Musculoskeletal Biomechanics Flashcards
What are the terms used in a Muscle contraction?
Twitch: single contraction resulting from a threshold stimulus, myosin pulling on actin causing sarcomeres to shorten
Latent Period: Time between when muscle stimulated and any actual sarcomere shortening
Summation: Addition of indiviudal twitch contractions to increase intensity of overall muscle tension
Tetanic contraction: Motor unit maximally simulated by its motor neuron
Describe the mathematical model which describes the tetanic contraction
Hill’s Model which describes the muscle mechanical response
One contractile element: Comes from force produced by actin and myosin cross briges in the sarcomere
Two non-linear spring elements
One in series: tendon and intrinsic elasticity of myofilaments
One in parallel: passive force of connective tissues responsible for muscle passive behavior when stretched
Show the mathematical equation of Hill’s model and describe what it represents
(v+b)(F+a) = b(F0+a)»_space; b = a*v0/F0
Shows that relationship between force and velocity is hyperbolic, meaning increased load results in decreased velocity
Describe the force and velocity relationship, in relation to concentric and eccentric movements.
CC: Force declines in hyperbolic fashion in relation to isometric force as shortening velocity increases (reaching 0 at certain max velocity)
EC: Force increases above isometric maximum when lengthening/stretched (reaching absolute maximum)
Explain why the force x velocity relationship for CC and EC occurs in that way
Force generated by muscle depends on total number of cross bridges attached
Relative filament velocity decreases»_space; more cross bridges have time to attach and generate force `
What are the types of tests used for testing in each area of the force velocity curve?
Maximum str - Isometric mid thigh pull»_space; high force gen, low speed requirements
Strength-speed - weighted jump squat»_space; med-high resistance req, as fast as possible
Speed-strength - Unweighted jumps (horizontal/vertical)»_space; low resistance, high velocity
Reactive strength - Drop jumps»_space; movement high velocity, low resistance
Speed - movement high velocity, low resistance
When do muscles show the greatest tension? In terms of force x length relationship.
Ideal length of 120-130% > optimal sarcomere overlap
Isometric tension generation in skeletal muscle is function of optimal magnitude of overlap between actin and myosin filaments
Too little tension, excessive overlap. Too much tension, inadequate overlap.
How does the Hill Model 3 elements fit into the force length relationship? Can you draw the force length curve diagram?
The passive tension increases while active tension decreases.
Stretch in 20-30% will increase tension by passive elements that is summed to tension by contractile element.
What is EMD in the Force x Time relationship?
Electromechanical delay, time lag between activation and muscle force production.
Assesses muscle function in healthy subjects
About >20 ms (Type 2)
<100 ms (Type 1)
Can you describe the schematic representation and what are the processes involved in the time lag / EMD?
Muscle stimulation: 0-6.05ms (synaptic transmission, EC coupling, Series Elastic Component)
Onset of Fascicle Motion: 6.05-8.42ms (aponeurosis)
Onset of Myotendinous junction motion: 8.42-11.64ms (tendon)
Onset of Force Production: 11.64ms
What is the Isokinetic Dynamometer and what does it assess? What are the different modes and what do they assess?
It assesses dynamic muscle strength during constant angular velocity movements
4 Test modes,
Passive Mode, Isometric Mode (length), Isokinetic Mode (angular velocity), Isotonic Mode (tension)
What are the Outputs for a Isokinetic Dynamometer? And what are the subsequent relationships we can obtain?
Joint Angle, Joint Speed, Joint Torque.
Subsequently
Torque-angle relationship: resembling force length relationship, quadratic shape
Torque-angular velocity relationship: resembles force x velocity relationship. Negative velocity = eccentric phase and Positive velocity = concentric phase.
What are the two types of imbalances ratio we can observe from the Isokinetic Dynamometer?
Ipsilateral: Opposite muscle groups
Contralateral: Opposite limbs
Describe the two ratios we can derive within the Ipsilateral group
Upper limb - Shoulder Rotator Cuff, External Rotator / Internal Rotator.
0.66-0.75 normal, <0.66 - high chance of injury
Lower limb - Knee ACL, Hamstring / Quadriceps ratio.
<0.50 - high chance injury, -0.50 - 0.80 - normal, >0.80 low
What are the identified factors that affect HQ ratio?
Warm up: Warm up increases HQ ratio FIFA11+
Fatigue: Decreases HQ ratio
Competitive Level: Pro > lower HQ ratio
Sex: Females higher risk, lower HQ ratio after LIST
Injury History: ACL injury > higher hamstring str»_space; lower HQ ratio`
