Biomechanics of Muscles Flashcards
Describe the Hill muscle model
Three-element Hill muscle model
- models combo of tendons and connective tissues with the muscle
- CC (contractile component)
- interactions between myofilments
- generates active force - SEC (series eleastic component)
- elasticity of tendon and myofilaments - PEC (parallel elastic component)
- connective tissue
Define the terms twitch, latency period, contraction, and relaxation time
twitch
- mechanical response muscle to stimulus
latency period
- time between stimulus and beginning of twitch
contraction time
- time from start of tension development to peak tension
relaxtation time
- time from peak tension to zero tension
Compare and contrast concentric and eccentric muscle contraction
Dynamic –> mechanical work is performed to produce joint mvmt
(both concentric and eccentric are dynamic)
Concentric:
- enough tension in muscles to overcome resistance –> shortening muscle causes mvmt
Eccentric:
- insufficient tension in muscles to overcome resistance –> lengthening muscles causes decelerated jt mvmt
Sketch the force-length and force-velocity relationship of muscles
Force (y) -length (x):
- active tension (contractile components of muscle)
- negative parabola (hill): peak is at the resting length of muscles (maximal overlap between myosin and actin) - passive tension
- 1/2 positive parabola that starts at resting length and increases as muscle length increases
(muscle belly is stretched when past resting length; passive muscle is viscoelastic)
Force-length relationships are the summation of both active and passive tension graphs
Force (y) - velocity (x):
1. concentric contractions
- force inversely related to velocity of muscle shortening
- eccentric contractions
- force (load) proportional to velocity of muscle lengthening
Note: when external load equals maximal muscle force = isometric contraction
Define and sketch the pennation angle as it relates to muscle
Pennation angle:
- angle between muscle’s fibers and its force-generating axis
let V = muscle volume
let I = fiber length
let PCSA = physiological cross-sectional area
let q = pennation angle:
PCSA = V / I * cos(q)
Define 2 differences between type 1, type 2A, and type 2B muscle fibres
Type 1: (slow-twitch oxidative)
- slow contraction (low activity of myosin ATPase)
- high aerobic activity
- small diameter = little tension
- suited for prolonged, low intensity work (high rate of blood flow = resistance to fatigue)
- red (high myoglobin content)
Type 2A: (fast-twitch oxidative)
- fast contraction
- both anaerobic and aerobic
- maintains tension for long period but fatigues at higher rates of activity (well developed blood supply)
- red (high myoglobin content)
Type 2B: (fast-twitch glycolytic)
- anaerobic activity
- large diameter (large tension, most susceptible to fatigue)
- white (low myoglobin content)
How do muscle tears occur and how do muscles reduce likelihood of ruptures?
Tears results from:
- direct injury to sarcomeres via eccentric contractions
Muscles reduce possibility of tears:
1. muscle architecture complexity
- increases strain required for rupture
- active muscle
- requires more force to rupture than passive
Describe 2 effects of a blunt trauma to a muscle
Muscles tense up in anticipation to blunt trauma.
- distributes impact force more broadly (compared to relax)
- reduce likelihood of tears - protects bones from impact
Describe how lengthening strains can progress from tears to ruptures
5 - 20% lengthening strain
- active muscle experiences injruy due to loss of actin and myosin interdigitation
25% lengthening strain
- dmg at muscle tendon junction in passive muscle
73 - 225% lengthening strain
- complete rupture of passive muscle
Describe the effect of muscle length and angle on force
Sarcomeres in series = longer myofibril / muscle
sarcomeres in parallel = thicker myofibril / muscle
Length:
- affects velocity and working range
(long fibers = increased velocity and range)
Cross-section:
- affects produced force of muscle
(short fibers + large cross-sectional areas = increased force)
Why is it important for elastic components to possess distensibility and elasticity properties? (5)
distensibility: ability to swell in response to internal pressure
- Readies muscles for contraction
- Smooth transmission of muscle tendeons during contraction (no jerky mvmts)
- contractile elements return to resting positon after contraction
- prevent overstretch of contractile elements when relaxed
- viscous properties allow SEC and PEC to:
- absorb energy proportional to rate of force application
- dissipate energy in time-dependent manner
Describe what happens in tetanus
- action potential for muscle contractions happens faster than contractions itself
- series of AP sent before twitch is complete –> summation of tension
- max freq occurs when tension in muscle can’t increase further w/ high freq sitmulation (tetanus)
Describe static and isometric contraction
Static:
- no mech work performed, jt position maintained
Isometric (type of static)
- muscle maintains length (not moving) but maintains certain position
compare and contrast isokinetic, isoinertial, isotonic
isokinetic:
- const velocity of muscle lengthening / shortening
isoiertial:
- const resistance during muscle contraction
(weightlifting)
isotonic:
- const tension throughout range of joint motion (during muscle contraction)
Describe how stretching, temperature, fatigue, and virbration effect the muscles
Pre-stretch
- muscle perform more work when it shortens in an already contracted state compared to in an relaxed (extended) state
Temperature
- increase temp –> increases conduction velocity across sarcolemma –> increase freq of stimulation –> increase muscle force
Fatigue
- prolonged stimulation of muscle at a given frequency –> diminishes muscle’s ability to produce sufficient ATP for contraction
- fatigue –> decrease in tension production until it ceases
Vibration
- vibration training improves muscle function by increasing ATP reserves
