Experiment 1: Observations

It is very clear from the results of experiment 1 using the Spine Simulator that the counterbalancing force was dependent on the location of the load.  Specifically, the force increased as the load got closer vertically to the shoulder joint and as the load moved farther laterally away from the shoulder joint, as illustrated in figure 26.  The best position to minimize the required Counterbalancing Force was the position lowest in the backpack and closest to the spine; in the “backpack” grid, that position is identified as BL, the Bottom Left position.  The worst position requiring the most counterbalancing force was high in the backpack and furthest from the spine; the TR or Top Right position.

Furthermore, it is evident from the tables and charts that the changes in counterbalancing forces were more sensitive to changes in position in the horizontal direction than in the vertical direction; in other words, keeping the load closer to the spine was more effective than lowering it to minimize the forces.  For example, in reference to the 3 kg load set of data (figure 21), using the ratio analysis, moving the load vertically upwards from the BL position to the MTL position caused a counterbalancing force to increase by a factor of 2.14.  The same spatial movement of the load in the horizontal direction from BL to BR caused the force to increase by a factor of 6.29

The same observation is made for the other loads tested.  Also the ratio analysis showed that the ratios were fairly consistent within the accuracy of the experimental errors. 

Figure 26: Grid Forces Distri9bution