Lecture 13 - Internal forces 2: Screening and prevention of ACL injuries

Question 1

What is muscle stiffness controlled by

Answer 1

• Stretch reflex

Question 2

How do you calculate muscle-tendon stiffness?

Answer 2

• Maximal force / displacement CM

Question 3

What biomechanical factors can be altered to reduce change of ACL injury?

Answer 3

• Reducing frontal plane knee joint angles
• Reducing frontal plane knee loading
• Increasing sagittal plane knee joint angles
• Reducing sagittal plane knee loading

Question 4

What are the mechanical varaibles of drop jumps?

Answer 4

• Impact Loading rate 10-90%
• Peak impact force
• Average impact force
• Peak propulsive force

Question 5

What is tendon length conorolled by ?

Answer 5

• Gamma motor neuron decided whether muscle should be long with a short tendon or short with long tendon.

Question 6

What is core stability training main goal?

Answer 6

• To improve muscle activation of postural stabilisers.

Question 7

If the stimulus is added that caused the participant to activate their muscle before hand, such as a fake floor, what is the result of this?

Answer 7

• If muscle are pre activated there in an increase in the activity of the relevant muscles resulting in possible a greater performance.

Question 8

Why is double leg landing practive not effective as an injury prevention measure for ACL?

Answer 8

• Different in neural demands, muscle activation and lack of familiarisation to single leg landings.

Question 9

What % of ACL injuries are non contact ?

Answer 9

• 70%

Question 10

What is the role of the Gamma motor neurons ?

Answer 10

• Keep the intrafusal fibres at the right length so that regardless of extrasfusal muscle length they can give feedback to CNS.

Question 11

What is surface instability training main goal?

Answer 11

• To restore neural factors, such as ligament feedback (proprioception) after removing the instable surface.

Question 12

With drop jumps how does the contribution from muscle change with height?

Answer 12

• As drop height increases the hip contributes more to energy absorption than at lower heights.

Question 13

What are normal q angles and what does an increased Q-angle increase the risk of?

Answer 13

• Normal male - 14 degrees
• Normal female - 17 degrees
• Increased Q angle increases risk of patellar subluxation.