Biomechanics Flashcards
what structure is responsible for the elastic behaviour of ligaments
elastin
ultimate stress occurs at what point on the stress-strain relationship curve
failure point
weight acceptance occurs during which component of the gait cycle
loading response
the ability of a material to absorb energy during plastic deformation before failure is called what
toughness
by how much (of resting length) can a muscle stretch before rupture
160%
the technique of surface emg is not generally used to provide information on which of the following…
- when a muscle is actively contracting
- the pattern of activation in skill aquisition
- the onset of fatigue
- potential adaptations within the nerves as a result of training
- single motor action potentials
single motor action potentials
which of the following causative extrinsic factors affect the emg signal?
- sampling rate
- cross talk
- orientation of electrodes with respect to the direction of fibres
- analysis software
- type of transducer
orientation of electrodes with respect to the direction of fibres
the hip and ankle positions during an isokinetic knee extension protocol are important considerations as they alter the length of which biarticular muscles
rectus femoris and gastrocnemius
during an isokinetic testing protocol, what happens to the duration of the isokinetic phase as the angular velocity increases
decreases
what sports performers would be more likely to display bilateral facilitation and why?
weightlifters as their movement uses both legs working at the same time
the measurement of the anatomical cross sectional area (ACSA) of a muscle should be made…
perpendicular to the long axis of the muscle
what is the advantage of an in-parallel muscle fibre arrangement
greater maximum force
what is the effect of the low pennation of the gastrocnemius in comparison to the high pennation of the soleus
gastrocnemius has increased range of motion
how does pennation effect the range of motion of a muslce
low pennation = higher range of motion
contralateral hamstring-quadriceps imbalances greater than what % are associated with greater injury risk
10%
the contraction velocity of type II motor units compared to that of the type I unit is…
three times greater
how do muscles with a small physiological cross-sectional area (PCSA) produce high joint torque
by having a large moment arm
which of the following testing conditions should not be violated when performing strength and power measurements
- movement pattern
- joint velocity
- load characteristics
- posture
- all of the above
all of the above
the anteroposterior (x-direction) GRF at foot contact with the ground during a landing drop jump was 180 N. If the foot’s mass was 1.2 KG and its x-acceleration was 50m/s^2, what was the anteroposterior joint reaction force at the ankle?
-120 N
what electrical variable is measured when analysing muscular activity using EMG
voltage
the term pronation (at the subtalar joint) is often used interchangeably with what other term
Eversion
2 crucial factors in how & where injury occurs
- the load
2. characteristics of the loaded structures
types of injury
chronic (overuse) injury
acute (traumatic) injury
chronic (overuse) injury definition
results from repeated overloads with insufficient time for recovery
acute (traumatic) injury definition
results from a single or a few repeated episodes
what’re the differences between stress and strain
- Stress: the measure of how much deformation arises from an applied load
- Strain: the amount of resistance to this deformation
what is the Young’s modulus of Elasticity (E)
the ratio between stress and strain (strain/stress)
define Wolff’s Law
bone forms in reaction to the force placed on it (force not stress)
types of bone fractures (Bartlett, 1999) and the load causing them
- Diaphyseal impaction (load = axial compression)
- Transverse (load = bending)
- Spiral (load = torsion)
- oblique transverse/butterfly (load = axial compression and bending)
- olblique (load = axial compression, bending and torsion)
examples of viscoelastic tissues
- tendons (tough cords of closely packed collagen fibres)
- aponeuroses (sheet-like tendons)
- deep fascia (bind muscles together)
(Kibler & Chandler, 1993) trainable factors which have a genetic/intrinsic source
- coordination
- incorrect BW
- poor posture
- lack of joint mobility
- lack or imbalance of muscle strength
anatomical differences in women that lead to increased injury risk…
- a wider pelvis (resulting in altered hip and knee loading)
- smaller bones and surfaces (typically 30% less than males)
- greater rate of loss of bone with age
- less muscle mass and higher fat content
reasons for abnormal gait (x7)
- neurological disorders
- skeletal disorders
- muscular disorders
- pain
- age
- personality (e.g. depression)
- inability to hear and see?
