These findings have been used to support the concept that glycolytic metabolism is limited in children. There are a number of possible explanations for the low blood lactate concentrations reported in this population. Large blood volumes relative to body size, typical of children, could produce a diluting effect on blood lactate. The high hepatic blood flow and lower sympathetic activity in children relative to adults may result in greater ability to remove lactate from muscle indicating that adult-oriented blood sample timing would be inappropriate. As a result, serial blood sampling would be the only manner in which maximal blood lactate values could be assessed.
Ethical constraints limit the use of such research design with children.
Moreover, intensities less than maximal would not be expected to produce high lactate levels, yet often studies reporting maximal blood lactate levels have only included submaximal intensities. Phosphorus is intimately involved in muscle bioenergetics since the energy stored in the Phosphorus-Oxygen bonds of ATP is used to drive cellular metabolism. The coil is positioned onto the surface of the muscle to be studied and the subject is placed in a high magnetic field of a large bore magnet. The non-invasiveness of this technology, and the ability to measure metabolism in 'real time' allows the researcher the ability to address some of the outstanding questions in pediatric physiology. While this new technology is quickly becoming accepted as the most effective means of measuring intramuscular aerobic and anaerobic metabolism in both adults and children, the expense of the procedures involved in 31 P-MRS research remains a severe limitation.