number of sarcomeres in series
Influence of Moment Arm
Greater lever or moment arm = greater mechanical advantage Consider the three examples Which position of force application is best for generating the most amount of torque? - force further from axis
Law of Action-Reaction
Ground Reaction Force (GRF) -External force acting on the human body. -Its direction and magnitude have implication for performance in sporting events and activities in daily living. Measured in 3 directions: -Vertical (GRF-Z) -Medial-Lateral (GRF-X) --> ice skaters Anterior-Posterior (GRF-Y)
Calculating Angular Momentum
H = Iω -H = angular momentum about an axis -I = moment of inertia about an axis -ω = angular velocity about an axis Units are kg*m2/s Right-hand thumb rule used to determine direction of angular momentum.
Horizontal Motion
Horizontal acceleration is 0 -Unless acted upon by air resistance Horizontal velocity is constant Horizontal motion is in a straight line
Horizontal Acceleration
How much force is required to accelerate something horizontally? -Imagine pushing a ball on the floor We now need to consider the forces of friction... To accelerate the ball and start it moving, the pushing force must be larger than the friction force of the floor.
Calculating Moment of Inertia
I=Σmk^2 -I = moment of inertia about a given axis -Σm = summation of the masses of the rotating segment -k = radius from axis of rotation to COM (e.g. radius of gyration). More often than not, human motion occurs with multiple segments rotating. -Each segment provides some resistance to change in angular motion.
Right-Hand rule
Identify the axis of rotation -Real or imaginary line around which rotation occurs -Axis of rotation is aligned with a plane Specify the plane of motion in which the object rotates Axis of rotation is always perpendicular to plane of motion Align right thumb with axis of rotation in positive direction Fingers of right hand curl in the + direction of rotation
Position
Identifying location in space -At the start? End? A specific time during movement? - running on a track, need to know where they started Use a fixed reference point to serve as origin -Volume origin Consider the dimensionality -1 dimension: starting line, finish line -2 dimensions: goal line, sideline, (0,0), Cartesian coordinate system -3 dimensions: ball on tennis court from baseline, from sideline, how high
Interpreting Newton's First Law
If an object is at rest and the next external force acting on it is 0, the object must remain at rest. If an object is at rest, the net external force acting on it must be 0. If an object is in motion and the net external force acting on it is 0, the object will remain moving at constant velocity in a straight line. If an object is in motion in a straight line, the net external force acting on it must be 0.
Vertical Acceleration
If the only force acting upon a projectile is the downward force of gravity, then the acceleration of the projectile will also be downward and proportional to the force
Horizontal vs. Vertical Acceleration
If you try to lift a bowling ball with one finger, can you do it? NO Why is it more difficult to accelerate the ball upward rather than horizontally? - requires less force b/c overcoming vertical acceleration of gravity In the vertical direction we have gravity!
Applying the Law of Inertia
Imagine holding a 44.5 N (10 lbs.) dumbbell in your hand. How large of a force must you exert on the dumbbell to hold it still? - exert same force with hand! Vertically, gravity exerts a force downward to equal the weight of the dumbbell. Your hand exerts a reaction force upward against the dumbbell. If the dumbbell is not moving, the net external force acting on the dumbbell must be zero (i.e. your reaction force equals the force of gravity).
Inflammation
Immediate reaction to injury - Necessary component of healing, but can lead to damage if not well controlled 5 signs of inflammation Redness Swelling Heat Pain Loss of function
Trajectory of a Projectile
In the absence of air resistance, the path or trajectory of the projectile will form a parabola. -"What goes UP, must come DOWN." - gravity acting on us at all times Parabola - type of plane curve. Apex - highest point of a trajectory.
Conservation of Momentum
In the absence of external forces, the total momentum of a given system remains constant - Only external forces will change the motion of a system Total momentum of a system of an object is constant if the net external force acting on the system is 0 Useful in analyzing collisions
Levers
Increase mechanical advantage and allow us to apply relatively small force to move a much greater resistance. Simple machine consisting of a rigid bar-like body that can rotate about an axis (fulcrum). Force further away will have a mechanical advantage over the other force because it creates greater torque for the same amount of force.
