Original Article
                                                                              DOI: 10.22374/1875-6859.14.3.5

Walaa S. Mohammad1 and Walaa M. Elsais2
 Department of Biomechanics, Faculty of Physical Therapy, Cairo University, Giza, Egypt,
 School of Health Sciences, PhD candidate, Salford University, UK.

Corresponding Author: walaa.sayed@pt.cu.edu.eg

Submitted: April 14, 2018. Accepted: June, 2018. Published: June 18, 2018.

Background and Objective
The muscle imbalance between abdominal and hip adductor muscles as an etiology for osteitis pubis is not
well understood. The concept of a relationship between eccentric/concentric ratios at the pelvis and osteitis
pubis in athletes is limited. This study aimed to compare the eccentric/concentric ratios for abdominal/
adductor, abdominal/back, and hip adductor muscles as well as eccentric abdominal/eccentric adductor
muscles in soccer players suffering from osteitis pubis with those in healthy athletes.
Material and Methods
Twenty male soccer athletes with osteitis pubis were recruited to participate and 20 healthy male soccer
athletes were recruited to participate. Peak torque/body weight (PT/BW) for the hip adductor, abdominal,
and back muscles during isokinetic concentric and eccentric contraction modes at a speed of 180°/s was
recorded for healthy players and soccer athletes with osteitis pubis. Eccentric/concentric ratios for the
abdominal/adductor, abdominal/back, and hip adductor muscles and the eccentric abdominal/eccentric
adductor muscles were measured for both groups.
There was a significant decrease in the eccentric abdominal/concentric hip adductor muscles ratio
(p = 0.000) and in the eccentric/concentric hip adductor muscles ratio (p = 0.016) between the osteitis pubis
group and the healthy control group.
Soccer players with osteitis pubis present with strength imbalance. The osteitis pubis group displayed ec-
centric weakness of the abdominal and adductor muscles, resulting in imbalances in the normal eccentric

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Abdominal/Adductor Strength Imbalance in Soccer Players with Osteitis Pubis

abdominal/concentric adductor and eccentric/concentric adductor ratios. Therefore, exercises that increase
the eccentric strength of abdominal and hip adductor muscles may be beneficial to include in rehabilitation
programs of patients with osteitis pubis.

