A Master’s Thesis
entitled
Core Muscular Endurance Differences in Recreational Runners With a Previous History
of Running-Related Musculoskeletal Injuries and Healthy Runners
by
Aya Kitagawa
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the
Master of Science Degree in Exercise Science
_________________________________________
Dr. Phillip Gribble, Committee Chair
_________________________________________
Dr. Abbey Thomas, Committee Member
_________________________________________
Dr. Brian Pietrosimone, Committee Member
_________________________________________
Dr. Patricia Komuniecki, Dean
College of Graduate Studies
The University of Toledo
May 2014
Copyright 2014, Aya Christine Kitagawa
This document is copyrighted material. Under copyright law, no parts of this document
may be reproduced without the expressed permission of the author.
An Abstract of
Core Muscular Endurance Differences in Recreational Runners With a Previous History
of Running-Related Musculoskeletal Injuries and Healthy Runners
by
Aya Kitagawa
Submitted to the Graduate Faculty as partial fulfillment of the requirements for the
Master of Science Degree in Exercise Science
The University of Toledo
May 2014
Context: Identification of core strength deficits in runners with running-related
musculoskeletal injuries (RRMI) has been documented. However, as running is typically
a long distance, endurance sport, core muscular endurance should be evaluated within the
RRMI population. Specifically, hip abduction (HABD) and external rotation (HER)
endurance, as well as lateral trunk flexion (LTF), trunk flexion (TFX), extension (TEX),
as these muscles are responsible for controlling the pelvis during running and maintaining
a neutral center of mass. Objective: To examine core muscular endurance differences
between recreational runners who have a previous history of a RRMI compared to
healthy matched controls. Methods and Measures: 12 recreational runners with a
previous history of RRMI (6 females, 6 males, 31.78 ± 8.72yrs, 174.28 ± 10.02cm, and
69.82 ± 11.52kg) and 13 healthy (7 females, 6 males, 30 ± 8.28yrs, 170.82 ± 8.67cm,
68.34 ± 12.8kg) runners participated in this study. HER, and LTF endurance measures
were collected at one session, while HABD, TFX and trunk extension TEX endurance
measures were collected at the second session, with sessions 2-5 days apart. All tests
were isometric fatiguing tests and were recorded in seconds. A mixed model repeated
iii
measures ANOVA for HER, HABD, and LTF endurance, and a 2x2 ANOVA for TFX
and TEX endurance were used for analyses, and paired samples t-tests were used for
post-hoc testing as needed. Results: A statistically significant limb by group interaction
was observed with LTF endurance (p=0.01). LTF endurance of the injured limb of the
RRMI group was greater than the injured limb of the healthy group (p=0.03); also the
LTF endurance of the injured limb of the RRMI group was greater than the contralateral,
non-injured limb (p=0.02). Although not statistically significant, HABD endurance in
RRMI females was lower than healthy females while HABD endurance in RRMI males
was greater than healthy males (p=0.08), and females displayed greater HER endurance
compared to males (p=0.08). No other statistical significances were observed.
Conclusion: Recreational runners with a history of a RRMI displayed greater LTF
endurance in the injured limb compared both to the contralateral non-injured limb and
also to the injured limb of the healthy group. Additionally, health females and RRMI
males displayed greater HABD endurance compared to their counterparts, and females
displayed greater HER endurance compared to males. These findings are clinically
relevant as this shows that clinicians should incorporate both endurance components as
well as strength components to rehabilitation of RRMIs.
iv
Thank you to my parents, Yoshihisa and Isoko Kitagawa, and my brother, Jun Kitagawa,
for their continued love and support.
Table of Contents
Abstract
iii
Table of Contents
vi
List of Tables
viii
List of Figures
ix
List of Abbreviations
x
I. Introduction
1
A. Statement of the Problem
2
B. Statement of the Purpose
3
C. Significance of the Study
3
D. Specific Aim and Hypotheses
3
II. Literature Review
4
A. Epidemiology
4
B. Defining Running-Related Musculoskeletal Injuries
4
C. Specific Running-Related Musculoskeletal Injuries
5
a. Patellofemoral pain
5
b. Iliotibial band friction syndrome
6
c. Stress fractures
7
d. Medial tibial stress syndrome
8
D. Visual Analog Pain Scale
9
E. Endurance Tests
10
F. Conclusion
11
III. Methodology
13
vi
A. Study Design
13
B. Participant
13
C. Instrumentation
14
D. Independent Variables
14
E. Dependent Variables
14
F. Procedures
15
G. Data Analysis
18
IV. Results
19
A. Hip endurance measures
19
B. Trunk endurance measures
20
V. Discussion
27
A. RRMI versus healthy association
27
B. Male versus female association
29
C. Injury group and sex interaction
30
D. Limitations
31
E. Conclusion and Clinical Relevance
32
References
33
Appendix A: Endurance testing positions
44
vii
List of Tables
Table 1
Demographic information for the running-related musculoskeletal injury
(RRMI) and healthy groups ............................................................................21
Table 2
Hip external rotation endurance times for the running-related
musculoskeletal injury (RRMI) and healthy groups .......................................22
Table 3
Hip abduction endurance times for the running-related musculoskeletal
injury (RRMI) and healthy groups .................................................................23
Table 4
Lateral trunk flexion endurance times for the running-related
musculoskeletal injury (RRMI) and healthy groups .......................................24
Table 5
Trunk flexion endurance times for the running-related musculoskeletal
injury (RRMI) and healthy groups .................................................................25
Table 6
Trunk extension endurance times for the running-related musculoskeletal
injury (RRMI and healthy groups ..................................................................25
Table 7
Hip external rotation (HER), hip abduction (HABD), and lateral trunk
flexion (LTF) endurance main effects and interactions ..................................26
Table 8
Trunk flexion (TFX) and trunk extension (TEX) endurance main effects and
interactions information ..................................................................................26
viii
List of Figures
Figure 1 Hip abduction (HABD) endurance test position ..............................................37
Figure 2 Hip external rotation (HER) endurance test position .......................................37
Figure 3 Trunk flexion (TFX) endurance starting position and testing position............38
Figure 4 Trunk extension (TEX) endurance testing position .........................................39
Figure 5 Lateral trunk flexion (LTF) endurance testing position ...................................39
ix
List of Abbreviations
HABD ........................Hip abduction
HER............................Hip external rotation
LTF ............................Trunk lateral flexion
TEX ............................Trunk extension
TFX…………………Trunk flexion
x
Chapter One
Introduction
Running is one of the most common forms of exercise in the United States.1-9
Unfortunately, overuse injuries are also common, as repetitive motions such as running
can cause insidious damage to the structures involved.7 There are a variety of overuse
injuries that runners experience, but the most commonly seen running-related
musculoskeletal injuries (RRMIs) include patellofemoral pain (PFP), iliotibial band
friction syndrome (ITBFS), medial tibial stress syndrome (MTSS) and stress fractures of
the lower leg.6,8,10-12
The rates of each injury in various populations of runners differ; however, they
are uniformly high making overuse running injuries the most common ailment across all
ages and intensities of runners. In the younger population of high school runners,
researchers have found injury rates of up to 47% as well as 2.4 injuries per 1000 athlete
exposures.13,14 In the college age population, Daoud et al.15 found that 75% of 52 Harvard
cross country subjects incurred an overuse injury within one year of competition.15 High
injury rates are also documented in the recreational runners’ population with a rate of up
to 70%.16,17
It is evident that RRMIs are widespread among runners, but researchers disagree
on the etiology behind these injuries. PFP is thought to originate from multiple sources.
Some authors have implicated excessive rearfoot eversion, while others attribute PFP to
decreased vastus medialis obliqous (VMO) strength and motor recruitment.18-22 However,
more recent research has cited poor hip and core muscle strength and kinematics as a
likely origin.23-25 Various researchers believe ITBFS originates from tightness of the
1
iliotibial band and excessive pronation, while others suggest it is caused by friction
between the lateral femoral condyle and the iliotibial band during running.26-30 More
recently, researchers have also cited decreased thigh abduction and external rotation due
to hip abductor weakness as a source of ITBFS.31 Bennell et al.32 explain that stress
fractures develop due to the imbalance between bone loading and bone remodeling where
the loading outweighs the remodeling and therefore creates a deficiency in the bone
strength and structure.32 Friberg33 as well as Bennell et al.34 found that leg length
discrepancy may have a significant effect on the development of lower extremity stress
fractures due to asymmetrical skeletal alignments and the resulting uneven wear to the
bony structures and muscular attachments at the hip.33,34 Beck et al.35 theorized that
medial tibial stress syndrome results from muscle or fascial traction on the periosteum
and tibial bending with weight-bearing, while Couture et al.36 found that pronation is a
more likely origin of MTSS.35,36
Nonetheless, it is clear that with each of these RRMIs, there is a recurring pattern
of poor strength and kinematics of the lower extremity, perhaps most interestingly at the
hip, which may be a causative factor.
