Kines Exam 1

vertebra structure

"Be able to label all components in this picture." Body of vertebra:weight-bearing = compressive forces =vertical trabeculae Neural Arch: ms pulls = bending and tensile forces=fan-shaped trabeculae Spinous processes and transverse processes: serve as sites for muscle attachments. Act as mechanical levers to increaseMA Sup. & inf. Articular processes • create articular pillar • house articular surfaces for facetjoints lamina are "landing point" forposterior elements• containspars interarticularis Pedicle :path from post elements to vert-body; transmits tensile and bending forces

Electromyography (EMG)

- the science of recording and interpreting the electrical activity that emanates from activated skeletal muscle •Through skilled analysis, the timing and magnitude of activation of several whole muscles during relatively complex functional movements can be determined •EMG is an important tool used in the diagnosis and treatment of certain neuromuscular pathologies •EMG combined with data such as time, joint kinematics, or external forces can provide valuable insight into the actions of muscle •In kinesiology, timing and amplitude of the EMG signal are the principal interest -Greater amplitude generally equals greater relative muscle force •Full-wave rectification - converts raw signal to positive voltages, results in the absolute value of the EMG; may be smoothed to flatten the peaks and valleys

nervous system adaptation in strength training

-Increased area of activity in the cerebral cortex during a motor task -Increased supraspinal motor drive -Increased motor neuron excitability -Greater discharge frequency of motor units -Decrease in neural inhibition at the spinal and supraspinal level •Supported by increases in strength through mental imagery and increases in strength of non-exercised muscles on the contralateral side

•Area Moment of Inertia (AMI)

-Resistance to stress from bending loads •AMI = (B*H^3)/12 •The greater the height, the greater resistance to bending

Effects of Rigid Fixation of hardware

-Stress concentration -Stress shielding •Hardware -Generally left in place by surgeons -If hardware is removed: •Bone is weaker until defect is filled in by new bone •Need to modify intensity, duration, and frequency of loading until bone completely fills in

2 primary functions of inter-vertebral discs

1) increase spine ROM 2) transmits loads (compressive forces) They also enhance movement. only translatory movement would be possible without them

Structural proteins function

1)Generate passive tension when stretched 2)Provide internal and external support and alignment of the muscle fiber 3)Help transfer active forces throughout the parent muscle

inter-vertebral discs size

20 - 30 % length of vertebral column is made up of IVDs Actual height is the smallest in the thoracic region because it has a smaller ROM Height is tallest in the lumbar region because stability and force displacement intermediate height in the cervical reagion for the weight of the head and mobility IVD to vertebral body ratio is: lowest in the thoracic region highest in the cervical region intermediate in the lumbar region Ratio of IVD height to vertebral height Calculation: ratio = disc height divided by vertebral body height

motion of the vertebral column

3 degrees of freedom (DOF) The motion segment of the vertebra is the 2 adjacent vertebra + IVD + soft tissues that connects them.

How is vertebral motion described?

According to how the top vertebral body moves on the one below e.g., Right rotation of C3: Look at C3's movement on C4 "Face" of C3 rotates right and SP of C3 points left

Anisotropy

Anisotropy - different material properties in different directions

What occurs during lateral flexion (side bending)?

Arthrokinematics: Interbody joints: Sup.vertebra laterally tilts &glides toward the side of SB Facet joints: Inferior glide on ipsilateral side of the SB(concavity of spinal curve) Superior glide on contralateral side to the SB (convexity of spinal curve) L SB =Top vertebral body tilts and glides LEFT on the vertebra below LEFT facets glide inf.;RIGHT facets glide Coupling: During side bending (primary motion), slight rotation also occurs For cervical spine: side bending and rotation occur in the SAME direction. For the lumbar spine:side bending and rotation occur in OPPOSITE directions. Upper t-spine follows the c-spine; lower t- Left SB of C-spine=primarily left SB with light left rotation Intervertebral foramen: widens on the contralateral side of the SB narrows on the ipsilateral side of the SB Anulus fibrosus: stretched on the contralateral side of the SB compressed on the ipsilateral side of the SB

What limits/checks axial extension?