Methods of increasing amplitude
Increasing the number of MU's -More MU = more force; greater EMG signal -Recruitment Increase the rate at which MU's are firing -More frequent MU firing = greater force -Better chance for summation, Tetany
Collisions
Injury happens when forces applied during an impact exceed the body tissues' ability to withstand the force Collision: forceful impact between 2 or more bodies (bat hitting a ball) In every collision, bodies undergo deformation -Plastic deformation: body's change in physical configuration is permanent --> wrist fracture -Elastic deformation: body recovers from deformation and returns to its original configuration when force is removed --> falling onto a pillow, rubberband -Most collisions involving the musculoskeletal system are elastoplastic in nature
Muscular injury
Injury is often a result of too much force transmitted through the muscle-tendon unit Acute muscle strain -Overstretching passive muscle -Dynamically overloading a muscle in either concentric or eccentric action Impact injury -Direct compressive impact Exercise-induced muscle injury -Contractile and connective tissue disruption following exercise •DOMS
Principles of Injury
Injury severity -Classification systems •Mild, moderate, severe •1st, 2nd, 3rd degree Injury type -Primary vs. secondary injury -Chronic vs. acute -Micro vs. macrotrauma Role of a tissues structure -Mechanical response for biological tissues will depend on their structural makeup (material, orientation, density, connective properties) Contributory factors
Skin injury
Injury to skin takes various forms involving different causal mechanism Blisters and abrasions -Friction between skin and another surface Contusions -Non-penetrating skin injury from blunt or violent trauma Puncture wounds -Sharp object impails the skin Lacerations -Knife or sharp object tears skin
Within Transverse Plane, Around Longitudinal Axis
Internal or external rotation Pronation or supination (wrist) Horizontal abduction or adduction (horizontal extension or flexion) Rotation left or right
What is an angle?
Intersection of two lines, two planes, or a line and a plane -Angle measures the orientation of the lines and/or planes -Represented by the Greek letter ⍬ (theta) - Units -Degrees (º): 360º in a circle (most common) -Radian (rad): 1 rad = 57.3º •Measure used when relating angular & linear motion -Revolution (turn, twist): complete 360º rotation - ex: gymnastics, ice skating, snowboarding
Consider standing on one leg and doing repetitive flexion/extension of the hip (e.g. swinging your leg) in the sagittal plane.
Is it easier to swing your leg with your knee flexed or extended? Why? - extended; more mas at longer length Is it harder to hold your hip in flexion when your knee is extended or flexed? Why? - bended; less length to hold (decreases torque)
Levers in the Human Body
Joint = axis of rotation (fulcrum) -Some joints have multiple axes of rotation (more than 1 DF). Bones = rigid segment that rotates about an axis of rotation. -Hold, push, or pull on the object. Muscles = contract to apply force to the system. -Cause (concentric), control (eccentric), or prevent (isometric) movement of the joints.
Joint injury
Joint mechanical loading is complex and not very well understood in terms of joint injury Common injuries: -Subluxation and dislocation •Sufficient force applied to joint -Synovitis •Irritation or trauma -Arthritis •Inflammation from variety of sources
Briefly explain the difference between kinematics and kinetics
Kinematics describes a linear and angular motion of a body. Kinetics describes applied forces in relation to its effect on the body.
Calculating Momentum
L=mv Where: L = linear momentum m = mass v = instantaneous velocity
Newton's Second Law
Law of Acceleration -F = ma -Explains the effect of the net force - larger mass, more force to move for acceleration The acceleration of an object depends on the mass of the object and the amount of force applied A force applied to a body causes 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 Why would jumping with a weighted vest on change the height of your jump compared to jumping with no vest? - higher mass = same force
Newton's Third Law
Law of Action-Reaction -For every action, there is an equal and opposite reaction. 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. For example, the weight of a person standing in the anatomical neutral position generates a reaction force by the ground that is equal in magnitude and opposite in direction to the weight. ex: harder you run, more force pushing back on the ground
Rigid-body mechanics
Objects assumed to be perfectly rigid, simplifying analysis (joint angles and forces) -Ex: elbow joint
Newton's First Law
Law of inertia -Inertia: resistance of an object to changing motion An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted upon by an unbalanced force
Units of Measurement in Biomechanics
Length -Position in space or change in position (how far, in m or cm) -An important performance measure for shot-put, high jump -A Critical component of success for golf, baseball -An important dimension in athletes: height Time -Duration of an event -Important performance measure: races -Critical component of success: reaction time -Important dimension in rules: game time, time outs - ex: how long a muscle contracts?
Lever Arm vs. Moment Arm
Lever Arm -Distance from the axis of rotation to the point of force application. - bigger the lever arm = less force needed Moment Arm -Perpendicular distance from the force vector to the axis of rotation.
