The purpose of this study was to prove or refute previous authors' suggestions that tolerance to +Gz is reduced when preceded by 0 Gz or -Gz. Six men and six women were subjected to one session of acceleration stresses that varied between -2 and +2.25 Gz on the NAMRL Coriolis Acceleration Platform (CAP). At the beginning and end of each session, we exposed the relaxed subjects to identical control segments that were comprised of +1 Gz for 30 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects were also exposed to three experimental segments that were comprised of 0, -1, or -2 Gz for 10 s, followed by +2.25 Gz for 15 s, and then return to +1 Gz. Subjects verbally reported any decrements in peripheral vision during exposure to +2.25 Gz. Blood pressure (BP) was reduced during each 15-s period at +2.25 Gz. The minimum BP was progressively lower during the 15-s period as the preexposure experimental conditions became more negative (+1, 0, -1, and -2 Gz). Episodes of peripheral vision loss increased as the preceding -Gz became more negative. BP during exposure to +Gz was significantly affected by the preceding 10-s exposure to -Gz, and is indicative of reduced +Gz tolerance. As this ''push-pull effect'' may result in unexpected incapacitation, it has important implications for aviation safety.
