Unit I

Mass moment of Inertia T = I ω (rotational) •T = Torque •I m moment of Inertia, •ω = a acceleration

T = I ω (rotational) •T = Torque •I mass moment of Inertia, •ω = angular acceleration

Basics: Coordinate systems Axis of motion is P to the movement of the joint. Not all joints move p in a one axis Bone shapes provide different angles - not all a perfect b and s

Axis of motion is PERPENDICULAR to the movement of the joint. Not all joints move perfectly in a one axis Bone shapes provide different angles - not all a perfect ball and socket.

Davis et al. 2020

Gait Retraining as an Intervention for Patellofemoral Pain •Kinematic Gait Retraining in order to: -Increase PFJ contact area: (a) reducing hip adduction, -Reduce PFJ force: (b) transition from a rearfoot strike pattern to a forefoot strike pattern, and (c) adopting a more forward trunk lean • •Spatiotemporal retraining Reduce peak hip adduction, PFJ stress (force/area

Convex-Concave Rule If a concave surface moves on a convex surface, roll and slide are in the what direction. If a convex surface moves on a concave surface, roll and slide are in what direction

If a concave surface moves on a convex surface, roll and slide are in the same direction. If a convex surface moves on a concave surface, roll and slide are in opposite direction

Arthrokinematic Motions Roll: Multiple points of one a surface contacting multiple points on the o. (tire on road) Slide/Glide: S point on one articular surface contacts m points on another articular surface ( tire s) Spin: A s point on one articular surfaces rotates on a s point of the other articular surface (rotating top)

Roll: Multiple points of one articular surface contacting multiple points on the other. (tire on road) Slide/Glide: Single point on one articular surface contacts multiple points on another articular surface ( tire skidding) Spin: A single point on one articular surfaces rotates on a single point of the other articular surface (rotating top)

Vectors have both x and y components •A smaller angle has a greater what component and a smaller what component •A larger angle has a smaller what component and a larger what component •The angle of application of a force, or the angle of velocity and acceleration matters!

•A smaller angle has a greater x component and a smaller y component •A larger angle has a smaller x component and a larger y component •The angle of application of a force, or the angle of velocity and acceleration matters!

•Inertia: tendency of the body to resist change in v (linear) •Proportional to bm (Think F=ma). •Units are the same as mass (eg Kg, though is inertia is NOT a mass) -Moment of Inertia: quantity that indicates its r to a change in a velocity •Proportional to not only mass, but c of r(m*r2) •Think F=ma combined with T=Fd

•Inertia: tendency of the body to resist change in velocity (linear) •Proportional to body mass(Think F=ma). •Units are the same as mass (eg Kg, though is inertia is NOT a mass) -Moment of Inertia: quantity that indicates its resistance to a change in angular velocity •Proportional to not only mass, but distance to center of roation (m*r2) •Think F=ma combined with T=Fd

Internal and External Forces •Internal Forces -Produced by the b -F of the Muscle -J reaction force • • •External Forces -Produced by forces o the body -Force of G on the center of mass of the arm (Wa) -Force of the external w in the hand (Wm)

•Internal Forces -Produced by the body -Force of the Muscle -Joint reaction force • • •External Forces -Produced by forces outside the body -Force of Gravity on the center of mass of the arm (Wa) -Force of the external weight in the hand (Wm)

Biomechanical Forces •Internal: -Produced by structures located within b -P or a •External -Produced by forces o body -Usually g or e load

•Internal: -Produced by structures located within body -Passive or active •External -Produced by forces outside body -Usually gravity or external load

Lever Systems •Lever: Simple machine consisting of a r rod suspended across a p point • •Internal and external forces produce torques through b levers • • Classified as first, second and third class levers -The body takes advantage of all three levers for each of their advantages. 1st: •Axis of rotation b opposing forces. 2nd:•Axis of rotation located at one e of the lever and what forces have greater leverage 3rd: •Axis of rotation located at one end of the lever and what forces have greater leverage

•Lever: Simple machine consisting of a rigid rod suspended across a pivot point • •Internal and external forces produce torques through bony levers • • Classified as first, second and third class levers -The body takes advantage of all three levers for each of their advantages. 1st: •Axis of rotation between opposing forces. 2nd:•Axis of rotation located at one end of the lever and Internal forces have greater leverage 3rd: •Axis of rotation located at one end of the lever and external forces have greater leverage

