Muscle Metabolism and Energy Sources

Study Notes

Muscles need energy to produce contractions, which is derived from ATP, creatine phosphate, muscle glycogen, and other sources.
The energy sources used depend on the intensity and duration of the workload.

ATP provides energy for muscle contraction and active-transport Ca++ pumps in the SR.
Muscle contraction requires sufficient amounts of ATP.
The amount of ATP stored in muscle is limited, sufficient for only a few seconds of contractions.

There are three mechanisms to regenerate ATP: creatine phosphate metabolism, anaerobic glycolysis, and aerobic respiration.

Creatine phosphate is a high-energy compound that stores energy in its phosphate bonds.
In a resting muscle, excess ATP transfers its energy to creatine, producing ADP and creatine phosphate.
Creatine phosphate is used to quickly create more ATP when needed.
The ATP-CP system is the first anaerobic energy pathway, yielding enough ATP for 10-15 seconds of energy.
Creatine phosphate synthesis requires three amino acids: glycine, arginine, and methionine (as S-adenosylmethionine).

The site of creatine phosphate synthesis is the kidneys and liver, and then transported to other tissues.
98% of creatine is present in skeletal and heart muscles.

The amount of creatine phosphate is proportional to muscle mass.
Creatine and creatine phosphate spontaneously form creatinine as an end product.
Creatinine is excreted in the urine, and serum creatinine is a sensitive indicator of kidney disease.

Anaerobic glycolysis is an ATP source that breaks down glucose to produce ATP.
Glycolysis occurs in the cytoplasm and is the second anaerobic energy pathway.
Anaerobic glycolysis provides energy for 1-3 minutes of high-level performance.
The sugar used in glycolysis comes from blood glucose or metabolizing glycogen stored in the muscle.
ATP is required for muscle work, and when oxygen supplies become limited, pyruvate is converted into lactic acid.