<P> H O also diffuses out of the cell into the blood stream, from where it is excreted in the form of perspiration, water vapor in breath, or urine from the kidneys . Water, along with some dissolved solutes, are removed from blood circulation in the nephrons of the kidney and eventually excreted as urine . </P> <P> The products of fermentation can be processed different ways, depending on the cellular conditions . </P> <P> Lactic acid tends to accumulate in the muscles, which causes pain of the muscle and joint as well as fatigue . It also creates a gradient which induces water to flow out of cells and increases blood pressure . Research suggests that lactic acid may also play a role in lowering levels of potassium in the blood . It can also be converted back to pyruvate or converted back to glucose in the liver and fully metabolized by aerobic respiration . </P>

Carbon dioxide heat and water are the by-products of aerobic exercise