Mechanical Advantage (MA) •MA of the internal force = what moment arm / what moment arm There is a mechanical advantage to the muscle when MA >1.0. What is the MA relative to 1.0 for each? 1 - probably what MA 2 - definitely what MA 3 - what MA

•MA of the internal force = Internal moment arm / External moment arm There is a mechanical advantage to the muscle when MA >1.0. What is the MA relative to 1.0 for each? 1 - probably >1 2 - definitely >1 3 - <<1. We just said this was the most common type of lever in the body - why make the muscles work so hard?

Recruitment (Spatial Summation) Activation of motor neurons that activate their associated muscle fibers • •A motor unit is recruited by altering the v potential across the membrane of the cell of the a motor neuron. -Summation of excitatory and inhibitory factors must reach a critical v for ions to flow across the cell membrane to produce the a p where it then propagates down to the motor endplate. Motor neuron S influences the order in which it is recruited. S neurons are recruited first, large l

•Activation of motor neurons that activate their associated muscle fibers • •A motor unit is recruited by altering the voltage potential across the membrane of the cell of the alpha motor neuron. -Summation of excitatory and inhibitory factors must reach a critical voltage for ions to flow across the cell membrane to produce the action potential where it then propagates down to the motor endplate. Motor neuron SIZE influences the order in which it is recruited. Small neurons are recruited first, large last.

Ageing •Ageing is associated with: -Decreased s -Decreased s of contraction -Which results in d muscle power •~10% loss of peak strength for every decade after 60 yo -Far more pronounced in s older adults -Loss more marked in LE than UE -What functions might this affect?? Sarcopenia •Loss of muscle f and size of fibers with infiltration of f and connective t into the muscle •Loss of a motor neurons

•Ageing is associated with: -Decreased strength -Decreased speed of contraction -Which results in decreased muscle power •~10% loss of peak strength for every decade after 60 yo -Far more pronounced in sedentary older adults -Loss more marked in LE than UE -What functions might this affect?? Sarcopenia •Loss of muscle fibers and size of fibers with infiltration of fat and connective tissue into the muscle •Loss of alpha motor neurons

Breaking down what EMG tells us •Amplitude -The greater the amplitude, the more m units are involved -Amplitude may v based on the number of m units, cs area of the muscle, c of the muscle •To compare across subjects, EMG is normalized to amplitude of a maximum voluntary isometric contraction (MVIC) • •Frequency -Lower frequency = s motor units -Higher frequency = f motor units

•Amplitude -The greater the amplitude, the more motor units are involved -Amplitude may vary based on the number of motor units, cross sectional area of the muscle, composition of the muscle •To compare across subjects, EMG is normalized to amplitude of a maximum voluntary isometric contraction (MVIC) • •Frequency -Lower frequency = slower motor units -Higher frequency = faster motor units

Inactivity •Atrophy -Loss of s produced by the muscle -Happens very quickly!! -Loss of 3-4% strength per day in first week -Average loss of 58% in 6 weeks. (Appell 1990) -For reference, 20% loss in CSA equates to a 40% loss in strength - •Reduced p synthesis -Largely in the s type muscle fibers -Conversion of slow fibers towards f fiber characteristics -Fiber type conversion starts within how many weeks of immobilization In those with SCI, type I->II conversion takes only ~6 months

•Atrophy -Loss of strength produced by the muscle -Happens very quickly!! -Loss of 3-4% strength per day in first week -Average loss of 58% in 6 weeks. (Appell 1990) -For reference, 20% loss in CSA equates to a 40% loss in strength - •Reduced protein synthesis -Largely in the slow type muscle fibers -Conversion of slow fibers towards fast fiber characteristics -Fiber type conversion starts within 3 weeks of immobilization In those with SCI, type I->II conversion takes only ~6 months

Kinetics •Branch of mechanics that describes the e of forces on the body. •Definitions: -Force: mechanical d or l (push or pull ) •In Newtons (N) •F = what*what •Need to know: -Point of a -D -M

