Ergonomic comparison of three modes of load carriage.

The purpose of this study was to examine the cardiorespiratory responses to carrying external loads on the head and by yoke. Ten physically fit male students carried three different external loads (11.6, 16.1 and 20.6 kg) on a level motor-driven treadmill at varying speeds (0.89, 1.23 and 1.57 m . s-1), using three different modes of load carriage systems, i.e., headpack (HP), transverse yoke (TY), and frontal yoke (FY). Physiological measurements were obtained for: heart rate (HR), pulmonary ventilation (VE), oxygen consumption (VO2), ventilation equivalent (VE) and oxygen pulse (OP). The analysis of variance showed significant main effects (mode, load and speed) and three interaction effects in the HR, VE and VO2 responses. Only the speed main effect was significant (P less than 0.05) for VE. For the OP variable, significant F ratios were found for the mode (P less than 0.05), load and speed (P less than 0.01) main effects, but not for the interaction between mode, load and speed (P greater than 0.05). Scheffé's simple cell mean contrasts indicated that the cardiorespiratory (HR, VE and VO2) responses for the TY and HP modes were lower (P less than 0.05) than the FY while transporting heavy (16.1 and 20.6 kg) loads at fast (1.23 and 1.57 m . s-1) walking speeds. Irrespective of the walking speed, the cardiorespiratory responses while transporting loads with the TY and HP modes were not statistically different (P greater than 0.05). The findings suggest that load transportation by the frontal yoke is ergonomically inadvisable.