Statement of the Problem
A large portion of the recreationally active population has a previous history of
RRMI, and evidence shows that strength deficits exist within this RRMI population
compared to healthy controls. However, most existing studies have given more emphasis
to muscular strength measurements compared to muscular endurance measurements. It is
unknown what impact muscular endurance, especially in the hip and core, may have on
running mechanics and the development of RRMI.
2
Statement of the Purpose
The purpose of this study was to examine core muscular endurance in recreational
runners with a previous history of RRMIs compared to healthy matched controls.
Significance of the Study
The significance of this study was to provide clinicians with information on
whether they need to emphasize correcting endurance deficits in the prevention of RRMIs
in a recreationally active population.
Specific Aim and Hypotheses
A1- To examine core muscular endurance differences in recreational runners with
a previous history of a RRMI compared to healthy matched runners. Specifically we
hypothesized that recreational runners with previous history of an RRMI, when compared
with healthy controls, will exhibit:
H1: Decreased hip external rotator endurance
H2: Decreased hip abductor endurance
H3: Decreased trunk lateral flexor endurance
H4: Decreased trunk flexor muscular endurance
H5: Decreased trunk extensor muscular endurance
3
Chapter Two
Literature Review
Epidemiology
Overall RRMI rates range between 19-79%.1,6,7,37-41 Across multiple populations
of runners, the 4 most common overuse injuries include patellofemoral pain (PFP),
iliotibial band friction syndrome (ITBFS), stress fractures of the lower leg, and medial
tibial stress syndrome (MTSS) 4,8,11,42. Looking at rates of specific injuries, PFP accounts
for up to 43% of sports medicine and physician’s office visits.23,43,44 Other injury rates
include ITBFS between 1.6-52% of RRMIs, stress fractures between 6-56%, and lastly,
MTSS at 4-35% of RRMIs.30-32,45-58 These 4 specific overuse injuries are all located at the
knee or below, accounting for 50-75% of all RRMIs2,11,59,60
Defining Running-Related Musculoskeletal Injuries
There are many variations of the definition of RRMI within the literature. Some
definitions are very broad, such as “any physical complaint developed in relation to
running activities and causing restriction in running distance, speed, duration, or
frequency.”42 This definition is very generic and could potentially include unwarranted
ailments such as simple aches and pains associated with running, versus a true runningrelated musculoskeletal injury or structural damage. Buist et al.2 uses a stricter definition,
“any musculoskeletal pain of the lower limb or back causing a restriction in running
(mileage, pace, or duration) for at least 1 day.2 Taunton et al.7 defines it as “pain during
or immediately after a run, feeling that the injury was running related, experiencing pain
at beginning of running regimen, stopped running, decreased mileage, or sought medical
4
attention.”7 These definitions are all individually valid; however, to be more thorough
with the definition, components of these definitions should be combined.
Specific Running-Related Musculoskeletal Injuries
Patellofemoral pain
Fulkerson12 cites the patellar retinaculum, subchondral bone, the
synovium, as well as the skin, muscles, and nerve around the knee as the anatomy
involved in the development of patellofemoral pain.61
PFP is defined as an insidious onset of pain of the retropatellar region, that is
aggravated with weight bearing exercises.19,24,25,43,62 Pain is commonly exacerbated with
ascending and descending stairs, squatting, running, walking, and sitting for a prolonged
period of time. Multiple etiologies at multiple joints have been speculated as contributing
factors to PFP. Previous authors have suggested excessive rearfoot eversion as a possible
contributing factor.18,20,63 It is theorized that excessive eversion creates an exaggerated
internal rotation of the tibia which in turn causes the femur to internally rotate in order to
properly reach knee extension, creating increased lateral patellofemoral joint stress. This
chain of events causes lateral patellar tracking to increase and subsequently, PFP to
develop.
Other researchers believe PFP to originate from dysfunction at the knee joint
itself. Fulkerson et al.12, found that PFP is a result of overload on the patellar retinaculum
and subchondral bone from the malalignment of the extensor mechanism.12 A
malalignment of the extensor mechanism is an altered extension motion and coupled with
the patellar retinaculum and subchondral bone overload it can potentially lead to PFP.12
Additionally, Powers25 found that PFP is associated with VMO strength and motor
5
recruitment.25 This causes a timing delay within the quadriceps muscle complex during
contraction leading the lateral section, namely the vastus lateralis, to have a stronger
contraction in contrast to the medial section. Repeated lop-sided contractions ultimately
lead the patella to track laterally and subsequently, PFP develops.25
More recently researchers have investigated the hip as a primary factor in the
etiology of PFP. Multiple researchers suggest that PFP may be a result of hip weakness
and a lack of functional control of the femur during weight bearing. More specifically,
several authors have found hip abductor and hip external rotators to be weak in subjects
with PFP.22-24
A new avenue in research of etiologies associated with PFP is the contribution of
the core. The abdominal muscles in conjunction with the lumbar extensors increase the
stability of the spine.64 Increased stability at the spine is essential in providing the lower
extremities with a stiff base of support for muscle contractions. A stable base of support
may prevent the body’s center of mass from deviating while also providing dissipation of
the forces generated at the lower extremities.65,66 Ireland et al.24 found that the abdominal
muscles limit excessive anterior pelvic tilt, which increases femoral internal rotation,
ultimately creating improper lateral patellar tracking and pain.
Iliotibial band friction syndrome
ITBFS involves a thick band of fascia, originating at the lateral iliac crest and
inserts on Gerdy’s tubercle on the lateral tibia.26,67
ITBFS is defined as pain over the distal, lateral aspect of the knee, or over the
greater trochanter of the femur, that is aggravated with activity, including running down
hills.26,28-30 Recently, researchers have found a relationship between ITBFS and the
6
surrounding hip musculature. When the tensor fascia latae (TFL) and gluteus maximus
contract during knee flexion, the iliotibial band will actually push inward toward the
femur.68,69 In slight knee flexion, the TFL pulls with more force compared to the gluteus
maximus which causes the anterior portion of the iliotibial band (ITB) to become more
prominent and taut. As knee flexion increases, the opposite occurs, the posterior portion
of the ITB then becomes more prominent. This shift between the anterior and posterior
protrusions of the ITB is what was mistaken as a “snapping” back and forth of the ITB in
previous etiologies. Noble27 was one of the first to describe the etiology of ITBFS as
training errors including excessive distances, poor running technique, and running on
hard surfaces, which result in friction of the iliotibial band against the lateral epicondyle
of the femur. Similarly, Racioppi and Gulick29 cite repetitive snapping of the iliotibial
band over the lateral femoral epicondyle as the cause of ITBFS.