•Branch of mechanics that describes the effects of forces on the body. •Definitions: -Force: mechanical disturbance or load (push or pull ) •In Newtons (N) •F = ma •Need to know: -Point of application -Direction -Magnitude

Center of Mass •Center of mass: Point at the exact c of an object's mass. -Mass is evenly d in all directions •Center of Gravity: point about which the effects of gravity are completely b. •CoM closely coincides with CoG -For the purposes of this class CoM = CoG

•Center of mass: Point at the exact center of an object's mass. -Mass is evenly distributed in all directions •Center of Gravity: point about which the effects of gravity are completely balanced. •CoM closely coincides with CoG -For the purposes of this class CoM = CoG

Closed packed and open packed positions Close packed positions: maximal c ("fits the best"), usually in or near the e of range of motion -Characteristics: most ligaments/capsule t -accessory movments are m - •Open packed: ("loose" packed) -Characteristics: ligaments and capsule s, least congruent near m

•Close packed positions: maximal congruency ("fits the best"), usually in or near the end of range of motion -Characteristics: most ligments/capsule taut -accessory movments are minimal - •Open packed: ("loose" packed) -Characteristics: ligaments and capsule slackened, least congruent near midrange

Composition of Forces •Combining two or more forces to determine n effect • •L forces are added together (if in line) or subtracted, if in o direction

•Combining two or more forces to determine net effect • •Linear forces are added together (if in line) or subtracted, if in opposite direction

Contractile and Structural Proteins •Contractile - provide a tension (s of the sarcomere) -A -M - •Number of active cross-bridges formed determine the f of the muscle contraction. -Greater the cross-bridges, the what the force of contraction • •The fiber length directly changes the amount of overlap between actin and myosin, thus affecting the p cross-bridges.

•Contractile - provide active tension (shortening of the sarcomere) -Actin -Myosin - •Number of active cross-bridges formed determine the force of the muscle contraction. -Greater the cross-bridges, the greater the force of contraction • •The fiber length directly changes the amount of overlap between actin and myosin, thus affecting the potential cross-bridges.

Arthrokinematics: •Describes the motion that occurs between the articular surfaces of the j. • •Usually occurring between curved surfaces, one typically convex and one concave. • •Three components: -R -G -S •Primary Motion: the p atrthokinematic component to achieve the joint motion •Accessory Motion: the s and te arthokinematic component(s) to achieve the joint motion

•Describes the motion that occurs between the articular surfaces of the joints. • •Usually occurring between curved surfaces, one typically convex and one concave. • •Three components: -Roll -Glide -Spin •Primary Motion: the perdominant atrthokinematic component to achieve the joint motion •Accessory Motion: the secondary and tertiary arthokinematic component(s) to achieve the joint motion

Effects of Strength Training •Dynamic strengthening i strength ~1%/day • •Neural changes -Increased area of c activation (fMRI and TMS) -Increased motor neuron e -Greater discharge f of motor units - •Hypertrophy -Adding p within a muscle cell in p •Hyperplasia Adding muscle c (not very common)

•Dynamic strengthening increases strength ~1%/day • • •Neural changes -Increased area of cortex activation (fMRI and TMS) -Increased motor neuron excitability -Greater discharge frequency of motor units - •Hypertrophy -Adding proteins within a muscle cell in parallel •Hyperplasia Adding muscle cells (not very common)

Types of Energy •Energy is the c to do work. We are most interested in m energy here (not so fair to the muscle). • •Kinetic Energy - "Energy in motion" -KE = what • •Potential energy -PE = what • •Strain/Elastic energy -what (spring equation) -Eg tendon stretched or spring compressed.

•Energy is the capacity to do work. We are most interested in mechanical energy here (not so fair to the muscle). • •Kinetic Energy - "Energy in motion" -KE = ½ m v2 • •Potential energy -PE = mgh • •Strain/Elastic energy -½ stiffness * (amount of deformation)^2 -Eg tendon stretched or spring compressed.

