Properties of Muscle Flashcards
When a muscle pulls perpendicular to an axis
- It causes the joint to move
- Stabilizes the joint axis
Muscle tissue properties
- Irritability/excitability
- Contractility
- Extensibility
- Elasticity
Irritability/excitability
- Response to chemical, electrical or mechanical stimuli
Contractility
- Ability to contract and develop tension against resistance
- Unique to muscle tissue
Extensibility
- Can passively stretch beyond its resting length
Elasticity
- Ability to return to its resting length after stretching
Muscle shape and fiber arrantement
- Affects force muscle will exert
- Influence range of that force
Factors influencing range of muscle force
- Cross section diameter of muscle
- Ability to shorten
Cross section diameter of muscle
- Greater cross section diameter exerts greater muscle force
Muscle ability to shorter
- Longer muscles can shorten through a greater range
- Beneficial to move a joint through a large range of motion
Muscle fiber arrangement
- Fibers arranged parallel to the length of the muscle
- Produce the greatest range of motion
Shapes of muscle
- Flat
- Fusiform
- Strap
- Pennate
Flat muscles
- Thin and broad
- Arise from aponeurosis
- e.g. Rectus abdominus and obliques
Fusiform muscles
- Spindle like with a central belly
- e.g. Biceps bracialis
Strap muscles
- More uniform in diameter
- Allows for focus on small bone insertions
- e.g. Sartorius
Pennate muscles (uni, bi, multi)
- Shorter fibers arranged obliquely to their tendons
- Increases cross-sectional area of the muscle ∴ increasing its force
- Produce the strongest contractions
Unipennate muscles
- Fibers run obliquely from one side of the tendon only
- e.g. Biceps femoris, EDL, Tibialis posterior
Bipennate musles
- Fibers run obliquely from a central tendon on both sides
- e.g. Rectus femoris, FDL
Anatomic determinants of muscle contractions
- Location of bone landmarks for origins and insertions
- Action of other muscles that may affect joint movement
Pectineal line
- Pectineus muscle
- Adduction of thigh
- Lateral rotation of thigh
- Flexion of hip
Linea aspera
- Adductor magnus
- Adductor brevis – upper 1/3 medially
Knee joint flexion
- Muscles posterior to knee axis
- Hamstring muscles
- Movement in the sagittal plane
Prime mover (agonist)
- Concentric contraction
- Does most of the work required (primary mover)
- “Assisters” (secondary movers)
Prime mover (agonist) example of knee felxion
- Hamstrings, sartorius, gracilis, popliteus and gastrocnemius are all agonists, but…
- The hamstrings are the primary mover
Antagonist
- Eccentric contraction
- Located on the opposite side of the joint from a prime mover
- Opposes the action of another muscle
Antagonist example of knee flexion
- Quadriceps oppose the hamstrings
- Knee extension
Flexion/stabilization
- Isometric contraction
- Steadies proximal parts while movement occurs in the distal segments
- Provide proximal stability
Synergist
- Compliments action of prime mover
- May be referred to as “guiding” muscles
Neutralizers
- Neutralize the action of other muscles
- Resist specific contractions of other muscles
Neutralizer example
- Biceps contracture
- The pronator teres would resist the supination component
Force coupling
- Allow for rotation around an axis
- Two or more forces are pulling in different directions
Force coupling example
- Steering with two hands
- One hand pulls wheel up and right
- The other pulls wheel down and left
Types of muscle fibers
- Oxidative red fibers (type I)
- Glycolytic white fibers (type IIa, IIb/x)
Oxidative red fibers (type I)
- Possess myoglobin
- Higher resistance to fatigue
- Generally produce less tension than white fibers
Glycolytic white fibers (type IIa, IIb/x)
- Produce greater forces
- Have a greater shortening velocity
- Fatigue more quickly
Type I (slow twitch) muscle fibers
- Oxidative
- Red fibers
- Use oxygen to generate ATP
- Fire slower, fatigue quicker
Type I (slow twitch) muscle fibers are used more for
- Continuous, extended contraction over a long time
- Endurance
Type IIA (fast twitch) muscle fibers
- Oxidative
- Intermediate fast twitch
- Red fibers
Type IIA (fast twitch) muscle fibers are used more for
- Sustained power activities
- Large amounts of myoglobin
Characteristics of type IIA (fast twitch) muscle fibers
- High capacity for generating ATP
- Fast contraction velocity
- Resistant to fatigue
Type IIB(X) fast twitch muscle fibers
- White fibers
- Generate ATP by anaerobic processes
- Highest contraction velocity
- Fatigue easily
Type IIB(X) fast twitch muscle fibers are used more for
- Short-duration, high intensity power bursts
- Relatively few mitochondria
Fiber length within the muscle affects