Other researchers have reported that muscle weakness, specifically hip abductor
weakness, can lead to the development of ITBFS.26,31,70 Weakness of the hip abductors
causes the antagonist hip adductors to create excessive force, leading to increased tension
at the iliotibial band, ultimately leading to development of ITBFS.26,31,70
Stress fractures
Symptoms of stress fractures typically accumulate gradually beginning with mild
discomfort over the site of the fracture during palpation and progressing to include pain
during running. Palpable swelling and calluses over the site may be present after some
time as well.71-73 Stress fractures account for 6 to 15.6% of all RRMIs, with the tibia
being the most common site accounting for 35 to 56% of all stress fractures.71-75 The
etiology has been linked to diet and sex in the past, but more recently, has been linked to
7
running mechanics.75 Pohl et al.75 found that excessive eversion along with increased hip
adduction and femoral eversion have a significant effect on the development of tibial
stress fractures.71,75 Other factors associated with stress fractures include training errors
such as an increase in frequency, duration, or intensity of runs as well as running on hard
surfaces.71,73 Bennell et al.32 suggests that because muscles of the lower extremities
function as shock absorbers during running, when they lack strength or endurance they
cannot properly dissipate the forces across the bony structures which can potentially lead
to the development of stress fractures .32
Medial tibial stress syndrome
Medial tibial stress syndrome is exercise-related pain on the posteromedial side of
the middle to distal tibia. The official AMA definition is pain or discomfort in the leg
from repetitive running on hard surfaces or forcible excessive use of the foot
flexors.46,47,53 Like many of the other overuse RRMIs, the onset of pain related to MTSS
is insidious with no traumatic event preceding the pain. Originally, MTSS was thought to
be caused by traction-related periostitis, or a swelling of the membrane surrounding the
bone, but more recent research found that the when the rate of bone resorption is faster
than bone replacement, MTSS starts to develop.35,53,76-78 Other researchers have cited
stress microfractures caused by tibial bending from repetitive contact with hard surfaces
as the cause of MTSS.46,47 Histological and anatomical studies have reported that the
soleus and flexor digitorum were the main contributors to traction-induced MTSS,
especially while the heel is in a pronated state.35,79 The aponeurosis connects the medial
aspect of the soleus to the medial border of the tibia and carries with it the potential for
creating traction stress on the attachment.35 Activities involving excessive repetitive
8
contractions and stretching to the soleus and flexor digitorum complex can ultimately
cause the muscle complex to avulse from its attachment causing bony damage. When this
bony damage is created at a higher rate than the replacement, MTSS develops. More
recently, poor lower extremity mechanics, such as pronation, have been linked to poor
core stability via the kinetic chain.31,36,66,80
Although each of these injuries have seemingly separate etiologies, all share a
common factor in that they originate from biomechanically altered kinematics of the
lower extremities. Each of these alterations can be tied to recent research into the role of
core muscles and core stability in the proper function of lower limb mechanics. Without
the ability of the core to stabilize properly, the lower extremities are unable to perform
biomechanically sound movements.81-83 Repeated inapt movements created at the lower
extremities, ultimately create damage to each of the structures involved in the movement,
leading to the development of running related injuries.24,31,84,85
Visual Analog Pain Scale
The visual analog pain scale is a subjective tool commonly used in health care to
assess the level of pain a patient is experiencing.86-89 The reliability has been established
in several studies (ICC = 0.60-0.96). 87-92 It consists of a 10-centimeter horizontal line
with two ends labeled with words expressive of opposite ends of the pain spectrum (ie:
no pain on one end and unbearable pain on the other). The patient is asked to mark a
vertical line at a portion of the horizontal line they feel is most accurately representative
of their pain. The terminology of the labels may differ slightly between users, however
the concept is the same.87-89 Participants in this study will be asked to fill out a VAS
assessing their pain during running over the past week.
9
Endurance tests
Measuring strength of a muscle group can give clinicians insight on the origin of a
pathology. However, strength is not the only aspect that should be examined. The
endurance of a muscle group may be just as important a component in assessing the
kinematics of movement. This is especially true when examining the core muscle group.
The structures that stabilize the core are a complex of osseous and soft tissue systems in
the lumbopelvic region.93 Although there is not currently a universal definition, most
researchers use the term “core stability” to refer to the ability of the core muscles to keep
the spine stiff and maintain a steady level of intra-abdominal pressure during muscular
contractions.94,95 The core is responsible for providing stability for the extremities as well
as providing strength and balance to optimize musculoskeletal function.66,94-96 If the
extremities are unable to work off of a solid surface, miniscule biomechanical changes
occur throughout the kinetic chain in order for the extremities to compensate for the lack
of stability at the core. Because running requires numerous and continuous muscular
contributions at the lower extremity, repetitive improper running mechanics can
potentially cause RRMIs to develop.95 Therefore, core endurance measures are an
important aspect of injury that needs evaluating.
To test trunk flexor endurance the most reliable method involves the use of a
wedge that has been premade to measure 60 degrees (ICC = 0.97).97 The participant will
sit with the hips and knees flexed to 90 degrees while the back lies on the wedge in order
for the participant to “feel” what 60 degrees of trunk flexion feels like without having to
hold the position and fatigue the muscles. The wedge is moved back 10 cm to start the
10
test as the clinician stabilizes the feet. The test will be measured in time until the trunk
angle falls below 60 degrees.97,98
Trunk extension endurance is most reliably measured by using the modified
Beiring-Sorensen test (ICC = 0.97, 0.98).97-101 This test is also measured using time,
specifically until the trunk falls below the level of the table, with stabilization over the
lower extremities.
The side-bridge hold is a very reliable method of testing lateral trunk flexor
endurance (ICC=0.99).97 The participant is asked to perform a side-bridge and hold for as
long as possible. There is no stabilization requirement for this test.97
There are variations in the literature on how much time should be given between
each test to prevent fatigue from overlapping between tests. Lanning100 has suggested
waiting 1 minute between tests citing that it was enough time to provide adequate rest;100
while Reiman98 and McGill97 used 5 minutes between endurance tests in order to ensure
the participant had enough time to rest and to prevent fatigue.97,98 Much larger rest
periods were used by Jacobs et al.102 with 15-minute break between tests, while Ito et al.99
utilized the longest break period with 72 hours between endurance tests to prevent
fatigue.99,102 With this information, it seems a rest period of 5 minutes is the most logical
as it will not over estimate or under estimate rest time providing optimal recovery.
Conclusion
Throughout the literature, the most common etiological factors in the
development of RRMIs are weak hip muscular strength and altered lower extremity
running kinematics. Newer avenues of research have begun to examine the kinetic chain,
more specifically the core, and its contributions to these injuries. However, there is
11
currently very limited research on the effect that core strength has on RRMIs and no
research on the effect of hip and core muscular endurance on the development of RRMIs.
12
Chapter Three
Methodology
Study Design
Retrospective, Case control
Participants
This study included 25 volunteers (12 male, 13 female) recruited from the
University of Toledo community, the local Toledo community, local sports medicine and
physical therapy clinics, and local physicians’ offices. All demographic data are reported
in Table 1.
All participants were between the ages of 18 and 45 and ran a minimum of 10
miles per week. Participants included in the RRMI group reported a previous history of
an RRMI including MTSS, PFP, ITBS and tibial stress fractures. Definition of an RRMI
consisted of the following: 1) one of the four specific RRMIs diagnosed by a physician,
physical therapist, or athletic trainer, and 2) rest or removal from running activity
(training or races) for at least 3 consecutive days at the time of injury. Exclusion criteria
for the RRMI group were as follows: 1) had a current RRMI in which the individual was
not approved to run by his/her physician 2) had a previous history of lower extremity
injury other than the specific RRMI within the last year, 3) had a surgical procedure that
would have caused major structural changes to the lower extremities, and 4) were
receiving rehabilitation during the study period. Participants included in the healthy
control group did not have a history of an RRMI within the past 12 months.
13
Instrumentation

Stop watch

Visual analog pain scale

Biodex dynamometer (Biodex Medical Systems, Inc., Shirley, NY and
System 2, Version 4.6.0)
Independent Variables

Group
o RRMI
o Healthy

Side
o Injured
o Non-injured

Sex
o Female
o Male
Dependent Variables
Endurance Measurements:

Hip External Rotation (HER)

Hip Abduction (HABD)

Lateral Trunk Flexion (LTF)

Trunk Flexion (TFX)

Trunk Extension (TEX)
14
Procedures
Volunteers who participated in this study were asked to report to the
Musculoskeletal Health and Movement Science Laboratory located in the Health and
Human Services building on the main campus of the University of Toledo. The
volunteers first reviewed and signed the informed consent form and were given the
opportunity to ask questions to the researchers. Participants completed two separate
sessions spaced 2-5 days apart, with the first session lasting approximately 1 hour, and
the second a half an hour. Upon reporting to the laboratory, the participant completed an
injury history form to determine group placement and injury diagnosis when applicable.
For both sessions participants were asked to wear shorts and a short-sleeved shirt for ease
of movement and measuring. Next, the participant’s height, weight, and age were
recorded.
At each session, prior to starting the endurance testing, participants completed a
5-minute warm up on the treadmill. At the first session, the participants performed
endurance tests for the bilateral hip external rotators and lateral trunk flexors. At the
second session, the participants performed endurance tests for the bilateral hip abductors
and trunk flexors and extensors. Verbal encouragement to continue performance was
provided during the endurance tests. Within-day randomization was performed, as well as
side randomization for participants.
Participant positioning for the HABD test was in the side-lying position on a
treatment table, with the head resting on a pillow and the test leg on top of the other side.
The axis of the Biodex was positioned at the hip joint center, and the Biodex attachment
arm was secured proximal to the lateral femoral condyle on the test leg. The pelvis was
15
secured to the table with a stabilizing strap to minimize compensatory movements.
(Figure 1)
The HER endurance test was performed in the prone position on a treatment table,
with the head resting on a pillow. The testing side was in a neutral hip position, with the
knee at 90 degrees of flexion. The axis of the Biodex was aligned through the femur, and
the Biodex attachment arm was placed approximately 5 cm proximal to the lateral
malleolus of the testing side. (Figure 2)
For HABD and HER endurance testing, the participant performed 3 maximal
voluntary isometric contractions (MVIC) of the respective muscle groups. Then an
average of the 3 trials was calculated, and the participant’s 50% MVIC was extracted.
