Anevidence-Based Videotapedrunning Biomechanicsanalysis: Richard B. Souza

An Evidence-Based
Videotaped Running
Biomechanics Analysis
a,b,c,
Richard B. Souza, PT, PhD, ATC, CSCS *
KEYWORDS
Biomechanics Running Motion analysis Form Injuries Observational
Video analysis
KEY POINTS
Running biomechanics play an important role in the development of injuries in recreation-
ally active individuals.
Performing a systematic video-based running biomechanics analysis rooted in the current
evidence on running injuries can allow the clinician to develop a treatment strategy.
The current literature has not risen to the level of proven injury prevention, suggesting that
recommendations for modification of running form in uninjured runners would not be ev-
idence based.
When the patient presentation and physical examination findings are in agreement with
abnormalities observed in a biomechanics running analysis, it serves as a potential for
intervention.
INTRODUCTION
Running is an extremely common form of exercise, whether recreational or competitive.

However, running injuries are also quite common. In particular, running injuries such as
patellofemoral pain, iliotibial band syndrome, and stress fractures to the tibia and meta-
tarsals have been identified as highly prevalent in runners.1 Although causative factors
of running injuries are undoubtedly multifactorial, most agree that running biome-
chanics play a key role in injury development.
Disclosure Statement: Dr R.B. Souza has a financial relationship with SportzPeak, Inc, a sports
wellness company.
a
Department of Physical Therapy and Rehabilitation Science, University of California, San
Francisco, 185 Berry Street, Suite 350, San Francisco, CA 94107, USA; b Department of Radiology
and Biomedical Imaging, University of California, San Francisco, 185 Berry Street, Suite 350, San
Francisco, CA 94107, USA; c Department of Orthopaedic Surgery, University of California, San
Francisco, 185 Berry Street, Suite 350, San Francisco, CA 94107, USA
* 185 Berry Street, Suite 350, San Francisco, CA 94107.
E-mail address: richard.souza@ucsf.edu
Phys Med Rehabil Clin N Am 27 (2016) 217–236

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218 Souza
Numerous recent studies have identified abnormal biomechanics in persons with

