exam questions

Question 1

explanation as to why technique B may be associated with lower risk of ACL injury compared to technique A. Please provide this explanation for Charlie. (5 marks).

Answer 1

• Technique B is characterised by a greater peak knee flexion angle
• A greater knee flexion angle will decrease the effectiveness of the quadriceps at inducing anterior shear force at the tibia.
• A greater knee flexion angle will increase the effectiveness of the hamstrings at inducing posterior shear force at the tibia.
• An anterior and posterior shear force at the tibia tend to load and unload the ACL, respectively.
• This would therefore reduce ACL loading and injury risk.

Question 2

the pain he had been feeling in his quadriceps has reduced since adopting the new technique. Provide a biomechanical explanation for why this is the case. (6 marks).

Answer 2

• Technique B results in a reduce peak vertical ground reaction force and/or its moment arm relative to the knee
• Since T = F x d, this will reduce the external flexion moment
• This means that the required internal extension moment will also reduce
• Therefore his quadriceps (knee extensors) will require less force production
• Since muscle force likely provokes pain…
• The reduced force production within the quadriceps muscle

Question 3

to reduce his risk of another ACL injury. Suggest an appropriate muscle for Charlie to strengthen, and provide a biomechanical rationale to support your choice. (4 marks).

Answer 3

• Hamstrings (or soleus would be reasonable too, for the same explanation)
• The ACL prevents anterior tibial translation (or could say that an anterior shear force loads the ACL).
• Hamstrings induce posterior shear at the tibia
• Therefore, hamstrings force unloads the ACL making it less likely to rupture

Question 4

explain why these would influence the ball release velocity in baseball pitching (4 marks).

Answer 4

• Greater forward trunk tilt
• Increase in acceleration arc
• Increase in momentum trunk contributes to the sequence
• Increases time & displacement of force production – impulse and work/energy
• Shoulder horizontal abduction/extension
• Puts the anterior aspect of the shoulder on stretch, increasing contribution of stretch shortening cycle
• Also, increases the acceleration arc

Question 5

Rick suggests he has been suffering back stiffness from sleeping on a new mattress. Discuss how could this have affected his technique and the potential knock-on effects upon his pitching speed. (4 marks).

Answer 5

• Stiffness will cause limited range of motion of the lumbar and/or thoracic regions of spine (1 mark).
• This limited range of motion of the trunk is likely to decrease the considerable angular momentum that is generated at the trunk and transferred down the kinetic chain in an effective pitch (1 mark).
• A shorter range of motion at the trunk will also act to decrease the total potential to generate total impulse, and peak force that can be delivered to the upper limbs (1 mark).
• A reduction in force that the trunk can deliver to the to the pitching shoulder is likely to result in the anterior shoulder not experiencing as much stretch, reducing the ability to store elastic energy to return to the pitch. (1 mark)

Question 6

briefly describe the suitability of at least two different biomechanical measurement technologies available, including which you would recommend using and why? (4 marks).

Answer 6

3D markerless motion analysis would enable Rick’s kinematics to be measured (i) in 3D, and (ii) without any attachment of markers/other external devices. It would also allow the tracking of the ball in order to identify the point of ball release (this would not be possible with IMU’s; and with 3D marker-based motion analysis would require the attachment of markers or reflective tape to the ball presenting a significant challenge).

Question 7

Explain what mechanics could be playing a role in this that do not involve the trunk or upper limbs. (3 marks)

Answer 7

• Lead knee flexion
• Lower knee flexion (straighter lead leg) places the upper body in a better position to rotate over/accelerate. This is movement is defined as checking.
• Also, reduces energy lost due to knee flexion during action phase
• Stability
• increasing stability at the base of support will increase the ability to deliver the momentum upwards in the kinetic chain