Differences and mechanisms
Background:
Running is a popular exercise associated
with a healthy lifestyle. Despite its benefits
however, the repetitive nature of running
can lead to musculoskeletal injuries [1] , with
patellofemoral pain (PFP) being one of the most
common [2] . Specifically, a high incidence of
PFP is reported amongst adolescent females,
with 15–30% developing the condition [3, 4] . and
many experiencing recurrent symptoms into
adulthood [5] .
Although the causes of PFP amongst adolescent
females are multifactorial [5–7] , altered sagittal
plane knee biomechanics such as a higher
peak knee flexion moment (KFM) may be a
contributor [8, 9] . For instance, higher peak
KFM is associated with higher patellofemoral
joint loads which, in turn, can increase risk of
developing PFP [8, 9] . Higher peak KFMs may be
driven by growth-related factors associated
with female pubertal development [10–12] .
Indeed, a recent study published by our group
confirmed that girls classified as early/mid- and
late/post-pubertal development exhibit higher
barefoot running-related peak KFM compared
to their pre-pubertal counterparts [13] . Given that
the girls in the aforementioned study are also at
higher risk of developing knee pathologies such
as PFP [3, 14–16] , further studies should consider
the biomechanical mechanisms contributing to
higher peak KFM in this cohort.
Girls and young adults typically wear a
variety of athletic footwear when running.
On the basis of previously published criteria
[17]
, athletic shoes are usually classified as
‘stability’ or ‘neutral’ shoes. Stability shoes
typically possess increased medial, midfoot and
longitudinal stiffness and support, whilst these
16
Pedorthic Footcare Association | www.pedorthics.org
characteristics are typically lower or absent in
neutral shoes [17] . Combined, these shoe features
have been shown to modify foot and knee
frontal plane mechanics [18, 19] . In addition, other
footwear features such as pitch (i.e., heel to toe
offset) and midsole thickness, typically higher
in stability compared to neutral footwear, likely
influence sagittal plane knee moments [8, 20, 21] .
Mechanistically, greater footwear pitch reduces
peak ankle dorsiflexion angle and increases
peak knee flexion angle [22, 23] , while increased
midsole thickness appears to increase knee
flexion excursion compared to barefoot [21].
Hence, it is plausible that these footwear-related
kinematic changes contribute to an elevation
in running-related peak KFM [8, 20] . Whilst no
previous studies have investigated whether
peak KFM differs between stability and neutral
footwear and barefoot in young females, such
an investigation is important to clarify which
type of footwear is likely to be most effective at
reducing the risk of developing PFP [3, 4] .
Although the available literature suggests
footwear increases peak KFM [8, 20] , the
biomechanical mechanisms contributing to
this phenomenon remain unknown. To date,
no published studies have investigated the
underlying mechanisms by which stability and
neutral shoes may alter running-related peak
KFM. Understanding mechanisms may help
guide footwear manufacturers and researchers
about more optimal footwear designs to lower
injury risk. As discussed, stability and neutral
footwear may increase, to a lesser or greater
extent, the peak KFM by augmenting a change
in lower limb kinematics, via decreased
dorsiflexion and increased knee flexion angles
compared to barefoot [20, 22, 23] . Higher peak
knee flexion wearing footwear likely leads to