specific running injuries.2–5 However, the vast majority of these studies used advanced
technological methods, which are expensive and uncommon in standard clinical prac-
tice. Although some variables associated with running injuries require high-tech equip-
ment, such as instrumented treadmills and 3-dimensional (3D) motion capture systems,
many of the kinematic abnormalities identified in runners with injuries can be measured
using a simple 2-dimensional (2D) video-based running analysis using readily available
and fairly inexpensive tools.
The objective of this article is to provide a framework for a systematic video-based
running biomechanics analysis plan based on the current evidence on running injuries.
Although some of the proposed variables of interest will have an impact on running
performance, the primary focus of this analysis plan is to identify biomechanical fac-
tors related to common injuries in runners. Furthermore, there are many other factors
that may be related or even causative for injuries while running, including training er-
rors, current health status (ie, recent injury), and/or structural abnormalities (ie, leg
length discrepancy, pes planus foot deformity etc).6,7 However, the focus of this re-
view is restricted to running kinematics, particularly those in the sagittal and frontal
plane, which may be easily viewed with standard 2D video. A running biomechanics
analysis should be an integral component of the evaluation, either for the injured
runner or for screening for injury prevention, to complement a physical examination
and thorough history.
ANALYSIS SETUP
Treadmill Setup
Although some studies have identified small differences in treadmill running when
compared with overground running, these differences have mostly been associated
with muscle activation patterns and joint forces.8,9 In general, kinematic patterns
during treadmill running are very similar to those observed during overground
running.10–12 As such, performing a video-based analysis of joint kinematics while
running on a treadmill should provide valuable insight into running kinematics during
overground running and is more practical for performing this evaluation.
Running velocity affects lower extremity kinematics.13 Therefore, matching tread-
mill speed to a similar speed at which an injured runner experiences symptoms
should be accommodated if possible. When evaluating a symptom-free runner, 1
strategy that can be used is to set the treadmill speed to match the running velocity
of the runner when performing a “long run,” which is a common term used for the
longest distance run in the recent past. The rationale for selecting this speed is
that if runners are demonstrating abnormal biomechanics while performing longer
runs, these faults will accumulate over the longer exercise period and may contribute
to running injuries.
Cameras
Many high-definition cameras are available at varying price points. Both image reso-
lution and temporal resolution should be considered when selecting cameras for
video-based movement analysis. Many video cameras have excellent image resolu-
tion, but are limited to 30 frames per second. Cameras with higher frame rates (eg,
120 Hz) can provide cleaner images that are easier to evaluate and more appropriate
for the evaluation of running kinematics. More recently released smartphones and tab-
lets can be adjusted to acquire video at high frame rates and provide adequate video
for this purpose.
Videotaped Running Biomechanics Analysis 219
Views
When performing a video-based analysis it is recommended that, at a minimum,
2 orthogonal (at right angles to each other) views are included. The analysis provided
in this article uses a lateral view and a posterior view. Others may include an anterior
view or lateral views from both sides. Multiple views from each camera, including
zoomed-in views on the foot and ankle as well as zoomed-out views of the entire
body, can be helpful. Many of these preferences will need to be modified to work
within the constraints of the clinical environment. Maintaining a reproducible camera
location and a fixed orthogonal angle to the treadmill is important to performing a reli-
able analysis. Recent studies have found the reliability of a single camera analysis to
vary significantly, with some metrics showing excellent reproducibility (knee flexion,
rear foot kinematics) and others demonstrating poor reproducibility (heel-to-center
of mass distance).14 There is also evidence that experience can improve the reliability
of measurements made on video-based kinematic evaluations, so it is important for
the clinician to practice running evaluations regularly to improve reliability.15
Markers
Application of markers for identification of anatomic landmarks can be useful when
performing a video-based running analysis. These markers need not be expensive
retroreflective tape-based markers. Any bright colored tape can be used for this pur-
pose. Whenever possible, tape should be applied directly to the runner’s skin. This is
imperative when performing research-level 3D motion analysis. However, adapting
these methods for use in a clinical setting may require markers over clothes. In these
situations, it is recommended that the runners wear tight-fitting running sportswear to
minimize the movement of the markers from clothing during running. In the images
presented throughout this article, the following landmarks are identified and marked:
C7 spinous process, posterior superior iliac spines, anterior superior iliac spine,
greater trochanter, lateral knee joint line, lateral malleolus, midpoint of the calf, supe-
rior and inferior portions of the heel shoe counter, and head of the fifth metatarsal. This
is an example of a common set of anatomy landmarks that are useful to evaluate dur-
ing running and can be modified to suit the needs to the evaluation.
Warmup and Analysis Plan

It is advisable to allow for a period of time for the runner to run on the treadmill at the
target speed to accommodate to the environment. Studies have identified changes in
kinematics deviating from normal running mechanics with treadmill running up to the
initial 6 minutes.16 Therefore, an acclimation period of 6 to 10 minutes should be used
when possible before evaluation. It is also important consider the nature of symptom
provocation in an injured runner. If a runner experiences symptoms after a number of
minutes or miles, it may be necessary to acquire video with the runner in a fatigued
state, after a period of running and consistent with their symptom history.
When performing a movement analysis of any type, it is critical to execute the anal-
ysis systematically. We present a distal-to-proximal analysis plan. The order of the
evaluation is not critical. However, it is extremely important to perform the entire eval-
uation, including all segments, joints, and whole body variables consistently, to avoid
missing subtle yet potentially important kinematic abnormalities. Although numerous
freeware options exist with extremely helpful tools for measuring biomechanical vari-
ables on running video (angles, distances, etc), it is generally not necessary. Most of
the metrics in this article can be easily identified visually on slow motion video, or eval-
uation when progressing through the video frame by frame. To date, cutoffs for
220 Souza
kinematics to be identified as abnormal, or predictive of injury, do not exist. As such,

