Lecture 17, Biomechanical Applications Flashcards
Canon of Proportions
- “the vitruvian man” created by leonardo da vinci in 1487 - see it in order to understand it - shows proportions (understand patterns within the human body)
- system of mathematical ratios based on measurements of parts of the human body (greek sculptor polykleitos 5th century BCE)
- the distance from the hairline to the bottom of the chin is one-tenth of a man’s height
- the distance from the top of the head to the bottom of the chin is one-eighth of a man’s height
- the maximum width of the shoulders is a quarter of a man’s height
- the length of the hand is one-tenth of a man’s height
Anthropometry
adolphe quetelet
- studied astronomy and statistics in paris (~ 1823)
◦ interested in the normal
distribution
- in 1835 he presented his theory of the Average Man
- in 1844, he examined if there was a relationship between body size and criminal behaviour
- in 1853 he devised the quetelet index (BMI)
this was the birth of the science of anthropometry
- the science of measurement of body size
- anthrop (human) metricos (measurement)
- how you are put together and how that affects the thinks you like to do or what you are better at
- if you look a certain way could that explain behaviours? - if you are built a certain way are you more predisposed for certain sporting events
- test kids from a young age and assume they are built for the sport so the develop the kids at the camps
The Anatomy of a Sprinter (heel)
a study compared the foot shape in sprinters and non-runners
- the heels were 25% shorter in sprinters than in non-athletes
- a shorter heal decreases the length of the lever (rigid body)
◦ this means that force is
applied over a smaller area
◦ sprinters are at a mechanical
disadvantage
- stress = force / area
◦ as area decreases, stress
increases
◦ a shorter heel puts more
stress on the achilles tendon
- compared college sprinters (top of their game) and then they found people who looked just like them (height, weight etc. - same body shape) but non-sprinters - is their something different about sprinters than non-sprinters
- anatomical difference: the sprinters had a shorter heel in comparison to non-sprinters - is not a good thing because force is applied over a shorter area - if force is applied over large area the likelihood of injury decreases - force applied over smaller area makes likelihood of injury increase and puts more strain on the achilles tendon (big band of connective tissue) -> plantar flexors really on it to hold everything in place
The Anatomy of a Sprinter (achilles tendon)
- sprinting is all about developing force quickly
◦ slack must be removed before
a muscle can generate force
◦ the longer the tendon the
faster you need to work to
take up the slack
◦ as velocity of contraction
increases, force decreases - sprinters have a shorter achilles tendon than non-athletes
◦ the calf muscles don’t have to
work as fast to generate force
◦ as velocity of contraction
decreases, force increases - sprinters sacrifice leverage
◦ but the muscles force-
generating capacity increases - the tendon in sprinters was shorter than in non-sprinters, muscles is a like a rubber-band, whenever you go to generate force the first thing you need to do is tighten the muscle and rolls over where it can generate force - if you have a lot of slack in a muscle that is a lot of time to tighten everything up - having a shorter tendon means you do not have to work very fast or long to tighten the tendon and get the muscle in force generating position - can generate force much quicker and they are not sacrificing as much because non sprinters have to work so much faster to get the same force generating capacity and get ready
- sprinters lose some stuff in bone shape but that result in shorter tendon which allows them to generate force quicker and muscles are ready to generate force quicker
- sprinters lose magnification of muscle (lever) but force generating capacity increases as a result
- does this happen during development, training or born - do not care but the sprinters body is different and that difference is beneficial - the bones and muscles look differen
The Anatomy of a Sprinter (bones - toes)
- sprinters have longer toes than non-runners
◦ having longer toes generates a
longer impulse
‣ the toes are in contact
with the ground longer
‣ more time to apply the
force against the ground - there is an energy cost to having longer toes though
◦ greater muscle effort required
to push the body - research has shown that toe length can change over time
◦ disease and activity can affect
how bones and tendons length
◦ evolutionary research
◦ long distance runners have
shorter toes - the toes in sprinters were longer in comparison to non-sprinters
- all about apply force to the ground to propel yourself forward so if you have longer toes you keep the foot in contact with the ground longer being able to apply torques over a much longer period of time generating a bigger impulse (change in momentum -> change in velocity)
- sprinters can create a bigger change in velocity because of longer toes as they can apply more force
- all designed to make them better at generating forces quicker - downside is you tire out quicker so you cannot run as long distances - endurance, long distance runners feet structure is different than that of sprinters
- long distance runners (bigger heel, shorter toes) have exact opposite composition to sprinters - what your foot looks like can determine what type of running you are suited for
- body shape does dictate what activities you may or may not be suited for
Exploring Muscle Activation Strategies
we can use electromyography to study signals in the muscles
- each one of the spikes look the exact same in one section meaning you are listening to one motor unit (on group of muscle cells being innervated by one motor neuron)
- bigger spike all have the exact same shape
- two muscle groups as they coordinate during activity
Recording EMG during Sub-maximal Actions (background information)
- the task was a sub-maximal endurance test
◦ participants held onto a small
object
◦ this created a low-level
contraction at the elbow
◦ instructions were to maintain
effort until fatigued - run out
of all the fibres - participants spent 6 weeks in an arm cast
◦ the idea was to “reset” the
nervous system
◦ the idea was to allow the
muscles to rest
◦ the idea was to remove any
“training” effects - the task was repeated immediately after the cast was removed
- had them perform a task before and after the cast (arm was not hurt) - did sitting around for six weeks have any effect?
