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

Muscle Model Whole Muscle CC SEC PEC 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

Viscoelastic Structures Tissue Viscoelastic Structures 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.

Stretch-Shortening Cycle Whole Muscle 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 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”

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

Sarcomere Organization Tissue 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)

3 sarcomeres in parallel Sarcomere organization example: Note that the values are not representative of actual sarcomeres. 1 sarcomere 3 sarcomeres in series 3 sarcomeres in parallel Force 1 N 3 N ROM 1 cm 3 cm Time 1 sec Velocity 1 cm/sec 3 cm/sec

Sarcomere Organization 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 sarcomeres in series sarcomeres in parallel

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

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

Fusiform vs. Pennate Tissue fusiform pennate 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

Fiber Types Tissue 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

Tissue Fiber Type Comparison

Active Length-Tension Tissue Active Length-Tension l0 - neither contracted nor stretched Length Tension l0

Length-Tension Tissue l0 l0 - neither contracted nor stretched physiological limit combined T passive active l0 L

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

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

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

Muscle Terms Whole Muscle 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 defining origin or insertion relative to action of bone is difficult e.g. hip flexors in leg raise v. sit-up

Functions of Muscle Whole 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

Functional Muscle Groups 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

Role of the Muscle Whole 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 SHOULDER ABDUCTION 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

Muscular Action Whole Muscle isometric action concentric 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

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

Elbow Actions Whole Muscle push-up catching a baseball 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

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

Number of Joints Crossed 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

Multiarticular Muscles 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

Insufficiency Whole Muscle 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

Insufficiency Example 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?

Movement/Activity Properties of Muscle Whole Muscle 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

Movement/Activity Properties of Muscle (cont.) 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

Muscular Strength Whole Muscle 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

Strength Gains Whole Muscle Magnitude of strength gains dependent on 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 from an “untrained state” 1st 12 weeks see improvement on the neural side via improved innervation later see increase in x-sectional area

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

Whole Muscle Muscle Injury Individuals at risk a) fatigued state b) not warmed-up c) new exercise/task d) compensation 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

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

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

What Causes Motion? Force or Torque? 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 (Fm) muscle torque (Tm) distance between pt of application and joint axis (dm)

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

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

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

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

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

Calculation of Muscle Torque Whole Muscle Calculation of Muscle Torque Fm Fm 60 o 400 N 60 o 0.03 m 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

Factors Affecting Torque 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) q - this changes throughout the ROM

Additional Factors Affecting Torque 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