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
Neural control of limb stiffness adjustments due to reflexes are involuntary and are controlled by the spinal cord while posture selection is controlled voluntarily. However, not each component of stiffness is strictly voluntary or involuntary. For example, Antagonistic muscle cocontraction can be either voluntary or involuntary. Additionally, because much of the legs' movements are controlled by the spinal cord and because of the larger neural delay associated with sending signals to the leg muscles, leg stiffness is more involuntarily controlled than arm stiffness. Researchers have begun implementing controllers in into robots to control for stiffness. One such model adjusts for stiffness during robotic locomotion by