Frolich, Human Anatomy, Mechanics of Movement Mechanics of Movement I: Muscle Force and Action Across Joints  Review muscle force generation  Muscle Mechanics --force versus cross section --length versus strain  Lever mechanics and agonist/antagonists  Stabilizing the joint—isometric and eccentric contraction

Frolich, Human Anatomy, Mechanics of Movement Muscle Structure Review  Muscle fiber = muscle cell  Fibers lined up = direction of pull  Tendon attaches to bone  Muscle pulls on bone

Frolich, Human Anatomy, Mechanics of Movement Muscle Origin and Insertion  Origin  Proximal  Fixed  Insertion  Distal  Moves  (usually!!)

Frolich, Human Anatomy, Mechanics of Movement Mechanics of Contraction  Muscle fiber is one cell made up of myofibrils, each filled with myofilament proteins actin and myosin, all lined up along length of muscle cell.  Action potential or depolarization of membrane releases calcium  Calcium changes shape of actin so myosin cross- bridges form and “row” or pull in to center of sarcomere.

Frolich, Human Anatomy, Mechanics of Movement Visualizing muscle contraction How actin- myosin complex (sarcomere) shortens muscle

Frolich, Human Anatomy, Mechanics of Movement Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement Levels of Muscle Organization

Frolich, Human Anatomy, Mechanics of Movement Muscle Mechanics: Cross section versus force  Cross sectional area is proportional to Force of muscle

Frolich, Human Anatomy, Mechanics of Movement Muscle Mechanics: length versus force  Force generation depends on current length of muscle or overlap in actin/myosin of sarcomeres  Muscle force strongest between % of normal resting length— WHY? (don’t forget role of cross-bridges)  Most muscles arranged to work in this range

Frolich, Human Anatomy, Mechanics of Movement Muscle Mechanics: length versus total shortening  Length of muscle is proportional to ability to shorten (strain)  Number of sarcomeres in series gives shortening ability  Short, fat muscles  Lots of force  Less shortening range  Long, skinny muscles  Less force  More shortening range

Frolich, Human Anatomy, Mechanics of Movement Types of fascicle arrangements  Affects length and cross section of muscle  Thus affects force and shortening properties of muscle  See Muscle Mechanics if this doesn’t make sense

Frolich, Human Anatomy, Mechanics of Movement Long thin straight muscle versus short fat pinnate muscle  Gastrocnemius (calf muscle)  Short and bulky  Pinnate fibers  Great force, low shortening distance  Pushes off each step—”spring- loaded”  Sartorius  Tailor’s or hackey-sac muscle  Longest muscle in body’  Thin and straight fibers  Low force, great shortening distance

Frolich, Human Anatomy, Mechanics of Movement Muscle movement across joints is like lever system

Frolich, Human Anatomy, Mechanics of Movement Agonist/Antagonist muscles

Frolich, Human Anatomy, Mechanics of Movement Stabilization and Control Around Joint AgonistMain MoverE.g. biceps AntagonistOpposite motion E.g. triceps SynergistAids agonistE.g. brachialis  Antagonist often “fires” or contracts or is stimulated simultaneously with agonist to stabilize around joint during movement  NOTE: Muscle “contraction” or stimulus to “fire” does not always result in muscle shortening

Frolich, Human Anatomy, Mechanics of Movement Relation between muscle contraction (or “firing”) and shortening  Concentric contraction—muscle contracts and shortens to cause movement across joint  Isometric contraction—muscle contracts but stays same length to hold joint or body in same position  Eccentric contraction—muscle contracts while lengthening to stabilize joint during movement (most common in antagonist to slow movement caused by agonist)