the analyses included here does not provide the reader with specific angles or mea-
sures that are “abnormal.” Each metric is described, and indicators of normal kine-
matics are provided. It is the responsibility of the evaluator to determine what
threshold for normal and abnormal should be applied to an individual runner and asso-
ciated with the biomechanical contributor to injury.
Phases
It is important to identify specific moments within the running cycle that can be used
for evaluation. Many of the phases of the running cycle are clear. However, particularly
for evaluating stride mechanics, it is important to differentiate between video frames of
rapidly evolving events. Take, for example, the images provided in Fig. 1. Fig. 1A is the
final frame of the swing phase, Fig. 1B displays initial contact, and Fig. 1C displays
loading response (which is identified by the presence of shoe deformation in the im-
age). Different kinematic variables are evaluated on images from different phases of
running. It is important for the evaluator to become familiar with identifying each of
these phases (and others as described elsewhere in this article). Inconsistent identifi-
cation of phases of running in evaluating biomechanics of running gait will make per-
forming a reliable analysis impossible.
SIDE VIEW
Foot Strike Pattern
Identification of foot strike pattern can be easily performed on slow motion video or by
evaluating video in a frame-by-frame manner (Fig. 2). It is recommended to always
confirm foot strike pattern in this fashion, because even after considerable practice,
it is not uncommon to misidentify a foot strike type when observing running at full
speed. Foot strike types can be categorized as forefoot strike (FFS), midfoot strike,
and rear foot strike. Recent literature suggests that video-based identification of
foot strike patterns by a single rater are highly reliable, although interrater measures
was found to be less reliable.17 At this time, there is limited evidence that any 1 foot
strike pattern is more or less likely to cause a runner to sustain an injury. However,
this is an area of active research and data on this issue are emerging.18,19 One study
on competitive collegiate runners suggested that runners with a rear foot strike pattern
developed more repetitive overuse injuries when compared with runners with an FFS
pattern.20 And although these finding suggest possible association between foot
Fig. 1. Key phases of running. (A) The end of terminal swing is identified as to the foot re-
mains elevated from the treadmill, just before initial contact. (B) Initial contact is identified
as the first frame when the foot hits the ground. (C) Loading response is identified as the
first frame in which the runner’s weight is being transferred onto the lead leg and is char-
acterized by the presence of shoe deformation.
Fig. 2. Foot strike patterns. (A) Forefoot strike. (B) Midfoot strike. (C) Rear foot strike.
strike patterns and running injuries, more work is necessary before broad conclusions
on foot strike recommendations can be made to modify injury risk.
Foot Inclination Angle at Initial Contact

The angle created by the sole of the shoe and the treadmill belt is noted as the incli-
nation angle of the foot (relative to a global coordinate system, not the tibia) at initial
contact (Fig. 3). This variable is not applicable for midfoot strike and FFS runners.
A recent study by Wille and colleagues21 found inclination angle to be particularly
important in estimating ground reaction forces and joint kinetics during running. Spe-
cifically, increased foot inclination angle was found to be related to higher peak knee
extensor moments, increased knee energy absorbed, higher peak vertical ground re-
action force, and greater braking impulse during running. Each of these variables has
been implicated in injury biomechanics, suggesting that a very high foot inclination
angle at initial contact may not be desirable. This may be a source for intervention
in runners who experience injuries associated with high ground reaction forces or
excessive joint kinetics. There are no cutoffs at which this angle is determined to be
abnormal. Rather, it is likely on a sliding scale, where lower values are generally asso-
ciated with lower ground reaction forces and joint kinetics, and higher values as asso-
ciated with increased forces. However, it should be noted that a high foot inclination
angle in isolation may be a benign finding and needs to be evaluated in the context of
the entire running evaluations (see Overstriding).
Fig. 3. Foot inclination angle. (A) A relatively high foot inclination angle in comparison with
a horizontal line. (B) A relatively low foot inclination angle.
222 Souza
Tibia Angle at Loading Response

