Differences and mechanisms
rigid body segments; trunk, pelvis, two thighs,
two legs and two feet. Joint moments were
calculated from the GRF and kinematic data
for the hip, knee and ankle across the whole
stance phase using inverse dynamics and
expressed in the distal anatomical reference
frame normalized to bodyweight (Nm/kg; [28] ).
All biomechanical variables tested in this study
are outlined in Table 1. Positive kinematic and
kinetic values indicate flexion whilst negative
indicates extension. The sagittal plane knee-
GRF lever arm and the resultant sagittal plane
GRF magnitude were both derived from a
custom-written Body Builder program (Vicon,
Oxford, UK) and averaged across three running
trials. Descriptive data pertaining to the
anthropometric segment lengths for the thigh
and shank were derived and extracted from the
kinematic model.
Statistics
Descriptive data (i.e., means and SD) were
calculated for all outcome variables. Repeated
measures ANOVA was used to examine
TABLE 1: Biomechanical variables of interest between footwear and barefoot conditions
Variable Definition
Peak KFM (Nm/kg) Peak external knee flexion moment during stance.
Positive values indicate higher KFM.
Stance time (s) Time of stance from initial contact (> 20 N) until toe off
(< 20 N).
Sagittal plane knee-GRF lever arm (mm) Perpendicular distance between GRF and knee joint
center in laboratory sagittal plane. Calculated at time of
peak KFM.
Sagittal plane resultant GRF magnitude (BW) Resultant magnitude of the sagittal plane GRF calculated
at time of peak KFM. Force was converted from Newton’s
to bodyweight (BW).
Knee flexion angle (°) Sagittal plane knee flexion angle at time of peak KFM.
Positive values indicate knee flexion.
Ankle dorsiflexion angle (°) Sagittal plane ankle dorsiflexion angle at time of peak
KFM. Positive values indicate dorsiflexion.
Hip flexion angle (°) Sagittal plane hip flexion angle at time of peak KFM.
Positive values indicate hip flexion.
Knee flexion excursion (°) Difference between the knee flexion angle at initial con-
tact and peak across stance phase.
Knee flexion at initial contact (°) Knee flexion angle at initial contact of force plate. Initial
contact designated as time when GRF > 20 N.
BW = bodyweight, KFM = external knee flexion moment, GRF = ground reaction force
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