No abstract

Soldiers must often carry heavy loads which can lead to symptoms of body soreness, aches, pains, and tiredness. This study assessed symptoms when soldiers carried loads in the standard U.S. Army ALICE pack (a single backpack) and in a prototype Double Pack (a two-pack system designed to alleviate symptoms by evenly distributing the load between a backpack and a frontpack). Each of 15 male soldiers completed a 20-km (12.4 mi) road march while carrying either 34, 48, or 61 kg (75, 105, or 135 lb) and while wearing either the ALICE pack or the Double Pack. Symptoms included feeling alert, good, and wide awake. Postmarch symptoms included tiredness, muscle tightness, and soreness of the legs, feet, back, and shoulders. Analyses of eight symptom factors showed that (a) as load increased, fatigue and muscle discomfort intensified, and alertness and feelings of well-being diminished and (b) distress and heat-illness indices were most intense at 61 kg with the Double Pack.

Sleep restriction degrades cognitive and motor performance, which can adversely impact job performance and increase the risk of accidents. Military personnel are prone to operating under sleep restriction, and previous work suggests that military marksmanship may be negatively affected under such conditions. Results of these studies, however, are mixed and have often incorporated additional stressors (e.g. energy restriction) beyond sleep restriction. Moreover, few studies have investigated how the degree of difficulty of a marksmanship task impacts performance following sleep restriction. The purpose of the current experiment was to study the effects of sleep restriction on marksmanship while minimizing the potential influence of other forms of stress. A friend-foe discrimination challenge with greater or lesser degrees of complexity (high versus low load) was used as the primary marksmanship task. Active duty Soldiers were recruited, and allowed 2 h of sleep every 24 h over a 72-h testing period. Marksmanship tasks, cognitive assessment metrics and the NASA-Task Load Index were administered daily. Results indicated that reaction times to shoot foe targets and signal friendly targets slowed over time. In addition, the ability to correctly discriminate between friend and foe targets significantly decreased in the high-cognitive-load condition over time despite shot accuracy remaining stable. The NASA-Task Load Index revealed that, although marksmanship performance degraded, participants believed their performance did not change over time. These results further characterize the consequences of sleep restriction on marksmanship performance and the perception of performance, and reinforce the importance of adequate sleep among service members when feasible.

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.

Sentry duty performance requires both rifle marksmanship accuracy and sufficient attention to detect the infrequent appearance of targets. Research has shown that marksmanship accuracy is in part a function of arm-hand steadiness, that arm-hand steadiness may be better in women than men, and that in men 200 mg caffeine heightens alertness and attenuates vigilance decrements. Study objectives were: (a) evaluate gender differences in speed of target detection and rifle firing accuracy during three hours of simulated sentry duty, and (b) determine if 200 mg caffeine enhances sentry duty performance in women as it has been shown to do in men. Twelve men and 12 women were pre-trained on the Weaponeer M16 Rifle Marksmanship Simulator. During 3-hour test sessions, the participant monitored the target scene of the Weaponeer and fired at targets when they appeared. For both men and women, target detection response time deteriorated with time on sentry duty and vigilance decrements were attenuated by 200 mg caffeine. For men, marksmanship accuracy was constant over time; for women, marksmanship accuracy deteriorated after 1.5 hours.