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Flashcards in Direct vs Indirect --> Internal Forces Deck (13):

What is the difference between external and internal forces?

External -> can change the state of a system (gravity)

Internal -> generated within the system (ligaments, muscles, tendons etc.)


What is the difference between indirect and direct clinical measurements?

Direct - optic fibres

Indirect - invasive, based on tendon suitability


What are the 2 different ways to indirectly test internal forces?

EMG => increases the correlations between muscle force and activity

Inverse Dynamics => calculates internal forces and the net turning torque of the joint


What are the different pieces of equipment used for kinetic/kinematic testing?

Kinetic - force plates, accelerometers

Kinematics - high speed cameras, infrared tracking


What are the different calculations used for calculating horizontal and vertical forces?

Horizontal = Frx = (m x ax) - Fx

Vertical = Fry = (m x ay) + (m x g) - Fy


What is the limitation with calculating segmental forces via moment of inertia?

Each segment is uniform in its density and rigidity
Segmental mass is a single point at the COM
Moment of inertia remains constant throughout the movement


What is a limitation to inverse dynamics?

Articulating surfaces encounter no friction
Forces act through the joint centre - so no change in the other segments


What is the relationship between muscle moments and muscle power?

Muscle Power = moment x angular velocity (Rad/s)

+ve moments = extensors -ve = flexors
+ve powers = concentric -ve = eccentric


What are the contributions of the lower body joints at long-jump take off?

HIP - flexors work concentrically

KNEE - extension (starts off eccentric then concentric)

ANKLE - dorsiflexion = concentric actions


What does training require to do?

- increase force generated by knee extensors
- increase force by ankle extensors
- hip acts passively


What are the limitations of the 2D model of forces acting on the forearm?

Ignores individual force and torques
Ignores forces and torques generated by other muscles
Calculations based on assumptions


What is Joint Reaction Forces (JRF)?

What are they influenced by?

net force across a joint
(reaction of a body segment to the forces exerted by the adjacent segment)

Influenced by muscle forces, soft tissue etc.


What are the steps to calculate JRF from the most distal joint to the most proximal?

1) Calculate JRF for distal segment (ankle)
2) Force and torque proximal to this are equal and opposite (knee)
3) As you know this value - calculate JRF and torque for the next proximal segment (knee)
4) Repeat for the hip