The vertical alignment of the lower leg during loading response can be a valuable in-
dicator of stride mechanics. Video of the runner should be evaluated using freeze-
frames at the moment of loading response (as the shoe begins to deform just after
initial contact). The alignment of the lower leg relative to a vertical line in the video field
of view can be evaluated easily. An extended tibia is identified when the lateral knee
joint marker is posterior to the lateral malleolus marker (Fig. 4A). Conversely, a flexed
tibia is identified when the lateral knee marker is anterior to the lateral malleolus
(Fig. 4C), and when these 2 markers are directly vertical to one another, this would
be identified as a vertical tibia (Fig. 4B). For a runner that suffers from impact-
related running injuries, an extended tibia is not ideal. A vertical or flexed tibia allows
the runner to dissipate impact more readily though knee flexion.
Similar to foot inclination angle, the tibia angle in itself may not be meaningful in
isolation. It is a variable that can be grouped in a series of stride mechanics variables
to better describe the characteristics of the runners stride and biomechanical risk
profile.
Knee Flexion During Stance

Peak knee flexion angle during stance may occur at slightly different phases in
different runners. It is recommended to scroll through stance phase frames to identify
maximum knee flexion. Key aspects of knee flexion during stance include the peak
amount of knee flexion and the knee joint excursion during stance (difference in angle
from initial contact to peak knee flexion). In general, normal peak knee flexion ap-
proaches approximately 45 at midstance (Fig. 5). Although explicit cutoffs have not
been developed for this variable, a runner who demonstrates considerably less than
45 of knee flexion may suggest reduced shock absorption, and intervention may
be warranted. Some data exist suggesting that lower knee flexion (<40 ) may be asso-
ciated with certain subgroups of patients with patellofemoral pain.22 Knee stiffness, a
variable that includes both reduced knee flexion and/or increased knee flexion
moment during stance phase, may be associated with tibial stress fractures.23
Hip Extension During Late Stance