•First Law: Law of Inertia -Object at rest will stay at r; objects in motion stay in (c) motion •Linear Motion: F is required to start, stop, accelerate, decelerate motion •Rotational Motion: T is required to start, stop, accelerate, decelerate motion

•First Law: Law of Inertia -Object at rest will stay at rest; objects in motion stay in (constant) motion •Linear Motion: Force is required to start, stop, accelerate, decelerate motion •Rotational Motion: Torque is required to start, stop, accelerate, decelerate motion

•Force Acceleration Relationship •Force Acceleration Relationship -Cause e relationship -Left side of equation = c -Right side of equation = e v∑▒〖F=m ×a 〗 v∑▒〖F=0〗 (static equilibrium) v∑▒█(F≠0 ( produces l acceleration)) v∑▒〖M=I ×α 〗 v∑▒〖M=0〗 (static equilibrium) ∑▒█(M≠0 ( produces a acceleration))

•Force Acceleration Relationship -Cause effect relationship -Left side of equation = cause -Right side of equation = effect v∑▒〖F=m ×a 〗 v∑▒〖F=0〗 (static equilibrium) v∑▒█(F≠0 ( produces @linear acceleration)) v∑▒〖M=I ×α 〗 v∑▒〖M=0〗 (static equilibrium) ∑▒█(M≠0 ( produces @angular acceleration))

Crutches vs Walker, Haubert et al.

•A Comparison of Shoulder Joint Forces During Ambulation With Crutches Versus a Walker in Persons With Incomplete Spinal Cord Injury •Objective: to compare shoulder joint reaction forces in each of 3 degrees of freedom. -AD's Lofstrand Crutches vs front wheeled walker -Population: Incomplete SCI

Joint Reaction Force •Force between the s of the joint that o the upward acceleration forces • •JRF = usually the difference between the m force and e force

•Force between the surfaces of the joint that oppose the upward acceleration forces • •JRF = usually the difference between the muscle force and external force

Tipping Force •Force must generate a torque that will overcome the torque created by the center of m Torque due to gravity = Fg * x (x=how much of distance of box) Torque due to the push = Fpush * what If Tpush > Tg Then the box will begin to t over

•Force must generate a torque that will overcome the torque created by the center of mass Torque due to gravity = Fg * x (1/2 width of box) Torque due to the push = Fpush * h If Tpush > Tg Then the box will begin to tip over

Rotatory motion •Forces applied at some distance p to an axis of rotation. • •T (moment) is the rotary equivalent to a force • •Formula for Rotatory motion - -For our purposes, Moment and Torque are the same

•Forces applied at some distance perpendicular to an axis of rotation. • •Torque (moment) is the rotary equivalent to a force • •Torque (moment) = Force x moment arm distance (d) -(T = Fxd) - -For our purposes, Moment and Torque are the same

Forces/Torques and Lever Systems •Forces have a m, point of a and a d •Torques are forces applied some d from an axis of rotation • •Internal vs External Force • •Levers are simple m that are described by the location of the i and e forces compared to the axis of rotation.

•Forces have a magnitude, point of application and a direction •Torques are forces applied some distance from an axis of rotation • •Internal vs External Force • •Levers are simple machines that are described by the location of the internal and external forces compared to the axis of rotation.

Friction •Friction - resistance that a surface or object experiences when moving over a. •Coefficient of friction: μ describes how "s" surface is • •Friction = what*what •S force

•Friction - resistance that a surface or object experiences when moving over another. •Coefficient of friction: μ describes how "sticky" surface is • •Ffriction = μ*N •Slipping force

Fatigue •High Frequency Fatigue •Impairment in what release at the end plate •Signal can't get to the muscle •Fatigue associated with b the muscle with high frequency electrical stimulation •Debate whether this can occur with v contraction •Low Frequency Fatigue •Impairment of E-C Coupling. C delivery and re-uptake is impaired •Twitch characteristics: l twitch time •EMG characteristics: •Decreased median frequency of the signal •Increased RMS of the signal

•High Frequency Fatigue •Impairment in ACh release at the end plate •Signal can't get to the muscle •Fatigue associated with blasting the muscle with high frequency electrical stimulation •Debate whether this can occur with voluntary contraction •Low Frequency Fatigue •Impairment of Excitation-Contraction Coupling. Calcium delivery and re-uptake is impaired •Twitch characteristics: longer twitch time •EMG characteristics: •Decreased median frequency of the signal •Increased RMS of the signal

