2. 5 Golden Rules of Skeletal Muscle Activity
Muscles produce movement by pulling on bones as a muscle
contracts
1. Movement occurs at the joint between the origin and the insertion.
2. Typically, the bulk of a skeletal muscle lies proximal to the joint
crossed.
3. All skeletal muscles have at least two attachments: the origin
and the insertion.
4. Skeletal muscles can only pull; they never push.
5. During contraction, the insertion bone is pulled closer to the
origin bone.
3. Muscle and Bone Interactions
• Tendons attach muscle to bone! Each muscle begins at
an origin, ends at an insertion, and contracts to
produce a specific action. Almost all skeletal muscles
either originate or insert on the skeleton.
• The origin is the more stationary bone
• The insertion is the more moveable bone
• Actions are the joint movements a muscle contraction
produces (ex: flexion/extension, abduction/adduction,
rotation, circumduction, pronation/supination,
protraction/retraction, elevation/depression, etc)
5. Muscle Groups
• Muscles in the body rarely work alone and are usually
arranged in groups surrounding a joint.
• A muscle that contracts to create the desired action is
known as an agonist or prime mover.
• A muscle that helps the agonist is a synergist.
• A fixator is a synergist that assists an agonist by
preventing movement of another joint, thereby
stabilizing the origin of the agonist.
• A muscle that opposes the action of the agonist,
therefore undoing the desired action, is an
antagonist.
6. The Affect of Exercise on Muscles
• Exercise increases muscle size, strength, and endurance
• Aerobic (endurance) exercise (biking, jogging) results in
stronger, more flexible muscles with greater resistance to
fatigue
• Makes body metabolism more efficient
• Improves digestion and coordination
• Resistance (isometric) exercise (weight lifting) increases
muscle size and strength
NOTE: Prolonged disuse causes muscles to atrophy (waste away)
Editor's Notes
Endurance training allows more efficient delivery of oxygen and nutrients to a muscle via increased blood flow