Bony impact Bulk of post ligaments as they bunch Small ratio of IVD height to vertebral body height Smaller disc to vertebral body height in T-spine andL-spine(compared to C-spine) = less extension ROM available in T-spine and L-spine Passive tension in anterior portion of relevant soft tissues: Anterior part of facet joint capsules Anterior fibers of annulus fibrosus ALL Anterior muscles

Packed positions

Close-packed position: position of maximal congruency Loose-packed positions: All positions other than a joint's close-packed position the ligaments and capsule are relatively slackened, allowing an increase in accessory movements

Concentric, eccentric, isometric

Concentric- The tension developed by the muscle is greater than resistance force Movement must occur eccentric- The tension developed by the muscle is less than resistance force. Movement must occur isometric- Muscle and resistance force equal each other NO movement occurs

Concave and convex joint relationship

Convex-on-concave surface movement, the convex member rolls and slides in opposite directions. Concave-on-convex surface movement, the concave member rolls and slides in similar directions.

surrounding tissues of muscle

Epimysium - surrounds entire surface of muscle belly Perimysium - beneath the epimysium; divides the muscle into fascicles; conduit for blood vessels and nerves Endomysium - surrounds individual muscle fibers; location of metabolic exchange between muscle fibers and capillaries •Extracellular connective tissues - collagen and elastin; non-contractile tissues that provide structural support and elasticity •Myofibrils - tiny strands that compose the muscle fiber; contain the contractile proteins of the muscle fiber; consists of many myofilaments

Physiologic cross-sectional area of muscle

Equals muscle volume ÷ muscle length •Assuming full activation, the max force potential of a muscle is proportional to the sum of the cross-sectional area of all its fibers •Thicker muscle generates greater force than thinner muscle of same morphology

The spine

Function: • Mobility • Stability • Houses nerves,spinal cord and vessels Vertebrae size increases from cervical through lumbar regions vertebral foraman size: cervical = large thoracic = small lumbar = medium the size is proportional to how much motion there is at the trunk at that level 33 vertevrae 7 cervical 12 thoracic 5 lumbar 5 sacral 4 coccygeal 23 intervertebral discs When a baby is born, ONE primary curve exists: kyphotic curve once matured, you have 2 kyphotic curves and 2 lordotic curves

Kinematics during axial rotation

Gapping of facets on ipsilateral side Compression (approximation) of facets on contralateral side§ Increased shear forces on vertebral body Coupled motions During rotation (primary motion), slight side bending also occurs Coupling patterns vary by region -For cervical spine: side bending and rotation occur in the SAME direction. -For the lumbar spine: side bending and rotation occur in OPPOSITE directions. -Upper t-spine follows the c-spine; lower t-spine follows l-spine

facet orientation of the spine

If superior and inferior facet surfaces of at least 3 adjacent vertebrae lie in a particular plane, motion within that plane is facilitated and motions in other planes are some what inhibited Cervical facets- about 45 degrees from frontal and horizontal planes = more ROM than thoracic and lumbar facets Thoracic facets - Frontal plane orientation = frontal plane motion facilitated Lumbar facets- sagittal plane orientation = sagittal plane motion facilitated

What limits motion in the axial spine?

In some regions: Regional variations e.g., ribs in T-spine and uncinate processes in C-spine In all regions (cervical, thoracic, and lumbar): Ligaments Capsules Muscles Other soft tissues Smaller disc to vertebral body height Fryette's 3rd Law Facet orientation

axial extension

Interbody joints sup. vertebral body tilts &glides posteriorly on inf. vertebral body Facet joints: inferior and posterior glide of bilateral facets This describes inf facets of top vertebra gliding on sup facets of vertebra below Other kinematics during axial extension IVD: Compressive forces increaseon posterior portion of anulus fibrosus Nucleus deforms in anterior direction Narrowing of intervertebral foramen SPs move closer together