Electromyography •How do we know what the muscle is actually doing? -Detect the e impulses that tell the muscle to perform a t (single motor unit action potential) • •Types of electromyography: -Surface •Electrodes on the skin over the muscle detecting whole m information -Fine wire •Wires inserted into the muscle to detect single f information

•How do we know what the muscle is actually doing? -Detect the electrical impulses that tell the muscle to perform a twitch (single motor unit action potential) • •Types of electromyography: -Surface •Electrodes on the skin over the muscle detecting whole muscle information -Fine wire •Wires inserted into the muscle to detect single fiber information

Resistance Training •Hypertrophy -m and p level changes as soon as 2-4 hrs following a bout of exercise. •S cells infiltrate and aid repair/laying of fibrils •Increase in d - improves transfer of t between muscle fibers -First 4 sessions of RT cause s induced increase in muscle CSA -8-12 sessions to detect h -~18 sessions over 6-10 weeks of RT to promote s hypertrophy.

•Hypertrophy -mRNA and protein level changes as soon as 2-4 hrs following a bout of exercise. •Satellite cells infiltrate and aid repair/laying of fibrils •Increase in desmin - improves transfer of tension between muscle fibers -First 4 sessions of RT cause swelling induced increase in muscle CSA -8-12 sessions to detect hypertrophy -~18 sessions over 6-10 weeks of RT to promote significant hypertrophy.

Force-Amplitude relationship •Increase in force results in an i in EMG amplitude •Rate coding: t increase. Increase frequency of f rate •Recruitment: S increase. Increase the n of motor units that contribute to force

•Increase in force results in an increase in EMG amplitude •Rate coding: temporal increase. Increase frequency of firing rate •Recruitment: Spatial increase. Increase the number of motor units that contribute to force

Base of Support •Increasing the width of the base of support now increases the t of the COM to overcome the tipping force (said differently - it now takes more force to tip the box) •Greater the area the base of support, the more s

•Increasing the width of the base of support now increases the torque of the COM to overcome the tipping force (said differently - it now takes more force to tip the box) •Greater the area the base of support, the more stability

Motor Unit Recruits Muscle Fibers •A motor unit is made up of one motor n and all of the muscle fibers that it i • •A motor unit is composed of only o fiber type (Type I, IIA, IIX) • •One motor unit may include very f muscles fibers for fine motor control, or may include m fibers for gross movements

•A motor unit is made up of one motor nerve and all of the muscle fibers that it innervates • •A motor unit is composed of only one fiber type (Type I, IIA, IIX) • •One motor unit may include very few muscles fibers for fine motor control, or may include many fibers for gross movements

Newton's Second Law •Second Law: -Describes behavior of objects when not in e! - -When the SUM of forces acting on an object is nonzero it will a in the direction of the of the net force. •Acceleration is dependent upon two variables: -N (Σ) force -M of the object. • ΣF = ma or Σ M= I α -takes place in the same direction of the force and inversely proportion to mass of the body

•Second Law: • -Describes behavior of objects when not in equilibrium! - -When the SUM of forces acting on an object is nonzero it will accelerate in the direction of the of the net force. •Acceleration is dependent upon two variables: -Net (Σ) force -Mass of the object. • ΣF = ma or Σ M= I α -takes place in the same direction of the force and inversely proportion to mass of the body

Spin as the primary motion •S -IR/ER when in 90 degrees abduction • •H -Flexion/extension - •H joint Supination/pronation

•Shoulder -IR/ER when in 90 degrees abduction • •Hip -Flexion/extension - •Humeroradial joint Supination/pronation

Equilibrium •Static Equilibrium: -linear and rotational velocities are ____ (body not m) -Net acting forces = 0: ∑ Fx= 0, ∑ Fy= 0 ∑ M = 0 v •Dynamic Equilibrium: -linear or rotational velocities are ________. -Net acting forces are still 0 (no an) ∑ Fx = 0 = max∑ Fy=0= may ∑ M =0= I x α

•Static Equilibrium: -linear and rotational velocities are zero (body not moving) -Net acting forces = 0: ∑ Fx= 0, ∑ Fy= 0 ∑ M = 0 v •Dynamic Equilibrium: -linear or rotational velocities are not zero but constant -Net acting forces are still 0 (no acceleration) ∑ Fx = 0 = max∑ Fy=0= may ∑ M =0= I x α

Contractile and Structural proteins •Structural - provide p tension and s & a (Think elastic energy) -E matrix -Titan (maybe) -Desmin •Properties of structural muscle tissue -E - temporarily stores a small portion of the energy that stretches the muscle -Viscoelasticity - resistance to stretch increases with s of stretch. • •Passive components help transmit the a tension. This contribution is very sl however. Not very useful in many circumstances due to -The significant amount of l that must occur before the tissue can generate meaningful passive tension.