    Osteitis pubis (OP) refers to a painful, inflamma-      have a central point of attachment – the “pivot point”
tory, non-infectious condition of the symphysis pubis       – on the symphysis pubis. However, these muscles
and surrounding structures.1 OP may present as acute        act antagonistically toward each other during kicking
abdominal, pelvic, or groin pain.2 The natural history      activity, predisposing the pubic symphysis to opposing
of OP is one of progressive deterioration with con-         forces.11 Muscle imbalance across the pubic symphysis
tinued activity, requiring a prolonged rehabilitation       occurs because of eccentric loading and overloading
period and time away from the sport.3 In addition, OP       from abdominal muscle pulling superiorly and hip
is one of the most common causes for groin pain in          adductor muscles pulling inferiorly. When an athlete
athletes.4 The initial presentation of OP often includes    kicks, the kicking limb is hyperextended at the hip
the insidious onset of hip adductor pain and abdominal      while the trunk is rotated laterally in the opposite
discomfort, along with pain in the pubic symphysis.5,6      direction.2,11 To estimate the balance or imbalance
    In soccer, the incidence of groin pain has been         of muscle forces acting on a joint, the torque ratios
demonstrated to be as high as 5–13%.7 OP is a potential     of muscles around the joint must be determined. The
cause of groin pain that can lead to missed playing         appropriate ratio is important for reducing the risk
time during training and competition for the soccer         of athletic injuries. If unbalanced forces exist, the
athlete and can potentially be a career-ending condi-       weaker group of muscles may be subjected to abnormal
tion.6,8 Playing soccer involves sprinting, twisting,       mechanical stress.12
turning, cutting, and kicking; the pathomechanics               Eccentric muscle contraction plays a significant role
of these activities produce forces leading to severe        in the activities of daily living and athletic exercise,
biomechanical strain on the symphysis pubis and             such as when the body is decelerating during walking,
its associated supporting structures.2,9 In OP, a mi-       running and lifting.13 Dvir, Keating 14 have suggested
crotear may occur at the pubic attachment of the            that the eccentric strength of the trunk extensors was
adductor longus. This tear is frequently a primary          higher than the concentric strength at the same an-
event, followed by the development of osteitis. The         gular velocity by a factor of 11–60%. Moreover, the
induced muscular instability, laxity, and impaction         importance of eccentric strength testing is derived
of surfaces at the symphysis may also produce OP.           from the fact that the eccentric deficiency may be
Why a microtear at the adductor attachment occurs           different from its concentric counterparts and hence
so frequently in soccer players is unclear. The small       may constitute an additional risk factor.
adductor attachment may increase the susceptibility             The pathogenesis of OP remains obscure; previous
of the adductor longus muscle to strain/overuse, and        studies1,15,16 were restricted to specific issues, such
a microtear might occur as a consequence of tendon          as demonstrating the clinical picture of patients and
stretching and applied traction due to twisting and         the radiographic findings of the symphysis pubis in
turning or, more likely, secondary to both.9                OP. Other studies5,7 the effects of specific treatment
    The most likely mechanism of OP development is          protocols on OP recovery, and one study17 found hip
repetitive stress from increased shearing forces on the     muscle imbalances in athletes with OP during con-
pubic symphysis or from increased stress placed on the      centric contraction. There is a paucity of literature on
joint from traction exerted by the pelvic musculature,      isokinetic evaluation of the abdominal and adductor
especially in the presence of muscle imbalance.10           muscles ratios in athletes with OP. Therefore, the pur-
Muscle imbalance between the abdominal muscles              pose of our study was to determine and compare the
and hip adductors has been suggested as an etiologic        eccentric/concentric (E/C) ratios for the abdominal/
factor in OP. The abdominal and adductor muscles            adductor, abdominal/back, and hip adductor muscles

                                       J Mens Health Vol 14(3):e33-e40; June 18, 2018
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Abdominal/Adductor Strength Imbalance in Soccer Players with Osteitis Pubis

