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Concepts of HMSSeminar 1 Core stability
- Should we train (core) stability?
- How should we train (core) stability?
- How should we monitor progress?
Question breakout session
- Do you do core stability exercises?
o Yes, I do.
- What do these exercises look like?
o Planking, sit-ups, low-back exercises, crunches.
- Considering the nature of the exercises, how would you define core stability, or in
other words what are you training?
o A person’s ability to stabilize their core. It is an ability to control the position
and movement of the core. Stability in the core is important for different kind
of other movements.
- Core = trunk → above the pelvis
Definition of core Stability
First appearance in Pubmed in 2003
- The functional integration of the passive spinal column, active spinal muscles and
the neural control unit in a manner that allows the individual to maintain the
intervertebral neutral zones withing physiological limits, while performing activities
of daily living (Liemohn et al., 2005)
- The ability to control the position and motion of the trunk over the pelvis, thereby
allowing optimum production, transfer and control of force and motion to the
terminal segment in integrated athletic, kinetic chain activities. (Kiber et al., 2006)
- Core stability is a hot issue but still a vague concept, not a clear definition
Towards a definition of stability
- The body’s ability to maintain or resume an equilibrium position of the trunk after
perturbation. (Zazulak et al., 2007)
- Merriam-Webster dictionary:
o The property of a body that causes it when disturbed from a condition of
equilibrium or steady motion to develop forces or moments that restore the
original condition.
Perturbation/disturbance
- “Ability to deal with perturbations”
- Force, moment, or torque that cause an unintended change of current equilibrium
(the planned state)
Assignment breakout session
- List a number of sports activities where a lack of ability to control trunk posture may
affect performance
o Tennis, soccer, hockey, rugby
Trunk stability and performance
- Core stability is important for precision (for your own breathing), balance, ballistic
movement.
,Assignment breakout session
- List a number of sport activities where a lack of the ability to control trunk posture
may be a cause of injury
o Snowboarding, mountain bike, gymnastic
Trunk stability and injury
- Videotapes of athletes captured during an ACL injury requiring reconstruction
compared to similar landings without injury
- Lateral trunk and knee abduction motion are important components of the ACL
injury mechanism
- Lack of control over trunk movements may cause large moments around lower
extremity joints
Instability, a muscle problem?
Core stability measures a risk factor for lower extremity injury in athletes
- Different kind of tests
o Hip abduction
o Hip external rotation
o Back extension → upper body is not supported; the person has to support the
upper body as long as possible
o Side bridge
- The hip external rotation predicts injury → a lower strength results in a higher risk of
injury.
Instability, a neural control problem?
Deficits in neuromuscular control of the trunk predict knee injury risk
- Different kind of tests
o Displacement after perturbation
▪ Lateral, extension of flexion
o Proprioception (APR)
- The lateral and extension displacement and APR are significant predictors for knee
injuries in subjects.
Instability, a joint problem?
Anterior drawer test: high laxity due to ACL rupture
Summary
Stability of / control over trunk movement is important for performance and for preventing
injury. Definitions of stability are often lacking or unclear. Factors considered important for
stability are different between disciplines
,Slidecast 1 A mechanical perspective
Pendulum model for control of joint angle
Posture/movement can be described in terms of joint angles
Body segments are rigid and cylinder or beam like
Joint contact surface is small
Pendulum
- CoM = center of mass
- R = joint (point contact)
- ß = joint angle
- Fg = gravity (-mg)
- Fr = (joint) reaction force
A mechanical definition of stability
Equilibrium
F=0
- Fg = -Fr
M=0
- Moments arms Fg and Fr = 0
Unstable condition
Gravity exerts a moment to the right.
- dM/dß > 0 → this is positive because they are
both to the right
The sum of the moments is not zero
- Second requirement: stable equilibrium:
o dM/dß < 0
Stable condition
Gravity exerts a different moment
The change of the moment has an opposite sign than the change of the joint angle
- dM/dß < 0
How to stabilize an inverted pendulum
The pendulum can be stabilized with a spring. The pendulum is not rigid and can still move a
little bit
Stability:
- -mgh(-sin(ß)) < -dMs /dß
For small angles (sin(ß)) = 1
- mgh <-dMs /dß
mgh → effect mass/ center of mass height
- if you increase the mass or the center of mass height , the pendulum is more difficult
to stabilize → spring moment has to be increase
-dMs /dß → rotational or bending stiffnes (Kb)
Ms = aFs → moment of the spring
Fs = - Kdl
Stiffness (K)
Fs = - Kdl
The force that the spring produces is proportional to the change of the length
If you pull on a spring you experience a resistance, a force in the opposite direction
, Stability can be described as mgh < Kb
Stiffness, stability and performance
Stiffness and damping
Damping is the dissipating of kinetic energy
Stiffness, damping and robustness
Robustness → describes the biggest perturbation that the system can handle
With small perturbation, the response is damped
With increasing perturbation, the pendulum will fall over
Higher robustness (through higher stiffness and damping: larger perturbation can be
handled, larger margin of safety
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