Angular Impulse
Linear Impulse -Change in linear momentum is proportional to an in the direction of the force applied to the system. -F = ma Angular Impulse -Change in angular momentum of an object is proportional to the net torque applied to a system. -Change is in the direction of the net external torque. -Units are Nm*s
5 primary variables of Linear Kinematics
Linear Kinematics -Description of linear motion of a body Described in terms of - Timing of movement - Position -Distance/displacement -Speed/velocity -Acceleration (last 4 variables can be described as either linear or angular)
Linear vs angular momentum
Linear Momentum -Depends on two variables: mass AND linear velocity -Mass of objects do not change -Change in linear momentum = change in linear velocity Angular Momentum -Depends on two variables: moment of inertia AND angular velocity -For rigid objects, changes in angular momentum depend only on changes in angular velocity (moment of inertia does not change) -For non-rigid objects, changes in angular momentum may result from changes in angular velocity or changes in moment of inertia or both (both are variable)
Categories of Motion
Linear motion (translation): all points on the body move at the same distance, in the same direction, at the same time Rectilinear translation: straight line -Figure skater gliding across the ice Curvilinear translation: curved line -Center of mass while airborne (projectile motion) -Horizontal and vertical motion superimposed - ex: throwing baseball
Injury-Causing Situations and Severity
Magnitude -How much force is applied? - quantify w/ #; big or small Location -Where on the body or structure is the force applied? Direction -Where is the force directed? - hit head on or at an angle? Duration -Over what time interval is the force applied? - long or short? Frequency -How often is the force applied? - ultra-endurance athletes (small forces over time) Variability -Is magnitude of force constant or variable over the application of the interval? - consistent in running; variable in triple long jump Rate -How quickly is the force applied? - sprinter = higher rate; marathon = lower rate
Units of Measurement in Biomechanics (continued)
Mass and inertia -Resistance to changing motion (inertia) Greater inertia, greater resistance to speeding up or slowing down Mass: quantity of matter in an object (part of linear kinetics) - ex: weight kg) Mass quantifies inertia - More massive an object, the more difficult it is to move, greater object's inertia - larger resistance to motion
Fracture types
May be: -Open or closed -Non-displaced or displaced -Complete or incomplete
Pressure (p)
Measure of force and its distribution. Measured in pascals (1 Pa = 1 N/m2) p = F (applied force)/A (area of contact) Relation to injury - considers how the force of impact is distributed across the surface being contacted -300N of impact force with a sharp object vs. blunt object will likely have different injury outcomes - pressure increases in small area
What is electromyography (EMG)?
Measure of myoelectric activity of living skeletal muscle -Recording and interpretation of electrical activity from skeletal muscle Can be measured with surface electrodes (sEMG) or fine wire needle
Mechanical Advantage
Mechanical effectiveness of a lever for moving a resistance. Ratio of force arm to the resistance arm for a lever. Mechanical Advantage: > 1: mechanically advantageous (1st and 2nd Class) < 1: mechanically disadvantageous (3rd Class) - work harder = 1: balanced lever system (1st class) - head in same position mostly
Static
Mechanics of objects at rest or moving at constant velocity - Acceleration equals 0 - No unbalanced force or torque acts on the object
Dynamics
Mechanics of objects in accelerated motion; Speeding up or slowing down -Acceleration not equal to 0 -Unbalanced forces and torques act on the object
Injuries may result from a single mechanism; however, most injuries are a result of mechanisms acting in combination
Mechanism = cause of injury
Moment Arm vs. Resistance Arm
Moment Arm -Perpendicular distance between location of force application to the axis. -Shortest distance from the axis of rotation to the line of action. -Distance from any force/weight that produces torque about the axis of rotation (fulcrum). Resistance Arm -Distance from the axis of rotation (fulcrum) to the point of resistance application (e.g. weight).
