EFFECTS OF HEAT STRESS AND EXERCISE ON SHOOTING PERFORMANCE

Purpose: The purpose of this study was to evaluate the effects of exercise and acute heat stress on marksmanship performance measures of accuracy, precision, aim time, and distance travelled by the point of aim in trained US military veterans. Methods: Subjects (N=8) (height 184.1 ± 10.9 cm (SD), weight 92.1 ± 10.6 kg, 21.1 ± 8.9% body fat, VO2max 47.25 ± 7.36 mL/kg/min, age 26.8 ± 4.3 yrs.) completed one-hour of walking at 50% VO2max in a hot (35˚C, 30% maximal relative humidity) or cool (22˚C, 30% maximal relative humidity) environment. Core temperature, heart rate (HR), and physiological strain index (PSI) were recorded throughout the exercise period. Shooting assessments and nude body weights were completed before and after exercise to determine % body weight loss, accuracy, horizontal and vertical deviation, precision, aim time, and distance travelled by the point of aim. Results: Core temperature, HR, and PSI increased from rest (35.7 ± 4˚C; 88 ± 4bpm) in both cool (37.8 ± .5˚C; 143 ± 20bpm, 5.5 ±1.6) and hot (38.5 ± .4˚C; 167 ± 13 bpm, 7.8 ±1.11) conditions at 60 minutes but were significantly greater in hot compared to cool in the latter half of the trial. Percent body weight loss was greater in the hot (1.5 ± 0.5 %) compared to cool (0.9 ± 0.5 %) trials. Aim time decreased for cool (3.2 ± 0.4 sec) and hot (2.9 ±0.3 sec) trials compared to rest (4.1 ± 0.4 sec). Vertical-deviation increased in the kneeling position (15.2 ± 1.3 mm SE) compared to prone (10.7 ± 1.38 mm SE) but standing (14.1 ± 1.2 mm SE) was not significantly different from either. There were no changes from rest for accuracy, distance travelled, or precision in either hot or cool trials. Conclusion: Despite elevated levels of physiological strain there were no decrements in marksmanship performance due to exercise or heat stress. Kneeling may alter vertical deviation more than prone or standing shooting positions during marksmanship tasks. These data also indicate a need for more work related to prolonged, elevated PSI and/or % body weight losses commensurate with or exceeding the suggested 2% criteria