Axial skeleton articulations

Interbody joints synarthrodial (cartilaginous) joints Vertebral bodies connected by cartilaginous material Facet joints Aka ,zygapophyseal or apophyseal joints 24 pairs plane synovial (diarthodial) joints Connected by joint capsules§ Lined with articular cartilage

Arthrokinematics during axial flexion

Interbody joints: sup. vertebral body tilts &glides anteriorly on inf.vertebral body Facet joints: superior and anterior glideof bilateral facets This describes inf facets oft op vertebra gliding on sup facets of vertebra below. Other kinematics duringaxial flexion IVD: Compressive forces increase on anterior part of anulus fibrosus Nucleus deforms posteriorly Intervertebral foramen opens SPs move farther apart

Fryette's Laws

Law 1 (pertains to Lumbar and Lower Thoracic Spines) SB from neutral position produces rotation to the opposite side Law 2 (pertains to Lumbar and Lower Thoracic Spines) SB from hyper-flexion or hyper-extension produces rotation to the same side Law 3 (pertains to Lumbar, Thoracic, & Cervical Spines) Introducing motion to a spinal joint in one plane automatically reduces its mobility in the other two planes.

Lever systems

Leverage describes the relative moment arm length possessed by a particular force. First class: axis of rotation positioned between the opposing forces. First-class levers may have an MA less than 1, equal to 1, or more than 1. Second class: axis of rotation is located at one end of a bone, AND the muscle (internal force), possesses greater leverage than the external force. Second-class levers always have an MA more than 1. Third class: axis of rotation is located at one end of a bone, AND the external force, possesses greater leverage than the muscle or internal force. Third-class levers always have an MA less than 1. Most muscle and joint systems in the body function with a mechanical advantage of less than one (third-class) 3rd class requires more muscle force, but increases relative speed of the distal portion of the limb A short 3rd class contraction distance of the muscle equates to large movement distances of the segment Greater 3rd class speed development can generate large contact forces with environment

Types of motion

Linear: Rectilinear: system moves in a straight line Curvilinear: system moves in a curved line Measured in linear units (meters, feet) Rotary: a point of a system is restricted or secured, which causes the system to rotate around the point Axis of rotation: point of restriction Angular motion: resultant motion of system Measured in angular units (degrees, radians) general motion or combination - linear and angular combined - most human movement (walking, football kicked end over end)

Muscles

Muscles or external force causes one bone to move at a joint Muscles shorten, elongate, or stay the same length while under tension or relaxation grater than 600 muscles Muscle activation (via motor neuron) causes the muscle to develop tension... The tension then acts upon BOTH attachments (origin and insertion) If the tension developed by the muscle is greater or lesser than resistance, movement occurs, if they equal each other then NO movement occurs (although the muscle is developing tension)

Nucleus pulposus vs Annulus fibrosus

Nucleus pulposus: Slightly more H2O type 2 collagen predominates Good at resisting compression Annulus Fibrosus Slightly less H2O Type 1 collagen predominates Good at resisting tension from all directions

Rate coding in muscle activation

Rate coding: •After a specific motor neuron has been recruited, the force produced by the muscle fibers is strongly modulated by the rate of production of sequential action potentials •A motor unit will discharge at ̴10 Hz when first recruited and may increase to 50Hz during a high force contraction •A muscle fiber twitch lasts much longer than the action potential stimulus, making it possible for a number of subsequent action potentials to begin during the initial twitch •If the muscle fiber relaxes completely before the subsequent action potential, the force of the 2nd fiber twitch will be equivalent to that of the 1st twitch •If the subsequent action potential arrives before the initial twitch has relaxed, the muscle twitches summate and generate a greater peak force

recruitment in in muscles activation

Recruitment: •Refers to the initial activation of specific motor neurons that excite and activate their associated muscle fibers •Action potential - electrical signal propagated down the axon of the alpha motor neuron to the motor endplate at the neuromuscular junction •Activation of the muscle fiber causes a contraction /twitch and a small amount of force is generated •More motor neurons recruited → more muscle fibers activated → more force generated within the muscle •Smaller motor neurons are generally recruited before larger motor neurons •Slow-twitch fibers - innervated by small motor neurons; twitch response is small in amplitude and long duration; fatigue resistant •Fast-twitch fibers - innervated by larger motor neurons; twitch response is high amplitude and brief duration; easily fatigued

