#3 - Applications of Work and Energy to Health and Injury

Applications of Work and Energy to Health and Injury

Potential: energy of position or deformation
- Positional (gravitational potential) energy.

Deformational (Strain) Energy
- Related to
  - Material and structural properties of tissues
  - Strain
Plyometric Exercise - risk??

Total Mechanical Energy (TME)
- “Most important determinant of injury…”
  - [(Robertson, 1998… “epidemiology of injury…”)]

If, probability of injury (Pinj) ~ TME
- Dissipation of Energy is a primary mechanism in Injury Prevention
How can we dissipate energy??
- E.g., airbags dissipate energy for the car, parachute, bending your knees cushions the blow of landing from a jump (technique), helmet, insoles (viscoelastic tissues), track for running, crumple zone for car, friction is a very efficient way to dissipate energy through friction (tissues), etc.
Pinj ~ Pressure

Player 4 exerts 14000N of force on the red player’s shin. The contact area of the force (foot contact on shin) was measured at 7500 mm2.

Assuming that the tibia bone has an ultimate pressure tolerance of 1 MPa, would the tibia fracture?

If the recipient player was wearing shin guards that increased the contact area of the force to 29,000 mm2, would the tibia fracture?

Joint Mechanics

Joint Play Testing - assessing the integrity of the elastic barrier
- Occurs within the parapsychologic space
- Springy “end feel”
- Need proper joint play to allow optimal and

painless voluntary movement.

Joint play dysfunction:
- Compromise of joint nutrition - leading to degeneration.
- Secondary muscle changes (atrophy, spasm)
SUBCLINICAL!!

Joint Stability:
- “Ability of a joint to maintain an appropriate functional position throughout its ROM.” (Burstein and Wright, 1994).
Spinal Stability
- “The ability of the spine under physiological loads to limit patterns of displacement so as to not damage or irritate the spinal cord and nerve roots and, in addition, to prevent incapacitating deformity or pain due to structural changes.”
Stability - redefined?
- Mechanical stability is defined as the “the ability of a loaded structure to maintain static equilibrium even at small fluctuations around the equilibrium position”
Which ball is more stable?

Stability…. Redefined? (Potvin, Derouin)
- U(m) = potential energy stored in the muscle
- F = muscle force (N)
- k = muscle stiffness (N/m)
- l = muscle length (m)

Joint Stability
- Joint stability is determined by:
  - Geometry of articular surfaces (contact area, bony fit).
  - Periarticular passive tissues (capsule, ligament).
  - Periarticular muscles.

Stabilizing Forces:
- Is stability always a good thing?
  - Increased degeneration
    - Not always good
      - E.g., athletes,

bending knees. lifting things.