Data from: Human walking biomechanics on sand substrates of varying foot sinking depth

Our current understanding of human gait is mostly based on studies using
hard, level surfaces in a laboratory environment. However, humans navigate
a wide range of different substrates every day, which incur varied demands
on stability and efficiency. Several studies have shown that when walking
on natural compliant substrates there is an increase in energy
expenditure. However, these studies report variable changes to other
aspects of gait such as muscle activity. Discrepancies between studies
exist even within substrate types (e.g. sand), which suggests that
relatively ‘fine-scale’ differences in substrate properties exert
quantifiable influences on gait mechanics. In this study, we compare human
walking mechanics on a range of sand substrates that vary in overall foot
sinking depth. We demonstrate that variation in the overall sinking depth
in sand is associated with statistically significant changes in joint
angles and spatiotemporal variables in human walking but exerts relatively
little influence on pendular energy recovery and muscle activations.
Significant correlated changes between gait metrics are frequently
recovered, suggesting a degree of coupled or mechanistic interaction in
their variation within and across substrates. However, only walking speed
(and its associated spatiotemporal variables) correlate frequently with
absolute foot sinkage depth within individual sand substrates, but not
across them. This suggests a causative relationship between walking speed
and foot sinkage depth within individual sand substates is not coupled
with systematic changes in joint kinematics and muscle activity in the
same way as is observed across sand substrates.