ABSTRACT
The first source of energy during intense muscle contraction is stored ATP and stored Phosphocreatine (PCr). This lasts from about 10–30 seconds depending on the intensity of exercise. Within seconds of the commencement of exercise muscle glycogen starts to break down. The production of lactic acid from this process produces 3 ATP from each glucose derived from glycogen. A consequence, however, of this glycogen breakdown is lactic acid accumulation in muscle. The hydrogen ion (H+) associated with the lactic acid production can cause muscular fatigue. The cause of fatigue between 30 and 90 seconds is likely acidosis. This acidosis can cause a number of problems with muscle contraction and energy metabolism. The next way glycogen is broken down is by aerobic means. The aerobic breakdown of muscle glycogen yields 39 ATP per glucose derived from muscle glycogen. This tends to happen after about 60–90 seconds of high-intensity exercise. Other potential fuels at this time appear to intramuscular lipid. However, we are not sure if this substrate is used or just lysed and liberated into the blood stream. Likely, during intermittent exercise at 95%–100% of VO2max, such as amateur wrestling, the fuel sources for exercise are confined to ATP-PCr and the anaerobic and aerobic use of muscle glycogen. This may change slightly to blood glucose in trained individuals, but clearly not much blood glucose is oxidized at 100% of VO2max as only 1% of the energy derived for exercise at 97% of VO2max was blood glucose with the remaining 99% coming from muscle glycogen in untrained individuals. Also, you will use more fat in the glycogen depleted state, but a side effect of this increased fat utilization is that performance suffers.
