Seminar 1 Core stability

Concepts of HMS Seminar 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?
• Yes, I do.
• What do these exercises look like?
• 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?

• 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:

• 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

• Tennis, soccer, hockey, rugby

Trunk stability and performance

• Core stability is important for precision (for your own breathing), balance, ballistic

movement. 1 / 4

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

• 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
• Hip abduction
• Hip external rotation
• Back extension → upper body is not supported; the person has to support the

upper body as long as possible

• 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
• Displacement after perturbation

▪ Lateral, extension of flexion

• 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

• / 4

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:
• 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 3 / 4

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

• / 4