week 2 in biomechanics covered the basics of skeletal muscle from a biomechanics perspective. skeletal muscle is the main muscle type in the body and is responsible for voluntary, gross movements, and makes up 40-50% of body weight. some muscle basics: tension produced by muscle is proportional to the amount of cross sectional muscle fibers. the strength of a muscle is defined as the tension produced from a single maximal effort, while the power produced by a muscle is the tension produced over time. muscle contractions can either be isotonic or isometric, the former being constant force with movement and the latter being varying force with no movement. within isotonic contractions, there are concentric contractions, in which the muscle gets shorter, and eccentric contractions, in which the muscle gets longer. the "line of pull" of a muscle is the primary direction in which the muscle pulls the bone.
each muscle is made of muscle fibers that are arranged in different ways according to the specific function of the muscle. parallel muscles such as the sartorius are designed for a greater range of motion / muscle shortening. fusiform muscles are similar to parallel except with a larger muscle belly, in a spindle shape, such as the biceps brachii. pennate muscles have muscle fibers oriented obliquely to the muscle tendon so as to increase the muscle's cross sectional diameter and increase strength- such as the deltoid muscles. convergent muscles such as the pectoralis major have a broad origin and a pointed origin, and varied lines of pull. circular muscles such as the sphincters and orbicularis oris have concentric muscle fibers that close over a hole when contracted.
agonists are defined as the prime muscle that produces a given movement. antagonists are the muscle that directly opposes the agonist movement- such as the biceps and triceps brachii. stabilizers are muscles that stabilize the action of the agonist-- such as the way that the rhomboids and pectoralis minor stabilize the deltoid by immobilizing its point of origin, the scapula. synergists are muscles that aid the movement of the agonist muscle.
muscles can be analyzed in terms of the type of "lever" that are schematically similar to. there are two important types of levers which produce complementary functions. a mechanical advantage lever is one in which the effort (the force applied) is far from the fulcrum (the point of rotation), which is close to the load (the object being moved). this type of lever (note that a car jack fits this description) lifts a large load a small distance for a small effort over a long distance. the other type of lever is a speed lever, in which the effort is close to the fulcrum, which is far away from the load. this type of lever allows for high speeds at the cost of high effort/tension. levers in the body can also be classified in the "class system"- first class levers have the fulcrum between the load and the effort, as in the posterior cervical muscles. second class levers are mechanical advantage levers that have the fulcrum between the effort and load and closer to the load, as in the gastrocnemius. third class levers are speed levers in which the effort is closer to the load than the fulcrum, as in the biceps.
questions
muscle introduction...
1. describe the role of skeletal muscle in the body.
2. how many skeletal muscles are there in the body and how much of the body weight do they take up?
3. a muscle's cross sectional diameter...
muscle types...
4. what are the different types of fiber arrangements in muscle and what are examples of each?
5. describe the arrangement and function of parallel muscles. what is an example of this type of muscle?
6. describe the arrangement and function of fusiform muscles. what is an example of this type of muscle?
7. describe the arrangement and function of pennate muscles. what is an example of this type of muscle?
8. describe the arrangement and function of convergent muscles. what is an example of this type of muscle?
9. describe the arrangement and function of circular muscles. what is an example of this type of muscle?
muscle contraction...
10. define muscle strength, power, and torque.
11. muscle contractions are either...
12. what is an isometric contraction?
13. what is an isotonic contraction?
14. what is the difference between a concentric and eccentric isotonic contraction?
15. what is the "line of pull" of a muscle?
16. what is an example of a muscle which has different actions because of a shifting line of pull?
17. how is line of pull related to proper muscle function?
18. what is the "angle of pull" of a muscle?
19. what are the two components to the angle of pull and what do they do?
muscle function terminology...
20. range of motion of a muscle depends on...
21. tension produced in a muscle depends on...
22. what is muscle irritability?
23. what is contractility?
24. what is extensibility?
25. what is elasticity?
muscle roles...
26. what are agonists?
27. what are antagonists? what is an example of an agonist/antagonist pair?
28. what are synergist muscles?
29. what are stabilizers? what is an example?
levers...
30. what is a fulcrum?
31. describe a mechanical advantage / power lever.
32. describe a speed lever.
33. what is a first class lever? what is an example in the body?
34. what is a second class lever? what is an example in the body?
35. what is a third class lever? what is an example in the body?
36. most levers in the body are...
answers
1. skeletal muscle is always attached to bone and is responsible for the movement of the body and all of its joints, as well as aiding in fluid and blood movement throughout the body, and providing protection and postural support.
2. over 600, 40-50% of body weight.
3. ...affects the muscle's ability to exert a force.
4. parallel, fusiform, pennate, convergent, circular.
5. muscle fibers are oriented parallel to muscle direction. designed for greater range of motion. example is sartorius.
6. similar to parallel muscles but with more of a spindle shape- larger cross sectional diameter in the middle. example is biceps brachii.
7. high cross sectional area muscle due to fibers being arranged perpendicularly to tendon. examples are extensor digitorum, rectus femoris, deltoid.
8. a muscle with a broad origin and a pointed insertion. the direction of pull can be varied. example is the pectoralis major.
9. fibers are arranged concentrically so as to form a sphincter. examples are orbicularis oris or sphincter muscles.
10. muscle strength= amount of tension a muscle can produce for a single maximal effort. muscle power= the amount of tension or contraction over a given period of time. muscle torque= muscle force causing rotation around an axis.
11. isometric or isotonic.
12. a muscle contraction in which the length of the muscle or the angle of the joint stays the same regardless of the tension.
13. a muscle contraction in which the tension in the muscle is relatively constant, producing motion in the joint or shortening / lengthening of the muscle.
14. concentric contraction is an isotonic contraction in which the muscle is being shortened, and in eccentric the muscle is being elongated.
15. the direction in which the muscle pulls when contracted.
16. when the humerus is abducted sufficiently such that the line of pull for the pectoralis major is above the glenohumeral joint, the pectoralis major can become an abductor of the humerus in addition to its primary flexion role.
17. each muscle has an optimal line of pull. an altered line of pull can cause hypertonicity and inefficiency, ultimately leading to weakness, trigger points, imbalance, etc.
18. the angle which is formed between the bone of insertion and the line of pull.
19. the verticle component (perpendicular to the bone of insertion) causes rotational movement at the join and the horizontal component causes a stabilizing force.
20. length of muscle fibers
21. total number of muscle fibers
22. muscle excitability- how sensitive or responsive the muscle is to chemical, electrical, mechanical stimuli.
23. ability of the muscle to develop tension when stimulated.
24. ability of the muscle to be stretched beyond its normal resting length.
25. ability of muscle to return to original length after stretching.
26. the prime muscle that provides the major force for a given movement.
27. muscle that produces a motion opposite to that produced by the agonist. example is biceps and triceps brachii.
28. a muscle which assists the agonist muscle.
29. muscles that support and improve the efficiency of the agonist. rhomboids and pec minor are stabilizers of the scapula when the deltoids are abducting the arm.
30. the fixed point of leverage, as in the joints of the body.
31. load is close to the fulcrum and the effort is far from the fulcrum. small effort over long distance can move a large load over small distance. (car jack)
32. load is far from the fulcrum and the effort is close to the fulcrum. large effort and fast movement.
33. a lever in which the fulcrum lies between the effort and the load, as in the posterior cervical muscles.
34. a lever in which the load lies between the fulcrum and the effort, as in the gastrocnemius. mechanical advantage levers.
35. a lever in which the effort lies between the fulcrum and the load, as in the biceps.
36. third class-- speed levers.
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