Circumduction (frontal and sagittal)
Multiple-axis joint action around transverse and AP axes Segment motion forms a cone-shaped surface
Joints
No joint cavity: - Synarthroidal - immovable (ex: sutures in skull) - Amphiarthroidal - slightly moveable (ex. pelvis) Has a joint cavity: - Diarthroidal - moveable
Smooth muscle
Not striated and not under voluntary control
Contributing factors also play a role and may increase or decrease the likelihood of injury occurrence
Not the same as the mechanism
Gravitational Acceleration (g's)
On Earth, gravity is always constant and acts in the negative vertical direction (e.g. downward). g = -9.81 m/s2 -NOTE: velocity due to gravity is NOT consistent When you jump off a box or drop a ball off a platform, you experience 1 g of acceleration If air resistance is not a factor, vertical velocity will change 9.81 m/s every second in the negative direction -If you throw a ball straight up, it slows down 9.81 m/s every second and speeds up 9.81 m/s every second on the way down Examples of g's in sport -50g for a tennis shot -5g for each foot strike during running -40-200g during a football tackle
Calculating power
P ̅= U/∆t Where: -P ̅ = average power -U = work (F ̅d) -△t = time taken to do the work Units: J/s = watt
Increasing momentum by increasing the time of force application
Peak A and peak C are the same, but peak C has a larger impulse because longer time
Pennation angle vs longitudinal pattern
Pennation: high force output, contract intensely - ex: quads - plays a role in force output and ROM Longitudinal: low force output, HIGH ROM (more flexible and pliable) - ex: patellar
Relationship Between Linear and Angular Displacement
Place forearm on desk or table in front of you Take note of where your hand and biceps tendon insertion area are located Flex your elbow and bring your hand off the table and move it towards your shoulder as far as possible while keeping elbow on table All parts underwent same angular rotation, but which moved further; your hand or the attachment point of your biceps tendon? - wrist traveled further
Center of Gravity (cg)
Point in a body or system where the entire mass may be assumed to be concentrate -cg is an imaginary point in space -Not a physical entity -Not a fixed point •Changes when parts of an object change position The force of gravity acts downward through the cg
Example - Figure Skater
Position 1 - Due to the radius of gyration of the arms about a vertical axis, moment of inertia is large à angular velocity is small. Position 2 - Radius of gyration of the skater about the vertical axis decreases. - Thus, moment of inertia is smaller so angular velocity will be larger compared to position 1. - decreased resistance to change and increased angular momentum
Positive and Negative Work
Positive mechanical work is done by a force acting on an object if the object displaces in the same direction as the force -Throwing -Jump takeoff Negative mechanical work is done by a force acting on an object when the object displaces in the opposite direction of the force acting on it -Catching -Jump landing
Positive and Negative Muscular Work
Positive muscle work: a muscle contracts and its points of attachment move in the direction of the muscle pull -Concentric contraction Negative muscle work: a muscle contracts and its points of attachment move in the direction opposite the muscle pull -Eccentric contraction Does an isometric contraction perform mechanical work? - NO --> there is no displacement
Nervous tissue injury
Potential to be the most debilitating type of injury May become injured through many sources -Chemical -Thermal -Ischemic -Mechanical •Entrapment •Compression •Tension Trauma
Power: Alternative Calculation
Power: How quickly or slowly work is done Power = Force × velocity Power output can be comparable when -High force, low velocity -Low force, high velocity - Any combination of force and velocity with the same product
Skeletal muscle
Prime executors of peripheral nervous system's motor division Sliding filament theory: allowing muscles to contract at the basic level - actin and myosin slide over one another, then relax and slide apart Muscle fiber types -Type 1: Slower contraction and relaxation time, fatigue resistant -Type 2A: fast-twitch but relatively fatigable -Type 2B: fast-twitch, most fatigable but highest contraction speeds
Factors Influencing Projectiles
Projection Velocity (velocity of release) -Magnitude of the resultant velocity - was it thrown or hit? Projection Angle (angle of release) -Angle from horizontal - can be straight, horizontal, or anywhere between Projection Height (relative height of release) -What height was the projectile release? -What height did the projectile land? - 5ft vs 6ft, were you sitting or standing?
