Differences and mechanisms
allowed approximately 5 minutes to familiarize
themselves with running in each footwear
condition in the laboratory. Following this,
participants were required to complete three
successful running trials in each condition:
i) barefoot, ii) neutral shoes and, iii) stability
shoes, with the order of the trials pre-
determined via block randomization.
A successful trial involved (i) a clean strike
of force plate with the dominant foot (i.e., foot
contact was within all borders of the plate)
and (ii) running speed 2.8–3.2 m/s (measured
via photoelectric timing gates). Running speed
was controlled given that variations between
participants can influence joint kinematics and
GRF and, in turn, net joint moments [29] . In the
event a participant ran faster or slower than
the designated time, instructions were given to
adjust speed accordingly until the correct speed
was attained via the photoelectric timing gates.
A secondary analysis of running speed was then
conducted post-session to confirm that each
participant ran at the required velocity. Velocity
was derived by calculating the average (m/s)
across the three trials from the mid-point of the
anterior superior iliac spine markers from the
biomechanical model. If a participant did not
run between the designated speed, they were
excluded from the study.
. Specifically, stability shoes were deemed to
possess: (i) a midsole that was denser medially
than laterally (i.e., medial post), (ii) < 10° midfoot
frontal plane (torsional) stiffness, (iii) < 10° heel
counter stiffness and (iv) < 45° midfoot sagittal
plane (longitudinal) stability. Based on these
criteria, the stability shoes tested in the present
study had a score of 9 on the motion control
properties scale of the FAT [17] . In contrast,
the neutral shoes were deemed to possess:
(i) a uniform midsole density, (ii) 10–45° heel
counter stiffness (iii) 10–45° torsional stiffness
and (iv) > 45° midfoot longitudinal stiffness.
In combination, these features contribute to a
score of 3 on the motion control properties scale
of the FAT [17] . As a result, the Asics Kayano-GS
was selected as the stability shoe and the Asics
Zaraca 3 as the neutral shoe.
[17]
Further technical features related to the high
support shoes (Asics Kayano-GS) include: (i)
heel stack height = 25 mm, (ii) forefoot stack
height = 12 mm, (iii) footwear pitch = 13 mm
and (iv) shoe mass = 260 g. For the low support
shoes (Asics Zaraca 3) these features included:
(i) heel stack height = 28 mm, (ii) forefoot stack
height = 18 mm, (iii) footwear pitch = 10 mm and
(iv) shoe mass = 240 g (Additional file 1: Figure
S1). Both shoes were the current model at time
of testing.
Footwear Motion analysis
There is currently no agreed definition for
classification of shoes into stability and neutral
shoes. Therefore, criteria were developed
a priori based on features outlined in the
Footwear Assessment Tool (FAT), including
increased medial compared to lateral midsole
density, and greater stiffness of the heel counter,
midfoot and longitudinal aspects of the shoe Kinematic (120 Hz) and GRF data (2400 Hz)
were collected using a 12-camera Vicon motion
analysis system (Oxford, UK) synchronized to a
concealed force plate (AMTI, Inc., Watertown,
MA, USA). Data were filtered using a fourth
order zero-lag Butterworth low-pass filter with
a cut-off frequency of 20 Hz. As per Schache &
Baker [28] , the kinematic model included eight
Current Pedorthics | March/April 2019
21