Hi! This is a complete summary of the master course of human movement science, 'Concepts in HMS'. I did visit/summarize all the lectures of the course and summarized all the chapters of the book and articles. Enough information to pass your exam! Good luck!
Hi! Dit is een complete samenvatting v...
Samenvatting hoorcollege Concepts in HMS + online boek en vragen
1. introduction
football coach asks you to design aerobic and strength training and you have to
advise them what is core stability and is it a useful training?
questions about abstract 1:
1. Does core stability prevent injury in athletes?
2. injury
3. hip abduction, external rotation, abdominal muscle function, and back
extensor and quadratus lumborum endurance.
4. Core stability has an important role in injury prevention.
5. to improve the strength of hip abduction and external rotation.
6. maybe, because a stronger hip abduction may reduce the lateral
displacements. which is a strong predictor of knee injuries.
questions about abstract 2:
1. is a reduced trunk neuromuscular control related to knee injuries?
2. trunk displacements, proprioception, and history of low back pain
3. knee, ligament and ACL injuries
4. Trunk displacement was greater in athletes with knee, ligament, and ACL
injuries than in uninjured athletes, lateral displacement was the strongest
predictor. But this does not count for the male athletes.
So, the concept of stability appears to be important in different contexts.
- joint instability which can be fixed with taping or a ligament reconstruction or…
- functionally unstable → ankle which has a reduced ability of control.
The aim of this class is to clarify the concept of stability and how it can be assessed
2. stability, a mechanical perspective
inverted pendulum: omgekeerde slinger waarvan het massamiddelpunt boven het
draaipunt ligt. het is instabiel en zonder ondersteuning valt het om.
The pendulum can be a model for a single body segment or for several segments over a
single joint, e.g. all segments cranial of the ankle
m = mass
h = height above hinge joint R
a hinge joint (scharnier) has 1 df → orientation y to describe the orientation of the pendulum.
movement can be described when the following are known: angular velocity (dy/dt) and
angular acceleration (d2 y/dt2).
,static equilibrium (ψ is constant and dψ/dt and d2 ψ/dt2 are zero) → in upright position
because otherwise, the gravity will cause a moment (acceleration = not equal to zero)
airflow from left to right that would cause a moment around R. Consequently, a negative
(clockwise) acceleration would occur and the pendulum would move to a new orientation in
which gravity would start to exert a moment (Figure 1B) that would cause the pendulum to
fall over in the clockwise direction.
any change in angle due to a perturbation will lead to an increase of the moment due to
gravity in the same direction. In other words, dM/dψ, with M representing the net moment on
the pendulum, is positive
asymptotic stability = A system is stable when it can successfully return to its planned
state after an infinitesimally small perturbation. More precisely, this is called asymptotic
stability.
Figure 1 = potential energy is the only gravity, which decreases when the system is
perturbed (mhg). potential E is maximal when the height is maximal in an upright position.
How can we stabilize an inverted pendulum?
The instability of the inverted pendulum as described above is due to the fact that dM/dψ is
positive. → M grows when the perturbation magnitude grows.
spring:
- It will change length with each perturbation (dψ)
- the length of the change will cause a force (Fs)
- it will exert a moment on the pendulum (Ms)
- if Ms is larger than the moment exerted by gravity dM/dψ is negative and the
pendulum is stable.
In terms of potential E: the increase in elastic potential energy due to perturbation dψ is
larger than the decrease in gravitational potential energy.
,K = stiffness of the spring.
Fs = -k * d*l
minor perturbation increases the stiffness of the spring. (figure 3)
questions: ????
1. What happens to the inverted pendulum after the perturbation for the lowest value of
K (top window in Figure 3)?
- will ends flat on the floor
2. Why does this happen?
3. What differences are apparent in the mechanical behavior of the pendulum between
the 2nd and 3rd rows?
- the lowest figure has a stiffer spring because the oscillations are higher.
4. What is the effect of damping on the mechanical behavior of the pendulum after the
perturbation?
- it will produce a force with a magnitude depending on the rate of change in
length of the pendulum with an opposite sign to the velocity of the change in
length.
lower K → system is unstable and a very large deviation of the orientation occurs, which
ends with the pendulum flat on the floor. regardless of the magnitude of the perturbation.
larger K → system is stable, that is the displacement is bounded (begrensd) and dependent
on the magnitude of the perturbation.
Stability formally only describes this dichotomy but in behavior, it can be observed as
different values of K at which the system is stable.
→ For higher values of K, the displacements of the pendulum are smaller and the
frequencies of the oscillations are higher.
snap ik niet???
It should be noted that increasing the moment arm of the spring will increase the effect of the
spring and it does so quadratically. This, because the elongation of the spring dl increases
linearly with the moment arm, and hence also the spring force Fs increases linearly, but the
increase in moment dMs produced with each increase in force is also a function of the
moment arm.
dampers: Dampers are elements that produce a force, with a magnitude depending on the
rate of change in length of the element (pendulum) and a sign opposite to that of the velocity
of the length change.
Fd= -b * dl/dt (b is coëfficiënt)
potential E: dampers dissipate kinetic energy and transform it to heat.
, performance of a system: can be defined as the ability of a stable system to limit the
effects of perturbations of a given magnitude. (the magnitude of resulting displacements, the
rate at which system can return to the planned state, or the number of oscillations.)
robustness of a system: is the property that describes the maximum perturbation that a
stable system can tolerate/ to describe to what extent a system will remain to be stable after
damage has occurred.
perturbations: forces, moments or torques that cause an unintended change of the current
equilibrium (the planned state)
- duw
- landen om 1 voet
- wind
- etc…
sports which need good core stability:
- a lot of different perturbations
- breathing is also a mechanical effect on the trunk
- cross country shooting: precision (breathing after the skiing, heartbeats can cause
perturbations)
- climbing: balance
- soccer: ballistic movement, rapid acceleration of the leg, it will cause perturbations on
the trunk
Important in injury risks: ACL injury in non-contact invents.
The lateral trunk and knee abduction motions after landing is a very important predictor.
not controlling the trunk will cause big moments on the knee joint/ lower extremity forces
make a list of physiological and biomechanical factors:
● strength
○ hip abduction
○ hip external rotation (p< 0.05 and OR of 0.86)
○ proximal muscles are important
● muscle endurance
○ keep your body horizontal for as long as possibly
● neuromuscular coordination
● neural control
○ displacement after perturbation
○ release the magnet
○ laterale displacement
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