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Full text of article
'Webb D, Wu J, Webb J,, 2019: BIOMECHANICAL EFFECTS OF CARRYING
A UNILATERAL LOAD ON HUMAN BIPEDALISM,
AS INDICATED BY FOOTPRINT TRAIL
PARAMETERS. Anthropologie (Brno) 57, 3: 299-313'. |
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| Abstract | | The evolution of bipedalism allowed hominins to carry tools, food and infants more easily. Now, humans
carry suitcases, grocery bags and toolboxes that sometimes comprise a large percentage of body weight. Preliminary
research suggested that when humans carry a heavy, unilateral load we in-toe on the side opposite the load and narrow
step width. This project was undertaken to test the idea that both of these changes in foot placement help compensate
for the imbalance produced while carrying a load in one hand. If so, a greater load should produce greater effects.
Thirty subjects of both sexes were asked to walk on a paper runner, while wearing paint-soaked socks and carrying
a canvas bag with various loads: empty; 7% of body weight; 14%; and 21%. Foot angle, medio-lateral foot placement,
step width and step length were recorded and analyzed. Cadence, speed and duty factor were calculated from videos
made during the footprinting procedure.
As load increased, foot angle decreased (intoeing), as did step width. Also, step length decreased and the variability of
all footprint trail parameters increased with increasing load. The increased variability in foot placement was taken as
an indication of 'staggering' and partially explains the shorter steps. Cadence, speed and duty factor did not vary
significantly with different loads, suggesting that changes in temporal characteristics of gait did not account for the
changes in footprint trail parameters.
Studies of modern footprint trails are the best way to understand ancient footprint trails. The results here suggest that
the unusual foot angle and step length of one of the Laetoli footprint trails are best understood as resulting from
pathology, rather than carrying or species differences. | | | | Keywords | | Foot angle – Step width – Step length – Staggering | | | | DOI | | https://doi.org/10.26720/anthro.18.10.08.1 | | |
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