Abstract des Autors

In an experimental study of load carrying effects of mass (O, 5.4, 10.4 kg) and type of support (shoulder or waist) on parameters of physiological strain were quantified to determine the factor(s) which limit carrying time. 4 categories of strain were investigated: metabolic (VO2), cardiovascular (heart rate), muscular (EMG) and skin pressure under the shoulder straps. 4 young male subjects were tested on a treadmill using different combinations of load and speed. While standing, VO2 was not influenced by the type or mass of the backpack, and averaged 10 VO2max. The heart rate increased significantly by 9 beats/min while standing wearing a backpack, independent of type of support or mass. While walking both heart rate and VO2 were significantly influenced by the mass carried, but both types of strain remained below the tolerance limits for prolonged wear. Standing supporting a load did not significantly increase the root mean square value of the EMG signal of the trapezius pars descendens muscle. While walking, load carrying significantly increased the root mean square value, and, converted to force, the largest increase amounted to 2.7 of the maximal force for a load of 10.4 kg suspended from the shoulders. This was below levels of force producing fatigue. The pressure on the skin under the shoulder straps during load carrying was more than a factor of 3 times higher than the threshold value for skin and tissue irritation. Load transfer to waist with a flexible frame reduced the pressure to below threshold value.