Biomechanics Exam 4

in class

Excitability (irritability)

the capacity to receive and respond to a stimulus

Contractility

The ability to contract or shorten

Extensibility

The ability to be stretched

Elasticity

The ability to return to its original shape after being stretched or contracted

How many individual muscles does the human body have?

more than 600

What is the muscles primary job?

to exert a physical force on other tissues and organs

How is the performance of the muscle tissue under varying loads and velocities determiend????

1. excitability

2. contractility

3. extensibility

4. elasticity

Agonist

prime mover

Antagonist

action opposite to the agonist

Stabilizers

fixate or stabilize the joint contract isometric

Neutralizer or synergists

• Creates a torque to cancel out unwanted action of other muscles

• assist or guide

Isometric

A muscular contraction in which the length of the muscle does NOT chanage

Isotonic (concentric and eccentric)

A muscular contraction where the length of the muscle changes

Isokinetic

• The muscle changes length during contraction

• A constant speed

• Common in rehabilitation and research

• An Isokinetic Dynamometer is required

Concentric contraction traits

• muscle shortens

• Net muscle force producing movement are in the same direction as the change in joint angle

• The limb movement is termed POSITIVE (joint actions are usually against gravity)

• Muscle force > Resistance

Static or Isometric contraction

• Muscle tension is generated against resistance to maintain position

• No change in muscle length

• Muscle force is equal to the resistance

• TOTAL TORQUE IS 0 but the muscle is active

Eccentric contraction

• muscle lengthens

• The muscle force is less than the resistance

• Torque by the muscle is in the opposite direction of the rotation of the limbs

• Limb movement is termed NEGATIVE (joint actions are usually moving down with gravity or are controlling rather than initiating a motion)

Muscle contraction analysis during activities: Against and towards the gravity exercises

• Find out the joint movements during the against-gravity phase

• Focus on the against-the-gravity phase to find the main muscles

• Primary mover muscles during against the gravity phase do the activity

• The against-the-gravity phase is concentric

• The direction towards the gravity phase is eccentric

What is another term for muscle cell?

Muscle Fiber

Fascicle

Muscle fibers bundled together in a group of 100 or more

(wrapped by perimysium)

What wraps around the entire muscle?

Epimysium

Sarcomere

A basic contractive unit

Myofilaments (active/contractive component)

Thick: myosin filaments

Thin: actin filaments

Z line / band (between disc)

Actin attached to Z line

Titin

Elastic filament, links myosin filaments to the Z liines

Endomysium

A sheath of connective tissue surrounds each muscle fiber (cell)

Perimysium

A sheath of connective tissue surrounds each fascicle (bundle)

Epimysium

A sheath of connective tissue encases muscles, covers the entire skeletal muscle

Fascia

A sheet of fibrous tissue enclosing of muscles, covers and separates muscles on the outside of the epimysium

Connective tissue

Inside or outside of muscle protect the muscle and can store elastic energy and produce passive force

Order of muscle force transmission

endomysium —> perimysium —> epimysium —> tendon —> bone

Sliding filament and cross bridge theory

1. Myosin heads split ATP and become reoriented and energized

2. Myosin heads bind to actin, forming cross-bridges

3. Myosin heads rotate toward the center of the sarcomere (power stroke)

4. As myosin heads bind ATP, the cross-bridges detach from actin (detach and relaxation)

3 components of the Hill Muscle Model

• 1 contractile component (CC)
  2 elastic components

  • parallel (PEC)

  • Series (SEC)

ADD PHOTO???