and for the eccentric abdominal/eccentric adductor            performed for 10 min (10 seconds hold stretch/10
muscles in soccer players suffering from OP with              seconds relax). The muscle groups (trunk and hip
those in healthy soccer players.                              muscles) for all subjects were tested in a randomized
                     METHODS                                  order to prevent a dependent ordering effect. Rest
                                                              periods of 5 min were provided between each muscle
Participants                                                  group test. Throughout testing, the participants were
    Twenty male soccer athletes suffering from OP were        verbally encouraged to perform maximal contractions
recruited to participate as volunteers in this study. A       through their range of motion (ROM).
sports medicine specialist and a team of orthopedic               For hip adductor muscle testing, the involved
surgeons, who referred the OP patients to our isokinetic      (affected) side of the OP group was tested; such
lab, conducted the clinical examinations. The criterion       as in the injured athletes, the kicking side was that
for diagnosing OP was that the athlete complained of          with unilateral inguinal and adductor pain, whereas
pain combined with tenderness over the symphysis              the dominant limb was tested in the healthy athlete
area that radiated inferiorly (adductors area) and/or         (control) group. Leg dominance was demonstrated
superiorly (lower abdominal area). The diagnosis was          according to the preferred kicking leg. Testing was
confirmed by magnetic resonance imaging (MRI).                performed with the participants in the standing posi-
Another group of 20 healthy (control) male soccer             tion, which is the most functional position despite
athletes were matched with the OP patient group ac-           being associated with less stabilization. To allow hip
cording to age, body weight, body height, and years           movement tests to be performed from the standing
of playing (both groups were collected from youth and         position, the hip attachment was inserted into the
first teams). They had no history of lower extremity          knee adaptor and secured to the dynamometer. The
surgery or trauma to the back or hip. The uninjured           participants performed isokinetic concentric and ec-
athletes and the athletes with OP were right-leg domi-        centric hip adduction at an angular velocity of 180°/s,
nant. The number of subjects was determined a priori          as previously recommended in the literature.18 During
based on statistical power analysis to ensure type I          hip abduction and adduction, the player was placed
error did not exceed 0.05 and type II error did not           in the standing position facing away from the dyna-
exceed 0.20. This analysis indicated that 36 subjects         mometer, with the axis of the dynamometer aligned
were required to find a power of 96% and level of             with the anterior superior iliac spine. The ROM for
significance of 95%. Table 1 presents the demographic         hip abduction/adduction was 65° (recorded from 20°
data of the participants in this study. Prior to undergo-     adduction to 45° abduction).
ing actual measurements, the participants received an             For trunk muscle testing, each subject was allowed
explanation of the study procedures and provided their        to sit on the adjustable seat of the Biodex isokinetic
written informed consent. This study was approved             dynamometer system. This sitting position was pre-
by the university’s institutional review board.               ferred, as the lower extremity muscles could influence
                                                              trunk muscle strength.19,20 The subjects were secured
                                                              in place using the available straps to prevent unwanted
   A Biodex 3 Multi-Joint Testing and Rehabilitation          motion. Two curved anterior leg pads were positioned
System (Biodex Medical Systems, Shirley, NY, USA)             to adjust the knee block position. In addition, a lumbar
was used. Torque values were gravity adjusted. Cali-          support pad was positioned against the lower spine.
bration of the Biodex dynamometer was automatically           The pelvis was stabilized to minimize contributions
performed at the beginning of each session.                   from the hip muscles and to prevent as much motion
Procedures                                                    from the pelvis as possible, allowing for lumbar mo-
   Participants executed a 10-minute warm-up proce-           tion only. Both thighs were stabilized by two straps,
dure prior to entering the laboratory and undergoing          and the feet were held in a dorsiflexed position above
hip and trunk strength measures. The warm-up pro-             the foot support of the dynamometer chair. The axis
cedure consisted of stretching exercises, which were          of the dynamometer was aligned at the intersection of

                                       J Mens Health Vol 14(3):e33-e40; June 18, 2018
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Abdominal/Adductor Strength Imbalance in Soccer Players with Osteitis Pubis

the mid-axillary line and the L5/S1 disc space in the         Statistical Analysis
vertebral column. The dynamometer’s ROM during                    Data were analyzed using SPSS (version 20.0 for
trunk flexion/extension was 80° (20° hyperextension           Windows; SPSS Inc., Chicago, IL, USA). A two-way
to 60° flexion).21–23 Participants performed isokinetic       multivariate analysis of variance (MANOVA) was
concentric and eccentric trunk flexion and extension          conducted for the abdominal/adductor, abdominal/
at a speed of 180°/s.24,25                                    back, and hip adductor muscle E/C ratios and for
    The subjects were instructed to perform three to          the eccentric abdominal/eccentric adductor muscle
four submaximal contractions through the predeter-            ratios to compare the groups. In case the F ratio was
mined ROM to familiarize them with the dynamometer            significant, the differences between peak torque/body
before the actual test. Maximum voluntary efforts             weight (PT/BW) were examined using Tukey’s test.
were recorded when the subjects were instructed to            The level of significance was set at p < 0.05 for all
perform trunk flexion and extension in both concen-           statistical tests.
tric and eccentric modes for a total of 5 repetitions/                              RESULTS
set, and 2 sets were performed. All the subjects were
encouraged to exert maximum effort during the tests.              For this study, 30 male soccer athletes suffering
In the same manner, maximum voluntary efforts were            from OP were identified as potential participants
recorded from the hip adductor muscles when the               (Figure 1), 7 athletes from screened participants were
subjects performed two sets of adductions at the same         excluded because they failed to fulfill the inclusion
angular velocity and in the same contraction mode.            criteria and three athletes refused to participate in the
    The highest value of the five repetitions in one set      study. Thus, 20 athletes with OP were included in the
was recorded, and the mean value of the two sets was          study (Table 1).
used for statistical analysis. The outcome parameter              The values for PT and PT/BW for the hip adductor,
was the peak torque (PT; expressed in Nm), which              abdominal, and back muscles at 180°/s angular velocity
was normalized to each participant’s body weight              are shown in Table 2. MANOVA was conducted for
(expressed in Nm/kg) in an effort to reduce inter-            the hip adductor, abdominal and back muscle ratios of
subject variability in the raw scores of the quantitative     the healthy athlete and OP groups in both concentric
muscle tests.                                                 and eccentric modes.

