Lecture 1 - Loading of the Musculoskeletal System

Question 1

What is the Young’s modulus of elasticity and what does it measure?

Answer 1

• This is the ratio between stress and strain E = o/e.

- Measures the stiffness of a material.

Question 2

What is resilience and some common % for this in biological materials?

Answer 2

• Resilience is the amount of energy returned as a percentage of the amount stored during deformation, it is also know as the coefficient of restitution.
• Resilin - 97%
• Collagen - 93%
• Elastin - 76%

Question 3

On the stress - strain relationship graph what is:

B, ER, PR, C and oc ?

Answer 3

• B - Elastic limit
• ER - Elastic range
• PR - Plastic range
• C - Failure point
• oc - Ultimate stress

Question 4

What is strain and stress?

Answer 4

• Strain is the amount of deformation that arises from an applied load.
• Stress is the amount of resistance to this deformation.

Question 5

To improve performance of a tendon what are the suggested training aims?

Answer 5

• Plyometric training to improve muscle-tendon stiffness
• Develop muscle strength ( Not size)
• Increase cross sectional area of important tendons, though strength and endurance training, to reduce injury risk level.

Question 6

What are the stages of the Stretch shortening cycle (SSC) ?

Answer 6

• Preload (Eccentric)
• Elastic energy storage
• Reflex potentiation

Question 7

What are the different load characteristics important in injury?

Answer 7

• Type of load - Tensile, Compressive, Shear, Torsion, Bending
• Magnitude of load
• Load rate
• Frequency of load repetition and number of repetitions.

Question 8

What is a Chronic injury (overuse) and an acute injury (traumatic) ?

Answer 8

• Chronic - Results from repeated overloads with insufficient time for recovery.
• Acute - Results from a single of a few repeated episodes (Watkins, 1999).

Question 9

What is the definition of an why an injury occurs?

Answer 9

• Injury occurs when the load applied to a tissue exceeds its failure tolerance (Bartlett, 1999).

Question 10

Why is it bad if a structure goes beyond B and into the PR zone on the stress strain graph?

Answer 10

• If a structure goes beyond B (Elastic limit) and into PR zone (Plastic range) it does not return to its original shape and will have deformed slightly.

Question 11

What are two crucial factors in how and where injury occurs ?

Answer 11

• The load - The sum of forces and moments of force acting.

- The characteristics of the loaded structures.

Question 12

How do tendons change with maturation (age)?

Answer 12

• Tendons become able to produce more force and do not elongate to the same degree.
• They are also able to tolerate higher levels of stress but reduced levels of strain (less deformation and higher resistance to this).

Question 13

What is the theory behind the shortening cycle (SSC) ?

Answer 13

• The SSC works by storing the elastic energy from the eccentric muscle contraction and adding this to the energy of the concentric contraction, resulting in an increased force production and stiffness.

Question 14

What are the factors that have an effect on injury?

Answer 14

• Material Properties
• Genetics, Age and Gender
• Fitness Level
• Skill Level
• Fatigue
• Surfaces and Equipment
• Load Characteristics

Question 15

What factors have been found in tendons of athletes that perform a higher levels?

Answer 15

Higher passive tendon stiffness resulting in:

• Smaller pre- and braking phase muscle activation
• Less tendon strain
• Stiffer tendon and more efficient recoil
• Less muscle activity (Contraction) and thus more efficiency.