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. 2020 Mar 2;10(1):3856.
doi: 10.1038/s41598-020-60795-9.

Biomechanical insights into the role of foot pads during locomotion in camelid species

Christofer J Clemente  1   2 , Taylor J M Dick  3 , Christopher L Glen  3 , Olga Panagiotopoulou  4   5
Affiliations

Biomechanical insights into the role of foot pads during locomotion in camelid species

Christofer J Clemente et al. Sci Rep. .

Abstract

From the camel's toes to the horse's hooves, the diversity in foot morphology among mammals is striking. One distinguishing feature is the presence of fat pads, which may play a role in reducing foot pressures, or may be related to habitat specialization. The camelid family provides a useful paradigm to explore this as within this phylogenetically constrained group we see prominent (camels) and greatly reduced (alpacas) fat pads. We found similar scaling of vertical ground reaction force with body mass, but camels had larger foot contact areas, which increased with velocity, unlike alpacas, meaning camels had relatively lower foot pressures. Further, variation between specific regions under the foot was greater in alpacas than camels. Together, these results provide strong evidence for the role of fat pads in reducing relative peak locomotor foot pressures, suggesting that the fat pad role in habitat specialization remains difficult to disentangle.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Schematic illustration showing the position, and relative size, of the pressure plates during experimental data collection. The dimensions of each plate were 0.605 m (width) and 2.122 m (length) with a 48 (width) by 160 (length) array of sensors to total 7680 sensors for each plate. Location of the 7 regions of interest (ROI) in (b) camel and (c) alpaca foot. Position of the fat pad in the camel foot is indicated by the vertically shaded structure. Photographic illustration of the alpaca and camel feet. (d) Sagittal view of the camel fore right foot. (e) Palmar view of the camel fore right foot. (f) Frontal view of the alpaca fore left foot. (g) Palmar view of the alpaca fore left foot.
Figure 2
Figure 2
Time-varying vertical ground reaction forces (vGRF; a,b), foot contact areas (c,d), and pressures (e,f) for camels (left) and alpacas (right). Forefeet are shown in lighter colours and hindfeet in darker colours. Lines represent means ± SE.
Figure 3
Figure 3
Relationship between mass (left) and velocity (right) with (a,b) vertical ground reaction force (vGRF), (c,d) contact area, and (e,f) relative pressure for camels (orange) and alpacas (blue). The thinner solid coloured lines indicate linear regression models for each group with 95% confidence intervals shown as the shaded regions bounded by the dashed lines. The thicker solid grey lines indicate the result of the linear mixed-effects models, including subject as a random factor.
Figure 4
Figure 4
Patterns of peak pressure distributions during the stance phase for the feet of camels (left) and alpacas (right). Camels more evenly distribute forces under their feet during locomotion. In the fore and hind feet, camels display the greatest pressures in the anterior region (ROI3 and ROI4), whereas alpacas display the greatest pressures in the mid-region of their feet (ROI2 and ROI5). Regions of interest (ROIs) are shown for each foot, and the variation among them is shown in the box plots. Data represents the average peak pressure in each foot for all subjects and strides. Boxes represent the median, with hinges representing the first and third quartiles; whiskers represent the 95% CIs, and dots represent outliers.
Figure 5
Figure 5
Density histograms (relative frequency), expressed as a fraction of stance phase duration, for (a) timing of peak vertical ground reaction force (vGRF) during stance, (b) timing to reach 80% of peak vGRF during stance and (c) timing to reach peak contact area during stance for camels (orange) and alpacas (blue). (a) shows that alpacas have a bi-modal distribution of peak vGRF with both an early and a late peak, whereas camels show only the latter peak. (b), the 80% of vGRF allows us to compare the initial loading rate given this bi-modal distribution in alpacas, and late peak in camels.
Figure 6
Figure 6
Contact area and body mass for 33 species of mammals based on Michilsens et al. and pers. comm. Michilsens. Linear regression and 95% confidence intervals are shown in the shaded region. Species of interest are indicated with silhouettes. Data from the current study is labelled, with dark colours representing forefeet and light colours representing hindfeet.
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