FIG. 1 Study flowchart of the OP soccer players participants.

                                       J Mens Health Vol 14(3):e33-e40; June 18, 2018
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Abdominal/Adductor Strength Imbalance in Soccer Players with Osteitis Pubis

TABLE 1 Demographic Data for Healthy and Athletes with Osteitis Pubis Groups

                               Healthy athletes group                             Osteitis Pubis group
                                    Mean ± SD                                         Mean ± SD
 Age (years)                         20.78 ± 3.35                                     19.94 ± 3.51
 Height (cm)                        176.00 ± 4.15                                     176.16 ± 4.93
 Weight (kg)                         71.33 ± 7.35                                     70.91 ± 7.26
 Body mass
                                     22.92 ± 1.33                                     22.78 ± 1.07

TABLE 2 The Peak Torque (Nm) and the Peak Torque/Body Weight (Nm/kg) of Hip Adductors, Abdominal,
and Back Muscles of Healthy and Athletes with Osteitis Pubis Groups

                                                Healthy athletes                           Osteitis Pubis
         Test statistics
                                          PT                    PT/BW                 PT                  PT/BW
                                       Mean ± SD               Mean ± SD           Mean ± SD             Mean ± SD
 Abdominal (Eccentric)                73.04 ± 12.55             1.01 ± 0.11        45.77 ± 11.34         0.65 ± 0.15
 Back (Concentric)                   181.36 ± 23.19             2.26 ± 0.18       100.85 ± 23.90         1.44 ± 0.33

 Hip adductors (Concentric)           124.11 ± 7.24             1.79 ± 0.19        120.06 ± 5.44         1.74 ± 0.14

 Hip adductors (Eccentric)            89.94 ± 15.61             1.12 ± 0.16        57.68 ± 14.62         0.74 ± 0.11

PT = peak torque; PT/BW = peak torque/body weight; SD = standard deviation.

   There were no significant differences between the            OP and healthy soccer players. An angular velocity of
healthy and injured groups for the eccentric abdominal/         180°/s was chosen to imitate the muscular performance
concentric back and eccentric abdominal/eccentric hip           during high-speed sports-specific activities such as
adductor muscle ratios (p > 0.05). However, there were          sprinting, kicking, and cutting, which were reported
significant decreases in both the eccentric abdominal/          to be provocative.26
concentric hip adductor muscle ratio (p = 0.000) and               Historically, clinicians and researchers have used
the eccentric/concentric hip adductors muscle ratio             comparisons of the concentric strength values from
(p = 0.016) in the OP group, as shown in Table 3.               the same muscle groups in opposite extremities to
                     DISCUSSION                                 evaluate the differences in muscle activity between
                                                                normal athletes and OP.17 However, isokinetic as-
    Our study was conducted to compare the E/C ratios           sessment provides technological advances to improve
for the abdominal/adductor, abdominal/back, and hip             the evaluation of many sports problems by using
adductor muscles and the eccentric abdominal/ec-                the eccentric mode of contraction, given that many
centric adductor muscles between soccer players with            muscles work concentrically and eccentrically while

