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Skeletal Muscle Mechanics . Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing these relationships. How to get more force in a muscle….

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skeletal muscle mechanics
Skeletal Muscle Mechanics
  • Explain muscle properties during contractions of varying strengths.
  • Distinguish the three lever types and solve equations representing these relationships.
how to get more force in a muscle
How to get more force in a muscle…
  • Increase action potential frequency in a motor unit (summation in fibers since twitch lasts longer than AP)
  • Increase number of motor units activated in the whole muscle
  • Maximize actin/myosin overlap
  • Increase number of myofibrils (body building; long term)
2 increase number of motor units activated
Muscle

Muscle Fibers

2. Increase number of motor units activated
  • THE MOTOR UNIT: One neuron and the fibers it innervates.
  • Motor unit recruitment increases force.

Somatic Motor Neuron

Motor Unit

the coding of contractile force
THE CODING OF CONTRACTILE FORCE
  • FREQUENCY CODING: HIGHER FREQUENCY OF INCOMING ACTION POTENTIALS GENERATES MORE FORCE
  • POPULATION CODING: MORE UNITS RECRUITED TO GET MORE FORCE
  • TOTAL FORCE POSSIBLE DETERMINED BY SIZE (CROSS/SXN) OF WHOLE MUSCLE
skeletal muscle mechanics1
Skeletal Muscle Mechanics
  • Distinguish the three lever types and solve equations representing these relationships.
levers 3 components
Levers - 3 components

Force

Load

Fulcrum

slide9
When most skeletal muscles contract, the bones to which they are attached rotate around a joint. We call this ‘rotational’ force a torque.

Torque = force x distance

Force

distance

The perpendicular distance from the pivot point to the line of the force.

slide10
An example of a balanced 1st Class Lever

A = 10 x 0.1 = 1

B = 5 x 0.2 = 1

0.1 m

0.2 m

F = 5 lb

F = 10 lb

At balance, force X distance on one side of a lever

= force X distance on the other side.

slide12
Biomechanics problem:

Upon C1 vertebra, for example, the head weighs approx. 10 lbs. If you bend the head forward 3 inches, the weight that is placed anterior to the facets becomes 3 inches times 10 lbs which is equal to 30 inch pounds

3" x 10 lbs = 30 inch pounds

The neck muscles which have to balance this load are positioned 2 inches behind the facets. How many pounds of force will these muscles will have to exert to balance the head?

3 " x 10 lbs = 2 " x 15 lbs

30 inch pounds = 30 inch pounds

slide15
Biomechanics problems:

Calculate the effort (muscle force) required to hold your arm bent and steady at your side.

arm + hand = 10 lbs.

distance from elbow to hand = 14 in.

center of gravity for arm = 7 in. from elbow

distance from elbow to biceps insertion = 2 in.

2. Calculate the effort (muscle force) required to curl a dumbell with your arm.

Dumbell weight = 20 lbs

(resistance arm is the full distance from elbow to hand in this case)

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