Muscles

1
Muscles
Types of Contractions
Agonist/Antagonist Muscles
Origins, Insertions Functions
Muscles as Levers
2
Muscles' Attachments to Bones
Indirect attachments -
The epimysium (sheath of connective tissue
surrounding exterior of muscle) extends past the
muscle as a tendon and attaches to the periosteum
of a bone
e.g. bicep (both to scapula and radius)
quadriceps to tibia, pectoralis to humerus
Direct attachments -
The epimysium adheres to and fuses with the
periosteum of a bone
e.g. pectoralis to sternum, triceps to humerus
adductor muscles to femur
3
Types of Muscle Contractions
Muscle contraction involving a controlled
shortening of the muscle
Isotonic -
Phase of an isotonic contraction when the muscle
is shortened
Concentric contraction -
Eccentric contraction -
Phase of an isotonic contraction when the muscle
is lengthened
4
Types of Muscle Contractions
Isometric -
Muscle contraction in which the muscle fibre
maintains a constant length throughout. There is
no motion and the exercises are usually performed
against an immovable surface
Muscle contraction involving the use of machines
to control the speed of the contraction
throughout the range of motion
Isokinetic -
5
Agonist/Antagonist Muscles
Skeletal muscles function only to contract.
Sometimes we categorize muscles as being either
pull or push. In reality all muscles
contract or pull. In order to allow movements of
bones in opposite directions, muscles are
arranged in agonist/antagonist pairs.
Agonist -
Muscle primarily responsible for movement of a
body part (prime mover) e.g. the bicep flexes the
arm at the elbow
Muscle that counteracts the agonist muscle,
lengthening while the agonist contracts e.g. the
tricep extends the arm at the elbow acting
in opposition to the bicep
Antagonist -
6
Agonist/Antagonist Muscles
Table 3.3 Examples of opposing muscle groups. (p.
38)
7
Origins Insertions
Origin -
The point where muscles attach to the more
stationary of the bones
Insertion -
The point where muscles attach to the bone that
is moved most
e.g. pectoralis major originate on the sternum,
clavicle and rib cage and insert at the bicipital
groove of the humerus
e.g. bicep originates on the scapula and inserts
on the radial tuberosity
8
Muscles as Levers
Skeletal muscles function as levers to move bones
at joints. Different muscles attach
(originate/insert) in different locations on
bones and therefore function as different types
of levers. There are three main classes of
levers (types 1, 2, 3).
The following site shows examples of the three
types of levers as well as examples as they
relate to joints in the body.
http//www.innerbody.com/image/musfov.html
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Muscles as Levers
Levers work on the the Physics principle of
Torque. Torques cause objects to pivot around
stationary points (fulcrums) like bones around
sinovial joints. Torque is defined as the
product of the Force and the distance b/w the
Force and the fulcrum (lever arm). In order for
an object to be at rest, all torques on the
system must equal zero.
Example How much force must a bicep muscle exert
in order to hold a 5.0kg mass (in the palm of the
hand)? See diagram on overhead.
Calculate the force if the insertion of the bicep
(radial tuberosity) is instead located 5.2 cm
away from the elbow.
The points of insertion vary from person to
person, elite athletes are often found to have
insertions located farther from joints than the
average person!