During the HABD and HER tests the participant was instructed to maintain 50% of his or
her MVIC for as long as possible. A stationary line indicating the participant’s 50%
MVIC appeared on a monitor positioned in front of the participant. As the participant
provided a force against the Biodex, a line tracking the participant’s contraction appeared
on screen to provide real-time visual feedback. The test ended when the volunteer could
no longer hold a contraction at or above 50% MVIC consecutively for 3 seconds, or if the
participant compensated by activating additional muscle groups and altering his or her
position. This was monitored visually by the evaluator.
The TFX endurance test started with the participant sitting with the back resting
against a 60° wedge, both hips and knees at 90° of flexion, and arms folded across the
chest. One tester stabilized the feet, while the other held onto the wedge and monitored
positioning. The participant was then told to activate his or her core and maintain the 60°
trunk flexion position as the wedge was pulled back 10 cm. Time (in seconds) started
16
when the wedge no longer supported the participant, and ended when the volunteer could
no longer maintain 60° of trunk flexion. (Figure 3)
For the TEX endurance test (aka the modified Biering-Sorensen test) the
participant was positioned in the prone position on a stable surface about 1.5 ft above the
ground. The participant’s anterior superior iliac spine was aligned with the edge of the
platform and the upper body suspended in a cantilevered fashion. A pillow was placed
under the participant’s ankles and a tester provided support on the participant’s calves.
When the participant was ready, he then crossed his arms over his chest, raised his upper
body up until it was parallel with the floor, and held this position for as long as possible.
Time started when the upper body was no longer supported, and ended when the upper
body fell below parallel. Verbal encouragement was given to maintain the position as
well as to raise up or down for proper positioning. (Figure 4)
The LTF test (aka the side plank) started with the participant in the side-lying
position with the legs extended, the top foot resting on top of the bottom foot, and the
upper body supported on the elbow and forearm. The side to be tested was the side
providing support from the elbow and bottom foot. The participant then lifted his trunk
off of the mat to support his entire weight on just the feet, elbow, and forearm of the
bottom arm, while the uninvolved arm lay straight on his side. The test started when the
participant’s trunk was lifted off of the ground, and ended when the participant could no
longer maintain proper positioning. Verbal encouragement was provided as well as
feedback to lift up or lower the hip, and to lean forward or backward at the torso to
maintain the correct testing position (Figure 5). All participants were given 5 minutes of
rest between tests.
17
Data Analysis
Group means and standard deviations from each assessment were used for
analysis. To remove any outliers from the data, we ran descriptive statistics and created
stem and leaf plots. Those values that were 2 or greater standard deviations away were
then removed and the subsequent data were used for the remainder of the analyses. We
ran paired samples t-tests between sides of the healthy control group for the following
variables, HER, HABD, and LTF endurance measures. To examine the dependent
variables of HER, HABD, and LTF, a mixed model repeated measures analysis of
variance (ANOVA) was used (group by sex by side). For the remainder of the dependent
variables, TFX and TEX, we ran a 2x2 ANOVA (group by sex). For statistically
significant interactions, a post hoc univariate analysis with pairwise comparison was
conducted to ascertain the location of significant differences. All statistical analyses were
performed with SPSS 19.0 software (IBM Corporation, Armonk, NY). Statistical
significance was set a priori at P ≤ 0.05.
18
Chapter 4
Results
No statistically significant differences in age, height, or mass were found between
groups (Table 1). There were no statistically significant differences between sides within
the healthy control group for HER, HABD, and LTF endurance. Therefore, we were
confident in matching sides of the healthy controls to the RRMI group for statistical
comparison without concern of an influence of side dominance.
Hip endurance measures
The means and standard deviations for HER can be found in Table 2, while the
main effect and interaction information can be found in Table 7. There were no
statistically significant main effects or interactions for HER. However, the main effect for
sex approached statistical significance (F1,20=3.30, p=0.08), with females having a greater
HER endurance time (92.44 ± 27.18s), compared to males (72.41 ± 26.8s). The
associated effect size for this relationship was moderate (d=0.72; 95%CI: -0.09, 1.53).
All other relationships for HER endurance were not statistically significant with effect
sizes that were weak.
The means and standard deviations for HABD can be found in Table 3, while the
main effect and interaction information can be found in Table 7. There was a nearly
significant group by sex interaction (F1, 17=3.44, p=0.08). A strong effect size indicated
that for the RRMI group males had greater HABD (45.75 ± 7.06s) compared to the
females (38.43 ± 7.06s) (d=-1.04; 95% CI: -2.3, 0.46). In contrast, for the healthy group,
a moderate effect size indicated that the females had greater HABD (45.34 ± 7.05s) than
the males (40.83 ± 7.06s) (d=0.64; 95% CI: -0.63, 1.8). All other relationships for HABD
19
were not statistically significant with effect sizes that were weak with confidence
intervals that crossed zero.
Trunk endurance measures
The means and standard deviations for LTF can be found in Table 4, while the
main effect and interaction information can be found in Table 7. A significant side by
group interaction was observed (F1,20=3.52, p=0.01). Post-hoc testing revealed that the
LTF endurance of the non-injured side of the RRMI group (60.01 ± 22.97s) was
significantly lower than the matched non-injured side of the healthy control group (85.3 ±
22.96s) (p=0.03; d=-1.06, 95%CI:-1.95, -0.16) and the injured side of the RRMI group
(76.23±31.81s) (p=0.02; d=-0.56, 95%CI:-1.38, 0.25). Additionally, the sex main effect
for LTF was nearly statistically significant (F1, 18=3.52, p=0.08), with a strong effect size
(d=0.77) with 95% confidence intervals crossing zero (95%CI:-0.1, 1.64), indicating that
the males displayed greater LTF endurance (84.27 ± 25.41s) compared to the females
(63.94 ± 25.41s). All remaining relationships were not statistically significant with weak
associated effect sizes.
The means and standard deviations for TFX can be found in Table 5, while the
main effect and interaction information can be found in Table 8. There were no
significant main effects or interactions for TFX, with weak associated effect sizes and
95% CI that crossed zero.
The means and standard deviations for TEX can be found in Table 6, while the
main effect and interaction information can be found in Table 8. A significant main effect
for sex was observed (F1, 22=4.18, p=0.05). The effect size was strong (d=0.81) with 95%
confidence intervals crossing zero (95%CI: -0.03, 1.64), indicating that females displayed
20
greater TEX endurance (169.8 ± 42.2s) compared to males (134.61 ± 42.2s). All other
relationships for TEX endurance were not statistically significant with effect sizes that
were weak.
