Fig. 2. Plasma norepinephrine and epinephrine levels at 10 days before flight (L-10), on landing day (R+0), and 2 to 4 days after landing (R+2/4) in two groups of astronauts differentiated according to mission duration. Astronauts in space for 4 to 7 days showed a significantly greater increase in norepinephrine (p = .02) and epinephrine (p = .03) after landing than those in space for 11 to 16 days.