Discussion of Results
Both experiment 1 using the Spine Simulator and experiment 2 using the Real Backpack confirmed that the counterbalancing force is spatially dependent on the load’s distribution within the backpack. However, the comparison is NOT in total agreement.
In the Spine Simulator experiment, it is very
clear that the position
TR
which corresponds to position
C in experiment 2’s real Backpack
is where the required counterbalancing load is the LARGEST. This is the only
position that the results from both experiments corroborated each other.
In the other 3 positions, experiment 2’s subjective evaluations of the counterbalancing forces were not conclusive in validating experiment 1’s results. During the survey, the subjects had to think hard to figure out how the other three positions A, B and D compared.
Referring back to tables 14 to 26 which summarized the counterbalancing forces over the grid “backpack”, the differences of some of the force measurements are not large. In the real backpack, these relative smaller differences might not have been easily felt by our test subjects. For example, the forces at the BR and TC positions are virtually the same. The subjects’ difficulties in ranking their evaluations and the resulting non-consensus are therefore understood.
However, the results of experiment 1 using the Spine Simulator did seem to support force diagrams found in the literature. Figure 38 is a reproduced diagram (Foerster and Miller, 2006) with the Spine Simulator superimposed. The force diagrams shown definitely support the findings in experiment 1 and that is, the counterbalancing forces become LARGER as the load is positioned higher in the backpack and further away from the spine.
