Biomechanics Jan 29 Flashcards
As muscle length increases, passive force __ and active force __ and MTU becomes unstable
increases
decr
As increase velocity of muscle force, ___ as velocity changes in both concentric and eccentric direction
decrease
Why do hamstrings fail?
- high active strain of m - large ecc contraction at a long length
When do muscle fasicles lengthen?
ea step/when external force on muscle is > force generated by m fibres to get ecc contraction of fasicles
What determines active force?
- capacity of muscle secondary to size (architecture)
- L of sarcomere
- V of contraction
- Level of activation
If muscle fibres had infinite time to lengthen, generation of force between type I, II would be?
same!
In preactivation m fasicles __ lengthen but get length from ?
do not
tendon
Muscle fasicles do not activate quickly, meaning that their lengthening is difficult…
to control
Tension time graph is an inverted U - where do you get popping of sarcomeres?
second half of U
Once m fasicle length is started, is it difficult to stop?
yes
What is the job of the hamstrings in high speed running?
- support body w, assist hip ext during stance (with glute max)
- MORESO: control knee ext and hip flexion to act as an ecc brake in the 2nd half of swing phase
In modelling of the hamstrings, where is the highest strain and v of lengthening?
later in swing
increased length and increase v highest fasicles
If hamstring is lengthened to a very long length in late swing, is there possibility to produce force at foot contact enough for internal force to combat length and ++ rapid length of fasicles and failure
NO
What is ideal biceps femoris MTU capacity (resting length, etc)
lengthening late swing secondary to tendoon elastic > m fasicle (fasicle therefore isometric and close to resting length)
What was interesting about the study on Turkeys in 2014 that were being dropped from height - how did their gastroc react?
tendon did massive work to attenuate the lengthening velocity
and gastroc activation prior to impact was key
When looking to see if hamstrings act as proximal vs distal muscles, in Bath elite athletes doing nordics, how does MTU react?
at slow ecc contraction MTU is decoupling of strain mtu and fasicle
as contraction velocoity increases, decoupling becomes less and fascicle length increases
some evidence of bicep fem and fasicle decoupling but str increase with increase in velocity
Why do we think hamstrings are able to achieve decoupling at fast velociity?
not just strength
due to timing of activation
Clear RF of hamstring injury
prior injury
sprint mechanics
hamstring weakness
short fasicle length (Timmins et al 2015 = sh and weak = bad bad)
Noted RF of hamstring injury but not well understood
lack of flex is contradictory
?Could be linked to short fasicle length
Data unclear
What can go wrong that makes hamstrings injure?
a. error in activation of m recruitment –> late glute activation and overrely on hamstrings +/- late activation of hamstrings
b. Fatigue - decrease margin of error in factors which determine active force generation
c. Alteration body/limb position –> greater strain on m fasicle (technique/hit a player etc) –> increase margin of error in system so can accommodate a non perfect stride
Ex Adam Gemelli at 2015 Brit champs
If m __ is enough and __ appropriately timed - fascicles SHOULD be able to maintain con/siom state and RQ MTU length by elastic element
strength
activation
Injury prevention recommendations from Dr. McGuigan - 3
strength ecc vs iso better?
fasicle length
appropriate activation at speed
technical adjustment to avoid over strain on MTU
