Skeletal Muscle Metabolism
How do muscles use energy?

WHAT
IS

ATP
 Mitochondria in muscle convert glucose, fatty acids, and amino acids into ATP
 ATP is used by the cell for any process that requires energy (such as muscle contraction)
 The amount of oxygen available to the muscle cells determines the amount of ATP that can be produced

ATP
P P P
3 Phosphate groups

ATP
ENERGY stored in bonds
P P P
3 Phosphate groups

P P P
ENERGY
RELEASED

Sources of ATP (times approximate)
• Stored ATP from processes below (4-6 seconds worth)
• Creatine Phosphate (10 seconds)
• Glycogen (stored carbohydrates in liver and muscle) or glucose in blood are used for glycolysis and lactic acid fermentation (30-40 second bursts)
• Glycogen, glucose, fatty acids are used in aerobic respiration (lasts for hours)

Glucose from glycogen in muscle and liver
O
2
Glycolysis
No O
2

Summary: With or Without
Oxygen?
Without oxygen (anaerobic)
 Glycolysis (splitting of glucose) follow by fermentation of lactic acid)



ATP produced quickly
Fewer ATP are generated
Duration: 30-60 seconds
With Oxygen (aerobic)
 cellular respiration using glucose, fatty acids, or amino acids (preceded by glycolysis)



ATP produced slowly
More ATP generated
Duration: hours

Muscle Fiber Types
 Slow-oxidative - endurance activities
(jogging) (smallest diameter)
 Fast - oxidative - short term activities requiring bursts of energy (sprinting, basketball, soccer, etc.)
 Fast-glycolytic - short intense movements where force production is maximal (lifting heavy weight, jumping, throwing) (largest diameter)

• All muscles are a mix of different fiber types
• Genetics determine the percentage of different fiber types in different muscle

Fatigue and Oxygen Debt


Occurs when ATP demand is faster than production (when O
2 supply is limited)
Lactic acid “burn” limits usefulness of ATP
 Oxygen Debt - the amount of O
2 that must be taken in to restore the muscles’ resting conditions (ATP regeneration, glycogen replenishment, creatine phosphate restoration, lactate breakdown)

Muscle Fiber Ratios and Athletic
Performance


Which of the above athletes have a greater composition of fast twitch muscle fibers?
How does this relate to athletic performance?

Hypertrophy - increase in the size of a muscle


Micro-tears (of the myofilaments) create a stimulus for hypertrophy.
Stressed fibers form more myofibrils, myofilaments (actin and myosin), and store more glycogen (fast-twitch more prone to growth)