Human Trackway Parameters on Hard and Soft Substrates

To understand ancient hominins' locomotion, our best comparison is with modern humans, and it is easiest to study humans walking in a laboratory setting. However, trackways made on tile or concrete might not be representative of those made in softer substrates like dirt or sand, suggesting that some laboratory studies might not be applicable to ancient hominins. Therefore, a number of authors have considered different substrates in their experiments and sometimes have tried to match the substrates in the laboratory with those at various ancient sites. We expand on those efforts by evaluating some aspects of human trackways that might be expected to differ in different substrates.

A group of 20 subjects walked on hard, medium, and soft substrates, and three parameters were measured: foot angle, step length, and step width. Linear, mixed-effects regression was used to evaluate the effects of substrate on these parameters.

Step width (p = 0.74) and step length (p = 0.19) were not significantly affected by substrate type. However, foot angle was (p = 0.002). Even so, the effect was very small and substrate accounted for only 1% of the variation in foot angle, whereas individual variation accounted for 50%. Also, the variance of all three measured parameters increased with softer substrates.

This work on trails of footprints complements pre-existing research on individual prints on various substrates. Results here are encouraging for those interested in laboratory research to compare modern human trackways with those of ancient hominins. Even trackways produced on hard floors are similar to those made in softer, sandy substrates and may therefore be useful in understanding our ancient relatives' locomotion. However, because variation in parameters increases as the substrate becomes softer, some differences due to substrate may be obscured by large variances.