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….
1. Increase action potential frequency.
Somatic Motor Neuron
3. maximize actin/myosin overlap
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
The perpendicular distance from the pivot point to the line of the force.
An example of a balanced 1st Class Lever
A = 10 x 0.1 = 1
B = 5 x 0.2 = 1
F = 5 lb
F = 10 lb
At balance, force X distance on one side of a lever
= force X distance on the other side.
First class lever
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
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)