CrÃ©er une prÃ©sentation
TÃ©lÃ©charger la prÃ©sentation

TÃ©lÃ©charger la prÃ©sentation
## Skeletal Muscle - Tension

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**1. **Skeletal Muscle - Tension (2) active tension (muscle activation)
Excitation-contraction coupling
Ca2+, ATP
Muscle size (cross-sectional area)
Muscle length (stretch)
Rate coding (frequency modulation) & motor unit recruitment
Shortening velocity
Temperature
Fiber-type
Reflexes

**2. **Force-velocity relationships: types of muscle contractions Isometric -
muscle length remains constant
Static mechanics
SFx,y = 0; ST = 0
Isotonic
Concentric (shortening)
Eccentric (lengthening)

**3. **Force-velocity relationships: types of muscle contractions Concentric Contraction - shortening contraction
The torque produced by the muscles at the joint overcomes resistance to movement
Inertia and weight of body segments/limb
Outside contact forces (impact, free weight, etc.)

**4. **Force-velocity relationships: types of muscle contractions Eccentric Contraction
The torque produced by muscles at the joint is less than the resistance to movement
1. Muscle must produce some tension
2. Usefulness
Braking against a powerful/rapid movement in order to protect joints/muscles (co-contraction)
Ex. Lifting a heavy weight
Braking against gravity (also protection)
Ex. Letting down a heavy weight
Precise movement towards a target
Ex. Catching a softball

**5. **Force-Velocity Relationship

**6. **Torque-angle relationships

**7. **Anatomical Analysis of Movement

**8. **Anatomical Analysis of Movement

**9. **Mechanical Work A force applied an object multiplied by the displacement of that object in the direction of the applied force
SYMBOL: W
FORMULA: W = F•d
UNITS: Metric - Joules (J) 1J = 1 N•m English – foot•lbs
Exs. Lifting a free weight, riding a cycle ergometer, pushing a sled (if frictional force measured - dynamometer)

**10. **Mechanical Work Problem: Calculate the work involved in lifting a 300 N weight a height of .6 m
W = F•d
W = (300N)(.6 m)
W = 180 N•m = 180 J

**11. **

**12. **Energy DEFINITION: the ability to produce work. It is manifested in various forms:
Motion (kinetic)
Position (potential)
Strain (spring)
Heat, light, sound
UNITS: Joules (J), calories

**13. **Energy Types: Formula:
Motion (kinetic) Ek = 1/2 m•v2
Position (potential) Ep = m•ag•h
Strain (spring) Es = 1/2k•x2
Heat, light, sound
UNITS: Joules (J), calories

**14. **Mechanical Gross Efficiency Efficiency = mechanical work/energy
Most exercises (weightlifting, climbing stairs, cycling) ~ 20% efficient!

**15. **Mechanical Efficiency Walking and running >>20% efficient!
Why?
“Natural springs” (arch of foot, Achilles’ tendon, muscles)

**16. **Strain Energy – ApplicationNatural Springs • For a man with a mass of 70 kg running at a velocity of 4.5 m/s, the arch of the foot will store about 17 J of energy when the foot is at maximum compression.
• Each Achilles’ tendon + plantar flexors stores about 35 J of energy.
• Other muscles (ex. quads) store >20 J of energy
• This equals a return of over 50% of the energy expended while running (~110 J).
• Energy Savings when recoil force used during pushoff

**17. **Mechanical Efficiency Walking and running >>20% efficient!
Why?
“Natural springs” (arch of foot, Achilles’ tendon, muscles)
Legs act as a pendulum in locomotion
f = 1/(2?)??(ag/l)
Where: ag = acceleration due to gravity
l = distance from axis of rotation to center of mass (gravity)
most efficient running speed will match the dynamic pendulum frequency of the limbs
this is a dynamic frequency which changes as joint angles change in a multi-segmented limb
Aging, stroke, injury, crutches, neuromuscular disease decrease efficiency dramatically

**18. **Power The amount of work performed in given time period (rate of work performed.
SYMBOL: P
FORMULA: P = W/Dt = F•d/Dt = F•v
strength x speed
UNITS: Metric – watts (W) 1W = 1J/sec
English – horsepower

**19. **Power and Work Calculation GIVEN: A person weighing 580 N runs up a flight of 30 stairs, each with a height of 25 cm. The time for this effort is 15 seconds.
FIND: The work and power done

**20. ** Power and Work Calculation

**21. **Force-Velocity Relationship

**22. **Concentric Force - Velocity Curve

**23. **Power – Velocity Curve

**24. **Power and Force – Velocity Curves

**25. **Muscle Dynamics Strength
Dead lift
Bench press
Lifting a suitcase
Power
100 m dash
High jump
Shot put
Speed
Badminton swing
Frisbee throw
Short shop stab for a line drive

**26. **Energy DEFINITION: The capacity to do work
UNITS: The same as the units for work (joules)
Two Forms of motion
Kinetic Energy
Potential Energy

**27. **Kinetic Energy DEFINITION: The energy of motion.
SYMBOL: KE
FORMULA: KE = 1/2(mv2) (Kinetic energy equals one-half of an object’s mass times the square of its velocity.)
For a motionless body, v = 0, therefore
KE = 0

**28. **Kinetic Energy Calculation GIVEN: A ball with a weight of 70 N is rolling with a velocity of 3 m/s.
FIND: The kinetic energy of the ball
m = weight / g = 70 N / 9.81 m/s2 = 7.14 kg
KE = 1/2(mv2) = 1.2(7.14 kg)(3 m/s)2
= 32.11 J

**29. **Potential Energy DEFINITION: The energy of position.
SYMBOL: PE
FORMULA: PE = m•ag•h (Potential energy equals the weight of an object times its height above a surface to which it could fall.)
Increasing an object’s height increases its potential energy.

**30. **Potential Energy Calculation GIVEN: A ball with a weight of 70 N is resting on a shelf that is 2 m above the floor
FIND: The potential energy of the ball
PE = m•ag • h = 70 N • 2 m = 140 J