Arthrokinematics

Roll- Multiple points along one rotating articular surface contact multiple poits on anther articular surface ( a tire rotating across the ground) Slide- a single point on one articular surface contacts multiple points on another articular surface ( a stationary tire skidding on icy ground) Spin- a single point on one articular surface rotates on a single point on another articular surface (a rotating toy top on one spot on the floor)

bones

Serve as attachments for muscles, levers 206 bones in the body Types: long, short, flat, irregular, sesamoid

What occurs to limit/check axial flexion?

Small ratio of IVD height to vertebral body height Smaller disc to vertebral body height in T-spine and L-spine(compared to C-spine) = less extension ROM available in T-spine and L-spine Passive tension in posterior portion of relevant softtissues: Supraspinous & Interspinous ligaments Facet joint capsules Lig. Flavum PLL Posterior annulus fibrosus Extensor muscles More ligaments limit flexion than extension. Only one ligament limits axial extension: ALL Likely reason the ALL is so strong compared to posterior ligaments.

types of motion in joints

Synarthroidial: immovable, found in sutures Amphiarthrodial: slightly movable Types Syndesmosis: held together by strong ligaments (coraclavicular and inferior tibiofibular joint) Synchrondrosis: separated by fibrocartilage (symphysis pubis and costochondral joints of the ribs) Diarthrodial: freely movable, synovial joints that have a joint capsule lined with synovial membrane Types: Arthrodial: gliding, carpals & tarsometatarsal joints Condyloidal: bi-axial ball and socket permits movement in 2 planes, radius and proximal row of carpals Enarthroidial: multiaxial ball and socket, movement in multiple planes, shoulder and hip Ginglymus: hinge, movement in one plane, elbow, knee Sellar: saddle, ball and socket type movement without rotation, 1st CMC joint Trochoidal: pivot, rotational movement around a long axis, rotation of the radius

inter-vertebral discs and the law of reaction

Under compressive loading: Nucleus pulposus attempts to expand <--> annulus pushes back

What limits lateral flexion (SB)throughout the axial skeleton?

What limits lateral flexion (SB)throughout the axial skeleton? Smaller ratio of IVD height tovertebral body height Passive tension in elementson convex side of the curve: Annulus fibers Intertransverse ligaments Joint capsule Muscles

Statics

factors affecting non-moving systems

Dynamics

factors affecting systems in motion

Hypertrophy

increased protein synthesis within the muscle fibers leads to an increase in the physiologic cross-sectional area of the whole muscle; usually greatest in fast twitch fibers

Transversely orthotropic

material properties are nearly the same in all directions within transverse plane

How do we get lordotic curves?

physical stress theory Changes in physical stress =adaptive responses 1. Decreased stress tolerance 2. Maintenance 3. Increased stress tolerance 4. Injury 5. Death

Force transmission path for a vertebra

posterior elements ---> laminae----> pedicles---> vertebral body Bending & pulling forces from internal & external forces & torques

Callus fracture healing

precursor to calcified bone, appears about 2 weeks post fx •Callus bone is more flexible and isotropic than lamellar bone •^'s AMI and PMI

sagittal, frontal, transverse

sagittal plane movement occurs around the frontal axis Sagittal Plane Movements flexion extension hyperextension dorsiflexion plantar flexion - point toes frontal plane movement occurs around the sagittal axis Frontal Plane Movements abduction adduction lateral flexion elevation depression radial deviation - toward thumb ulnar deviation - toward pinkie eversion - outward rotation of sole inversion - inward rotation transverse plane movement occurs around the long axis Transverse Plane Movements medial rotation - toward midline lateral rotation supination - outward rotation of the forearm (anatomical) pronation - inward rotation horizontal flexion or horizontal adduction horizontal extension or horizontal abduction

System definition

something under movement study...a joint, body segment, or the entire body...must be defined relative to discussion

Kinetics

study of forces acting on a body that influence its movement

Kinematics

study of time and space factors of motion of a system

Kinesiology definition

the study of human movement Historically, the terms kinesiology and "biomechanics" have been interchangeable. Biomechanics is based on the application of Newtonian principles of physics to the system of levers comprising the structure of the human body.

