internal motors of human body responsible for all movements of skeletal system only have the ability to pull must cross a joint to create motion can shorten up to 70% of resting length Muscle

Muscle-Tendon Model 3 components SEC series elastic component CC contractile component PEC parallel elastic component

Muscle Model Whole Muscle Contractile Component (CC) –active shortening of muscle through actin-myosin structures Parallel Elastic Component (PEC) –parallel to the contractile element of the muscle –the connective tissue network residing in the perimysium, epimysium and other connective tissues which surround the muscle fibers Series Elastic Component (SEC) –in series with the contractile component –resides in the cross-bridges between the actin and myosin filaments and the tendons PEC CC SEC

Tissue SEC CC PEC Both SEC & PEC behave like springs when acting quickly but they also have viscous nature If muscle is statically stretched it will progressively stretch over time and will slowly return to resting length when the stretching force is removed. Viscoelastic Structures

Stretch-Shortening Cycle a quick stretch followed by concentric action in the muscle Store energy in elastic structures Recover energy during concentric phase to produce more force than concentric muscle action alone examples –vertical jump: counter-movement vs. no counter-movement –plyometrics Whole Muscle SEC CC PEC

Tissue Properties of Muscle irritability - responds to stimulation by a chemical neurotransmitter (ACh) contractibility - ability to shorten (50-70%), usually limited by joint range of motion distensiblity - ability to stretch or lengthen, corresponds to stretching of the perimysium, epimysium and fascia elasticity - ability to return to normal state (after lengthening) Tissue

Muscle Structure “Bundle-within-a-Bundle” Tissue

Sliding Filament Theory 1) Myosin filaments form a cross-bridge to actin 2) Myosin pulls actin 3) x-bridge releases 4) Myosin ready for another x-bridge formation actin myosin Tissue

Dendrite Soma (body) Axon receives and integrates information Motor Neurons transmits information

Motor Unit A motor unit is composed of a motor neuron and all of the muscle fibers it innervates It is the smallest functional unit of muscular shortening

Motor Unit (cont) each muscle has many motor units (m.u.) # of fibers in a m.u. is dependent on the precision of movement required of that muscle (average: fibers per m.u.) –more precision is obtained with more neurons –100 to 2000 motor neurons per muscle # of m.u.’s in a muscle decreases in the elderly

Precision of 2 Muscles 1st muscle2nd muscle10,000 fibers 100 motor neurons200 motor neurons 100 motor units200 motor units 100 fibers/mu50 fibers/mu less precisionmore precision

MuscleNumber of Muscle Fibers Number of MU’s Mean Number of Fibers Per MU Platysma27,1001,10025 Brachioradialias>129,200330>410 FirstLumbrical10, Tibialias Anterior 250, Gastrocnemius (medial head) 1,120, ,000

Neuromuscular Control a motor nerve action potential stimulates the release of acetylcholine (ACh) from the nerve ending ACh binds to the muscle fiber which causes depolarization and results in the release of calcium ions from the sarcoplasmic reticulum (5 ms) the calcium ions permit the actin-myosin interaction, which produces force the contraction stops when the calcium ions are removed by a pumping action (100 ms) Monitor this action potential using Electromyography

Control of Tension excitation of each motor unit is an all-or- nothing event increased tension can be accomplished by: –increasing the # of stimulated motor units (recruitment) –increasing the stimulation rate of the active motor units (rate coding)

Stimulation vs Activation Voltage threshold ALLNOTHING

Recruitment each motor unit has a stimulation threshold at which it will begin to produce force small motor units have a lower threshold than large motor unit, therefore they are recruited first (size principle)

Rate Coding summation (B) - the overall effect of added stimuli tetanus (C) - sustained maximal tension due to high frequency stimulation

Fiber Types all fibers within a motor unit are of the same type within a muscle there is a mixture of fiber types fiber type may change with training recruitment is ordered –type I recruited 1st (lowest threshold) –type IIa recruited second –type IIb recruited last (highest threshold) Tissue

Fiber Type Comparison Tissue

Fiber Types MuscleFiber Type (%SO, %FOG, %FG) vastus medialis50, 15, 35 erector spinae58, -,42 soleus80, -, 20 orbicularis oculi15, -, 85 From: Multiple Muscle Systems, Winters and Woo

Sarcomere Organization the number of sarcomeres in series or in parallel will help determine the properties of a muscle 3 sarcomeres in series (high velocity/ROM orientation) 3 sarcomeres in parallel (high force orientation) Tissue

