Assessment of Physical Activity Intensity during Infantry Combat-Simulated Operations
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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The purpose of this study was to estimate the intensity of physical activity of infantrymen during a combat-simulated five day field operation by means of continuous heart rate HR recordings. Subjects were 29 soldiers forming 4 rifle squads. Each squad rotated daily through 4 separate terrain areas, each with its own combat-simulated scenario, performing the same scenario on the first and last day. Sleep was limited to one 5 hour period per night. Physical activity was estimated by taping HR with Oxford Medilog cassette recorders with an electrocardiographic ECG channel. Mean daily average HR excluding sleep and resupply time decreased from a high of 101 beats per min bpm on day one to a low of 89 bpm on day five. This suggests the progressive development of physical fatigue, as the five day operation progressed. A 10 km forced march proved to be the single most demanding event resulting in a mean HR of 128 bpm for 140 minutes. Other periods of sustained high HR were associated with moving to and from mission objectives. Time at or above 50 of maximal HR averaged only 37 minutes per day while HR 75 was only 2.5 minutes, both times tending to decrease from day 1 to day 5.
- Stress Physiology