Aerobic & Anaerobic Metabolism in Muscles. Objectives. Recognize the importance of ATP as energy source in skeletal muscle. Understand how skeletal muscles derive and utilize ATP for energy. Differentiate between energy metabolism in red and white muscle fibers. ATP.
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Recognize the importance of ATP as energy source in skeletal muscle.
Understand how skeletal muscles derive and utilize ATP for energy.
Differentiate between energy metabolism in red and white muscle fibers.
ATP or adenosine triphosphate is the energy currency used by our body everyday to perform a number of tasks:
Breakdown of ATP into ADP+PO4 releases energy.
Muscles typically store limited amounts of ATP – enough to power 4-6s of activity
So resting muscles must have energy stored in other ways.
The process that facilitates muscular contraction is entirely dependent on body’s ability to provide & rapidly replenish ATP
1- ATP-CreatinePhosphate system
2- Glycolytic system
3- Oxidative system
% Capacity of Energy System
Aerobic Energy System
ATP – Creatine Phosphate
The three energy systems often operate simultaneously during physical activity.
Relative contribution of each system to total energy requirement differs depending on exercise intensity & duration.
Magnitude of energy from anaerobic sources depends on person’s capacity and tolerance for lactic acid accumulation (Athletes are trained so that they will have better tolerance for lactic acid).
As exercise intensity diminishes & duration extends beyond 4 minutes, energy more dependent on aerobic metabolism
Source of energy:
mainly fatty acids, then carbohydrate
CO2, H2O & ATP
Recovery period: begins immediately after activity ends
Oxygen debt (excess post-exercise oxygen consumption)
i.e. the amount of oxygen required during resting period to restore muscle to normal conditions
White muscle : (glycolytic)
mostly fast fibers
pale (e.g. chicken breast)
Red muscle: (oxidative)
mostly slow fibers
dark (e.g. chicken legs)
Most human muscles are:
During periods of muscular rest ATP is required for:
1- Glycogen synthesis (glycogenesis)
i.e. storage form of glucose to be used
during muscular exercise
2- Creatine phosphate production
i.e. energy storage compound to be used at the beginning of muscular contraction
Resting muscle fibers takes up free fatty acids from blood.
Fatty acids are oxidized (in the mitochondria) to produce acetyl CoA& molecules of NADH & FADH2
Acetyl CoA will then enter the citric acid cycle (in the mitochondria)ATP, NADH, FADH2 & CO2
NADH& FADH2will enter the electron transport chain.
synthesis of ATP
At the beginning of exercise, muscle fibers immediately use stored ATP
For the next 15 seconds, muscle fibers turn to the creatine phosphate.
This system dominates in events such as the 100m dash or lifting weights.
After the phosphagen system is depleted, the process of anaerobic glycolysiscan maintain ATP supply for about 45-60s.
Glycogen stored in muscles Glucose 2pyruvic acid + 2 ATPs
2 Pyruvic acid 2 lactic acid
Lactic acid diffuses out of muscles blood liver Glucose (by gluconeogenesis) blood muscles
* It usually takes a little time for the respiratory and cardiovascular systems to catch up with the muscles and supply O2 for aerobic metabolism.
1- Large amounts of glucose are used for very small ATP returns.
2- Lactic acid is produced leading to muscle fatigue
Type of sports uses anaerobic metabolism?
Sports that requires bursts of speed and activity e.g. basketball.
ATP sources in working muscle cont.
Occurs when the respiratory & cardiovascular systems have “caught up with” the working muscles.
During rest and light to moderate exercise, aerobic metabolism contributes 95% of the necessary ATP.
Compounds which can be aerobically metabolized include:
Fatty acids, pyruvic acid (made via glycolysis) & amino acids.
ATP sources in working muscle cont.
Liver converts lactate into glucose via gluconeogenesis
The newly formed glucose is transported to muscle to be used for energy again
1- Pyruvatefrom glycolysis during exercise
2- NH2produced from normal protein degradation
Pyruvate + NH2 Alanine
Alanineis transported through the blood to liver
Liver converts alanine back to pyruvate
Alanine – NH2 = Pyruvate
Pyruvateis converted to glucose (gluconeogenesis).
Glucose is transported to muscle to be used for energy again.
Liver converts NH2 to urea for excretion (urea cycle)