Flight-induced changes in human amino acid excretion.

A biomedical appraisal of flight stress was made by means of a battery of urinary determinations on crewmen who participated in a 96-h airborne alert. The crewmen were divided into three teams, each consisting of 16 members and each manning an EC-135J aircraft. These teams took turns so as to assure that one team was airborne at all times during the alert; flights lasted either 8.5 or 12 h. Preflight baseline data were collected from only one of the three teams. Based on baseline and flight data obtained for that team, urea excretion correlated well with amino acid output which, in turn, correlated remarkably well with alpha-amino nitrogen output. These data collectively revealed the following flight effects: a) marked anticipatory stress immediately before the start of the airborne alert, b) marked flight stress late in each flight flown during the first 48 h, and c) adaptation to flight stress during the final 48 h.