Biology Lecture Week 6 - Loading of Musculoskeletal System

Question 1

Define Injury …

Answer 1

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

Question 2

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

Answer 2

1. the load - the sum of the forces and moments of force acting
2. the characteristics of the loaded structures

Question 3

Define a Chronic (overuse) Injury …

Answer 3

Results from repeated overloads with insufficient time for recovery

Question 4

Define an Acute (traumatic) injury …

Answer 4

Results from single or a few repeated episodes (Watkins, 1999)

Question 5

‘Overtraining may result in injury but this is not always the case’. Why ?

Answer 5

The result instead is often psychological (eg. boredom, burnout)

Question 6

Name the 5 types of load ?

Answer 6

• Tensile
• Compressive
• Shear
• Torsion
• Bending

Question 7

Name the different load characteristics important in injury ?

Answer 7

• Types of load
• Magnitude of load
• Load rate
• Frequency of load
• Strain

Question 8

Define load rate …

Answer 8

The rate of change of force with time (Δf/Δt)

Question 9

What affects overuse injury ?

Answer 9

Frequency of load and number of repetitions

Question 10

Define strain …

Answer 10

Strain is the amount of deformation that arises from an applied load, and stress is the amount of resistance to this deformation

Question 11

Define strain(ε) as part of the stress - strain relationship …

Answer 11

Strain (ε): deformation as a proportion of the dimensions of the material when unloaded. Strain is calculated as a percentage of change

Question 12

Define stress (σ) as part of the stress - strain relationship …

Answer 12

Stress (σ): load per unit cross-sectional area (i.e σ = Force / Area)

Question 13

What is the unit of stress (σ)

Answer 13

N/cm² or Nm² (1N/m² = 1 pascal)

- A pascal is relatively small, so we often use megapascals (MPa) instead. 1 MPa = 100 N/cm²

Question 14

What is Young’s modulus of elasticity (E) ?

Answer 14

• Also known as the elastic modulus, it is the ratio between stress and strain
• E = σ / ε

Question 15

What does Young’s modulus of elasticity measure ?

Answer 15

The stiffness of the material

Question 16

What are the stages involved in the stretch-shortening cycle ?

Answer 16

• Preload
• Elastic energy storage
• Reflex Potentiation (Komi, 1992)

Question 17

Finish the sentance,

‘In the stretch shortening cycle, eccentric contraction enhances…’

Answer 17

In the stretch shortening cycle, eccentric contraction enhances force production in the succeeding concentric contraction (and increases stiffness)

Question 18

What is a good example of the effectiveness of the stretch shortening cycle ?

Answer 18

Using a skipping rope;
The eccentric contraction occurs upon landing, the calf muscles are stretched, and when they shorten it adds to concentric contraction. Because of the elastic energy given by this process, it is quite easy to skip for long durations without getting tired. This is part of the reason why plyometric training is effective in speed training

Question 19

Hysteresis - Resilience is defined as ?

Answer 19

The amount of energy returned as a percentage of the amount of energy stored during deformation

Question 20

Give three examples of values for resilience (also known as coefficient of resistitution) …

Answer 20

1. Resilin (found in insect wings) : 97%
2. Collagen (found in tendons and ligaments) : 93%
3. Elastin (found in tendons/ muscles) : 76%

Question 21

Define what leads to a hysteresis loop …

Answer 21

Although, in the elastic component, the strain is recoverable, the stress-strain curve is not the same for loading and unloading. Such materials instead exhibit viscoelasticity, involving both elastic and viscous components, which at normal loading and unloading rates leads to a hysteresis loop

Question 22

Tendon Strength and Resilience can be improved through …

Answer 22

Strength Training (Reeves et al., 2003)

Question 23

Why are east african distance runners the best in the world ?

Answer 23

They have a better tendinous structure. Kenyan distance runners have better tendon recoil and better use of elastic energy storage/ return (Sano et al., 2013)

Question 24

What are the 4 factors that contribute to ‘high passive stiffness of tendons’ for better performing tendons ?

Answer 24

1. Smaller pre- and breaking phase muscle activation
2. Less tendon strain
3. Stiffer tendon and more efficient recoil
4. Less muscle activity (contraction) and thus more efficiency