Muscle Fatigue & Energy Systems

Three Sources of Energy for Muscle Contraction

1)      The first source of energy that is used to reconstitute the ATP is the substance phosphocreatine, which carries a high-energy phosphate bond similar to the bonds of ATP.

2)      The second important source of energy, which is used to reconstitute both ATP and phosphocreatine, is a process called glycolysis-the breakdown of glycogen previously stored in the muscle cells.

3)      The third and final source of energy is oxidative metabolism, which means combining oxygen with the end products of glycolysis and with various other cellular foodstuffs to liberate ATP.

More than 95% of all energy used by the muscles for sustained long-term contraction is derived from oxidative metabolism.

Events occurring in skeletal muscle  during prolonged fasting
➤ Decreased use of ketone body to spare it for brain.
➤ Use of fatty acid almost exclusively.
➤ Decreased protein catabolism with decreased urinary nitrogen loss.
Events occurring in brain
➤ Uptake and utilization of ketone bodies