•Structural - provide passive tension and structure & alignment (Think elastic energy) -Extracellular matrix -Titan (maybe) -Desmin •Properties of structural muscle tissue -Elasticity - temporarily stores a small portion of the energy that stretches the muscle -Viscoelasticity - resistance to stretch increases with speed of stretch. • •Passive components help transmit the active tension. This contribution is very small however. Not very useful in many circumstances due to -The significant amount of lengthening that must occur before the tissue can generate meaningful passive tension.

Extraocular Eye Muscles •Superior Oblique Actions -I -D -A •Inferior Oblique Actions -E -E -A - Why SO tested in adduction while SR and IR are tested in abduction the SR and IR are too short to elevate and depress the eye, so the IO and SO do the acti

•Superior Oblique Actions -Intorsion -Depression -Abduction •Inferior Oblique Actions -Extorsion -Elevation -Abduction - - Why SO tested in adduction while SR and IR are tested in abduction the SR and IR are too short to elevate and depress the eye, so the IO and SO do the acti

Impulse •The quantity of n force and the time over which the f was applied. -ΣF t •Impulse is essentially the change in m -equation - -Therefore net force required to change the original momentum is just the change in momentum over time.

•The quantity of net force and the time over which the force was applied. -ΣF t • •Impulse is essentially the change in momentum -ΣF t = Δmv -ΣF = Δmv/t - -Therefore net force required to change the original momentum is just the change in momentum over time.

Power •The rate at which w is done -P=what -Units: Joule/sec = Watt - - -Example if m = 100 kg g = 9.8 m/s h = 2 m •Wk = what= 1960J •Raise the barbell slowly: 5s: Power = what W •Raise the barbell quickly: 1.5s Power = what W

•The rate at which work is done -P=Work/time -Units: Joule/sec = Watt - - -Example if m = 100 kg g = 9.8 m/s h = 2 m •Wk = mgh= 1960J •Raise the barbell slowly: 5s: Power = 392 W •Raise the barbell quickly: 1.5s Power = 1306.7 W

Conservation of Momentum •The total momentum of any given system will remain constant unless acted upon by an e force" • •"The momentum b a collision is equal to the momentum a a collision" •(Ball experiment) •Bowling: -(mass ball)(velocity rolling ball) + (mass pins)(velocity stationary pins) = (mass ball)(velocity slower roll) + (mass pins)(velocity flying pins) -Do you think it's possible to have a ball NOT knock over a pin??

•The total momentum of any given system will remain constant unless acted upon by an external force" • •"The momentum before a collision is equal to the momentum after a collision" •(Ball experiment) •Bowling: -(mass ball)(velocity rolling ball) + (mass pins)(velocity stationary pins) = (mass ball)(velocity slower roll) + (mass pins)(velocity flying pins) -Do you think it's possible to have a ball NOT knock over a pin??

Work-energy •The work done by the net force acting on a body is equal to the change in the body's e (KE,PE,SE) -Work = Δenergy

•The work done by the net force acting on a body is equal to the change in the body's energy (KE,PE,SE) -Work = Δenergy

Newton's Third Law •Third Law: -For every reaction, there is an e and o reaction - -When two objects interact - what each object experiences is dependent on its m -Application: •G reaction force (foot strikes the ground) •J reaction force

•Third Law: -For every reaction, there is an equal and opposite reaction - -When two objects interact - what each object experiences is dependent on its mass - -Application: •Ground reaction force (foot strikes the ground) •Joint reaction force

Translation vs. Rotation •Translation: -Definition: portions of a rigid body travel in the s direction and in parallel to every part of the body -Linear motion (rectilinear) -Straight of curved line motion (curvilinear) •Variables: -P/displacement (meters, feet, inches) -V (m/sec) -A (m/sec2)

