Biology Lecture Week 6 - Loading of Musculoskeletal System Flashcards
Define Injury …
Injury occurs when the lod applied to a tissue exceeds its failure tolerance (Bartlett, 1999)
What are the two crucial factors in how and where injury occurs ?
- the load - the sum of the forces and moments of force acting
- the characteristics of the loaded structures
Define a Chronic (overuse) Injury …
Results from repeated overloads with insufficient time for recovery
Define an Acute (traumatic) injury …
Results from single or a few repeated episodes (Watkins, 1999)
‘Overtraining may result in injury but this is not always the case’. Why ?
The result instead is often psychological (eg. boredom, burnout)
Name the 5 types of load ?
- Tensile
- Compressive
- Shear
- Torsion
- Bending
Name the different load characteristics important in injury ?
- Types of load
- Magnitude of load
- Load rate
- Frequency of load
- Strain
Define load rate …
The rate of change of force with time (Δf/Δt)
What affects overuse injury ?
Frequency of load and number of repetitions
Define strain …
Strain is the amount of deformation that arises from an applied load, and stress is the amount of resistance to this deformation
Define strain(ε) as part of the stress - strain relationship …
Strain (ε): deformation as a proportion of the dimensions of the material when unloaded. Strain is calculated as a percentage of change
Define stress (σ) as part of the stress - strain relationship …
Stress (σ): load per unit cross-sectional area (i.e σ = Force / Area)
What is the unit of stress (σ)
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
What is Young’s modulus of elasticity (E) ?
- Also known as the elastic modulus, it is the ratio between stress and strain
- E = σ / ε
What does Young’s modulus of elasticity measure ?
The stiffness of the material
What are the stages involved in the stretch-shortening cycle ?
- Preload
- Elastic energy storage
- Reflex Potentiation (Komi, 1992)
Finish the sentance,
‘In the stretch shortening cycle, eccentric contraction enhances…’
In the stretch shortening cycle, eccentric contraction enhances force production in the succeeding concentric contraction (and increases stiffness)
What is a good example of the effectiveness of the stretch shortening cycle ?
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
Hysteresis - Resilience is defined as ?
The amount of energy returned as a percentage of the amount of energy stored during deformation
Give three examples of values for resilience (also known as coefficient of resistitution) …
- Resilin (found in insect wings) : 97%
- Collagen (found in tendons and ligaments) : 93%
- Elastin (found in tendons/ muscles) : 76%
Define what leads to a hysteresis loop …
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
Tendon Strength and Resilience can be improved through …
Strength Training (Reeves et al., 2003)
Why are east african distance runners the best in the world ?
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)
What are the 4 factors that contribute to ‘high passive stiffness of tendons’ for better performing tendons ?
- Smaller pre- and breaking phase muscle activation
- Less tendon strain
- Stiffer tendon and more efficient recoil
- Less muscle activity (contraction) and thus more efficiency