Load

The external forces that act on the body and produce deformations, stresses or displacements in the structure

The strength of a biological material is affected by:

• Loading (type, direction, and velocity)

• microstructure

• age

• fluid content

• level of activity

Internal force

The force that acts on the inside of the material

• shear

• bending

• torsion

• compression

• tension

  • external forces that act on the body are resisted by internal forces that cause deformation

External force

The force comes from the source out of the system (gravitational force or weight)

Stress

When a material is subjected to an external force, a resisting force is set up within the component; this internal resistance force is stress

Strain

The quantification of the deformation of a material

Types of load/stress/strain

Uniaxial

• Tensile

• Compressioin

• Shear

Biaxial & multiaxial stress

• Bending (tension + compression)

• Torsion: (twisting = tension + compression + shear)

Load

Tensile: The axial load occurs when two opposite forces tend to pull the material apart

Compression: the axial load when two forces tend to push or squash the molecules more tightly together

Shear: A transverse load when two parallel forces tend to slide the material’s molecules past each other

Bending: A biaxial load that is a combination of tensile and compressive loads. acts on 2 sides of the material

Torsion: The multiaxial load that is a combination of two opposite direction torques acting on the material at the same time

Stress

Tensile: axial or normal stress that occurs as a result of a load that tends to pull apart the molecules bonding the object together

Compression: axial stress that occurs as a result of a compressive load

Shear: A transverse stress that occurs as a result of a shear load

Bending: A biaxial stress that occurs as a result of a bending load. One side undergoes tensile and the other is compressive

Torsion: A multiaxial stress that occurs as a result of a torsion load

Strain

Tensile: The axial deformity or lengthening that occurs as a result of a load that tends to pull apart the molecules bonding the object together.

Compression: Axial deformity or shortening that occurs as a result of compressive load

Shear: A transferase deformity that occurs with a change in orientation of adjacent molecules as a result of these molecules slipping past each other.

Bending: the biaxial deformity or curving in the material that occurs as a result of a bending load

Torsion: a multiaxial deformity or twisting that occurs as a result of a torsion load

What components are used in a tensile test?

Tendon, ligament, and muscle

Elastic region

The portion of the curve where the material will return to its original shape if the load is removed

Elastic Behavior

The object will return to its initial shape and size when these forces are removed

Plastic region

The portion of the curve where the material will NOT return to its original shape if the load is removed (some permanent deformation may occur)

Yield point or elastic limit

The point on the stress-strain curve where further stress cause permanent deformation (plastic region)

max stress a material can withstand and still return to it’s original shape after the stress is removed.

Stiffness

The slope of the stress-strain graph, which is the ratio of stress to strain

What happens physiologically during a concentric contraction?

• An actin-myosin cross-bridge is formed

• ATP downgraded to ADP + Pi

• Myosin does mechanical work on the Actin, the Myosin arm that rotates, shortening the muscle fiber

  • As the muscle shortens, the number of attached crossbridges is reduced.

What happens physiologically during a isometric contraction?

• An actin-myosin cross-bridge is formed

• ATP downgraded to ADP + pi

• Myosin attempts to rotate and shorten the fiber

• The number of bridges attached remains constant

• External force causes the fiber to lengthen

• Connective tissue stretch and add more tension

• From this lengthened position, the myosin arm rotates and shortens the fiber

• Force comes from the contractile component (CC) and the elastic component

  

What happens physiologically during a eccentric contraction?

• An Actin-Myosin cross-bridge is formed

• ATP downgraded to ADP + Pi

• Myosin attempts to rotate and shorten the fiber

• External force causes the fiber to lengthen

• Connective tissue stretch and add more tension

• Force comes from CC and the Elastic component

  

Comparison of muscle contractions and force production

• Eccentric contraction is capable of greater force output

• Concentric contraction generates the lowest force output of the three types

• Force is related to the number of cross-bridges formed in the myofibril and the elastic energy stored in the connective tissues

Comparison of muscle actions

Active Tension

• Tension by making a cross-is created bridge and filament sliding

• Active component or contractile component: Actin and Myosin filament

Passive Tension

• Tension by streteching of the connective tissue

• Passive component: sarcolemma, endomysium, perimysium, epimysium, and tendon

Muscle length and tension relationship

What % can max tension be developed in a whole muscle?

