Upload
margaretmargaret-rogers
View
230
Download
0
Tags:
Embed Size (px)
Citation preview
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…
• 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)
One twitch (fiber contraction) per excitation. Subsequent twitches can increase force w/ limit at tetanus
1. Increase action potential frequency.
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
3. maximize actin/myosin overlap
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 Mechanics
• Distinguish the three lever types and solve equations representing these relationships.
Levers - 3 components
Load
Fulcrum
Force
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.
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.
First class lever
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
Second class lever
Third class lever
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)