Unfused tetanus and fused tetanus

unfused tetanus - a series of summated mechanical twitches caused by a set of repeating action potentials that each activates the muscle fiber before relaxation of the previous twitch Fused tetanus (tetanization) - •occurs as a result of unfused tetanus generating greater force until the successive peaks and valleys of mechanical twitches fuse into a single stable level of muscle force. •Fused tetanus represents the greatest force level possible for a single muscle fiber

Polar Moment of Inertia (J)

used to predict an object's ability to resist torsion, in objects (or segments of objects) with an invariant circular cross-section and no significant warping or out-of-plane deformation •Resistance to stress from torsional loading •J = (r04-r14)/2 •The greater the radius, the greater resistance to torsional loading

Senile sarcopenia

•- loss in muscle tissue with advanced age; primary cause of reduced strength in healthy aged persons; cause is not fully understood, but may be associated with normal biologic process of aging, or changes in physical activity, nutrition, and hormone levels -reduction in the number of muscle fibers -atrophy of all existing fibers •Reduced ability of the nervous system to maximally activate the available muscle fibers also plays a role in strength and power loss •Fortunately, age itself does not drastically alter the plasticity of the neuromuscular system -Resistive exercise can help maintain the critical level of muscle force and power required for ADL's

Effects of Temperature on tendons and ligaments

•37-40°C (thermal transition) -Increase in stress relaxation -Increases the rate of creep -Reduced rupture load and strain (Must exercise CAUTION!)

Force-Velocity Relationship

•A force-velocity curve expresses the relationship between the velocity of a muscle's change in length and its max force output •Reflects the fact that muscles produce greater force with eccentric activation Concentric contraction: •During max-effort activation, the amount of force produced is inversely proportional to the velocity of muscle shortening •Due to the limited speed of attachment and re-attachment of the crossbridges •In an isometric state (zero velocity), a maximum number of attached crossbridges exists within the sarcomere, i.e. - a muscle produces greater force isometrically than at any speed of shortening Eccentric contraction: •During max-effort activation, the amount of force produced is directly proportional to the velocity of muscle lengthening •Difficult for most to maximally activate muscles eccentrically, especially at high velocities •Possible protective mechanism against muscle damage produced by excessively large forces Power and work: •Power - the rate of work; expressed as a product of force and contraction velocity •Positive work - concentric contraction against a load •Negative work - eccentric activation against an overbearing load

Changes in Muscle with Advanced Age

•Aged persons typically show greater losses in power than in peak force •After age 60, healthy persons experience a decline in peak strength of ̴10% per decade, which is more pronounced in the LE muscles •A sedentary lifestyle or underlying pathology can accelerate strength declines

Fatigue and EMG

•Amplitude of the signal increases throughout the repeated sub-max efforts •The increased signal reflects the recruitment of additional larger motor units as the other fatigued units cease or reduce their discharge rates

Composition of Articular Cartilage

•Aneural and avascular •70-85% weight is H20 •15-30% Solid matrix -Type II collagen -Ground substance -Chondrocytes < 2%

Joint Lubrication Methods of articular cartilage

•Boundary Lubrication (low loads) - molecule complex layer on each articulating surface •Fluid film lubrication (high loads) - larger volume of synovial fluid trapped between articular surfaces

Mechanical Behavior of articular cartilage

•Constant low level loading ▪Fluid continually displaced throughout articular sponge and into joint space •Higher speeds of loading -stiffer and less hysteresis ▪Stiffness may lead to OA ▪Lack of recovery of creep prior to loading

