Performance during simple and complex military psychomotor tasks at various altitudes.

Background: The purposes were to determine the following: 1) the threshold between 2500-4300 m at which simple and complex military task performance is degraded; 2) whether the degree of degradation, if any, is related to changes in altitude illness, fatigue, or sleepiness at a given altitude; and 3) whether the level of hypoxemia, independent of altitude, affects simple and complex military task performance.

Methods: There were 57 lowlanders (mean +/- SD; 22 +/- 3 yr; 79 +/- 12 kg) who were exposed to either 2500 m (N = 17), 3000 m (N = 12), 3500 m (N = 11), or 4300 m (N = 17). Disassembly and reassembly of a weapon (DsAs, simple), rifle marksmanship (RM, complex), acute mountain sickness (AMS), fatigue, sleepiness, and arterial oxygen saturation (SaO2) were measured at sea level (SL), and after 8 h (HA8) and 30 h (HA30) of exposure to each altitude.

Results: DsAs did not change from SL to HA8 or HA30 at any altitude. RM speed (target/min) decreased from SL (20 +/- 1.5) to HA8 (17 +/- 1.5) and HA30 (17 +/- 3) only at 4300 m. AMS, fatigue, and sleepiness were increased and SaO2 was decreased at 2500 m and above. Increased sleepiness was the only variable associated with decreased RM speed at 4300 m (r = -0.67; P = 0.004). Greater hypoxemia, independent of altitude, was associated with greater decrements in RM speed (r = 0.27; P = 0.04).

Conclusions: Simple psychomotor performance was not affected by exposures between 2500-4300 m; however, complex psychomotor performance (i.e., RM speed) was degraded at 4300 m most likely due to increased sleepiness. Greater levels of hypoxemia were associated with greater decrements in RM speed.