Energy cost and efficiency of a demanding combined manual materials-handling task

Energy cost and crew performance were studied during a 45-hour continuous field-artillery loading exercise using a howitzer simulator. An interrupted peak $\dot{V}_{0_{2}}$ test, conducted in the simulator, was used to develop individualized equations to predict energy cost from heart rate. Nine experienced crew members rotated through six 1.5-hour loading cycles. Mission time (the time elapsed from the order to fire until task completion) was recorded and summed over cycles. Measures made at the end of each cycle included profile of mood state (POMS); rating of perceived exertion (RPE); rating of pain, soreness, and discomfort (RPSD); and isometric hand-grip strength. Results showed a significant decrease (p<0.01) in energy cost (8.0-6.2 kcal·min-1) and mission time (28.1-24.3 min) from Cycle 1 to Cycle 6. The POMS revealed an increase in fatigue and tension and a decrease in vigor (p<0.05); RPE increased (p<0.05) over time as did RPSD reported for the shoulders, arms, and hands (p<0.05). Isometric hand-grip strength decreased 8.6% (p<0.05) from Cycle 1 to Cycle 6. The efficiency of howitzer loading performance increased; however, the changes in RPE, POMS, hand-grip, and RPSD suggest that longer duration exercises may result in performance decrements. These data indicate that simulators can improve the performance of this task.