Bone Structure

•Cortical (compact) ▪< 30% volume non-mineralized tissue ▪2% strain at failure •Trabecular (spongy/cancellous) ▪> 30% volume non-mineralize tissue ▪7% strain at failure •Composition ▪60-70% Minerals: calcium carbonate, calcium phosphate ▪22-35% Protein: collagen ▪5-8% Water

Structure of Ligaments and Tendons

•Dense regular connective tissue •Fiber bundles arranged in parallel fashion Composition ▪Cellular (fibroblast) - make up 20% ▪Extracellular matrix - other 80% •Proteoglycan and elastin •Type I collagen fibers

Muscle Morphology

•Describes the basic shape of a whole muscle •Two most common shapes are: ▪Fusiform muscles - fibers run parallel to one another and to the central tendon, e.g. - biceps brachii ▪Pennate muscles - fibers approach their central tendon obliquely; contain a larger number of fibers and generate relatively large forces; classified as unipennate, bipennate, or multipennate

Function of Articular Cartilage

•Distributes and disperses compressive forces to the subchondral bone •Reduces friction between joint surfaces, low coefficient of friction (μ: 0.005-0.02) ▪5-20x more slippery than ice on ice •Forces of normal weight-bearing activities reduced to a load level that can be absorbed without damaging the skeletal system •Contact pressure = Contact force/contact area •Absence of perichondrium eliminates a ready source of primitive fibroblasts used for repair, significant damage to adult cartilage is often repaired poorly or not at all

Mechanical Behavior of Ligaments and Tendons

•Effect of rate of force application •Effects of temperature •Effects of maturation and aging •Effect of hormones •Immobilization and re-mobilization

Stress-Strain Curve

•Elastic region - the initial nonlinear and subsequent linear regions of the curve •Toe region - nonlinear region; collagen fibers within the tissue are initially crimped and must be drawn taught before significant tension is measured •Stiffness - ratio of the stress (Y) caused by an applied strain (X), also referred to as Young's modulus •Plastic region - microscopic failure has occurred and the tissue remains permanently deformed •Yield point - point reached when a tissue has been elongated beyond its physiologic range; increased strain results in only marginal increased stress •Ultimate failure point - point when the tissue partially or completely separates and loses its ability to hold any tension -8%-13% beyond pre-stretched length for most healthy tendons

Material Properties

•Elasticity - material returns to original size after removal of load, linear relationship between load and deformation (loading and unloading) e.g. rubber band •Viscosity - does not deform instantaneously from applied load, strain is delayed, depends upon rate of loading •Viscoelasticity - typically deforms slowly in nonlinear fashion •Plasticity - material retains its change in size and shape when load is removed •Creep - progressive strain of a material when exposed to a constant load over time (e.g. dynasplint); reversible

Electrode in Electromyography

•Electrodes measure the sum of the change in voltage associated with all action potentials involved in the activation of muscle fibers •Surface electrodes - placed on the skin overlying the muscle; easy to apply, noninvasive, and can detect signals from a relatively large area -Arrangement: 2 electrodes over the muscle belly; 1 ground electrode over a bony area; placed in parallel with the long axis of the muscle fibers •Fine wire electrodes - inserted directly into the muscle belly; monitors a more specific region of a muscle; allows for monitoring of deeper muscles not accessible by surface electrodes; can discriminate single action potentials produced by one or a few motor units •Strategies to minimize noise: bipolar and ground electrode configuration (previous slide), adequate skin prep, proper electrical shielding of recording equipment, and pre-amplification of signals at the electrode site

Mechanical Fatigue(Fatigue Fracture)

•Failure of material as a result of cyclic loading -High loading, fewer number of cycles -Low loading, greater number of cycles •Endurance limit - load at which infinite # of cycles may occur without failure •Example - stress fracture

Active length-tension curve

•Force generated actively in response to stimulation from the nervous system •Sliding filament hypothesis - active force is generated as actin filaments slide past myosin filaments, causing approximation of the Z-discs and narrowing of the H-band; produces a shortening of each sarcomere

Osteoporosis

•From ages 35-92, bone strength changes ▪Young's modulus decreases 2.3% per decade. ▪Fracture toughness decreases 4% per decade ▪Bending strength decreases 4% per decade •Walking and impact aerobic activities help stimulate increase bone formation in the lumbar spine and hip.