Newton's Second Law - Angular Equivalent
Propulsive torque increases the velocity of the rotation. -Increases velocity in the direction of the rotation. Braking torque decreases the velocity of the rotation. -Decreases velocity in the direction of the rotation. -Torque will not always be in the same direction as the motion of the rotating body. Why? --> opposite direction Measured in Nm
Linear Momentum
Quantity of motion possessed by a body Product of the objects mass and its linear velocity -Units = kg * m/s Faster an object moves with more mass, the greater its momentum. - ex: skiing and big jump - want to be larger b/c faster and momentum (gravity will be less forgiving)
Moment of Inertia (I)
Quantity that describes angular inertia. -Resistance to change in angular momentum -Measured in kg*m2 Represents the resistance to angular acceleration based on both mass and the distance the mass is distributed from the axis of rotation. More difficult to speed up or slow down the rotation of an object with more angular inertia
Optimal Projection Principle
Range of angle(s) that an object is projected to achieve a particular goal -What sport applications can you think of? - soccer, javelin, throwing a baseball, gymnastics "Optimal" is loose term -Many things may impact the "optimal" range of angles •Weather: wind resistance, rain •Individual: fatigue, height •Obstacles •Others --> weight, power
Instantaneous Speed or Velocity
Rate of motion at an instant in time -Time duration very short -Change in position very short (interval of a race) - Could calculate speed or velocity for ever 5 meters of a race - ex: office with a speed gun
Surface EMG
Records myoelectric signal from area of muscle beneath the electrodes
Angular Momentum
Remember that linear momentum was the product of mass and velocity (L = mv). - Quantity of linear motion possessed by a body. - Measured in kg*m2/s Angular momentum is the quantity of angular motion possessed by a body. Measured as the product of moment of inertia and angular velocity.
Anatomical Planes
Sagittal plane Frontal plane (coronal plane) Transverse plane (horizontal plane)
Type 1 fiber
Slower contraction and relaxation time, fatigue resistant
Bone
Specialized connective tissue -One of hardest and strongest tissues - grows and remodels over lifespan Bone perpetually remodels and responds to alterations in mechanical loading, hormones, and serum calcium levels -Why is this concept important from biomechanics perspective?: because bone is constantly undergoing change Intramembranous ossification --> development of flat bones Endochondral ossification --> production of long bones
Speed
Speed = distance/time -Rate of change in linear distance -Scalar quantity (direction doesn't matter) -Meters per second (m/s)
Anatomical System for Describing Limb Movements
Standardized descriptions of body positions and movements are used by movement professionals The anatomical position -Standing upright -Facing forward -Feet aligned with toes forward -Arms hanging straight at the sides -Palms forward with fingers extended
Cardiac muscle
Striated and not under voluntary control
Skeletal
Striated and under voluntary control
Sport and Exercise Biomechanics
Study of forces and their effects on humans in exercise and sport Goals of sport and exercise biomechanics -Performance improvement -Injury prevention
Tendons and Ligaments
Tendon = white, collagenous, flexible bands connecting muscle to bone Aponeurosis = fibrous, ribbonlike membrane, similar to tendon, all fibers run in a singular direction Ligament = dense, regular connective tissue connecting bone to bone - contains sensory receptors for giving the nervous system information about movement, position, and pain
Joint actions
Terminology for limb motions (within plane, around axis) Typically describe relative angular motion (another body part) -Motion between two segments on opposite sides of a joint
Conservation of Angular Momentum
The angular momentum of a system of an object remains constant unless acted on by an external torque. When angular momentum is conserved, there is a trade off between moment of inertia and angular velocity. Conserving Angular Momentum (no external torque) -Small I --> Large ω -Large I --> Small ω
Energy
The capacity or ability to perform work
Angular Kinematics
The description of angular motion (elbow flexion, trunk rotation) -All points move in a circular path about the same axis (goniometer measures ROM) Most human motion is a result of angular motion of the joints that occur around the joints (reference is always anatomical position) -Sagittal plane motion --> medio-lateral axis -Frontal plane motion --> anteroposterior axis -Transverse plane motion --> longitudinal axis Descriptors of angular motion -How far? -What direction? -How fast? -Speeding up, slowing down?
Torque
The effect of a force that tends to cause a change in a body's state of angular position or motion
Net Torque
The effect of the sum of all torque vectors acting on a body is proportional to the change in angular velocity. Positive net torque = increase in angular velocity. Negative net torque = decrease in angular velocity. Zero net torque = no movement occurs (e.g. torque is balanced).
Pressure
The measure of force and its distribution
The Work-Energy Principle
The net work done by all the external forces acting on an object (or system) causes a change in the mechanical energy of the object F ̅d = △total mechanical energy F ̅d = △KE + △PE F ̅d = (KEf - KEi) + (PEf - PEi)
Angular Position
The orientation of a line with another line or plane Absolute angular position -Angle of a single body segment with respect to a known vertical or horizontal Relative angular position (goniometer) -Angle of one segment relative to another •Joint angle: angle between two body segments
Linear Impulse
The product of a force and the time interval over which a force acts -Equal to the change in linear momentum -Measured in Newton seconds (N*s) When an impulse acts on a system, the result is a change in the systems total momentum (e.g. acceleration).