•Translation: portions of a rigid body trabel in the same direction and in parallel to every part of the body -Definition: all -Linear motion (rectilinear) -Straight of curved line motion (curvilinear) -Describe motion of this body: head, shoulders, COM, ankle? •Variables: -Position/displacement (meters, feet, inches) -Velocity (m/sec) -Acceleration (m/sec2)

Work-Energy Relationship •Work = f x p distance -When force is not parallel to distance traveled - use trig. • •We already calculated joint loading for isometric conditions. What is the work performed during an isometric muscle contraction?

•Work = force x parallel distance -When force is not parallel to distance traveled - use trig. • •We already calculated joint loading for isometric conditions. What is the work performed during an isometric muscle contraction?

Mechanics of temporal summation •Mechanical response to a signal stimulus of its motor nerve is called a t -First s is taken up in the muscle (contributes to the electromechanical delay) -Then tension develops until peak t (time to peak) -Following peak tension, r occurs until no tension remains - -When multiple messages arrive in quick succession, more t is created before full r can occur - s -When the firing rate of the nerve is great enough to never allow r during summation - t •Tetanic contractions allow s movements produced by skeletal muscle.

•Mechanical response to a signal stimulus of its motor nerve is called a twitch -First slack is taken up in the muscle (contributes to the electromechanical delay) -Then tension develops until peak tension (time to peak) -Following peak tension, relaxation occurs until no tension remains - -When multiple messages arrive in quick succession, more tension is created before full relaxation can occur - summation -When the firing rate of the nerve is great enough to never allow relaxation during summation - tetanus. •Tetanic contractions allow smooth movements produced by skeletal muscle.

Impulse-Momentum Relationship •Momentum -The q of motion. -Any object that has both mass and velocity has a m -M = m*v •Where m = what and v = what •Units = Kg*m/s or Ns -Uses •Measurement in describing i/c between people, between objects, and between a person and an object •Conservation of Momentum -"The total momentum of any given system will remain constant unless acted upon by an external force" -"The momentum before a collision is equal to the momentum after a collision"

•Momentum -The quantity of motion. -Any object that has both mass and velocity has a momentum -M = m*v •Where m = mass and v = velocity •Units = Kg*m/s or Ns -Uses •Measurement in describing impact/collision between people, between objects, and between a person and an object •Conservation of Momentum -"The total momentum of any given system will remain constant unless acted upon by an external force" -"The momentum before a collision is equal to the momentum after a collision"

Factors related to (active) strength •Morphology -Pennate (most common) •Muscles that insert into their tendon in o angles -Fusiform •p all inserting to their tendon at the s angle •Architecture -Physiologic Cross-Sectional Area •Amount of active proteins to generate f -Pennation Angle •Angle of i of the muscle into the tendon.

•Morphology -Pennate (most common) •Muscles that insert into their tendon in oblique angles -Fusiform •parallel all inserting to their tendon at the same angle •Architecture -Physiologic Cross-Sectional Area •Amount of active proteins to generate force -Pennation Angle •Angle of insertion of the muscle into the tendon.

Force-Velocity relationship. •Muscle actually produces different m forces under different v of contraction. •I forces are greater than c contractions •As velocity increases the ability to produce force d •E force is greater than both isometric and concentric (think back to the sarcomere) •As velocity increases the eccentric contractions produce m force, but may have a limit to f production capabilities (p may be a limiting factor)

•Muscle actually produces different maximal forces under different velocities of contraction. •Isometric forces are greater than concentric contractions •As velocity increases the ability to produce force decreases •Eccentric force is greater than both isometric and concentric (think back to the sarcomere) •As velocity increases the eccentric contractions produce more force, but may have a limit to force production capabilities (pain may be a limiting factor)

Laws that Govern Motion •Newton's Laws! -1st Law: Law of I -2nd Law: Law of E -3rd Law: Law of a and r

•Newton's Laws! -1st Law: Law of Inertia -2nd Law: Law of Equilibrium -3rd Law: Law of action and reaction