when it’s a little longer than 120% of the resting length

Active Insufficiency

Inability to produce more force when the muscle is too short usually in multi-joint muscles

Passive insufficiency

Inability to produce more force when the muscle is too extended, usually in multi-joint muscles

Force-length relationship in training

• our muscles have an ideal angle where they produce the greatest tension

• The length is usually the midpoint of the range of motion

How to train to optimize force-length (designing programs)

• The muscles must train in their FULL range of motion and in a range close to the optimal length

• The optimal length will get involves active components (Actin and Myosin)

• The training in a longer length (full range of motion) involves the passive components (connective tissue)

• Single muscle fiber force production is greater during stretch training when the passive elements can contribute to tensile force in the contraction

What is the “extra force” provided by?

Titin!!!!

• When the muscle is elongated to long lengths titin senses the mechanical loading that it is exposed to, and triggers longitudinal fiber hypertrophy to occur

Force and velocity relationship

Eccentric > Isometric > Concenetric

• The max muscle force or tension is related to the velocity of shortening of the muscle

  

  V=0 means no movement

Concentric Cross-bridge cycle (3 steps)

Cross bridge, Pull (power stroke), Detach

• A high force at a slower velocity because of the slower detachment rate —> more attached cross-bridge

• A low force at fast velocity because of a higher detachment rate —> less attached cross bridge

• Ability to produce more force during slower motion:

  • 4 pN (piconewton) from myosin motor for fast velocity

  • 5 pN from myosin motor for slow velocity

Eccentric Cross-bridge cycle (3 steps)

*The connective tissues stretched, adding more tension

• External force causes the fiber to lengthen, storing elastic energy in connective tissues.

• Muscle-tendon unit is a viscoelastic material

• The viscoelastic response of the musculotendonous unit means that a slow stretch will create less passive tension; a faster stretch will create more passive tension

  • 10 pN for slow velocity

  • 20 pN for fast velocity

Force-velocity relationship (graph)

concentric - against gravity

eccentric - same position but WITH gravity

Different tempos during 4 phases of a repition

1. Eccentric rep (lowering the weight)

2. Isometric rep (midpoint - bottom of the rep)

3. Concentric rep (lifting the weight)

4. Isometric rep (starting point)

Which tempo is best? - Concentric

Fast contraction: less time under tension but recruits more and larger motor units

Slow contraction: higher force by individual muscle fibers but recruits less number and smaller motor units

Which tempo is best? - Eccentric

Fast contraction: Involve more passive force by connective tissues and less active force, stimulate greater increase in fiber length

Slow contraction: High time under tension and recruits more and larger motor units

Which tempo is best? - Isometric

• Velocity doesn’t matter

• Tempo shows the time under tension

What does high levels of tension during strength training at the force end of the force-velocity relationship stimulate?

Specific “tension-related” adaptations that lead to greater maximum strength.

What does high levels of tension during strength training at the VELOCITY end of the force-velocity relationship stimulate?

Specific “velocity-related” adaptations that lead to an improved ability to produce force at high speeds

same output (low vs high gear)

Low gear - small forces on the pedals but spin the crank fast

High gear - exert large forces spin crank very slowly

The best gear: allows to spin the crank at the moderate speed and keep muscle’s velocity of shortening near to max power (30-33% velocity of shortening)

Power equation

Force x velocity = work/time

The power output of a muscle is the tensile force produced by the muscle times the velocity of shortening of the muscle

Work equation

Force x Displacement

In joints: work = torque x ROM (J)

What is torque and ROM during concentric contraction if a higher velocity?

