DOI: 10.5061/dryad.v9s4mw6sz
title: The extensibility of the plantar fascia influences the windlass mechanism during human running

description: The arch of the human foot is unique among hominins as it is compliant at
 ground-contact but sufficiently stiff to enable push-off. These behaviours
 are partly facilitated by the ligamentous plantar fascia whose role is
 central to two mechanisms. The ideal windlass mechanism assumes that the
 plantar fascia has a nearly constant length to directly couple toe
 dorsiflexion with a change in arch shape. However, the plantar fascia also
 stretches and then shortens throughout gait as the arch-spring stores and
 releases elastic energy. We aimed to understand how the extensible plantar
 fascia could behave as an ideal windlass when it has been shown to strain
 throughout gait, potentially compromising the one-to-one coupling between
 toe arc length and arch length. We measured foot bone motion and plantar
 fascia elongation using high-speed x-ray during running. We discovered
 that toe plantarflexion delays plantar fascia stretching at foot-strike,
 which likely modifies the distribution of the load through other arch
 tissues. Through a pure windlass effect in propulsion, a quasi-isometric
 plantar fascia’s shortening is delayed to later in stance. The plantar
 fascia then shortens concurrently to the windlass mechanism, likely
 enhancing arch recoil at push-off.
description: High-speed biplanar videoradiography and markerless tracking
 algorithms measured the kinematic orientation and position of the bones
 (calcaneus, tibia, first metatarsal, first proximal phalanx and
 sesamoids). The provided data contains both filtered and unfiltered data,
 and is normalized to stance phase (101 points). All methods are explained
 in the manuscript.
description: <strong>Provided data:</strong>
 The resultant joint angles, ligament lengths (all participants
 have plantar fascia length, one participant also has spring ligament, and
 long/short plantar ligaments), and vector coding results are contained in
 a structured MATLAB variable "results_norm" which are normalized
 to 101 points of stance phase. The unfiltered ('crop') and
 filtered ('filt') data are contained within this
 structure.  The structure contains:
 - "angles" which has substructures for ZYX Tait Bryan
 angles of [reference bone]_[bone] i.e. results_norm.angles_filt.tib_cal
 gives the DP (dorsiflexion +, plantarflexion -), SP (supination +,
 pronation -) and AD (adduction +, abduction -) of the calcaneus angles
 relative to the tibia in 12 rows (each participant) and 101 points (1% of
 stance).  - "lig" is the length of the
 plantar fascia (pf) and the length normalized to the maximum length
 (pf_strain). The participants are depicted in rows, and the there 101
 columns for each % of stance phase. The proximal arch ligaments are
 present for particpant 12: spring ligament (plantar calcaneonavicular
 ligament - PCNL_med is the medial component, PCNL_inf is the inferior
 component), short plantar ligament (plantar calcaneocuboid ligament -
 PCCL), deep fibres of the long plantar ligament (plantar long plantar
 ligament-  PLPL) - "kinemat" contains the
 arch deformation that is not angular; i.e. it is the linear 3D distance
 between two inferior points, one on the calcaneus and one on the first
 metatarsal. This is used with the simple windlass model.
 - r_sens is the radius of the metatarsal head in mm, multiplied
 by pi/180 to automatically convert the MTPJ angle into radians when
 calculating arc length. There is also the colormap used
 throughout the paper as "colorblind_map.mat".
 <strong>Provided code:</strong> To
 make the figures in the manuscript and understand the provided .mat
 structure, please open the "makePlots.m". If you run it, it will
 produce the base graphs of the manuscript figures. -
 "codingPFphases.m" produces the colourful graphs, such as Figure
 4. - "makeStatsDotPlot.m" produces the dot
 plots, such as Figure 5.