Torque in the Human Body
The product of muscle tension and muscle moment arm produces torque at the joint crossed by the muscle. --> changes through ROM Moment arm for a muscle is the perpendicular distance from the muscle line of action to the joint center. Moment arm for a muscle will change as the segment moves through the range of motion.
Power
The rate of work production (work that can be done in given amount of time)
Friction
The resistance created at the interface of two bodies in contact with one another and acting in a direction opposite impending or actual movement
Inertia
The resistance to movement linearly and is the property of matter by which it remains at rest or in uniform motion in a straight line - To move an object at rest, we must overcome it's inertia, or its tendency to remain stationary
Recruitment and Firing Frequency
The two most important factors influencing the magnitude and density of the signal are the recruitment of motor unit action potentials (MUAPs) and the rate of the firing frequency. These are the main control strategies to adjust the contraction process and modulate the force output of the involved muscle. The sEMG signal directly reflects the recruitment and firing characteristics of the detected motor units within the measured muscle.
Cartilage
Three primary types Hyaline (aka articular cartilage) - Most abundant - Surface lubrication for joints - Has tensile strength; mechanical stiffness/strength vary w/ changes in collagen fiber organization - Examples: joint surfaces, ribs, and respiratory systems Elastic - Very flexible - Examples: esophagus, ears, larynx Fibrocartilage - Strong and flexible - Found at stress points where friction could be problematic - Examples: meniscus, labrum, disk in spine, in tendons - Cartilage has no intrinsic blood vessels, nerves, or lymph vessels -Removes waste and receives nutrients through diffusion!
Biomechanics of Trabecular Bone
Trabecular bone elastic modulus ranges from 10-2,000 MPa -Cortical bone is around 13-17 GPa •1 GPa = 1,000 MPa
T/F: Ligaments contain sensory receptors that are capable of providing the nervous system with information about movement, position, and pain.
True
T/F: Regardless of the tissue type (bone, ligaments, tendons, cartilage, etc.) the tissue can be compromised with too little or too much loading.
True
T/F: The probability of injury increases when the load exceeds the physiological range
True
T/F: When you apply a compressive load to a long bone along the long axis, the bone has greater elastic modulus and strength than if you applied the same compressive load at a right angle to the long axis.
True
Potential Energy
Two forms of potential energy (PE) Gravitational PE Energy inherent due to an object's position relative to the earth - ex: on top of the mountain Strain PE -> sport-related Energy stored due to an object's deformation
Use vs Disuse in articular cartilage
Use - Exercise causes articular cartilage to swell - With excessive loading, synthesis may decrease and cause degradation of the cartilage Disuse - If loading is substantially reduced, cartilage can atrophy or degenerate - Reduction in synthesis - After immobilization, cartilage deforms more rapidly when compressed
Use vs disuse in bone
Use - Growing bone responds to low-moderate exercise - Bones may respond negatively above a certain threshold - Long term benefits of exercise are only retained if you continue exercising Disuse -Commonly associated with bed rest, immobilization, or space flight -Without normal loading, resorption increases and deposition of bone decreases
Use vs Disuse in tendons and ligaments
Use -Exercise causes normal tendons and ligaments to adapt to greater loads -Normal ADLs sufficient for maintaining 80-90% of ligaments mechanical potential Disuse - If loading is substantially reduced or joint is immobilized, loss in strength and stiffness occurs
Bone Injury
Variety of injury to bone is possible -Osteonecrosis •Death of bone cells due to lack of blood flow -Osteopenia •Loss of bone classified by BMD 1-2.5 standard deviations below the mean recorded for young healthy adults -Osteoporosis •"Bone that is porous" •Progressive diminution of skeletal mass rendering bone increasingly vulnerable to fracture -Fracture •Most commonly associated with bone injury •"Break"
Vertical motion
Vertical acceleration is constant -Gravity Vertical velocity changes Vertical velocity at apex is 0
Kinematics of Projectile Motion
We analyze the horizontal and vertical components of projectile motion separately The vertical component is influenced by gravity. -Vertical acceleration is equal to the acceleration due to gravity (g = -9.81 m/s2) -Vertical velocity changes (specifically it decreases) at a constant rate (-9.81 m/s every second) The horizontal component is not influenced by gravity -Horizontal acceleration is zero (neglecting air resistance) -Horizontal velocity does not change = constant
Why is it important to understand these different tissue types in relation to studying biomechanics?
