Effect of load position on physiological and perceptual responses during load carriage with an internal frame backpack.

The purpose of this study was to determine the effect of load position in an internal frame backpack on physiological and perceptual variables. Ten female participants walked on a level treadmill for 10 min carrying 25% of their body weight in a high, central, or low position. The variables measured included oxygen consumption (VO2), heart rate (HR), respiratory exchange ratio (R), respiratory rate (RR), minute ventilation (VE), and rating of perceived exertion (RPE). VO2, VE, and RPE were significantly lower in the high position (18.6 +/- 2.3 ml/kg/min, 31.7 +/- 5.0 l/min, 2.8 +/- 0.8, respectively) compared to the low position (22.2 +/- 3.0 ml/kg/min, 38.6 +/- 7.5 l/min, 3.7 +/- 1.0, respectively). HR, R, and RR did not change significantly as the load was moved from the high (129.8 +/- 16.8, 0.89 +/- 0.06, 30.3 +/- 4.2, respectively) to the low position (136.0 +/- 25.3, 0.92 +/- 0.04, 33.8 +/- 5.2, respectively). The results of this study suggest that load placement is an important factor in the physiological and perceptual responses to load carriage, and that packing heavy items high in the backpack may be the most energy efficient method of carrying a load on the back.