Table 1. Demographic information for the running-related musculoskeletal injury
(RRMI)
and healthy groups (Mean±SD)
Group
Mean ± SD
P-value
RRMI (n=13)
31.78 ± 8.72
Age (years)
0.85
Healthy (n=12)
30 ± 8.28
RRMI (n=13)
174.28 ± 10.02
Height (cm)
0.75
Healthy (n=12)
170.82 ± 8.67
RRMI (n=13)
69.82 ± 11.52
Mass (kg)
0.38
Healthy (n=12)_
68.34 ± 12.8
21
Table 2. Hip external rotation endurance times for the running-related musculoskeletal
injury (RRMI) and healthy groups (Mean±SD)
Sex
Group
Time (s)
RRMI (n=7)
88.96 ± 43.99
Female
Healthy (n=5)
112.24 ± 43.25
Total (n=12)
98.66 ± 43.35
RRMI (n=6)
69.97 ± 29.39
Injured
Male
Healthy (n=6)
86.59 ± 18.67
Total (n=12)
78.28 ± 25.03
RRMI (n=13)
80.2 ± 37.74
Total
Healthy (n=11)
98.25 ± 33.2
Total (n=24)
88.47 ± 36.15
RRMI (n=7)
75.07 ± 41.59
Female
Healthy (n=5)
93.49 ± 42.22
Total (n=12)
82.75 ± 41.01
RRMI (n=6)
58.07 ± 30.49
Non-Injured
Male
Healthy (n=6)
75.03 ± 12.92
Total (n=12)
66.55 ± 24.02
RRMI (n=13)
67.22 ± 36.47
Total
Healthy (n=11)
83.42 ± 29.82
Total (n=24)
74.65 ± 33.89
Female total=92.82 ± 42.51, n=25; Male total=72.41 ± 24.73, n=24
RRMI group total=73.71 ± 36.96, n=26; Healthy group=93.12 ± 32.87, n=23
22
Table 3. Hip abduction endurance times for the running-related musculoskeletal injury
(RRMI) and healthy groups (Mean±SD)
Sex
Female
Injured
Male
Total
Group
Time (s)
RRMI (n=4)
37.22 ± 8.46
Healthy (n=6)
Total (n=10)
RRMI (n=5)
Healthy (n=5)
Total (n=10)
RRMI (n=9)
Healthy (n=11)
Total (n=20)
48.54 ± 10.31
44.01 ± 10.82
47.03 ± 8.05
41.8 ± 8.46
44.42 ± 8.26
42.67 ± 9.27
45.48 ± 9.7
44.21 ± 9.37
RRMI (n=4)
39.64 ± 6.01
Female
Healthy (n=6)
42.13 ± 12.44
Total (n=10)
41.13 ± 9.99
RRMI (n=5)
44.47 ± 4.44
Non-Injured
Male
Healthy (n=5)
39.86 ± 9.16
Total (n=10)
42.17 ± 7.21
RRMI (n=9)
42.32 ± 5.47
Total
Healthy (n=11)
41.1 ± 10.6
Total (n=20)
41.65 ± 8.49
Female total=43.04 ± 9.99, n=22; Male total=44.37 ± 24.73, n=21
RRMI group total=44.11 ± 8.75, n=21; Healthy group=43.29 ± 10.17, n=22
23
Table 4. Lateral trunk flexion endurance times for the running-related musculoskeletal
injury (RRMI) and healthy groups (Mean±SD)
Sex
Group
Time (s)
RRMI (n=6)
58.71 ± 20.16
Female
Healthy (n=5)
72.06 ± 38.31
Total (n=11)
64.78 ± 28.97
RRMI (n=6)
93.75 ± 29.12
Injured
Male
Healthy (n=5)
77.7 ± 38.95
Total (n=11)
86.45 ± 33.18
RRMI (n=12)
76.23 ± 30.08
Total
Healthy (n=10)
74.88 ± 36.54
Total (n=22)
75.62 ± 32.36
RRMI (n=6)
45.32 ± 15.74
Healthy (n=5)
79.68 ± 11.02
Female
Total (n=11)
60.94 ± 22.24
RRMI (n=6)
74.7 ± 23.98
Male
Healthy (n=5)
90.92 ± 34.97
Non-Injured
Total (n=11)
82.07 ± 29.13
RRMI (n=12)
60.01 ± 24.69
Total
Healthy (n=10)
85.3 ± 25.15
Total (n=22)
71.51 ± 27.5
Female total=63.44 ± 24.85, n=23; Male total=87.37 ± 33.36, n=23
RRMI group total=68.45 ± 27.62, n=25; Healthy group=83.69 ± 34.42, n=21
24
Table 5. Trunk flexion endurance times for the running-related musculoskeletal injury
(RRMI) and healthy groups (Mean±SD)
Sex
Group
Time (s)
Female
Male
Total
RRMI (n=6)
Healthy (n=5)
Total (n=11)
RRMI (n=6)
Healthy (n=4)
Total (n=10)
RRMI (n=12)
Healthy (n=9)
Total (n=21)
219.77 ± 104.61
267.72 ± 84.25
241.57 ± 94.54
238.93 ± 34.19
174.87 ± 38.27
213.31 ± 47.24
229.35 ± 74.87
226.46 ± 80.58
228.11 ± 75.38
Table 6. Trunk extension endurance times for the running-related musculoskeletal injury
(RRMI) and healthy groups (Mean±SD)
Sex
Group
Time (s)
RRMI (n=6)
157.53 ± 38.43
Female
Healthy (n=6)
182.14 ± 48.12
Total (n=12)
169.83 ± 43.46
RRMI (n=6)
124.59 ± 30.25
Male
Healthy (n=6)
144.63 ± 49.13
Total (n=12)
134.61 ± 40.28
RRMI (n=12)
141.06 ± 37.19
Total
Healthy (n=12)
163.38 ± 50.33
Total (n=24)
152.22 ± 44.76
25
Table 7. Hip external rotation (HER), hip abduction (HABD), and lateral trunk flexion (LTF)
endurance main effects and interactions information
Variable
Side Group
main main
effect effect
Sex
main
effect
Side x sex
interaction
F1,20
2.4
2.92
3.30
HER
p
0.14
0.10
0.08
Power 0.31
0.37
0.41
F1,16
0.90
1.05
1.24
HABD
p
0.36
0.32
0.28
Power 0.13
0.06
0.07
F1,18
0.35
1.22
3.52
p
0.56
0.28
0.08
LTF
Power 0.09
0.18
0.43
A-priori level ≤ 0.05.
Asterisk (*) denotes statistical significance.
0.06
0.80
0.06
0
0.99
0.05
0
0.99
0.05
Side x
Group x
Side x sex
group
sex
x group
interaction interaction interaction
0.02
0.90
0.05
0.67
0.43
0.12
7.47
0.01*
0.73
0.03
0.86
0.05
4.27
0.05*
0.41
1.20
0.29
0.18
0.02
0.89
0.05
0.89
0.36
0.14
0.33
0.57
0.09
Table 8. Trunk flexion (TFX) and trunk extension (TEX) endurance main effects and
interactions information
Group
Sex main
Group x sex
Variables
main
effect
interaction
effect
F
0.6
1.26
2.92
TFX
p
0.81
0.28
0.11
Power
0.06
0.19
0.36
F
1.68
4.18
0.02
TEX
p
0.21
0.05*
0.9
Power
0.24
0.5
0.05
A-priori level ≤ 0.05.
Asterisk (*) denotes statistical significance.
26
Chapter 5
Discussion
The primary purpose of this study was to examine differences in core muscular
endurance between runners with a previous history of a RRMI and healthy controls.
While previous investigators have targeted muscular strength among injured and healthy
runners, to our knowledge this is the first study to analyze core muscular endurance in
this population. There were important findings from this study indicating isolated core
muscle endurance differences in runners with and without a history of RRMI, as well
influences of sex on some of the measures of core and hip muscle endurance.
RRMI versus healthy association
For LTF, a greater endurance time was observed in the RRMI group on the
injured side compared to the non-injured side. This difference could be in part explained
by the kinematic alterations in running gait demonstrated by runners with PFP compared
to healthy runners. It is assumed that a healthy runner, during the stance phase of
running, demonstrates a stable, level pelvis from which the lower extremity moves. On
the other hand, runners with PFP may demonstrate pelvic drop of the contralateral, noninjured limb during the stance phase of running,25 which creates a shift in the center of
mass (COM) away from the injured/stance limb and the midline of the body. To
counteract the shift in COM and maintain balance, one must perform an ipsilateral trunk
lean. As running is a repetitive, long distance sport, this compensation mechanism of
activating the lateral trunk muscles to maintain pelvic obliquity occurs often. Therefore,
after weeks or months of running with an irregular gait pattern the endurance of the
lateral trunk flexor muscles, particularly in the injured side of a runner, could increase.
27
Further research is warranted into the direct relation between lateral trunk flexion
endurance and pelvic obliquity during running. In regards to this kinematic
compensation, with increased LTF endurance we would expect to also see decreased
HABD endurance because of the hip strength deficit that is the start of this faulty running
gait. However, no difference in HABD endurance was observed between groups. This
could be due to the contribution of other factors such as rehabilitation efforts, especially
those focused on increasing HABD and HER strength within the RRMI population. 6 of
the 13 runners in the RRMI group underwent rehabilitation to correct his or her RRMI. If
these 6 runners underwent a rehabilitation program incorporating hip strengthening
exercises, as suggested in the literature,4,19,23,31,40,103 then we could expect to see an
increase in HABD endurance as well as strength.
We hypothesized that we would find decreased hip endurance in the RRMI group,
similar to findings by researchers who reported hip strength deficits within a variety of
injury subgroups from the RRMI population. In particular, these researchers observed hip
abductor and hip external rotator weakness in runners with PFP and ITBFS compared to
healthy runners.19,23,26,31,40,103,104 As this was the first study to examine hip endurance
differences in runners there were no established protocols to follow for endurance testing
procedures. Therefore, testing procedures were selected from studies examining the
effects of fatigue within the lower extremity. Jacobs et al.102 isolated and fatigued the hip
abductor muscle group using 50% of maximum isometric HABD strength. This
procedure was found to have very high intrasession reliability for testing HABD
endurance (ICC=0.99). Unfortunately, as there was no established testing procedure for
HER endurance we used the HABD procedure, with altered testing position to isolate the
28
hip external rotators. Hence, further investigation into alternative testing procedures for
hip muscular endurance, for example utilizing a repetitive-movement endurance test
instead of an isometric endurance test, is warranted.
