AMS symptoms begin to appear after 6 hours, increase from 6 to 24 hours, and reach maximum severity after 30 to 40 hours of exposure (Carson et al., 1969; Hackett, 1980). The time courses of other symptoms and mood states appear similar to that of AMS symptomatology, although these changes are not as well documented (Shukitt and Banderet, 1988). The time course of performance impairments, however, appears somewhat different. One study (Banderet et al., 1986) found decreased levels of performance on all seven tasks administered 1 or 6 hours after ascent to 4,600 m (15,092 ft). At 14 or 19 hours, only four tasks were still impaired, and by 38 or 42 hours, only two were still impaired (Figure 22-9). Therefore, changes in performance were most severe at 1 to 6 hours, the time when AMS symptoms are only beginning to appear. Additionally, performance changes return to baseline when AMS symptoms are most severe (after 30 to 40 hours).
Shukitt-Hale et al. (1991a) conducted a study to determine whether individuals afflicted with initial symptoms of AMS would be more susceptible to adverse changes in other symptoms, moods, and performance, since they may be differentially affected at this point in time. The AMS-Cerebral (AMS-C) factor of the Environmental Symptoms Questionnaire (ESQ) was chosen as the best measure of altitude sickness, since it is a standard index of the degree of illness. Other measures were chosen to assess symptoms, moods, and performance.