- task: with your non dominant hand you had to hold on to something and have a low level contraction where everyone was generating a certain amount of force and start to shake because they fatigue after recruiting all of the fibres
- measured the EMG in the elbow flexor muscles and coordination of those muscles and looked at how long it took you to reach the level of fatigue until you could no longer do it (repeated it twice, before and after cast)
Recording EMG during sub-maximal actions (men vs women in a cast)
- see a little bit of activity in the beginning and as you fatigue you see more activity as you recruit bigger muscle cells and have a larger electrical signal
- how much force you are generating holding onto the object
- EMG looked the same for all of them before they were casted
- activation pattern in males after casting - exact same EMG activity from elbow flexor muscles before and after casting - the only difference was they were weaker after six weeks so they could not last as long
- the electrical activity in women was different - the muscles come on with a lot of activity at the beginning and they start to go quiet and then start to come back on (hockey lines: one line comes on and plays when they get tired another one comes on etc.) - burst of activity right away in brachialis and they it goes quite but enough muscle (brachioradialis) jumps in and it has a lot more activity - EMG pattern shows that when ones goes off the other covers - women could outlast the men in performing the task after casting
- the activation pattern delayed the onset of fatigue - women outperformed men on the task (as look as it is a sub-maximal task the patterns remained the exact same across other tests as well)
- strength and power will typically have men outperforming women due to larger and stronger muscles but in endurance competitions men and women come closer
- typically untrained and male athletes use carbohydrates as primary energy source (release glucose) whereas women due to energy source rely on fat as energy source but it is harder to get out however it is richer energy source that is in system for longer and different EMG pattern (delay onset on muscle) - can explain why we see performance pattern in low force, longer endurance activities
- through training in men who do longer endurance stuff begin to adapt this newer pattern
- fast glycolytic fibres give you 60-90 s max but small oxidative fibres are able to keep cycling because the energy is getting to them and we not need to worry about waste products interfering with the metabolism
The Force-Length Relationship
the task was to push against a force-plate with the foot - EMG was measured from the gastrocnemius and soleus muscles
- with the leg extended, both muscles are at an optimal force-producing length
- with the knee flexed, the bi-articular gastrocnemius muscle has been shortened
◦ the soleus length, however,
remains unchanged
- together they generate 70% of the force that exists in your ankle when you plantar-flex
- soleus is largely made up of slow oxidative type I fibres whereas gastrocnemius is largely made up of fast glycolytic type II fibres
- gastrocnemius attaches above the knee playing a role in knee flexion whereas soleus attaches below the knee so it is unaffected by our knee position (so does knee play a role in how we activate these two muscles?)
- long (both are as long as possible) and short position (flexing at the knee shortens the gastrocnemius - gone from tight tissue to flabby rubberband but soleus remains unchanged) are in reference to the gastrocnemius
- EMG measured from the soleus and motor unit activity from the gastrocnemius
- the moment a motor unit came on they were told to hold the force and contraction and that level - looked at when gastrocnemius is activated in comparison to the soleus in one of two position
Knee Extended vs Knee Flexed
- full wave rectification so all you see is positive signal and then envelope which is average signal giving general sense of what happens in soleus - the higher that line the more activity and vice versa
- torque at the ankle - how much force someone is pushing the forceplate (what is measured and how closely the participants matched it)
- motor unit recording from the gastrocnemius muscle - push and it becomes active (listening to one motor unit)
- A line is when they started pushing and generating force where the B line represents the moment gastrocnemius became active
- going into a specific part of the muscle so you can miss another active motor cell in another part so that is why there is separation between A and B cause it only measures what is nearby
The Force-Length Relationship (2)
the task was to push against a forceplate with the foot - EMG was measured from the gastrocnemius and soleus muscles
- with the leg extended, both muscles are at an optimal force-producing length
◦ gastrocnemius is primarily responsible for force production
- with the knee flexed, the bi-articular gastrocnemius muscle has been shortened
◦ soleus is primarily responsible for force production (lots if activity)
- when the knee is extended (both muscles are long) the gastrocnemius comes on right away so very little separation between A and B line in optimal producing length (very little activity in the soleus)
- when you flex the knee and you take a tight gastrocnemius and make it all lose - when the muscle is in a non optimal force producing length it does not do a whole lot (the person pushes but you do not see much for a long time but it eventually comes on and it is a fast glycolytic where you activate the biggest ones cause you are desperate
- eventually is comes on in the flex where you activate the biggest one as you are desperate
- when both muscles are in optimal force producing length, it is the gastrocnemius that is primarily active as it is the bigger, active muscle and can generate lots of force quickly
- the moment you shorten gastrocnemius it becomes in a non optimal force producing length, the muscle is insufficiently able to produce force so another muscles takes over where soleus is mainly active (in this way you can train the weaker muscles as they do not get as much activity when the bigger ones are active
- needle and wire electrodes have recording sites just at the end of it so nothing else gets picked up as opposed to surface electrodes