For both TFX and TEX there were no differences in endurance performance
between RRMI and healthy control groups. The TFX and TEX endurance tests utilized,
although reliable, did not identify differences between our injury groups.81,97 Since
running is a repetitive physical activity, perhaps the use of repetitive concentric tasks in
lieu of isometric fatigue tests would better identify differences in endurance between
groups. Investigation into the use of tests such as a repetitive curl-up or back extension to
fatigue to identify differences between injured and non-injured runners should be
considered in future studies.
Male versus female association
In general, males are stronger than females due largely in part to muscle mass
differences.19,100,104-106 Because of this, sex differences in muscle endurance could be
theorized to have the same effect; however, we observed the opposite result for HER and
TEX with female runners exhibiting greater HER (+20.03 seconds) and TEX (+35.22
seconds) endurance times compared to male runners. The primary muscle contributor to
hip external rotation and extension is the gluteus maximus. A possible explanation for
these findings could be the differences in upper body mass distribution, with females
generally having more body mass distributed anteriorly on their upper body. Although
not their primary focus of the study, Ford et al. found that females run with an anterior
trunk lean when compared to males.107 Owing to the fact that females must constantly
account for additional anterior upper body mass, it is likely that the trunk and hip
29
extensors are constantly activated in order to compensate for the anterior load and to
maintain an upright body posture during standing, walking, and running. This constant
activation and training of the back and hip extensors may be the reason why females
displayed greater HER and TEX endurance compared to males. Additional investigation
is needed of the kinematic and muscle activation patterns of the hip and trunk during
running gait to explore these theories.
Injury group and sex interaction
Females of the RRMI had lower HABD endurance compared to the healthy
female runners. It has been previously demonstrated within several subgroups of injured
runners that injured, female runners have decreased HABD strength compared to their
healthy counterparts.19,23,26,31,40,103,104 Therefore, female runners that display either
decreased HABD endurance or strength may be unable to maintain a neutral pelvis
during running, increasing the risk for a RRMI as we have discussed above. Further
investigation into the correlation between HABD endurance and contralateral pelvic drop
during running is merited.
Interestingly, the present study found the opposite relation in males, where
healthy males displayed lower HABD endurance compared to RRMI males. A possible
explanation for this finding could be related to the rehabilitation compensation mentioned
earlier. Perhaps the RRMI males have greater HABD endurance due to the rehabilitation
efforts to increase HABD strength, since the literature provides clinicians with validation
as to why hip strengthening is warranted.4,19,23,31,40,103However, we did not collect data on
specific rehabilitation exercises completed by these runners and therefore, we cannot be
30
certain that rehabilitation played a role in our findings. Continued work is needed to
determine what factors that we did not record could be influencing HABD endurance.
In addition, similar to what this study found with HABD endurance, Nakagawa et
al.104 found no statistical differences in HABD strength between injured and non-injured
runners, when including both sexs. However, when taking sex into account, Nakagawa et
al.104 found that males exhibited greater eccentric HABD torque, validating the need to
analyze HABD and sex separately. For the present study, when analyzing HABD
endurance within each sex and between groups, HABD endurance was lower in the
injured females and greater in the healthy females, and the opposite relation was observed
between the male groups. When collapsing sexs and analyzing between groups, this could
mask any true differences between the groups. Therefore, future research that examines
HABD endurance should examine the male and female sexs separately.
Limitations
There were several limitations to our study design and methods. Due to a very
specific testing population, we were only able to test 25 volunteers, making the power of
our analyses very low for some comparisons. Also, during testing for LTF, 72% of
participants reported fatigue in the shoulder of the testing side before the lateral trunk;
therefore, our results may reflect fatigue in muscle groups other than our intended lateral
trunk flexor group. Furthermore, during the endurance tests additional recruitment of
surrounding musculature may have occurred, although specific instructions were given
prior to testing. For example, the gastrocnemius and hamstring muscles were visibly
active and confirmed by participants to be contracting while testing HER endurance.
Because we used a subjective analysis of fatigue and did not include electromyography
31
(EMG) during the endurance testing we cannot state for sure the participants reached a
fatigued state. Lastly, the procedures we used were isolated, open kinetic chain endurance
tests, which may not be applicable for running. Therefore, future studies should consider
what other endurance tests might translate into better insight in to running-related
musculoskeletal injury development.
Conclusion and Clinical Relevance
This study represents the first study to investigate the influence of injury and sex
on core and hip muscle endurance differences in runners. The results highlight some of
the differences that exist in these populations, but there is a clear need for additional
investigation to fully realize the role that endurance of these muscle groups plays in
running mechanics and injury development. The information from this study may provide
clinicians with evidence that endurance, in addition to strength, need to be the focus of
rehabilitation for runners with RRMIs. All of these observations may provide insight for
further research on rehabilitation regimens for targeted core muscular endurance with the
goal of reducing injury rates and improvement of patient outcomes in the RRMI
population.
32
References
1.
Bredeweg S, Zijlstra S, Buist I. The GRONORUN 2 study: effectiveness of a
preconditioning program on preventing running related injuries in novie runners. The
design of a randomized controlled trial. Bmc Musculoskeletal Disorders. 2010;11:2-8.
2.
Buist I, Bredeweg S, Bessem B, van Mechelen W, Lemmink K, Diercks R. Incidence and
risk factors of running-related injuries during preparation for a 4-mile recreational
running event. British Journal of Sports Medicine. 2008;44(598-604).
3.
Door C, Tonoli E, Cumps I, Aerts E, Verhagen R. Incidence, risk factors and prevention
of running related injuries in long-distance running: a systematic review. Sport and
Geneeskunde. 2010;5:12-18.
4.
Fields K, Sykes J, Walker K, JC J. Prevention of running injuries. Current Sports
Medicine Rep. 2010;9(3):176-182.
5.
Paluska S. An overview of hip injuries in running. Journal of Sports Medicine.
2005;35(11):991-1014.
6.
Ryan M, MacLean C, Taunton J. A review of anthropometric, biomechanical,
neuromuscular and training related factors associated with injury in runners.
International Sportmed Journal. 2006;7(2):120-137.
7.
Taunton J, Ryan M, Clement D, McKenzie D, Lloyd-Smith D, Zumbo B. A retrospective
case-control analysis of 2002 running injuries. British Journal of Sports Medicine.
2002;36(95-101).
8.
Wen D. Risk factors for overuse injuries in runners. Current Sports Medicine Reports.
2007;6:307-313.
33
9.
Willson JD, Kernozek TW, Arndt RL, Reznichek DA, Straker JS. Gluteal muscle
activation during running in females with and without patellofemoral pain syndrome.
Clinical Biomechanics. Aug 2011;26(7):735-740.
10.
Devereaux M, Lachmann S. Patello-femoral arthralgia in athletes attending a sports
injury clinic. British Journal of Sports Medicine. 1984;18:18-21.
11.
Fredericson M, Misra A. Epidemiology and aetiology of marathon running injuries.
Journal of Sports Medicine. 2007;37(4-5):437-439.
12.
Fulkerson J. Diagnosis and treatment of patients with patellofemoral pain. The American
Journal of Sports Medicine. 2002;30(3q):447-456.
13.
Rauh M, Koepsell T, Rivara F, Margherita A, Rice S. Epidemiology of musculoskeletal
injuries among high school cross-country runners. American Journal of Epidemiology.
2005;163(2):151-159.
14.
Ristolainen L, Heinonen A, Turunen H, et al. Type of sport is related to injury profile: a
study on cross country skiers, swimmers, long-distance runners, and soccer players. a
retrospective 12-month study. Scandinavian Journal of Medicine and Science in Sports.
2009;20:384-393.
15.
Daoud A, Geissler G, Wang F, Saretsky J, Daoud Y, Lieberman D. Foot strike and injury
rates in endurance runners: a retrospective study. Medicine and Science in Sports and
Exercise. 2012:1325-1334.
16.
Hreljac A. Impact and overuse injuries in runners. Medicine and Science in Sports and
Exercise. 2004;36(5):845-849.
17.
Hreljac A, Ferber R. A biomechanical perspective of predicting injury risk in running.
International Sportmed Journal. 2006;7(2):98-108.
18.
Bates B, Osternig L, Mason B, James L. Foot orthotic devices to modify selected aspects
of lower extremity mechanics. Am. J. Sports Med. 1979;7(6):338-342.
34
19.