Reduced hip extension during late stance is a common observation in the recreational
runner (Fig. 6). It is traditionally believed that lack of hip extension may be associated
with reduced flexibility of the iliopsoas muscle. However, the optimal amount of hip
extension during running remains elusive. It is possible that the required amount of
hip extension is not the same for each runner, but related to other characteristics of
Fig. 4. Tibia angle. (A) Extended tibia. (B) Vertical tibia. (C) Flexed tibia.
Fig. 5. Knee flexion during stance. (A) A runner demonstrating limited knee flexion during
stance and (B) a normal amount of knee flexion during stance.
their running form. For example, a fairly slow runner may have a very compact stride,
demonstrate approximately 10 of peak hip extension and not require any intervention.
However, a different runner, with a long stride and perhaps a faster pace, may also
have approximately 10 of hip extension, but also concurrently demonstrate a signif-
icant overstride pattern (landing with the foot out in front of the center of mass) with
higher impact loading and braking forces. The latter runner may require stride modifi-
cation or improved hip extension during running to modify these forces that could
contribute to injury. Commonly observed compensations for persons with reduced
hip extension include (1) increased lumbar spine extension, (2) bounding, a strategy
Fig. 6. Hip extension during late stance. (A) Runner with normal hip extension. (B) Runner
with limited hip extension.
224 Souza
to increase float time to increase overall stride length in the absence of adequate hip
extension, (3) increased overstriding, including excessive reaching during initial con-
tact as a strategy to increase stride length, and (4) increased cadence to increase
running speed in the presence of a limited hip extension.
Trunk Lean
Trunk lean is a variable that has received little attention in the scientific literature. How-
ever, this is not the case in the popular running non–peer-reviewed literature. Many
running styles, including ChiRunning, pose running, and even barefoot running have
included cues for novice runners to increase trunk lean. A focus on leaning “from
the ankles,” rather than increasing hip flexion to achieve the trunk lean, seems to be
a priority for some styles. Many running experts suggest that trunk lean is a key
component to correct running posture. However, very little has been done on the
research side of this issue. A recent article by Teng and Powers24 demonstrated
that a small increase in trunk lean (w7 ) resulted in a significant lowering of the stress
across the patellofemoral joint without a significant increase in ankle demand, sug-
gesting that this strategy may be important for runners with patellofemoral pain. The
overall findings were that reduced trunk flexion (more upright posture) was associated
with greater knee loads. In contrast, increased trunk flexion shifted demand away from
the knee joint, and to the hip and ankle (although the latter was not statistically
higher).25 However, the authors warn that this study was performed in healthy subjects
and more work is necessary to understand the relationship between trunk lean and
running injuries. Furthermore, the authors noted that the trunk lean in these subjects
was not purely from the ankles, as is recommended by some running styles, but rather
a combination of hip flexion, pelvis anterior tilt, and other small kinematic adjustments.
Nonetheless, evaluating trunk lean in runners may become an important variable as
additional research emerges (Fig. 7).
Fig. 7. Trunk lean. (A) A relatively upright trunk posture and (B) a runner a forward trunk
lean.
Overstriding
Increased stride length has been found to be associated with an increased risk of tibial
stress fractures in runners.5 However, it is likely that a long stride is not the cause of
high impacts associated with stress fractures and other running injuries. Rather, the
presence and magnitude of overstriding may be the key risk factor. Many accom-
plished runners with very long strides have large amounts of hip extension without
the presence of overstriding. It can be argued that these runners are not at risk for
the injuries associated with high impacts.26 It is important to differentiate stride length
from overstriding in this context. Overstriding is a description of a running pattern in
which the foot lands in front of the person’s center of mass, and is associated with
reaching, including hip flexion with knee extension, before initial contact. A recent
study by Wille and colleagues21 identified a metric that is closely related to over-
striding—the distance from the heel at initial contact to the runners center of
mass—is a significant predictor of knee extensor moment (the sagittal plane torque
across the knee joint during stance) and braking impulse (an important contributor
to shock attenuation and running energetics) during running. These data strongly sug-
gest that overstriding is an important kinematic metric to consider when advanced
technology, such as force platforms or tibia accelerometers, are not available.
As discussed, overstriding can be evaluated through a variety of metrics. Supportive
measures such as the foot inclination angle at initial contact, tibial angle at loading
response, and knee flexion at initial contact can inform the clinician about the tendency
for overstriding. Ultimately, 1 strategy for determination of overstriding on video can be
assessed by evaluating the runner at loading response.27 By drawing a vertical line from
the runner’s lateral malleolus and extending upward, the relationship between the ankle
position and the pelvis can be evaluated. Ideally, the vertical line will fall within the run-
ner’s pelvis, indicating that the foot is landing under the center of mass of the runner
(Fig. 8A). If the vertical line is observed anterior to the pelvis (Fig. 8B), this indicates
an overstride. Note that this dichotomous metric is not without limitations. In particular,
it does not account for trunk flexion angle, which impacts the actual center of mass of
the runner, and may be less useful for runners with a midfoot strike or FFS. Nonetheless,
it is a very useful tool for identifying the presence of overstriding in runners.
Fig. 8. Overstriding, measured at loading response. (A) A runner demonstrating normal

stride mechanics and (B) a runner demonstrating an overstride, characterized by a vertical
line through the lateral malleolus falling anterior to the runners pelvis.
226 Souza
Vertical Displacement of the Center of Mass