We have multiple tissues all over and structure imitates function; tissues can withstand different forces
adaptation of bone
What internal and external factors affect the structure, composition, and quantity of bone? Wolff's Law -Bones will adapt based on imposed loading Modeling = adding new bone -Occurs primarily in growing years Remodeling = resorption and reformation of existing bone
What happens to bone when it is not being used or stressed (ex. bed rest, immobilization, space flight)?
When a bone is not being used or stressed from bed rest or constant load application, the bone's mineral density begin to decrease, as well as becoming more sensitive to lighter loads being applied to the bone. If the bone is overused or stress, microcracks can start to form in the osteons which will increase the chance of possible fractures and damage the bone.
Assume -Swimming to the right is in (+) direction -Swimmer has relatively constant velocity (0 horizontal acceleration) -As her hand touches the wall, there is a (-) acceleration that slows her down, then speeds her up in the negative direction as she starts swimming again in opposite direction.
When she goes to the other wall (left side of pool) -What is her acceleration as she slows down? positive -Is her negative velocity increasing or decreasing? decreasing b/c (+) acceleration -If she heads back towards right side of the pool, is her velocity negative or positive? Acceleration? positive and positive
Angular and Linear Acceleration
When ⍵ increases, the vT of points on the body increase -⍵ = instantaneous angular velocity (must be in rad/s) -vT = Instantaneous linear velocity tangent to circular path (m/s)
Distance
a ---> b; how far moved - scalar
Which of the following describes how nervous tissue can be injured a. All answers are correct b. Chemically c. Entrapment d. Direct trauma
a. All answers are correct
________ refers to the deformation of a tissue as a constant load is applied. a. Creep b. Disuse c. The toe region d. The point of failure
a. Creep
Newton's 3rd law of motion states that a. For every action there is an equal and opposite reaction. b. A force acting on a body with mass with produce an acceleration proportional to the force. (F = ma) c. All of these are correct. d. A body at rest or in uniform linear motion will tend to remain at rest or in uniform motion, unless acted upon by an external force.
a. For every action there is an equal and opposite reaction.
Indirect injury to the tendon is commonly a result of excessive ____________ loads applied to the tendon. a. Tensile b. Compression c. Torsional d. Direct insult
a. Tensile
Describe the difference between absolute and relative angles
absolute angle: angle of a single body segment (horizontal or vertical) relative angle: angle of one segment relative to another
What is acceleration?
acceleration = change of velocity/time (m/s2) - rate of change in linear velocity
Slowing down or stopping acceleration
acceleration is in the opposite direction of motion
Speeding up or starting acceleration
acceleration is in the same direction of motion
The __________________ travels down the motor neuron that is connected to the muscle fiber and begins the process of muscular contraction.
action potential
What is angular displacement?
amt of angle; angle between the final and initial angle - change in degrees - ex: 0-130-0 = 260 degree change
What is angular velocity?
angular displacement over time
Load
application of external force to the body - if load exceeds the physiological range, probability for injury increases - overuse or chronic injury - acute injury
Increasing momentum by increasing the magnitude of the force
area under B is 25% greater than area under A - peak B is higher than peak A so impulse will be greater
Base of support
area under points of contact - more pressure and force = less stable
Impulse
area under the curve
The glenohumeral joint is considered a ______________ joint. a. Amphiarthroidal b. Diarthroidal c. Synarthroidal d. None of the answers are correct.
