No abstract

Altitude exposures above 3,000 m produce changes in symptoms, moods, and cognitive/motor performance of unacclimatized individuals and should produce graded effects on these parameters as elevation and duration are increased. This study examined effects on these parameters as a function of altitude level and duration of exposure by administering standardized tests from 1 to 3 times to 23 males in an altitude chamber during 4.5-hour exposures to 3 levels of hypobaric hypoxia: 500 m, 4,200 m, and 4,700 m. Exposure to altitude significantly affected symptoms, moods, and performance in an elevation-dependent fashion. Adverse changes increased with higher altitudes (all measures were affected at 4,700 m, whereas only some were at 4,200 m) and usually with longer durations. Therefore, specific aspects of symptoms, moods, and performance are significantly degraded after only a few hours of exposure to hypobaric hypoxia, and the severity of the effects dramatically increases when testing is conducted at 4,700 m compared to 4,200 m.

Studies of exhaustive exercise on marksmanship are inconclusive and have not measured trigger pull latencies (LAT) nor considered impact of added torso loads. This study examined the impact of exhaustive whole-body exercise and torso loading on accuracy, precision, and latency during a marksmanship test. Twelve men lifted a 20.5-kg box on to a 1.55-m high shelf until they could not maintain a 12 lifts·min⁻¹ pace. Within 25 seconds of ending the lifting task, the subjects started a 10-minute rifle marksmanship test (8 shots·min⁻¹). During lifting and shooting, the subjects wore 2 different loads: NOLOAD = boots, uniform, and helmet (5.9 kg) and LOAD = a torso-borne load (29.9 kg) + NOLOAD. With the LOAD, the subjects were only able to work for 69% as long, perform 31% as many lifts, or do 38% as much total work compared with the NOLOAD condition. Despite performing less total external work during LOAD, the heart rate (HR) was more than 25% higher than NOLOAD. Measures of accuracy and precision improved and stabilized after minute 3. Overall, LAT increased (p < 0.025) for LOAD (mean ± SE, 2,522 ± 81 milliseconds), compared with NOLOAD (2,240 ± 121). During 0-4 minutes, LAT for LOAD was 14% greater than for NOLOAD (p < 0.05); from 4 to 10 minutes, LAT did not differ. Exhaustive whole-body exercise transiently degraded accuracy regardless of load. In the LOAD condition, LAT was immediately increased and sustained for 10 minutes; in the NOLOAD condition, LAT increased gradually. Although load did not decrease accuracy, it increased the time to engage targets, which can impact fighting effectiveness and survivability.