The vertical displacement of the center of mass is a very important metric to evaluate
in runners. It is easily measured by comparing frames of video from the runner’s high-
est point during float, to the lowest point during stance (Fig. 9). There are inherent er-
rors in measuring this variable, because the actual location of the center of mass is
impossible to assess on video. One strategy is to identify a location on the runner’s
pelvis and then to use this as a surrogate for the center of mass. Vertical displacement
during running has key implications for injury mechanics as well as energetics.
Increased excursion of the center of mass vertically has been found to be predictive
of the peak knee extensor moment, the peak vertical ground reaction force, as well
Fig. 9. Vertical displacement of the center of mass. (A) A bounding runner characterized by
a large vertical displacement and (B) a relatively efficient runner with less vertical
displacement.
as braking impulse during running, all very important variables in running mechanics.21
This variable can become a problem in “bounders,” runners who increase float time,
often in response to other deficits (eg, reduced hip extension). The end result is
increased work required by the runner to perform this type of running. It has been
found that increasing cadence by 10% during running can reduce significantly the ver-
tical displacement of the center of mass.28
Additional Variables
Auditory
A lot of information can be gathered from the sounds made during running. Certainly,
auditory information differs between treadmills and runners of varying sizes. However,
the clinician can quickly calibrate the normal or typical impact sounds of their tread-
mill, and this can be very useful in gathering information about impact during running.
Greater noise with striking the treadmill may be associated with higher impact forces.
In addition, asymmetries can quickly be identified by listening to the foot strike pat-
terns of the runner. All of this information can be very valuable for a biomechanics
running analysis.
Shaking of the treadmill