1 sarcomere 3 sarcomeres in series 3 sarcomeres in parallel Force1 N 3 N ROM1 cm3 cm1 cm Time1 sec Velocity1 cm/sec3 cm/sec1 cm/sec Sarcomere organization example: Note that the values are not representative of actual sarcomeres.

the longer the tendon-to-tendon length the greater number of sarcomeres in series the greater the physiological cross-sectional area (PCSA) the greater number of sarcomeres in parallel Sarcomere Organization sarcomeres in seriessarcomeres in parallel

Muscle Structure Fusiform (parallel) fibers run longitudinally generally fibers do not extend the entire length of muscle

tendon runs parallel to the long axis of the muscle, fibers run diagonally to axis (short fibers) Muscle Structure Pennate Tissue

Pennation Angles MusclePennation Angle (deg) gastrocnemius10-25 soleus15-30 tibialis anterior5-10 biceps femoris0 From: Multiple Muscle Systems, Winters and Woo

Fusiform vs. Pennate fusiform –advantage: sarcomeres are in series so maximal velocity and ROM are increased –disadvantage: relatively low # of parallel sarcomeres so the force capability is low pennate –advantage: increase # of sarcomeres in parallel, so increased PCSA and increased force capability –disadvantage: decreased ROM and velocity of shortening Tissue

Muscle Attachment - Tendons Fusion b/w epimysium and periosteum Tendon fused with fascia Whole Muscle

Muscle Terms attachment can be directly to the bone or indirectly via a tendon or aponeurosis Origin -- generally proximal, fleshy attachment to the stationary bone Insertion -- generally distal, tendinous and attached to mobile bone Whole Muscle defining origin or insertion relative to action of bone is difficult e.g. hip flexors in leg raise v. sit-up

Functions of Muscle produce movement - when the muscle is stimulated it shortens and results in movement of the bones maintain postures and positions - prevents motion when posture needs to be maintained stabilize joints - muscles crossing a joint can pull the bones toward each other and contribute to the stability of the joint Whole Muscle

Functional Muscle Groups generally have more than 1 muscle causing same motion at a joint together these muscles are referred to as a functional group e.g. elbow flexors -- biceps brachii, brachialis, and brachioradialis - all flex elbow Whole Muscle

Role of the Muscle prime mover - the muscles primarily responsible for the movement assistant mover - muscles used only when more force is required agonist - muscles responsible for the movement antagonist - performs movement opposite of agonist stabilizer - active in one segment to stabilize a bone so that a movement in an adjacent segment can occur neutralizer - active to eliminate an undesired joint action of another muscle Whole Muscle

agonist: deltoid antagonist: latissimus dorsi stabilizer: trapezius holds the shoulder girdle in place so the deltoid can pull the humerus up neutralizer: teres minor if latissimus dorsi is active then the shoulder will tend to internally rotate, so the teres minor can be used to counteract this via its ability to externally rotate the shoulder SHOULDER ABDUCTION Whole Muscle

Muscular Action isometric action –no change in fiber length concentric action –shortening of fibers to cause movement at a jt eccentric action –lengthening of fibers to control or resist a movement Whole Muscle

Whole Muscle

eccentric concentric Eccentric action: work with gravity to lower the body or objects slow down body segments or objects Concentric action: work against gravity to raise the body or objects speed up body segments or objects Whole Muscle

push-up  up - concentric action of elbow extensors  down - eccentric action of elbow extensors catching a baseball  eccentric action of elbow extensors throwing a baseball  concentric action of elbow extensors pull-up  up - concentric action of elbow flexors  down - eccentric action of elbow flexors Elbow Actions Whole Muscle

The countermovement elicits an increase in force production the increase in force production is 30% neural and 70% elastic contribution Greatest return of energy is achieved using a “drop- stop-pop” action with only an 8”-12” drop Whole Muscle

Number of Joints Crossed uniarticular or monoarticular - the muscle crosses 1 joint, so it affects motion at only 1 joint biarticular or multiarticular - the muscle crosses 2 (bi) or more (multi) joints, so it can produce motion across multiple joints Whole Muscle

Multiarticular Muscles can reduce the contraction velocity can transfer energy between segments can reduce the work required of single-joint muscles more susceptible to injury Whole Muscle

Insufficiency a disadvantage of 2-joint muscles –active insufficiency - cannot actively shorten to produce full ROM at both joints simultaneously –passive insufficiency - cannot be stretched to allow full ROM at both joints simultaneously Whole Muscle

Insufficiency Example squeeze the index finger of another student move the wrist from extreme hyperextension to full flexion What happens to the grip strength throughout the ROM? WHY? Whole Muscle

Active Length-Tension l0l0 - neither contracted nor stretched Length TensionTension l0l0 Tissue

