Two types of frame backpack, the internal-frame pack and the external-frame pack, are commonly used by hikers to carry heavy loads. The centre of volume of the internal-frame pack is lower and closer to the body than that of the external-frame type. This study examined how carrying each pack type changed the body posture compared with the typical standing posture as a control. The packs were loaded with 19#x2009;kg loads for the men and 14#x2009;kg loads for the women. The positions of the knees, hips, shoulders and ears were recorded photographically; the whole-body centre of gravity and the partial centres of gravity above the knee and hip were calculated. The nine female and seven male subjects were experienced in carrying packs. Both types of packs caused the subjects to lean forward; the bend was greatest above the hips but the knees and hips were also forward of the control position. The internal-frame pack caused a greater displacement and also a greater uncompensated torque at the hips: The female subjects overwhelmingly preferred the external-frame pack, while the male subjects preferred the internal-frame pack; no difference in parameters was seen between the men and the women that might explain these preferences. Although the internal-frame pack seems less adaptive in a static test, it would provide greater stability and less moment of inertia during walking.
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