Muscle Power •Power = (Muscle v of contraction) x (a of muscle force) -Velocity is how f the fiber contracts -Amplitude is how much t it produces - •This is critical so that a person is able to exert force at speeds characteristic with a given sporting movement. -A powerlifter squatting maximal weight is producing the highest possible muscular force at l velocities •The resistance is high -A shot-put thrower is producing the highest possible muscular force at h velocities •The resistance is l

•Power = (Muscle velocity of contraction) x (amplitude of muscle force) -Velocity is how fast the fiber contracts -Amplitude is how much tension it produces - •This is critical so that a person is able to exert force at speeds characteristic with a given sporting movement. -A powerlifter squatting maximal weight is producing the highest possible muscular force at low velocities •The resistance is high -A shot-put thrower is producing the highest possible muscular force at high velocities •The resistance is low

Rate Coding (Temporal Summation) •Rate Coding: Temporal Summation •The s the time between depolarizations of the motor neuron, twitches can add the force of the twitches t •Longer periods of time between depolarizations allow muscle r to occur

•Rate Coding: Temporal Summation •The smaller the time between depolarizations of the motor neuron, twitches can add the force of the twitches together. •Longer periods of time between depolarizations allow muscle relaxation to occur

Recruitment and Rate Coding •Recruitment: Spatial Summation -Activation of a m neurons activates their a muscle fibers -The larger the m to the motor neuron pool, the more m neurons that are recruited. -Motor neuron S influences the order in which it is recruited. what neurons are recruited first, what last. - •Rate Coding: Temporal Summation -The smaller the t between depolarizations of the motor neuron, twitches can a the force of the twitches together. -Longer periods of time between depolarizations allow muscle r to occur

•Recruitment: Spatial Summation -Activation of a motor neurons activates their associated muscle fibers -The larger the message to the motor neuron pool, the more motor neurons that are recruited. -Motor neuron SIZE influences the order in which it is recruited. Small neurons are recruited first, large last. - •Rate Coding: Temporal Summation -The smaller the time between depolarizations of the motor neuron, twitches can add the force of the twitches together. -Longer periods of time between depolarizations allow muscle relaxation to occur

Resolution of Forces •Replacing a s force with two or more components. When combined will a to the original force • •Usually resolved into v (Fy) and h (Fx)Forces • •For our purposes every force (F) will have: -an X component (Fx) -A Y component (Fy) -**sometimes one of these (Fx or Fy) may be 0

•Replacing a single force with two or more components. When combined will add to the original force • •Usually resolved into vertical (Fy) and horizontal (Fx)Forces • •For our purposes every force (F) will have: -an X component (Fx) -A Y component (Fy) -**sometimes one of these (Fx or Fy) may be 0

Electrical Stimulation •Reverse recruitment when stimulating the muscle a -V = I R •A large diameter muscle fiber (F muscle) has a l resistance •A small diameter muscle fiber (S muscle) has a sresistance -Vcrit = I R •Small current needs a l resistance to generate a voltage that will depolarize the membrane. • -How might you use this clinically?

•Reverse recruitment when stimulating the muscle artificially -V = I R •A large diameter muscle fiber (Fast muscle) has a large resistance •A small diameter muscle fiber (Slow muscle) has a small resistance -Vcrit = I R •Small current needs a large resistance to generate a voltage that will depolarize the membrane. • -How might you use this clinically? Reverse order of recruitment

Rotation •Rotation: -Definition: c path around the pivot point -Variables •D (degrees, radians) •V (degrees/sec) •A (radians/sec2)

•Rotation: -Definition: circular path around the pivot point -Variables •Distance (degrees, radians) •Velocity (degrees/sec) •Acceleration (radians/sec2)

Vector vs Scalar •Scalar: m only -E.g. mass, energy, temperature - •Vector: m and d -E.g. force, moment , velocity, acceleration

•Scalar: magnitude only -E.g. mass, energy, temperature - •Vector: magnitude and direction -E.g. force, moment , velocity, acceleration

Overload Principle Overload High d on the muscle leading to fatigue Period of rest and recovery (~how many hrs) R •FITT Using what 2 aspects

Overload High demand on the muscle leading to fatigue Period of rest and recovery (~48 hrs) Repeat •FITT -Frequency -Intensity -Time Type