1. Conduct observational, human-use, study to compile a normative reference database for NIRS-measured tissue perfusion in the uninjured upper extremity and the injured and non-injured legs of up to 120 injured subjects, from varying ethnicities (skin pigmentations) in varying degrees of hemodynamic status (stable, critically injured) to test the 3 hypotheses listed above. The study groups consist of one control group (critically ill without leg injuries) and one investigational group (critically injured with leg injuries):