- Magnitude of joint motion
Concentric contraction of a muscle is
- The sum of sarcomere shortening
Sarcomere arrangement
- Arranged in series
- The more sarcomeres in a fiber, the longer the fiber is…
- The more it is able to shorten
Actin (thin) filaments
- The “I band”
- Change length along with the sarcomere
- Anchored at both ends of sarcomere by z disks
Myosin (thick) filaments
- The “A band”
- Relatively constant in length during contraction
Sliding filament theory
- Myosin is able to “grab” actin filaments
- Through cross-bridges with actin it can pull the z-bands together
- Results in muscle shortening and concentric muscle contraction
Angle of application
- The location of the muscle on the bone and the line of pull of the muscle and limb to which the muscle attaches
The length of the moment arm will influence
- Excursion of the joint
- A muscle with a longer lever arm must be able to shorten more
Muscles are the effort in levers
- Fulcrum = joint axis
- Resistance = load, body part being lifted
- Effort = muscles
Class 1 levers
- Designed for balance
- The mechanical advantage (MA) is balanced (MA = 1)
- Force arm = resistance arm
Class 2 levers
- Mechanical advantage is greater than 1
- Force (effort) arm > resistance (load) arm
Class 3 levers
- Possess the mechanical advantage of range of motion
- MA < 1
- Force (muscle) arm < resistance (load) arm
Factors that influence muscle strength
- Muscle size
- Muscle moment arm
- Stretch of the muscle
- Contraction velocity
- Level of muscle fiber recruitment
- Fiber types within the muscle
Muscle actions on joint movements
- Cause (initiate, accelerate)
- Control (slow down, decelerate)
- Prevent (stabilize against external forces)
Muscle mass components
- 85% muscle fibers
- 15% connective tissue
Isotonic contraction types
- Concentric
- Eccentric
Isometric contractions
- Tension is developed within the muscle
- Joint angles remain constant
- Considered to be static contractions (active tension)
Isometric contractions functions
- Stabilize joints
- Resist external forces
Characteristics of isometric contractions
- Length remains constant
- No movement occurs
- Muscle tension increases to resist gravity or other antagonistic forces
Isometric contraction in the arm example
- Biceps is maintaining elbow in flexed position (triceps is agonist)
- Triceps is maintaining elbow in flexed position (biceps is agonist)
- Both isometric contractions
Isometric contractions are helpful for
- Effective for sculpting
- Help maintain strength
- Will improve strength only in one particular position
Active tension in muscles of isotonic contractions
- Cause joint angles to change
- Control joint angle change initiated by external forces
Isotonic contractions can involve
- Lengthening of the muscle
- Shortening of the muscle
Concentric isotonic contraction
- Muscle shortens
- Movement occurs
- Contractions result in shortening of muscle
- The force generated by the muscle is less than its maximum
Eccentric isotonic contraction
- Muscle lengthens
- Antagonizes prime mover
- Acts as brake
Concentric isotonic contraction examlpe
- Biceps is agonist causing flexion of the elbow: concentric contraction (triceps is antagonist)
- Triceps is agonist causing extension of the elbow: concentric contraction (biceps is antagonist)
Concentric isotonic contractions will occur when
- Muscle shortens
- Muscle develops enough force to overcome the applied resistance
- Movements against gravity
- Joint angle changes in direction of applied force
- Accelerate movements of a body segment
Muscle lengthening in eccentric contractions
- The external force on the muscle is greater than its maximum
- The muscle lengthens under active tension
- Tensions are high, but gradually lessen to control descent of movement
- Decelerate movement of a body segment
Eccentric contraction examples
- Biceps is controlling elbow extension; triceps is agonist or prime mover
- Triceps is controlling elbow flexion; biceps is agonist or prime mover
Physiologically common effects of eccentric contractions
- Much of normal muscular activity occurs while lengthening
- More forceful
Effects of eccentric contractions on muscles
- Muscle injury and soreness (selectively associated with eccentric contractions)
- Muscle strengthening (eccentric may be most beneficial)
Common examples of movements utilizing eccentric contractions
- Going down stairs
- Running downhill
- Lowering weights
- The downward motion of squats, push ups or pull ups
- Common in controlled or resisted type of movements
Eccentric exercise set example
- Begin with straight leg with the ankle in plantarflexion
- In a controlled manner, lower foot below step edge )this dorsiflexes the ankle but eccentrically affects the tendo achilles)