Bolgla L, Malone T, Umberger B, Uhl T. Comparison of hip and knee strength and
neuromuscular activity in subjects with and without patellofemoral pain syndrome. The
International Journal of Sports Physical Therapy. 2011;6(4):285-296.
20.
Buchbinder M, Napora N, Biggs E. The relationship of abnormal pronation to
chondromalacia of the patella in distance runners. The Journal of the American Podiatry
Association. 1979;69(2):159-162.
21.
Noehren B, Pohl MB, Sanchez Z, Cunningham T, Lattermann C. Proximal and distal
kinematics in female runners with patellofemoral pain. Clinical Biomechanics. May
2012;27(4):366-371.
22.
Souza R, Powers C. Differences in hip kinematics, muscle strength, muscle activation
between subjects with and without patellofemoral pain. Journal of Orthopaedic & Sports
Physical Therapy. 2009;39:12-19.
23.
Cichanowski HR, Schmitt JS, Johnson RJ, Niemuth PE. Hip strength in collegiate female
athletes with patellofemoral pain. Medicine and Science in Sports and Exercise. Aug
2007;39(8):1227-1232.
24.
Ireland M, Willson JD, Ballantyne B, Davis I. Hip strength in females with and without
patellofemoral pain. Journal of Orthopaedic & Sports Physical Therapy.
2003;33(11):671-676.
25.
Powers C. The influence of altered lower-extremity kinematics on patellofemoral joint
dysfunction: a theoretical perspective. Journal of Orthopaedic & Sports Physical
Therapy. 2003;33(11):639-646.
26.
Khaund R, Flynn S. Iliotibial band syndrome: a common source of knee pain. American
Academy of Family Physicians. 2005;71(8):1545-1550.
27.
Noble C. The treatment of iliotibial band friction syndrome. British Journal of Sports
Medicine. 1979;13:51-54.
35
28.
Norris C. Pain in the lateral hip and ITB: diagnoses and rehabilitation. SportEX
Dynamics. 2012;34(October):15-23.
29.
Racioppi E, Gulick D. Iliotibial band friction syndrom. Athletic Therapy Today.
1999;4(5):9-10.
30.
Vo A. Diagnosis and rehabilitation for the knee pain syndromes. Physical Medicine and
Rehabilitation. 2002;16(3):459-485.
31.
Fredericson M, Cookingham. Hip abductor weakness in distance runners with iliotibial
band syndrome. Clinical Journal of Sport Medicine. 2000;10(3):169-175.
32.
Bennell K, Matheson G, Meeuwisse W, Brukner P. Risk factors for stress fractures.
Journal of Sports Medicine. 1999;2:91-122.
33.
Friberg O. Leg length asymmetry in stress fractures: a clinical and radiological study.
Journal of Sports Medicine. 1982;22:485-488.
34.
Bennell K, Malcolm S, Thomas S. Risk factors for stress fractures in track and field
athletes: a 12 month prospective study. Am. J. Sports Med. 1996;24(810-818).
35.
Beck B, Osternig L. Medial tibial stress syndrome. The journal of Bone and Joint
Surgery, Incorporated. 1994;76A(7):1057-1061.
36.
Couture C, Karlson K. Tibial stress injuries-decisive diagnosis and treatment of 'shin
splints'. Physician and sportsmedicine. 2002;30(6):29-36.
37.
Cuff S, Loud K, O'Riordan M. Overuse injuries in high school athletes. Clinical
Pediatrics. 2010;49(8):731-736.
38.
Macera C, Pate R, Powell K, Jackson K, Kendrick J, Craven T. Predicting lowerextremity injuries among habitual runners. Archives of Internal Medicine.
1989;149(11):2565-2568.
39.
Mahieu N, Witvrouw E, Stevens V, Van Tiggelen D, Roget P. Intrinsic risk factors for
the development of Achilles tendon overuse injury. The American Journal of Sports
Medicine. 2006;34(2):226-235.
36
40.
Niemuth P, Johnson RJ, Myers M, Thieman T. Hip muscle weakness and overuse injuries
in recreational runners. Clinical Journal of Sport Medicine. 2005;15(1):14-21.
41.
van Gent R, Siem D, van Middelkoop M, van Os A, Bierma-Zeinstra SMA, Koes B.
Incidence and determinants of lower extremity running injuries in long distance runners:
a systematic review. British Journal of Sports Medicine. 2007;41(469-480).
42.
Bovens A, Janssen G, Vermeer H, Hoeberigs J, Janssen M. Occurrence of running
injuries in adults following a supervised training program. International Journal of Sports
Medicine. 1989;10(3):186-190.
43.
Catelli D, Kuriki H, Polito L, Azevedo F, Negrao Filho R, Alves N. Patellofemoral pain
syndrome: electromyography in a frequency domain analysis. Journal of Physics.
2011;313:1-6.
44.
Thijs Y, Pattyn E, Van Tiggelen D, Rombaut L, Witvrouw E. Is hip muscle weakness a
predisposing factor for patellofemoral pain in female novice runners? Am. J. Sports Med.
2011;39(9):1877-1882.
45.
Azevedo L, Lambert M, Vaughan C, O'Connor C, Schwellnus M. Biomechanical
variables associated with Achilles tendinopathy in runners. British Journal of Sports
Medicine. 2008;43:288-292.
46.
Craig D. Medial tibial stress syndrome: current etiological theories part 1-background.
Athletic Therapy Today. 2008;13(1):17-20.
47.
Craig D. Medial tibial stress syndrome: evidence-based prevention. Journal of Athletic
Training. 2008;43(3):316-318.
48.
Grau S, Krauss I, Maiwald C, Axmann D, Horstmann T, Best R. Kinematic classification
of iliotibial band syndrome in runners. Scandinavian Journal of Medicine and Science in
Sports. 2011;21:184-189.
49.
Jariwala A, Bruce D, Jain A. A guide to the recognition and treatment of plantar fasciitis.
Primary Health Care. 2011;21(7):22-24.
37
50.
Kvist M. Achilles-tendon injuries in athletes. Sports Medicine. 1994;18(3):173-201.
51.
Marti B, Vader J, Minder C, Abelin T. On the epidemiology of running injuries. The
American Journal of Sports Medicine. 1984;16(3):285-294.
52.
McCrory J, Martin D, Lowery R, Cannon D, al e. Etiologic factors associated with
achilles tendinitis in runners. Medicine and Science in Sports and Exercise.
1999;31(10):1374-1381.
53.
Moen M, Tol J, Weir A, Steunebrink M, De Winter T. Medial tibial stress syndrome- a
critical review. Journal of Sports Medicine. 2009;39(7):523-546.
54.
Roxas M. Plantar fasciitis: diagnosis and therapeutic considerations. Alternative Medicine
Review. 2005;10(2):83-93.
55.
Wearing S, Smeathers J, Urry S, Hennig E, Hills A. The pathomechanics of plantar
fasciitis. Journal of Sports Medicine. 2006;36(7):586-611.
56.
Young C. Plantar fasciitis. Annals of Internal Medicine. 2012:1-14.
57.
Clansey A, Hanlon M, Wallace E, Lake M. Effects of fatigue on running mechanics
associated with tibial stress fracture risk. Medicine and Science in Sports and Exercise.
2012;44(10):1917-1923.
58.
Milner C, Ferber R, Pollard C, Hamill J, Davis I. Biomehcnical factors assicated with
tibial stress fracture in female runners. Medicine and Science in Sports and Exercise.
2006;38(2):323-328.
59.
Lopes A, Barreto H, Neto J, Grangeiro J. A survey of participation in competitive sports
despite musculoskeletal complaints: a cross-sectional study. International Sportmed
Journal. 2012;13(2):43-47.
60.
Lysholm J, Wiklander J. Injuries in runners. Am. J. Sports Med. 1987;15(2):168-171.
61.
JP F. Diagnosis and treatment of patients with patellofemoral pain. The American Journal
of Sports Medicine. 2002;30(3):447-456.
38
62.
Willson JD, Binder-Macleod S, Davis I. Lower extremity jumping mechanics of female
athletes with and without patellofemoral pain before and after exertion. Am. J. Sports
Med. 2008;36(8):1587-1596.
63.
Barton CJ, Levinger P, Crossley KM, Webster KE, Menz HB. The relationship between
rearfoot, tibial and hip kinematics in individuals with patellofemoral pain syndrome.
Clinical Biomechanics. Aug 2012;27(7):702-705.
64.
Bergmark A. Stability of the lumbar spine: a study in mechanical engineering. Acta
Orthopaedica Scandinavica Supplementum. 1989.
