Lecture 12 - Inverse Dynamics –Strengths and Limitations

Question 1

What are the types of equipment used to calculate internal forces, both kinetic and kinematic.

Answer 1

• Kinetic
  •Force Plates
  •Linear Transducers
  •Accelerometers

-Kinematic
•High speed video cameras
•Infrared auto tracking
•Cineradiography

Question 2

What is a benefit of the 2D model of acting forces on the forearm?

Answer 2

• The reduction method allows the collection of some information about the dynamics of a movement.

Question 3

What are some limitations of inverse dynamics?

Answer 3

• The articulating surfaces in the joints are smooth and do not create a frictional force
• The forces act through the centre of the joint and the centre of the joint does not change in relation to the corresponding connecting segments
• The foot segment is assumed to be one rigid segment that included the metatarsal segment and joint.

Question 4

What are joint reaction forces, and what are they influenced by?

Answer 4

• A net force acting across a joint is referred as a joint reaction force -it is the reaction of a body segment to forces exerted by an adjacent segment.
• The joint reaction force is a 3-dimensional force (FRy, FRx, FRz).
• The joint reaction is influenced by: muscle forces, soft tissue forces, and various external forces

Question 5

How do you calculate the joint reaction forces for each joint moving proximally from the ankle.

Answer 5

• Firstly, calculate the Joint Reaction Forces and Muscle Torque for the distal segment (ankle) by using external force data obtained by the force plate.
• Reverse the forces and torques for the foot and apply them to the knee
• Calculate JRF and muscle torque for knee
• Then reverse these and apply to hip.

Question 6

What are internal forces and external forces?

Answer 6

• External forces can change the state of a system (gravity, ground reaction or other external forces, air resistance)
• Internal forces are generated within the system (musculoskeletal forces)

Question 7

What are the indirect ways of measuring muscle forces

Answer 7

• EMG and Inverse dynamics calculations.

Question 8

What are the factors found that influence mechanical work ?

Answer 8

• Positive work influenced by energy transfer and net positive work provided by elastic energy and the concentric contraction of muscles.
• Negative work influenced by non muscle sources and the eccentric contraction of muscles.

Question 9

What implications were found from the Carl Lewis and Mike Powell long jump analysis?

Answer 9

• Training movements require:
• High force generated by knee extensors Eccentric to concentric
• High force generated by ankle extensors Eccentric to concentric
• The Hip acts passively (Carl Lewis)
• High force generated by the hip extensors Eccentric to concentric –Mike Powell

Question 10

What are the direct ways of measuring internal forces and the limitation associated with these?

Answer 10

• Buckle transducers and Optic fibres
• Limitations are :
• Invasive procedure
• Ethical issues
• Tendon suitability (not all tendons are suitable for measurements)
• Calibration

Question 11

What is muscle power ?

Answer 11

• Muscle Power = Muscle Moment multiplied by angular velocity (Rad/s)

Question 12

What are mechanical and performance variables for vertical jump tests?

Answer 12

• Impulse
• Take-off velocity
• Power (average, peak)
• Height of the jump (CG)
• Rate of force development
• Speed-Strength (jump squat)
• Reactive Strength (drop jumps)

Question 13

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

Answer 13

• It ignores the individual forces and torques since there is a grouping of the prime movers involved.
• It ignores forces and torques generated by other muscles (antagonists and stabilisers).
• It ignores the joint contact force
• It ignores individual forces and torques generated by other structures (e.g. ligaments).
• The calculations are based on kinematic data and other assumptions.

Question 14

What can calculating mechanical joint power and work give you ?

Answer 14

• Levels of mechanical effort

Question 15

What is the link-segment model for calculating sequential joint forces for the lower body.

Answer 15

• Since the foot is linked with the leg at the ankle joint the joint reaction forces and muscle torque calculated for the ankle can be used to calculate the joint reaction forces and muscle torque for the proximal joint of the leg (knee joint). Likewise, the knee data can be used to calculate the joint reaction forces and muscle torque for the hip joint.