- Repeat
Passive stretch
- Muscle is lengthened while in a passive state
- Tension occurs outside the cross-bridge mechanism
Benefits of passive stretch
- Increased flexibility
- Increased blood flow to muscles
Myosin in cross bridges
- Globular end called the S1 region
- S1 region can bend or “reach up” to grab the actin binding sites
- The tail (S2 region) also demonstrates flexibility and rotates with S1 contraction
Cross bridge cycle
- The process is repeated
- Myosin-actin cycling occurs
- These myosin S1-actin bonds are the cross bridges
- Contraction of the S1 segment (power stroke)
- ATP is required
Tropomyosin
- Can block myosin binding to actin filament
- It rotates around the actin filament to expose binding sites
- Requires calcium
Troponin
- Shifts the position of tropomyosin
- Requires calcium
Contractile component of muscle
- Actin-myosin crossbridges
- 85% of muscle mass
Parallel elastic component of muscle
- Muscle connective tissue
- 15% of muscle mass
Series elastic component of muscle
- Connective tissues within the tendon
Passive tension
- Through external forces
- Muscle stretched beyond its resting length
Active tension
- Number of motor units and fibers recruited
- Greatest amount of tension: 100 to 130% of its resting length
Muscle active tension greater than 130%
- Decreased ability to develop tension
Muscle active tension less than 50-60%
- Decreased ability to develop tension
Active length-tension curve of muscle
- Bell shaped
When active muscle is at its longest or shortest
- Force is minimal
- Potential cross-bridge formation is minimal
When active muscle is at 1/2 length
- Maximum force
- Maximum cross-bridges can be formed
- Resting length
Passive length-tension curve
- Begins at resting length
- Tension exists in the muscle when stretched beyond its resting length
As muscle begins to stretch passively
- Tension rises slowly
- Will then rise quickly until the yield point is reached
- Beyond this point, injury will occur
Total force produced by a muscle
- Active Force generated by the actin-myosin cross bridging plus…
- The Passive Force from the non-contractile elements when stretched beyond resting length
Parallel elastic component of muscle (muscle connective tissue)
- Endomysium
- Perimysium
- epimysium
Endomysium
- Sheath of individual muscle fibers
Perimysium
- Divides muscle into a series of “compartments”
- Made up of fascicles
Epimysium
- Surrounds the entire muscle
- Connected to the deep fascia
Tendons
- Transmit force created bymuscleto bone
- Arise from muscle at the myotendinous junction
- Attach to bone through the enthesis
Tendon forms a gradient to bone
- Type 1 collagen
- Fibrocartilage
- Cartilage
- Unite with bone
Purpose of tendons
- Active role in joint movements
- Increase muscle movement distance
- Centralize strength
- Distribute force load to several bones
- May connect two muscles
Example of tendon strength centralization
- Achilles tendon
Example of tendon force load distribution
- Posterior tibialis
Example of tendon connecting two muscles
- Conjoined tendon of adductor hallucis
Pulley systems
- Provide directional advantage
- The force and its magnitude remain the same on both sides
- Change the direction of the force
Pulley systems act as as class 1 lever
- Patellar tendon
- Lateral malleolus
Tendon shape varies
- Round = respond equally to tensile loads
- Flat = resistant to compression and shear forces
Fiber alignment of tendons may change position
- Tendo Achilles
- Soleus fibers begin deep to gastrocnemius
- Posterior fibers rotate laterally ~90 degrees
Series elastic component of muscle (tendon)
- Parallel arranged, tightly packed collagen fibrils
- Interlaced with elastic fibers
- Possess a “wavy” or “crimped” appearance at rest
- Have a proteoglycan matrix
- Fibroblasts
Stress-strain curve for tendon elastic region (two parts)
- Section 1 = the toe
- Section 2 = Young’s modulus
Toe section of stress-strain curve
- Collagen fibers uncrimping
- Little tension
Young’s modulus section of stress-strain curve
- Fibers elongate 3-4% before the yield point
Stress-strain cure for tendon plastic region
- 4-6% additional strain until failure
Properties of tendons
- Elastin content (dry weight) ~2%
- 7-10% strain before failure
Properties of ligaments
- Elastin content (dry weight) up to 60%
- ~15% strain before failure
- Lower percentage of collagen
- Higher percentage of proteoglycans and water
- Less organized collagen fibers
Commonalities between tendons and ligaments
- Transfer forces between musculoskeletal tissues
- Low oxygen and nutrient requirements
- Low cell density
- Poor regenerative capacity
- Poor vascular supply
