Developing the ability to habitually walk and run upright on two feet is one of the most significant transformations to have occurred in human evolution. Many musculoskeletal adaptations enabled bipedal locomotion, including dramatic structural changes to the foot and, in particular, the evolution of an elevated medial arch. The foot’s arched structure has previously been assumed to play a central role in directly propelling the center of mass forward and upward through leverage about the toes and a spring-like energy recoil. However, it is unclear whether or how the plantarflexion mobility and height of the medial arch support its propulsive lever function. Here we show, using high-speed biplanar x-ray, that regardless of intraspecific differences in medial arch height, arch recoil enables a longer contact time and favorable propulsive conditions at the ankle for walking upright on an extended leg. This mechanism may have helped drive the evolution of the longitudinal arch after our last common ancestor with chimpanzees, who lack this plantarflexion mobility during push-off. We discovered that the generally overlooked navicular-medial cuneiform joint is primarily responsible for arch recoil in human arches, suggesting that future morphological investigations of this joint will provide new interpretations of the fossil record. Our work further suggests that enabling longitudinal arch recoil in footwear and surgical interventions may be critical for maintaining the ankle’s natural propulsive ability.

This dataset supports the conclusions from the manuscript "Mobility of the human foot’s medial arch helps enable upright bipedal locomotion".

All methods are described in the article.

Description of the data and file structure

Biplanar videoradiography motion for the tibia (tib), talus (tal), calcaneus (cal), navicular (nav), medial cuneiform (cmm), first metatarsal (mt1) and first proximal phalanx (ph1) are provided between maximum arch flattening and maximum metatarsophalangeal joint dorsiflexion. The transforms moving the provided bone meshes (in boneStruct) from CT space to x-ray space (dataStruct().Tx) for each frame of motion (captured at 125 Hz for walking and 250Hz for running) are provided, in addition to the modelled transforms for the rigid arch (dataStruct().Tx_fix) and simulated tibia positions (dataStruct().Tx_fix.tib_at_takeoff and dataStruct().Tx_fix.tib_sim_rigidarch_takeoff). The translation component is in millimeters. The last section of the included code (Arch_Recoil_Example_Plots.m) demonstrates how to plot the bones using each transform using the provided function (visualizeBone.m). 

Joint angles for the medial arch joints (dataStruct().angles) and the talar centroid positions (dataStruct().talar_centroid) are included (in millimeters). Angles are the first Tait-Bryan rotation  that prioritizes dorsi/plantarflexion in degrees. The angles are all distal joints relative to proximal. The convention for naming is [angle]_[proximal][distal] i.e. DP_calmet represents the motion of the first metatarsal relative to the calcaneus in dorsiflexion/plantarflexion, where dorsiflexion is positive. Note that the angles are not normalized relative to any posture. Instead, the magnitudes describe the anatomy of the participant. For example, the participant with the highest arch (PRFC012) has an arch angle (DP_calmet) starting at -54 deg. This indicates a higher initial starting posture from the bony anatomy than the subject with the lowest arch (PRFC016) who starts at -23 deg. The unloaded arch angle is stored in the subject structure (subjStruct). See below for more details.

The corresponding frames of stance (dataStruct().stance_frames) indicate each frame's corresponding % of stance to facilitate plotting as a function of % stance. 

Key frames in gait are provided for each trial. The maximum arch flattening (dataStruct().keyFrames.max_archFlat) is the time in stance of peak dorsiflexion of the metatarsal relative to the calcaneus. The maximum metatarsophalngeal joint dorsiflexion angle is used to standardize across participants (dataStruct().keyFrames.max_mtpDP). The case where the rigid arch is moved with the tibiotalar joint in the takeoff position (dataStruct().Tx_fix.tib_at_takeoff) is best matched with the measured mobile arch's takeoff position is in dataStruct().keyFrames.match_tib. The frame indicating the beginning of propulsion as a function of the anterior ground reaction force becoming positive is given in dataStruct().keyFrames.anteriorGRFPropulsion.

The centre of mass position during the stride (in meters) is provided between the beginning of propulsion, as defined by the first frame when the anterior-posterior ground reaction force becomes positive, and maximum metatarsophalangeal joint dorsiflexion. 

The subjStruct contains the anonymized subject demographic information. Height is in metres and weight is in kilograms. The subject bone meshes are provided and are stored in CT space. They can be plotted using the bone points and connections (all 1 based). See the last section of the provided code for an example. Coordinate systems are provided in the subjStruct under the bones sub structure. For example, for the tibia, subjStruct().bones.tib.T_inertial  provides the 4x4 inertial coordinate system for the tibia in CT space.  [...].T_long axis provides the coordinate system that is biased to align the z-axis with the tibial shaft, which is used to align the tibia in the simulated take-off positions in gait. [...].T_TC is aligned based on a cylinder fit to the talocrural surface on the tibia to describe talocrural dorsiflexion as a function of the joint surface. A similar coordinate system is given in the talus bone information : subjStruct().bones.tal.T_TC is made similarly, with a cylinder fit to the talar dome (the talar component of the talocrural joint). 

The subjStruct also contains the unloaded arch dorsiflexion angle between the calcaneus and the metatarsal in degrees. 

The tibLeanStruct contains the chimpanzee and human tibial lean data. tibLeanStruct.human has both the mobile and rigid arch tibia lean angles relative to the vertical axis in degrees for each motion frame (dataStruct().COM.anterior and .superior).  The human data corresponds to the data in the dataStruct. The chimpanzee data has been normalized to 101 points of the gait cycle.

The provided code (Arch_Recoil_Example_Plots.m) uses this data to recreate the base plots in the manuscript. Run the code with the arch_recoil_data.mat on the path. All plots should generate automatically. Please contact Lauren Welte at l.welte@queensu.ca if you encounter any issues.  

MATLAB is required to use these files. Please contact the corresponding author if you are interested in the data in an alternative format.