what muscle acts as a stabiliser to the hip abductors
gluteus medius
describe the process of SSC fatigue (4 points)
- deteriorated muscle function
- reduced tolerance to impact
- loss of elastic energy potential
- increased work during push-off phase
3 potential sites of failure/fatigue
- those within the CNS
- those concerned with the neural transmission from CNS to muscle
- those within the individual muscle fibres
sources of metabolic fatigue
1) simply muscles running out of fuel (muscle glycogen)
2) lactate build up in muscles, affecting the binding of calcium to troponin and also the functioning of enzymes
essential characteristics of a running shoes (x6)
- attenuation of single/multiple impact forces
- preservation of foot stability (rearfoot control)
- adequate friction/traction
- provision of different foot-strike patterns
- heat dissipation
- comfort
what are the neural factors which influence force generation (x3)
- the number of motor neurons that are activated (recruitment)
- the size of the activated motor neurons
- the rate of which they discharge action potentials (rate coding)
process of picking up a signal (EMG)
detection of the potential fluctuations (electrodes) -> signal transmission (hard wire/telemetry/data logger) -> signal modification (amplifier) -> storage of the resulting waveform (computer)
examples of intrinsic (non-controllable) factors affecting EMG signal
- physiological: number of active MU’s, MU firing rate, fibre type, blood flow…
- anatomical: fibre diameter, depth & location of fibres
examples of extrinsic (causative) factors affecting EMG signal
- impedance: skin prep, electrode impedance tester
- orientation of electrodes
- location of electrodes: not on outside edge/motor point/tendon
how can we manipulate neural factors during training
by manipulating…
- training intensity
- cadence
- number of reps
methods of reducing cross talk
- decrease electrode size and spacing
- placing electrodes on muscle belly
- double differential technique (3 electrodes)
advantages of MVC
- allows comparisons with other muscles/subjects and between studies
- eliminates any influence of the detection conditions
disadvantages of MVC
- ability to consistently elicit MVC varies between individuals
- poor repeat ability of EMG from MVC
- mechanics of movement (MVC at fixed angle)
Baltzo and Gleeson (2001) produced a deterministic model highlighting several physiological and mechanical factors affecting strength and power. Within this model which of these factors is associated with joint position?
moment arm
what is the % of force produced by a muscle that can be attributed to the CSA according to Semmler & Enoke (2001)?
50%
the maximal conduction velocity of a large alpha motor neuron is…
up to 101 m/s
mechanisms associated with PAP (x4)
- an increased sensitisation to the phosphorylation process on the myosin light chains
- increased alpha motor neuron recruitment
- reduced reciprocal co-contraction
- decreased angle of pennation
methods of eliciting PAP (x3)
- vibration activation methods
- isometric activation methods (electrically/voluntary induced)
- dynamic activation methods (isometric strength/plyometric exercises)
Post-activation potentiation (PAP) definition
implementing a resistance exercise prior to an explosive movement has improved subsequent performance above the athletes perceived best
physiological and mechanical factors affecting strength (x5)
- types of muscular actions
- length & velocity of isolated muscle
- moment arm
- joint velocity (muscle groups)
- joint position (muscle groups)
in a single muscle fibre, at what length is force the greatest (and why)
- force is greatest at intermediate lengths & decreases at shorter & longer lengths
- because… more binding sites available & consequently greater number of cross-bridge attachment at intermediate lengths
at the whole muscle level, at what length is force the greatest (and why)
-strongest at most stretched due to elastic component of tendon
in what type of muscle action is force production the greatest?
Eccentric
variation in net muscle torque depends on… (x2)
- the location of the attachments to the skeleton
- the contribution of multiple muscles to the net effect about a joint (one vs two joint muscles)
what are the advantages when the tendon inserts further from the joint
the muscular moment arm will be longer and the mechanical advantage increased
what are the disadvantages when the tendon inserts further from the joint
- the muscle has to contract more to make the joint move through a given ROM
- this translates to less speed
how does the moment arm influence the demands of an exercise (dead lift)
- dead lift = large moment arm which is a mechanical disadvantage
- different stance = smaller moment arm, easier to produce force as hip is closer to the bar
how does moment arm explain hamstring injuries (during sprint)
- has smallest moment arm as it has to be stretched the most
- inter muscle differences in hamstring moment arms about the hip & knee may be a factor contributing to the greater propensity for hamstring strain injuries to occur in the BF muscles
how does moment arm explain the effect of stature (height)?
-tall athletes immediately at a disadvantage because levers are long and form huge resistance arms
when and when is not PCSA equal to ACSA
PCSA = ACSA in parallel arrangements
PCSA does not = ACSA in pennate arrangements
key properties of Type II Motor Unit
- fast contraction velocity
- fatiguable
- increased Motor neuron size, fibre diameter & innervation ratio
key properties of Type I Motor Unit
- slow contraction velocity
- fatigue resistant
how does high pennation influence muscles
- increased strength
- pennation allows the PACKING OF MORE MUSCLE FIBRES PER CSA, thus generating greater force
how does low pennation influence muscles
-increased range and velocity
how does pennation influence muscle thickness
high pennation = decreased thickness
low pennation = increased thickness
how does fibre length effect joint contractions
- longer fibre length = greater ROM & velocity of contraction
- shorter fibre length = increased force production BUT worse for fast contractions
purpose of strength assessments
- ability to distinguish between athletes at different levels
- indicator of good athletic performance
- correlation with athletic performance
- sensitivity to training adaptations
- availability of normative data for comparison