Length-Tension L T l0l0 passive l0l0 - neither contracted nor stretched physiological limit active combined Tissue

velocity of contraction Force - Velocity Relationship v < 0 (eccentric) v > 0 (concentric) v=0 (isometric) force Tissue

v F Power (F*v) 30% v max Power - Velocity Relationship Tissue

Electromechanical Delay electromechanical delay - stimulation begins before force is developed –it is thought that this is the time necessary to “take up the slack in the SEC”

Movement/Activity Properties of Muscle flexibility - the state of muscle’s length which restricts or allows freedom of joint movement endurance - the ability of muscles to exert force repeatedly or constantly Whole Muscle

Movement/Activity Properties of Muscle (cont.) strength - the maximum force that can be achieved by muscular tension power - the rate at which physical work is done or the force created by a muscle multiplied by its contraction velocity Whole Muscle

Muscular Strength measure absolute force in a single muscle preparation in real life most common estimate of muscle strength is maximum torque generated by a given muscle group Whole Muscle

Strength Gains from an “untrained state” 1st 12 weeks see improvement on the neural side via improved innervation later see increase in x-sectional area Training focuses on developing larger x-sectional area AND developing more tension per unit of x-sectional area Magnitude of strength gains dependent on 1) genetic predisposition 2) training specificity 3) intensity 4) rest 5) volume Whole Muscle

Training Modalities Isometric Exercise Isotonic Exercise Isokinetic Exercise Close-Linked Exercises Variable Resistance Exercise Whole Muscle

Muscle Injury Greatest Risk a) 2-joint muscles b) muscles that limit ROM c) muscles used eccentrically Soreness v. Damage damage believed to be in fiber soreness due to connective tissue Individuals at risk a) fatigued state b) not warmed-up c) new exercise/task d) compensation Whole Muscle

Muscular Force Components rotary component –causes motion –perpendicular to the rotating segment stabilizing or dislocating component –parallel to rotating segment –stabilizing is toward joint –dislocating is away from joint Whole Muscle

Muscular Force Components components depend on the joint angle small rotary large stabilizing large rotary small stabilizing medium rotary medium dislocating Whole Muscle

What Causes Motion? Force or Torque? angular motion occurs at a joint so technically torque causes motion torque is developed because the point of application of the force produced by muscle is some distance away from the joint’s axis of rotation muscle force (F m ) distance between pt of application and joint axis (d m ) muscle torque (T m ) Whole Muscle

Calculation of Muscle Torque 60 o 400 N 0.03 m T m = F m d * Torque = 400 N * 0.03 m becasue F m is not perpendicular to the forearm!!! To solve problem we must resolve the vector F m into components which are perpendicular (F m ) and parallel (F m ) to the forearm. FmFm FmFm FmFm Whole Muscle

Calculation of Muscle Torque FmFm FmFm FmFm FmFm FmFm FmFm Only the perpendicular component will create a torque about the elbow joint so only need to calculate this. Whole Muscle 400 N 0.03 m

400 N 0.03 m F R = 200 N T = 200 N * 0.03 m = 6 Nm F R = 345 N 400 N 0.03 m T = 345 N * 0.03 m = 10.4 Nm F R = 345 N Whole Muscle Angle of Pull Affects Torque

F R = 345 N 400 N 0.03 m T = 345 N * 0.03 m = 10.4 Nm F R = 345 N 600 N 0.03 m T = 520 N * 0.03 m = 15.6 Nm F R = 520 N Size of Muscle Force Affects Torque Whole Muscle

F R = 345 N 400 N 0.03 m T = 345 N * 0.03 m = 10.4 Nm F R = 345 N 400 N 0.1 m F R = 345 N T = 345 N * 0.1 m = 34.5 Nm Moment Arm Affects Torque Whole Muscle

Calculation of Muscle Torque 60 o 400 N 0.03 m FmFm FmFm FmFm FmFm FmFm FmFm 60 o NOTE: The torque created by the muscle depends on 1) the size of the muscle force 2) the angle at which the muscle pulls 3) the distance that the muscle attaches away from joint axis Whole Muscle

Factors Affecting Torque Changing any of these 3 factors will change the torque: 1) muscle force - changed by increased neural stimulation 2) d - can’t change voluntarily but use of other muscles in same functional muscle group gives a different d 3)  - this changes throughout the ROM Whole Muscle

Additional Factors Affecting Torque Muscle Force 1) level of stimulation 2) muscle fiber type 3) PCSA 4) velocity of shortening 5) muscle length Angle of pull Moment arm Whole Muscle