65.
Kibler W, Press J, Sciascia A. The role of core stability in athletic function. Sports
Medicine. 2006;36(3):189-198.
66.
Leetun D, Ireland M, Willson JD, Ballantyne B, Davis I. Core stability measures as risk
factors for lower extremity injury in athletes. Medicine and Science in Sports and
Exercise. 2004;36(6):926-934.
67.
Bauer J, Duke L. Examining biomechanical and anthropometrical factors as contributors
to iliotibial band friction syndrome. Sport Science Review. 2011;20(1-2):39-53.
68.
Fairclough J, Hayashi K, Toumi H, et al. The functional anatomy of the iliotibial band
during flexion and extension of the knee: implications for understanding iliotibial band
syndrome. Journal of Anatomy. 2006;208:309-316.
69.
Kline C. The surprising iliotibial band. Journal of the American Chiropractic
Association. 2011:1-6.
70.
Noehren B, Davis I, Hamill J. Prospective study of the biomechanical factors associated
with iliotibial band syndrome. Clinical Biomechanics. 2007;22:951-956.
71.
Harrast M, Colonno D. Stress fractures in runners. Clinics in Sports Medicine.
2010;29:399-416.
72.
Fitch K. Stress fractures of the lower limbs in runners. Australian Family Physician.
1984;13(7):511-515.
39
73.
Hulkko A, Alen M, Orava S. Stress fractures of the lower leg. Scandinavian Journal of
Sports Sciences. 1987;9(1):1-8.
74.
Bennell K, Brukner P. Epidemiology and site specificity of stress fractures. Clinics in
Sports Medicine. 1997;26(2):179-196.
75.
Pohl M, Mullineaux D, Milner C, Hamill J, Davis I. Biomechanical predictors of
retrospective tibial stress fractures in runners. Journal of Biomechanics. 2008;41:11601165.
76.
Clement D. Tibial stress syndrome in athletes. The Journal of Sports Medicine.
1974;2(2):81-85.
77.
Johnell O, Rausing A, Wendeberg B, Westlin N. Morphological bone changes in shin
splints. Clinical Orthopaedics and Related Research. 1982(167):180-184.
78.
Moen M, Bongers T, Bakker E, et al. Risk factors and prognostic indicators for medial
tibial stress syndrome. Scandinavian Journal of Medicine and Science in Sports.
2012;22:34-39.
79.
Michael R, Holder L. The soleus syndrome a cause of medial tibial stress (shin splints).
The American Journal of Sports Medicine. 1985;13(2):87-94.
80.
Dierks T, Manal K, Hamill J, Davis I. Proximal and distal influences on hip and knee
kinematics in runners with patellofemoral pain during a prolonged run. The Journal of
Orthopaedic and Sports Physical Therapy. 2008;38(8):448-456.
81.
Biering-Sorensen F. Physical measurements as risk indicators for low-back trouble over a
one-year period. Spine. 1984;9(2):106-119.
82.
Evans K, Refshauge K, Adams R, Aliprandi L. Predictors of low back pain in young elite
golfers: a preliminary study. Physical Therapy in Sport. 2005:122-130.
83.
Luoto S, Heliovaara M, Hurri H, Alaranta H. Static back endurance and the risk of lowback pain. Clinical Biomechanics. 1995;10(6):323-324.
40
84.
Nadler S, Malanga G, Feinberg J, Prybicien M, Stitik T, DePrince M. Relationship
between hip muscle imbalance and occurrence of lowe back pain in collegiate athletes.
American Journal of Physical Medicine and Rehabilitation. 2001;80:572-577.
85.
Kannus P. Etiology and pathophysiology of chronic tendon disorders in sports.
Scandinavian Journal of Medicine and Science in Sports. 1997;7(2):78-85.
86.
Carlsson A. Assessment of chronic pain. I. Aspects of the reliability and validity of the
visual analogue scale. Pain. 1983;16:87-101.
87.
Bijur PE, Silver W, Gallagher EJ. Reliability of the visual analog scale for measurement
of acute pain. Acad. Emerg. Med. Dec 2001;8(12):1153-1157.
88.
Lingjaerde O, Foreland A. Direct assessment of improvement in winter depression with a
visual analogue scale: high reliability and validity. Psychiatry Reserach. 1998;81(3):387392.
89.
Scott J, Huskisson EC. Graphic representation of pain. Pain. 1976;2(2):175-184.
90.
Sriwatanakul K, Kelvie W, Lasagna L, Calimlim J, Weis O, Mehta G. Studies with
different types of visual analog scales for measurement of pain. Clinical
Pharmacological Therapy. 1983;34(2):234-239.
91.
Couper MP, Tourangeau R, Conrad FG, Singer E. Evaluating the effectiveness of visual
analog scales - A web experiment. Soc. Sci. Comput. Rev. Sum 2006;24(2):227-245.
92.
Boonstra A, Schiphorst Preuper H, Reneman M, Posthumus J, Stewart R. Reliability and
validity of the visual analogue scale for disability in patients with chronic
musculoskeletal pain. International Journal of Rehabilitation Research. 2008;31(2):165169.
93.
Solomonow M, Zhou B, Harris M, Lu Y, Baratta R. The ligamento-muscular stabilizing
system of the spine. Spine. 1998;23(23):2552-2562.
94.
Chuter V, Janse de Jonge X. Proximal and distal contributions to lower extremity injury:
a review of the literature. Gait and Posture. 2012;36:7-15.
41
95.
Kibler W, Press J, Sciascia A. The role of core stability in athletic function. Journal of
Sports Medicine. 2006;36(3):189-198.
96.
Willson J, Dougherty C, Ireland M, Davis I. Core stability and its relationship to lower
extremity function and injury. Journal of the American Academy of Orthopaedic
Surgeons. 2005;13:316-325.
97.
McGill S, Childs A, Liebenson C. Endurance times for low back stabilization exercises:
clinical targets for testing and training from a normal database. Archive of Physical
Medicine and Rehabilitation. 1999;80:941-944.
98.
Reiman MP, Krier A, Nelson J, Rogers M, Stuke Z, Smith B. Reliability of alternative
trunk endurance testing procedures using clinician stabilization vs. traditional methods.
Journal of Strength and Conditioning Research. 2010;24(3):730-736.
99.
Ito T, Shirado O, Suzuki H, Takahashi M, Kaneda K, Strax T. Lumbar trunk muscle
endurance testing: an inexpensive alternative to a machine for evaluation. Archive of
Physical Medicine and Rehabilitation. 1996;77:75-79.
100.
Lanning C, Uhl T, Ingram C, Mattacola C, English T, Newsom S. Baseline values of
trunk endurance and hip strength in collegiate athletes. Journal of Athletic Training.
2006;41(4):427-434.
101.
Wilkerson G, Giles J, Seibel D. Prediction of core and lower extremity strains and sprains
in collegiate football players: a preliminary study. Journal of Athletic Training.
2012;47(3):264-272.
102.
Jacobs C, Uhl T, Mattacola C, Shapiro R, Rayens W. Hip abductor function and lower
extremity landing kinematics: sex differences. Journal of Athletic Training.
2007;42(1):76-83.
103.
Boling MC, Padua DA, Creighton RA. Concentric and eccentric torque of the hip
musculature in individuals with and without patellofemoral pain. Journal of Athletic
Training. 2009;44(1):7-13.
42
104.
Nakagawa TH, Moriya ETU, Maciel CD, Serrao FV. Trunk, pelvis, hip, and knee
kinematics, hip strength, and gluteal muscle activation during a single-leg squat in males
and females with and without patellofemoral pain syndrome. Journal of Orthopaedic &
Sports Physical Therapy. 2012;42(6):491-501.
105.
Lindle R, Metter E, Lynch N, et al. Age and gender comparisons of muscle strength in
654 women and men aged 20-93 yr. Journal of Applied Physiology. 1997;83(5):15811587.
106.
Clark B, Manini, Thé D, Doldo N, Ploutz-Snyder L. Gender differences in skeletal
muscle fatiguability are related to contraction type and EMG spectral compression.
Journal of Applied Physiology. 2003;94:2263-2272.
107.
Ford K, Taylor-Haas J, Genthe K, Hugentobler J. Relationship between hip strength and
trunk motion in college cross-country runners. Medicine and Science in Sports and
Exercise. 2013;45(6):1125-1130.
43
Appendix A
Endurance Testing Positions
Figure 1. HABD testing position
Figure 2. HER testing position
44
Figure 3. TFX starting and testing positions
Starting position:
Testing position:
45
Figure 4. TEX testing position
Figure 5. LTF testing position
46