- injury prevention
benefits of strength testing
- easily performed
- execution of a similar movement to the one performed during the sporting activity
- some quantification during submaximal lab based tests
- suitable communication to coaches & athletes
limitations of strength testing
- typically little scientific analysis
- some quantification techniques not as accurate as lab based tests
- issues with accuracy and reliability
- inability to test specific muscle groups
strengths of isometric strength testing
- muscle group isolation
- accurate & reliable
- quantification & detailed biomechanical analysis
- allows collection of accurate & reliable EMG data
- availability of normative data for comparisons
limitations of isometric strength testing
- specific joint position strength
- difficulty to elicit an MVC
what 2 distinct bonds make up the ACL and what is their roles
anteromedial (protective when knee flexors) and posterolateral (protect when knee is extended)
how could you reduce the chances of an ACL injury by altering the biomechanics of an athlete’s movement
- decrease frontal plane knee joint angles
- decrease frontal plane knee loading
- increase sagittal plane knee joint angles
- decrease sagittal plane knee loading
key kinematic variables of a drop jump (x4)
- impact loading rate 10-90%
- peak impact force
- average impact force
- peak propulsive force
how to calculate muscle tendon stiffness
maximal force / displacement CM
what training methods have been observed to improve strength
- iso-inertial training
- isometric training
- isokinetic training
- neuromuscular electrical stimulation
factors that can affect the type/magnitude of adaptations (x7)
- age
- training history
- gender
- genotype
- concurrent activities
- training programme design
- nutritional status
What adaptations did Cormie et al (2010) find in strength vs. power training (similarities and differences)
Similarities
-both methods increase jumping & sprinting performance (BUT via different pathways)
Differences
-power training = increased neural drive & force + RFD
-strength training = increased neural drive, muscle thickness, force and RFD
what are the 3 primary stimuli of muscle hypertrophy
- tension
- muscle damage
- metabolic stress
what is inclusion training + what does research say about it (include possible mechanisms)
- method of restricting blood flow by placing an pneumatic cuff at the most proximal part of the arms/legs
- been shown to increase muscle size and strength
- possible mechanisms: increased MU recruitment, pooling of intramuscular metabolites
strength improvements in the absence of increases in muscle size may result from… (x3)
- non-hypertrophic muscular adaptations
- neural adaptations
- limitations with the techniques used to quantify changes in CSA
potential sites of neural adaptations (x8)
- enhanced output from supraspinal centres
- reduced co-activation of antagonist muscles
- greater activation of agonist & synergist muscles
- enhanced coupling among spinal interneurons
- changes in descending drive
- shared input to motor neurons that increase MU synchronisation
- greater muscle activation
- heightened excitability & altered connections onto motor neurons
to what extent does disuse halt the activation of involved muscles (Semmler et al, 2000 findings)
- EMG of elbow flexor muscles with arm cast on
- findings: decreased bicep brachii and brachioradialis by 38% & 29% respectively
- also women displayed a greater reduction in EMG than men
the underlying causes of immobilisation affecting muscle size
- reduction in the rate of protein synthesis (Gibson et al, 1987)
- loss of muscle fibres (Oishi et al, 1992)
causes of hind limb suspension
- no changes in EMG of suspended legs
- muscle atrophy (greater in type I muscles)
- increase in EMG of fore limb
how does lower limb strength affect key gait characteristics in older adults
diminished peak GRF’s were associated with slower walking speeds…
-increased risk of mobility limitations, disability, poor health & loss of independence
what is sarcopenia and what is it caused by
What is.. -age associated reduction in muscle mass alongside reduction in muscle strength and/or function Caused by... -reduction in size of individual fibres -loss of individual muscle fibres -or BOTH
which of these bones is commonly broken during strangulation;
- atlas
- axis
- hyoid
- mandible
Hyoid
what is the name of the peg on the second cervical vertebra that projects upwards through the first cervical vertebra?
Dens
what is the most commonly broken bone in the body
clavicle
which of these is NOT a muscle forming part of the quadriceps femoris group;
- vastus femoris
- vastus lateralis
- vastus medialis
- vastus intermedius
vastus femoris
what type of contraction will the trapezius muscle be undergoing during the raising phase of a barbell curl?
Isometric
the cranial nervous system is made up of how many pairs of nerves?
12
which of these is the only muscle which flexes both the hip and the knee;
- rectus femoris
- biceps femoris
- gracilis
- sartorius
Sartorius
in which part of the body would you find the lunate bone
Wrist
moving the thumb towards any other of the four fingers is known as…
Opposition
what is the shoulder joint also known as?
Glenohumeral
What bone has a surgical neck and an anatomical neck?
Humerus
classic formula to calculate muscle size is…
total load lifted / BW (to the power of two thirds)
what 2 lines make up the Q angle
- ASIS to patella
- patella to tibial tubercule
what can pes planus (flat feet) lead to…
- internal tubial torsion
- increased internal femoral rotation
how much more is muscle stiffness encountered in concentric than eccentric muscle contractions and down to what mechanism
- x200 greater in concentric
- due to reflex control
how does articular cartilage decrease stress on joints?
by increasing the load bearing area
what’re the consequences from a ligament injury
- loss of stability
- joint misalignment
- abnormal contact pressure
3 stages of the SSC
- preload
- elastic energy stored
- reflex potentiation
what does the hysteresis loop show
-the energy absorbed during one loading-unloading cycle (area within loop on load-deformation graph)
how do running shoes aid rear foot control
-materials of midsole should be different…
lateral = softer
medial = denser
-reduction of the flare can decrease joint pronation
-a neutral flare is ideal