In addition to auditory information, the reaction of the treadmill at the time of impact
can also provide important information. Some large, sturdy treadmills may not provide
this information, but many models provide differing amounts to shaking or giving way
in response to impact, and this can be very informative to the observant evaluator.
Cadence
The step rate, or cadence, should be evaluated in all runners. This variable is easily
measured in a variety of ways. One strategy is to count the number of right heel strikes
over a 1-minute period. This number is equivalent to the “stride rate.” Multiplying this
number by 2 equates to the “step rate.” Several recent studies have evaluated the
biomechanical consequences of manipulating cadence.28–32 These data suggest
that an increase in cadence can result in several biomechanical changes in running
form, many of which may be desirable in specific runners. For example, it has been
demonstrated that increasing cadence by 10% can reduce center of mass vertical
excursion, braking impulse, and mechanical energy absorbed at the knee, as well
as decrease peak hip adduction angle and peak hip adduction and internal rotation
moments during running.28 The optimal cadence has been an area of debate, with
some suggesting that approximately 180 steps per minute being ideal. However,
the majority of support for this comes from running economy studies, not studies on
injury mechanics.33,34 Although it may be too early to suggest that all runners should
run at a specific cadence, it is becoming clear that cadence is an important biome-
chanical running variable, and one that can be easily manipulated in runners when
appropriate.
POSTERIOR VIEW
Base of Support
Evaluating the base of support can be an important variable to make note of in specific
runners. Running step width can vary as a function of running speed, but may also be
related to common running injuries. A general rule can be followed that, when viewed
from a posterior video, the left and right feet should not overlap in their ground contact
location. It is not necessary that there be a large gap between the foot placement
locations of the left and right feet, but there should be some space. A narrow base
228 Souza
of support has been linked to tibial stress fractures, iliotibial band syndrome, and
several kinematic patterns that have been associated with running injuries, such as
excessive hip adduction and overpronation.35–37 As such, this variable should be eval-
uated in all runners, and runners with a “cross-over sign” or “scissoring gait,” charac-
terized by an overly narrow base of support, may consider modification.
Heel Eversion
Foot pronation in runners is a variable that has received considerable attention over
many years.38–41 However, measuring foot pronation on 2D video presents significant
challenges. One component of foot pronation that can be evaluated is heel eversion.
By placing markers at the top and bottom of the shoe heel counter (Fig. 10), evaluation
of the vertical relationship of the hindfoot can be assessed easily. It is important to
evaluate not only the peak magnitude of heel eversion (ie, the relationship of the supe-
rior marker to the inferior marker), but also the rate of pronation (Fig. 11). The image in
Fig. 11B occurs 5 frames after Fig. 11A, equating to approximately 20 milliseconds
(collected at 240 frames per second). This rapid heel eversion is worthy of note as
eversion velocity may play a role in specific running injuries. Several studies have
linked excessive heel eversion to various running injuries, such as tibial stress frac-
tures, patellofemoral pain, and Achilles tendonopathy.41–43 Furthermore, it has been
suggested that runners with excessive calcaneal eversion be prescribed orthotics,44
or higher level of support shoes; however, the effectiveness of these strategies has
been questioned, and current evidence is inconclusive.45,46
Foot Progression Angle
The foot progression angle is the transverse plane position of the foot during stance
phase. As a transverse plane variable, it is not easily quantified on 2D video using
our suggested setup. However, a general assessment can be made from a posterior
video. A typical amount of toe-out observed during running results in the lateral aspect
of the shoe being visualized from the posterior view (Fig. 12A). This usually equates to
approximately 5 to 10 of toe-out. A mild toe-in abnormality and severe toe-in abnor-
mality are displayed in Fig. 12B, C, and can be identified by the visualization of the 1st
ray and medial aspect of the shoe. Abnormally toe-in foot progression angle may be
associated with hip internal rotation, knee internal rotation, ankle internal rotation, or
Fig. 10. Heel eversion. (A) A runner with normal alignment of the heel during running and
(B) a runner with mildly excessive heel eversion during running.
Fig. 11. Rate of heel eversion. A runner demonstrating excessive heel eversion and a high
rate of heel eversion excursion. (A) Initial contact with the runner’s heel in an inverted po-
sition and (B) 20 milliseconds later the heel has rotated more than 20 into eversion.
some combination of these. Several studies have identified these motions in connec-
tion with various running injuries, suggesting that this variable should be considered in
a biomechanics running analysis.47–49 Excessive toe-out is also not uncommonly
seen. Although fewer studies have linked excessive toe-out or lower extremity external
rotation to running injuries, it is reasonable to speculate that abnormal flexibility,
including tight hip external rotators, may play a role in excessive toe-out while running.
Further research is need in this area.
Heel Whips
A heel whip is another transverse plane variable that can be challenging to measure
accurately on 2D video. However, a recent study has found this metric to be reliably
measured from a posterior approach.50 The whip angle is measured by comparing
Fig. 12. Foot progression. (A) Normal foot progression angle. (B) Mild toe-in abnormality.
(C) Severe toe-in abnormality.
230 Souza
the angle of the plantar surface of the shoe at initial swing with the plantar surface at
the point of maximum rotation (Fig. 13). Although very little has been published on this
variable, and the significance of this metric remains unknown, data suggest that an
angular rotation of more than 5 in either the medial (see Fig. 13A, B) or lateral (see
Fig. 13C, D) is observed in more than one-half of recreational runners.
Fig. 13. Heel whips. Medial heel whip at initial swing (A) and maximum whip angle (B) and
lateral heel whip at initial swing (C) and maximum whip (D).
Knee Window
Excessive hip adduction, excessive hip internal rotation, and excessive knee valgus
have all been implicated in running injuries.3,49,51,52 Each of these variables has the po-
tential to impact the runner’s “knee window.” Evaluation of the knee window is a sim-
ple, dichotomous assessment of the presence or absence of a space between the
knees at all times of the running cycle, and is a measure of the alignment of the hip,
knee, and ankle from a posterior (or anterior) view (Fig. 14). The knee window does
not need to be large—an excessively large knee window may suggest a varus defor-
mity, an alignment issue that also presents with potential problems. However, the vast
Fig. 14. Knee window. (A) Normal knee window and (B) “closed” knee window.
majority of recreational runners who fail to demonstrate a normal knee window or lose
the window during the gait cycle, associated with the kinematic pattern described—
namely, excessive hip adduction and internal rotation, and knee valgus. Although
identification of this variable is quite simple, it should be noted that correcting an
abnormally “closed” knee window is not as simple.53 There are some limitations to
this measurement. It is important for runners to wear shorts or tight-fitting pants so
that this variable can be assessed. In runners with excessive soft tissue on the medial
aspect of the knee, this measurement can be inaccurate. Finally, swing limb hip
adduction can also create the impression of a closed knee window, even in the pres-
ence of good hip–knee–ankle alignment. Nonetheless, this measurement can be a
valuable component of a biomechanics running evaluation, and several recent studies
have found this variable to be modifiable through a variety of methods.54–56
Pelvic Drop
Assessing the amount of pelvic drop, or maximum pelvic obliquity during stance
phase, can be augmented with the application of markers on the posterior superior
iliac spines (Fig. 15). By comparing stance limb and swing limb marker positions,
the amount of pelvic drop can be estimated. Excessive pelvic drop during running
contributes to excessive hip adduction, a variable that has been linked to numerous
running injuries.49,51 A recent study found that a 2D quantitative assessment of this
variable demonstrated excellent reliability but was poorly correlated with a 3D mea-
surement of pelvic drop.57 However, the clinical significance of 3D-measured pelvic
drop has also been called into question.2,58 It is possible that pelvic drop may serve
as a surrogate measure for hip and/or core muscle weakness. Pelvic drop during
running has been reported to be significantly related to both hip abductor strength
and hip extension strength, and fatiguing of these muscles have been observed to
result in excessive pelvic drop.59,60 Looking for side to side differences can be helpful
232 Souza
Fig. 15. Excessive pelvic drop. (A) At initial contact the runner’s pelvis is fairly level and (B)
during stance demonstrating excessive pelvis drop.
in detecting excessive pelvic drop and correlation with associated kinetic chain defi-
cits should be performed to see how this contributes to injury. Although further
research is necessary in this area, pelvic drop remains as a variable of interest in a
biomechanics running analysis.
SUMMARY
Running biomechanics play an important role in the development of injuries in recrea-

