Glycolysis involved in glycolysis. The burning sensation in muscles during hard exercise can be attributed to the release of hydrogen ions during the shift to glucose fermentation from glucose oxidation to carbon dioxide and water, when aerobic metabolism can no longer keep pace with the energy demands of the muscles. These hydrogen ions form a part of lactic acid. The body falls back on this less efficient but faster method of producing ATP under low oxygen conditions. This is thought to have been the primary means of energy production in earlier organisms before oxygen reached high concentrations in the atmosphere between
Asynchronous muscles is sufficient Ca. This can be achieved in one of two ways. First, two antagonistic muscles can be configured with elastic structures such that the contraction of one muscle stretches the other, causing it to activate and vice versa. This configuration is found in the power muscles of flying insects. Second, a single asynchronous muscle can deform an elastic element which then stretches the muscle and causes the muscle to contract again. This setup is used by "Drosophila" to oscillate mechanosensory organs known as halteres. As long as neural stimulus turn the muscles "on," both systems will continue to oscillate.