Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths....

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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.

Transcript of Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths....

Page 1: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

Skeletal Muscle Mechanics

• Explain muscle properties during contractions of varying strengths.

• Distinguish the three lever types and solve equations representing these relationships.

Page 2: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

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)

Page 3: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

One twitch (fiber contraction) per excitation. Subsequent twitches can increase force w/ limit at tetanus

1. Increase action potential frequency.

Page 4: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

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

• Motor unit recruitment increases force.

Muscle

Muscle Fibers

Somatic Motor Neuron

Motor Unit

Page 5: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

3. maximize actin/myosin overlap

Page 6: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

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

Page 7: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

Skeletal Muscle Mechanics

• Distinguish the three lever types and solve equations representing these relationships.

Page 8: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

Levers - 3 components

Load

Fulcrum

Force

Page 9: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

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

Forcedistance

Torque = force x distance

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

Page 10: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

An example of a balanced 1st Class Lever

F = 10 lb

F = 5 lb

0.2 m0.1 m

B = 5 x 0.2 = 1A = 10 x 0.1 = 1

τtotal=τA −τB =1−1=0

At balance, force X distance on one side of a lever = force X distance on the other side.

Page 11: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

First class lever

Page 12: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

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

Page 13: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

Second class lever

Page 14: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

Third class lever

Page 15: Skeletal Muscle Mechanics Explain muscle properties during contractions of varying strengths. Distinguish the three lever types and solve equations representing.

Biomechanics problems:

1. 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 elbowdistance 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)