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Chapter 2

Kinesiology 2241A/B Chapter 2: CHAPTER 2 TEXT NOTES

Course Code
Kinesiology 2241A/B
Thomas Richard Jenkyn

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Muscle Architecture
-A whole muscle is composed of muscle fibers (cells) made up of bundles of
-Each myofibril is composed of sarcomeres arranged in series, end to end, along the
-Bundles of myofilaments make up each myofibril, and the striations (stripes) seen
along the length of the myofibril identify the string of sarcomeres
-Myosin and actin are capable of changing their length. The cross-bridge theory of
muscle contraction is based on the interaction of the actin and myosin proteins
-whole muscles respond to the muscle fiber forces occurring within them; but
without the connective tissue matrix (network) that joins the muscle fibres to the
tendons attached to the movable bones, these forces would have no way to act on
their body segments
-Skeletal (striated) muscles are very important because they are the force-
producing agents causing and controlling movements of our body
-Important skeletal muscle tissue functional properties: irritability, conductivity,
contractility, distensibility and elasticity.
Irritability responds to nervous stimuli that set up a wave of excitation in the
muscle (conduction) to cause contraction or tension to pull its end (attached
via tendon to bones) closer together.
The end of contraction is relaxation. Contraction takes time to reach maximum
value, and relaxation takes time to occur completely as contraction diminishes.
Maximum contraction and relaxation times varies between muscle.
Muscle and tendon can be distended, or stretched, within limits, to allow for non
restricted joint movement cause by an antagonist (opposite) muscle or some other
force. Elasticity is the property of muscle and its connective tissue network that
gives it the ability to recoil from stretch.
Flexibilty: term used to refer to a joint’s range of motion ROM. ROM of a joint is
dependent on the bony structure of the joint and the permissiveness of the tissues
surrounding the joint. Muscle and its tendon make up the majority of the tissues
permitting joint ROM. ROM between two segments is identified by the angle formed
between them and is typically measured in degrees
Strength: the maximum amount of force that can be exerted by a muscle-tendon
unit. Since muscles don’t act individually, measures of strength are typically
obtained for the group of muscle-tendon units exerting tension on a segment.
Strength can vary depending on many factors (instrument used to record it, the
position of the joint across which the muscle group acts, and whether the muscle
group is getting shorter, longer, or remaining the same length).
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