b. Diarthroidal
Which of the following cartilage types is most abundant throughout the body? a. elastic b. hyaline c. fibrocartilage d. Interarticular fibrocartilage
b. hyaline
Which of the following movements occur at the subtalar joint? a. Dorsiflexion and plantarflexion b. Inversion and eversion c. Internal rotation and external rotation d. All of the above
b. inversion and eversion
If sign of velocity and sign of acceleration the opposite
body is slowing down
If sign of velocity and sign of acceleration the same
body is speeding up
If the blood vessels stop delivering blood to/in the bone, then
bone won't receive the nutrients it needs
The injury most commonly associated with bone is: a. Osteoporosis b. Osteopenia c. Fracture d. Osteonecrosis
c. Fracture
Tangential acceleration
component of linear acceleration tangential to the circular path - represents change in linear velocity - any point on a circle where you can draw a line and only touch that line Mathematically: aT (instantaneous tangential acceleration) = ⍺r (instantaneous angular acceleration and radius)
Centripetal (radial) acceleration
component of linear acceleration to the center (radius) of the circular path -Caused by the centripetal force (towards the center of the path) Two equations for centripetal acceleration -One related to instantaneous tangential velocity -One related to instantaneous angular velocity (in rad/s) Expressed as related to angular velocity (⍵) Mathematically: ar = r⍵ Where -ar = instantaneous centripetal acceleration -r = radius -⍵ = angular velocity (must be in rad/s) Expressed as related to tangential velocity (vT) Mathematically: ar = "vT2" /r Where -ar = instantaneous centripetal acceleration -vT = instantaneous tangential velocity -r = radius
Economics Perspective on injury
cost of insurance, taxing of health care system
Linear Work
equal to the product of force (F) and displacement (d) through which a body is moved -U = F*d - d = displacement
Angular work
equal to the product of torque (T) times the angle (θ) through which a body moves -U∠ = T*θ - ex: bicep curls
Psychological Perspective on injury
fear or change of injury
Horizontal acceleration considers the forces of
friction
Coagulation phase
histamine and prostaglandins released vasodilatory phase - capillaries dilate and clotting begins - chemotactic factors attract phagocytic cells - phagocytes consume pathogens and cell debirs
The average angular velocity of a batter's swing may determine whether or not he or she contacts the ball, but it is the bat's instantaneous velocity at ball contact that determines
how fast and how far the ball will go.
Scientific Perspective on injury
how/why injuries have (math, structure)
Center of Mass
in any body, there exists a point at which, if we concentrated, the body's mass into a point mass, the point mass would move exactly that same as the body would in its distributed state - point at which a body's mass is equally distributed
Tendon healing
inflammation --> proliferation --> remodeling (consolidation) --> remodeling (maturation)
As a moving object rises up in the air -Kinetic energy decreases (velocity decreases) -Potential energy increases (height increases) -Total energy remains constant What happens as the object lowers down in the air?
kinetic = increase potential = decreases - so energy remains constant
Large Net Torque =
large and rapid change in angular momentum -Example - muscular torque during ballistic movements.
Angles below 45º result in
larger horizontal displacement In most throwing or striking events, when a mix of maximal horizontal speed and displacement are of interest, the optimal angle of projection tends to be 45º
What is tangential acceleration?
linear part of tangent circle - circular path of change in linear velocity
What is the right hand rule?
oriented in the same direction axis is + = thumb is + - curl fingers down = + direction - curl fingers up = - direction
The center of mass (COM) of a projectile will travel in a
parabolic path regardless of the motion of the individual body segments - COM creates the shape
Mechanical Work
performed by a force acting through a displacement in the direction of force. - Measured in Joules (1 J = 1 Nm)
Moment arm
perpendicular distance from the force vector to the axis of rotation
Safety Professionals Perspective on injury
prevention programs for injuries and applying knowledge
Mass
quantity of matter in a body - measured in kg - ex: body weight
What is centripetal acceleration?
radial component of linear acceleration to the circular path - center point or axis of radius in tangent circle
When we measure joint motion using a goniometer, are we measuring absolute or relative angles?
relative angles
Modeling is the addition or formation of new bone, where as ___________ is the resorption and formation or reformation of existing bone.
remodeling
Small Net Torque =
small and slow change in angular momentum. -Example - spinning the big wheel on Price is Right.
What is speed?
speed = distance/time - change in LINEAR direction - how quickly we cover distance over time speed is FASTER than velocity!
Branches of rigid-body mechanics
static and dynamic (kinetics/kinematics)
Biomechanics is the
study of the structure and function of biological systems by means of the methods of mechanics. - i.e., The study of forces and their effects on living systems
Epidemiological Perspective on injury
the prevalence of injury in a population at risk
Conservation of Mechanical Energy
the total mechanical energy of an object stays constant if no external forces other than gravity act on the object. (KEi + PEi + SEi) = (KEf + PEf + SEf) KEi and PEi should be in opposite directions
if the only force acting upon a projectile is a downward force of gravity
then acceleration will be downward and also proportional to the force - i.e. gravity
Toughness is a measure of
tissues ability to absorb mechanical energy - Cortical bone = tough Bone is somewhat ductile until about 40yrs -Can be deformed somewhat without fracture - can absorb more mechanical energy - As we age, bones become more brittle
Displacement, velocity, and acceleration are all
vector measurements - include magnitude and direction
What is velocity?
velocity = displacement/time (m/s) - rate of change in LINEAR direction