Lower torque

Lower ROM (usually)

Exteroceptors

• Responses to stimuli come from outside of the body

• Five senses: sight, hearing, taste, smell, and touch

Interoceptors

• Responses to stimuli come from within the body

• Proprioceptors

  • Specialized sensory receptors that are located within joints, muscles, and tendons

    • Muscle spindle: muscle length

    • GTO

Reflexes

Involuntary response to stimuli, it is under spinal cord control

Muscle spindle

SKM sensory receptors within the body of a muscle

Primarily detect:

• Changes in the length of the muscle

• Axial alignment and limb position

• Velocity of the changes

Muscle spindles have both sensory and motor components

Stretch reflex (of muscles spindle)

Plays an important role in regulating the contraction of muscles by activating motor neurons to resist muscle strength

Muscle spindle detects the stretch of a muscle or muscles, relative changes in length, and velocity of changes

Causes of stretch reflex

1. Efferent impulses to alpha motor neurons: contraction in muscle after stretching (resist against stretch)

2. Efferent impulses to antagonist muscles: inhibit contraction of the antagonist muscle (reciprocal inhibition)

Stretch-shortening cycle (plyometric exercises)

• The stretch-shorten cycle: an eccentric contraction followed by an immediate concentric contraction

• Additional force is produced during the concentric phase of a stretch - shorten cycle

• The less time between the stretching and contraction (Amortization phase) = greater force

What does plyometric training involve?

Short, intense bursts of activity that target fast-twitch muscle fibers in the lower body. These fibers help generate explosive power that increases speed and jumping height

Plyometric exercises

• Conditioning protocol that utilizes pre-stretching

  • single leg bounds, depth jumps, stair hopping

What is the extra force attributed to in the stretch-shortening cycle?

1. Stored elastic energy (tendon, and titin) (80% of total energy)

   • Faster stretching: higher stored elastic energy (velocity-dependent behavior in viscoelastic tissues)

   • Faster contraction: Less wasting in stored elastic energy (use it or lose it)

   • Eccentric phase pre-stretches the muscle, so the concentric phase begins at a longer length and so a higher force (force-length relationship)

2. Eccentric phase elicits a stretch reflex (Just 20%)

   • Increase activation in agonist muscles

   • Increase relaxation in antagonist muscles

Golgi tendon organ

• Report the muscle tension with the tendon

  • Protects the muscle from rupturing

• Response:

  • Inhibitory: turn off the muscle

Proprioceptive Neuromuscular Facilitation

• Technique of combining passive stretching and isometric contraction to achieve maximum static flexibility

• PNF was initially developed as a method of rehabilitation

1. A muscle group is passively stretched 5- 10s (muscle spindle activation: contraction on the muscle and relaxation on the antagonist)

2. Isometric contraction against resistance 5- 10s (increase the tension on the muscle and GTO activation: a powerful relaxation on the target muscle groups)

3. Passively stretched again (improve the flexibility)

The two nervous system mechanisms to control muscle force

• Recruitment and size of stimulation

• Frequency of stimulation

Recruitment and size of stimulation

• Recruitment: muscle force depends upon the number of fibers that are stimulated ( The number of active motor units)

  • Recruitment occurs generally in an orderly sequence from small to large motor units.

Frequency of stimulation

One mechanism to control muscle force is to increase the Rate of Stimulation (firing rate)

Twitch (frequency of stimulation)

• Single, brief contraction

• Not a normal muscle function

Tetanus (frequency of stimulation)

Summing of contractions

• One contraction is immediately followed by another

• The effects are added

Unfused tetanus (frequency of stimulation)

Incomplete tetanus

• Some relaxation occur between contractions

• The results are summed

Fused (frequency of stimulation)

Complete tetanus

• No evidence of relaxation before the following contractions

• The result is a sustained muscle contraction

Action Potential

The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell

Resting membrane potential (RMP)

Potential difference exists across the sarcomere

What do EMGs measure?

The electrical activity of muscles when they’re at rest and when they’re being used. Electromyography detects the electrical potential generated by muscle cells when these cells contract and relax.

Surface EMG

most reliable and applicable technique between other type in kinesiology and exercise science