Changes in Muscle with Strength Training

•In the context of this chapter, strength refers to the maximal force or power produced by a muscle or muscle group during a max voluntary effort •Repeated sessions of activating a muscle with progressively greater resistance will result in increased strength and hypertrophy •1 RM - one repetition max; max load that can be lifted once as a muscle contracts through the joint's full ROM; commonly used to quantify strength gains •Increases in strength are specific to the type and intensity of the exercise program -High-resistance eccentric and concentric training, 3x week for 12 weeks = ↑ 1 RM by 30-40%

Effects of Rate of Force Application on ligaments and tendons

•Increase in force application leads to increases in stiffness and ultimate loads (ligament failure more likely by rupture, mid-substance) •Avulsion fractures (failure) seen at lower speeds

Isometric Muscle Force

•Max isometric force of a muscle is often used as a general indicator of a muscle's peak strength •Indicator of neuromuscular recovery after injury •Internal torque generation can be measured isometrically at several joint angles •The internal torque produced isometrically by a muscle group can be determined by performing a max-effort contraction against a known external torque (dynamometer) •With encouragement, most healthy adults can achieve near-max activation in a max-strength test •The magnitude of isometric torque differs considerably based on the angle of the joint •Clinical measurements of isometric torque should include the joint angle so future comparisons are valid

Fibrocartilage

•Mixture of dense connective tissue and articular cartilage •Combines the resilience and shock of absorption of articular cartilage with the tensile strength of ligaments and tendons •Support and stabilize the joints, guide arthrokinematics, and help dissipate forces •Composed of dense bundles of type I collagen, proteoglycans, and varying amounts of chondrocytes and fibroblasts within a dense and multi-directional collagen network •Found in intervertebral disks, labra, pubic symphisis, and the menisci of the knee •The dense interwoven collagen fibers allow the tissue to resist multidirectional tensile, shear, and compressive forces •Mostly aneural •Direct blood supply to the outer rim only •Diffusion of nutrients assisted by intermittent weight bearing ▪Insufficient nourishment to intervertebral disks when spine is held in fixed posture for extended periods

muscle activation

•Muscle is excited by impulses from alpha motor neurons •Motor unit - an alpha motor neuron and the muscle fibers it innervates •Recruitment and rate coding are the primary methods of activating motor units

Remodeling of bone

•Of the tissues involved with joints, bone has the greatest capacity for remodeling, repair, and regeneration •Bone remodels constantly according to applied loads

Muscle Architecture

•Physiologic cross-sectional area and pennation angle significantly affect the amount of force transmitted through the muscle and its tendon ▪Physiologic cross-sectional area - reflects the amount of active proteins available to generate a contraction force; expressed in cm2 ▪Pennation angle - angle of orientation between the muscle fibers and the tendon

pennation muscle angle

•Ranges from 0-30° in humans •If muscle fibers attach parallel to the tendon, pennation angle =0° •Orienting fibers obliquely to the central tendon allows for more fibers in a given length of muscle

Possible Muscular Mechanisms Contributing to Fatigue

•Reduced excitability at the neuromuscular junction •Reduced excitability at the sarcolemma •Changes in excitation-contraction coupling because of reduced sensitivity and availability of intracellular calcium •Changes in contractile mechanics, including a slowing of crossbridge cycling •Reduced energy source (metabolic) •Reduced blood flow and oxygen supply

Possible neural mechanisms of fatigue

•Reduced excitatory input to supraspinal centers •Net decline in excitatory input to alpha motor neurons Persons with nervous system disease, such as MS, may experience even greater muscle fatigue due to delays or blocks in the conduction of central neural impulses

Effects of Hormones and other factors on tendons and ligaments

•Relaxin -Pregnancy •Estrogen ACL injuries •Corticosteriods -May lead to tendon rupture •Vascularity -Generally poor blood supply (tendons) -"watershed" areas (rotator cuff humeral insertion, Achilles tendon)

