THE INFLUENCE OF THE ARMY PACK ON POSTURAL STABILITY AND STANCE MECHANICS

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Abstract
The size, wt. and method of carrying the Army pack are standardized without allowing for modification in relation to variations in build and stature. The effect of the regulation pack was observed on the stance mechanics of 5 Army officers and 2 cadets varying in ht. by 20.8 cm. and in wt. by 31.6 kg. Each man was observed for 2 min. in a natural comfortable stance, the military posture, carrying the pack in regulation position, too high and too low. Biplane center of gravity observations synchronized with sagittal and back view posture pictures were made at 5 sec. intervals. The military stance reduced involuntary postural sway and carrying a pack suppressed it further. To counter-balance the pack, the body leaned forward in toto over the ankle joints without significant realignment of other segments. A too high placement of the pack unstabilized the stance of the tall men. A too low pack was associated with a forward shift of the center of gravity of the body as a whole, increasing to a maximum the strain on the foot. The regulation position probably represents the best autonomous compensation for the load since the vertical projection of the center of wt. as related to the margins of static security then most nearly approximates that observed in the unloaded posture. The small man exhibited no disadvantage which could not be met adequately by automatic compensatory adjustments.

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