tionally active individuals. Performing a systematic, video-based running biome-
chanics analysis rooted in the current evidence on running injuries can allow the
clinician to develop a treatment strategy for injured runners. The majority of the current
literature has not risen to the level of proven injury prevention strategies in correcting
each aspect of running gait detailed in this review, suggesting that recommendations
for modification of running form in uninjured runners would not be evidence based.
However, when the patient presentation and physical examination findings are in
agreement with abnormalities observed in a biomechanics running analysis, it serves
as a potential for intervention.
The analysis plan described is not intended to be taken as a “gold standard” or a
comprehensive running evaluation. Numerous other running evaluations from a biome-
chanics perspective are available and should be incorporated into each clinician’s pro-
tocol.61,62 It is simply a well-tested and frequently revised evaluation plan that has been
successful in evaluating recreational runners. Furthermore, it is expected that this anal-
ysis plan will continue to evolve as future research emerges. Certain variables will likely
materialize as critical to injury development and prevention, and others will turn out to be
unrelated. Nonetheless, the components outlined in this review may serve as a template
for a systematic evaluation plan to be improved upon by others, as more information
about running biomechanics surfaces. Running biomechanics play a key role in injury
development and prevention. Identifying simple 2D surrogates for 3D biomechanic vari-
ables of interest will allow for widespread translation of best practices, and have the
best opportunity to impact this highly prevalent problem.
ACKNOWLEDGMENT
The author thanks Nicole Haas, PT, OCS, and Suzanne Souza, PT, OCS for review-
ing this article, and providing invaluable clinical input.
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An Evidence-Based

Running is an extremely common form of exercise, whether recreational or competitive.

Phys Med Rehabil Clin N Am 27 (2016) 217–236

Numerous recent studies have identified abnormal biomechanics in persons with

Warmup and Analysis Plan

kinematics to be identified as abnormal, or predictive of injury, do not exist. As such,

Foot Inclination Angle at Initial Contact

Tibia Angle at Loading Response

Knee Flexion During Stance

Hip Extension During Late Stance

Fig. 8. Overstriding, measured at loading response. (A) A runner demonstrating normal

Vertical Displacement of the Center of Mass

Shaking of the treadmill

Running biomechanics play an important role in the development of injuries in recrea-

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