MUSCULAR SYSTEM
NOTES
ANAEROBIC METABOLISM
 Byproduct is lactic acid
 Occurs when muscle cells have used all the oxygen available
to them (muscles bulge during intense exercise which
compresses blood vessels)
 Pathway is glycolysislactic acid fermentation
 Uses large amounts of glucose to produce small amounts of
ATP
 Lactic acid buildup in cells leads to muscle soreness
AEROBIC METABOLISM
 95% of energy during rest/light muscle activity comes from
aerobic metabolism
 Provides 38 ATP total from 1 glucose molecule
 Slow process compared to anaerobic metabolism
MUSCLE FATIGUE
 Physiological inability to contract despite still receiving
stimulus
 Dif ferent than psychological/central fatigue (flesh able, but
we are wimps)
 Depleted levels of ATP lead to contractures (state of
continuous contraction)
 Cross bridge unable to detach without ATP available
 Rigor mortis
 Accumulation of lactic acid leads to fatigue (changes shape of
contractile proteins)
 Ion imbalances (K+ accumulates in T tubules)
OXYGEN DEBT
 Defined as the extra amount of oxygen that the body must
take in for the body to replenish its supplies
 Body must convert lactic acid to pyruvic acid, ATP must be
resynthesized, glycogen stores replenished
HEAT PRODUCTION
 Major function of muscular system
 Comes from muscle contraction (friction) as actin and myosin
move across one another
 40% of energy released from ATP is converted to work energy
 Remaining 60% is released as heat energy
 To compare, only about 15% of energy in gasoline is used to move
the vehicle, other 85% is released as heat and sound
 Shivering causes quick contractions of the muscle fibers,
creates large amounts of heat while using minimal energy
T YPES OF MUSCLE FIBERS
 Slow twitch
 Fast twitch
 Main dif ference is in the speed of ATPase (enzyme that breaks
down ATP during muscle contraction)
SLOW TWITCH FIBERS
 Contracts relatively slowly (slow ATPase)
 Depends on oxygen delivery (functions through aerobic
processes)
 Fatigue resistant (high endurance)
 Fibers are thin
 Small amount of contractile power (limited myofibrils)
 Multiple mitochondria
 Lots of capillaries
 Very red
FAST TWITCH FIBERS
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Contracts rapidly
Depends on glycogen reserves
Fewer mitochondria
Low capillary density
White color
Very dense and large compared to slow twitch fibers
Prone to fatigue quickly
Very powerful contractions for short times
SLOW TWITCH VS FAST TWITCH
Fast twitch are used in short spurts (sprinting)
Slow twitch are used in longer exercises (running a mile)
Light meat vs dark meat
Muscles that maintain posture (erectors) have slow twitch
fibers, while muscles that are used for propelling (quads,
gastrocnemius) are fast twitch fibers
 All muscles have a mixture of slow and fast fibers, but are
usually predispositioned towards one or the other
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MUSCLE ENDURANCE
 Aerobic exercise leads to muscles working longer before
becoming fatigued
 More mitochondria are formed in each cell
 More capillaries surround the cells
 Result in much more ef ficient metabolism
ISOTONIC VS ISOMETRIC CONTRACTION
 Isotonic contraction: muscle length changes
 Concentric contractions: when a muscle shortens and does work
(kicking a stupid soccer ball)
 Eccentric contractions: when a muscle generates force as it
lengthens
 Useful for walking and coordination
 Microtears occur during this form of contraction (muscle soreness)
 Isometric contraction: muscle length stays the same
ACTIVIT Y
 Come up with 2 examples of an isotonic and isometric
contraction (not ones I gave you)
 Compare and contrast slow twitch fibers with fast twitch
fibers (venn diagram)