Direct vs Indirect --> Internal Forces Flashcards
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
