Differences and mechanisms
differences between footwear conditions
(barefoot, stability and neutral) for each
biomechanical variable outlined in Table 1. In
the event of a significant main effect of footwear
condition, post-hoc analysis using Fisher’s Least
Significant Difference tests were performed,
whereby the mean difference (MD) and 95%
confidence intervals (CI) were reported for all
significant variables.
Following this, the difference between the
baseline measurement and each of the
stability shoe and neutral shoe measurements
was taken and considered as the dependent
variable in regressions. A linear mixed model
with a random intercept for participant was
fit to account for the potential similarity of
measurements on each subject and identify
variables predictive of the change in peak
KFM (i.e., dependent variable) wearing shoes
compared to barefoot. Before fitting this model
for change in peak KFM, a preliminary step
TABLE 2: Participant characteristics
Variable Mean ± SD (n = 60)
Age (years) 15.6 ± 5.4
Weight (kg) 49.6 ± 13.8
Height (m) 1.6 ± 0.1
Estradiol (pmol/L) 8.1 ± 5.1
Thigh segment length (cm) 41.2 ± 3.5
Shank segment length (cm) 36.8 ± 3.2
SD standard deviation
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was performed to determine if any interactions
between footwear condition and biomechanical
predictors (Table 1) should be included in the
final model (i.e., if the effect of any predictors of
change in peak KFM from barefoot depended
on the type of shoe worn, Additional file 2: Table
S1). If an interaction between footwear condition
and each of the change in lower limb kinematics,
change in sagittal plane knee-GRF lever
arm, change in sagittal plane resultant GRF
magnitude or change in stance time variables
were evident this interaction term was included
in the final linear mixed model including all
predictors (Additional file 2: Table S1). Footwear
condition (defined as stability and neutral shoes)
was entered as a fixed effect with independent
predictors (i.e., change in lower limb kinematics,
change in knee-GRF lever arm and change in
resultant sagittal plane GRF magnitude) and any
interactions terms as covariates in the model.
The fixed effect estimates, 95% CI and p values
were reported. All data were analyzed using the
SPSS (version 23, IBM) and p < 0.05 was used to
indicate statistical significance.
Results
Participant demographics are shown in Table
2. Included in the study were 29 pre-menarche
girls, 20 eumenorrheic girls and 11 girls
using the monophasic OCP. A mean value of
8.1 ± 5.1 pmol/L confirmed low estradiol levels at
the time of testing (Table 2).
Differences in peak KFM, GRF and lower limb
kinematics between footwear conditions
Analysis revealed no statistically significant
differences in running velocity between
footwear conditions (p > 0.05), yet a main effect
of footwear was found for stance time (p < 0.001,