Passive length tension curve

•Series elastic components - tissues that lie in series with the active proteins, e.g. - tendon and large structural proteins (titin) •Parallel elastic components - tissues that surround or lie in parallel with the active proteins, e.g.- perimysium •Passive tension - occurs when a whole muscle is stretched by extending the joint; both series and parallel elastic components are elongated, generating a spring-like resistance in the muscle

stress-strain relationship

•Stress - the internal resistance generated as the ligament resists deformation, divided by its cross-sectional area (N/mm2) •Strain - percent increase in a tissue's stretched length relative to its original length

Wolff's Law (1892)

•The form of a bone being given, the bone elements place or displace themselves in the direction of functional forces and increase or decrease their mass to reflect the amount of the functional forces. i.e. - bone is laid down in areas of high stress and reabsorbed in areas of low stress •Trabecular lines - "Form follows function"

Changes in Muscle with Reduced Use

•Trauma or illness resulting in immobilization or bed rest can lead to atrophy and marked reductions in strength •Strength loss of up to 3%-6% per day can occur within the first week alone •Healthy persons can see a decrease of up to 40% of 1 RM in only 10 days •Reduced strength after immobilization is usually 2x that of the muscle atrophy •Protein synthesis is reduced more notably in slow twitch fibers than fast twitch fibers -Subject to greater relative disuse because they are the primary fibers used in ADL's •Loss of strength is greatest when muscle is maintained in its shortened position •Anti-gravity and single-joint muscles show more rapid atrophy -soleus, vastus medialis, vastus intermedius, and multifidus •Knee extensors generally affected more than knee flexors •Strengthening programs that incorporate eccentric activation have shown the greatest gains in strength and increases fiber size •Low-intensity, long-duration muscle activations early in the exercise program help target the fibers associated with smaller motor units

Effects of Aging and Maturation on tendons and ligaments

•Young and old - lower maximal tensile loads •Ligament and tendon's ability to withstand tensile loads decreases with age •Mode of failure -Avulsion fractures in skeletally immature -Midsubstance ligament failure in skeletally mature

Muscle fatigue

•exercise induced decline in max voluntary muscle force or power, despite max effort •Excessive or chronic muscle fatigue is not normal and is often a symptom of an underlying neuromuscular disorder •Can be subtle and is not always noticeable to the observer •In contrast to sub-max effort, sustained max effort contraction results in a much more rapid rate of decline in max force -EMG amplitude declines as muscle force declines •Magnitude or rate of muscle fatigue is specific to the performance of the task and the duration of the rest-work cycle -High intensity, short duration: recovers quickly -Low intensity, long duration: longer recovery time •Type of activation also influences fatigue -Repeated eccentric activation will result in less fatigue than repeated concentric activation with the same velocity and external load - Use caution when employing eccentric activation as a primary rehabilitative tool! -DOMS from repeated eccentric activation is typically more severe than that experienced from repeated concentric or isometric activation

axis of rotaion

•sagittal axis or AP axis - parallel to sagittal plane/transverse plane perpendicular (90°) to frontal plane movements of abduction, adduction, and lateral flexion •frontal axis or mediolateral axis - parallel to frontal plane and transverse plane but perpendicular to sagittal plane movements of flexion, extension, and hyperextension •longitudinal axis or vertical axis - parallel to frontal and sagittal planes perpendicular to transverse plane movements of rotation

Structural Organization of muscles

•sarcomere: fundamental unit; shortening of each sarcomere generates shortening of the fiber; ultimate force generator within the muscle actin and myosin: within the sarcomere; interact to shorten the muscle fiber and generate an active force •Non-contractile protein - often referred to as "structural proteins"; titin and desmin; constitute much of the cytoskeleton within and between the muscle fibers

Bone Cells

▪Osteoblast - forms bone tissue ▪Osteoclast - resorbs bone tissue ▪Osteocyte - mature osteoblast