What are the relations between mechanics, gait parameters, and energetics in terrestrial locomotion?

This research investigates the relationship between body mechanics, gait parameters, and energy use in terrestrial locomotion across various species.

Overview of the Study

The researchers looked into whether different energy-conserving body mechanisms (pendulum and spring) utilized in various gaits are mirrored in gait and energy parameters. They used both published data on several species as well as experimental data on horses as their research materials.

Findings on Mechanics

• When the mechanics switch from pendulum to spring, the slope of metabolic rate (MR), being an indicator of energy use, changes in against speed across all species. However, there is no step increase in birds and quadrupeds. The results for humans remain conflicted with varying reports.
• At the trot-gallop transition, speculated as the shift from spring mechanics to a blend of spring and pendulum mechanics, there is a noticeable change in the slope of MR vs speed in horses, while this change isn’t observed in other species.

Stride Frequency Data

• The stride frequency (SF) is found to be a logarithmic function of walking speed across all species. When it comes to trotting/running speed, SF behaves as a linear function and appears to be almost speed-independent when galloping.
• In humans and horses, a discontinuity in SF is observed at the transition from walk to trot (run) but not in bird species.

Time of Contact and Duty Factor

The time of contact against speed slope does not appear to be noticeably affected by change in mechanics for most species except humans. For humans and horses, discontinuities have been observed at the walk-trot (run) transition. More data from different species would be required to generalize these findings.

As far as Duty Factor (DF – proportion of one cycle in which a foot is on the ground) is concerned, in humans, it was found to be greater than 0.5 while walking (using pendulum mechanics) and less than 0.5 when running (using spring mechanics). Not all species were seen to follow this rule. Some of them indicated DF more than 0.5 at the slowest speeds when using spring mechanics. For example, when trotting at low speeds, horses exhibited a forelimb DF greater than 0.5 and hind limb DF less than 0.5. This makes it challenging to distinguish between walking and running based solely on DF.

Conclusion

Through their research, the scientists demonstrate that the associations between body mechanics, gait parameters, and energetics in terrestrial locomotion are complex, and not all species follow the same patterns. Further, using Duty Factor (DF) to differentiate between walking and running might not be a reliable method as it varies considerably across species and different speeds. The gait mechanics of humans and horses feature certain distinctive patterns which deserve more in-depth exploration in future research.