                                        J Mens Health Vol 14(3):e33-e40; June 18, 2018
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Abdominal/Adductor Strength Imbalance in Soccer Players with Osteitis Pubis

TABLE 3 The Hip Adductors, Abdominal, and Back Muscle Ratios of Healthy Athletes and Athletes with
Osteitis Pubis

                                                      Healthy athletes ratios   Osteitis Pubis ratios
                      Test statistics                                                                        p value
                                                            Mean ± SD                Mean ± SD

 Eccentric Abdominal/Concentric Back                        0.77 ± 0.19              0.83 ± 0.12             0.216
 Eccentric Abdominal/Eccentric Adductor                     1.04 ± 0.27              1.24 ± 0.39             0.311
 Eccentric Abdominal/Concentric Adductor                    0.61 ± 0.06              0.38 ± 0.09             0.000*
 Hip adductors Eccentric/Concentric                         0.64 ± 0.06              0.43 ± 0.08             0.016*

*Significant < 0.05

kicking. Consequently, any abnormalities in eccentric/           eccentric contraction, resulting in more stretch and
concentric ratios may reveal pathologies or identify             shear on the symphysis pubis.
athletes who may be at risk for injury.27                            The absolute PT values for the concentric strength
    The high eccentric abdominal/concentric back ratio           of the back muscles and the eccentric strength of the
in the OP group results from both back and abdominal             abdominal muscles for healthy athletes in the current
muscles imbalances, including concentric weakness                study were 181.36 and 73.04, respectively (see Table
of the back muscles and eccentric weakness of the ab-            2). These values were compared to those observed by
dominal muscles (see Table 2). Both imbalances result            Müller, Müller, Stoll, Fröhlich, Baur, Mayer 31, who
in non-significant differences in eccentric abdominal/           presented a nearly identical value for the PT of back
concentric back muscle ratios between healthy and                muscles in healthy adolescent athletes (187 Nm) but
OP athletes. In the same context, Mohammad, Ab-                  a different value for abdominal muscles (146 Nm).
delraouf, Abdel-aziem28 assessed the trunk muscles               This difference may be due to their use of a different
in healthy soccer players, compared them to soccer               angular velocity.
players with OP and found significant decreases in                   It has been suggested in the literature that OP in
concentric and eccentric contractions of the back and            soccer players is related to the repetitive stress on the
abdominal muscles, respectively. A possible expla-               abdominal and hip adductor muscles during kicking,32
nation they proposed for these observations was an               without clarification or substantiation of the phase of
increased anterior pelvic tilt produced by decreased             kicking or the type of contraction during which this
hip flexor length 29 and an increased PT/BW value                stress occurs. Our finding of a decreased eccentric
of the hip flexor muscles in OP.17 Conneely, Sullivan,           abdominal/concentric hip adductor ratio observed in
Edmondston 30 reported excessive extension of the                OP athletes compared to healthy athletes may have
lumbar spine and anterior pelvic tilt in OP patients             clinical relevance to this injury pattern. When an athlete
during hip extension due to their inability to actively          kicks, the kicking limb is hyperextended at the hip
isolate these movements. This excessive anterior pelvic          in the backswing phase of kicking, while the trunk is
tilt puts a strain/passive tension on the insertion of           rotated laterally in the opposite direction,11,33 which
the abdominal muscles. Stretching of the abdominal               results in eccentric loading and possibly overloading
muscles may lead to pain and to reflex inhibition of back        from abdominal muscles, which pull superiorly, while
muscles rather than to actual weakness. In addition,             the adductor muscles pull inferiorly.
eccentric weakness of the abdominal muscles leads to                 The backswing phase of kicking is followed by the
less effective stabilization capacity and uncontrolled           acceleration phase, where the angular velocity of the

                                             J Mens Health Vol 14(3):e33-e40; June 18, 2018
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Abdominal/Adductor Strength Imbalance in Soccer Players with Osteitis Pubis

thigh is positive until ball impact,33 and during which        athletes in the eccentric/concentric ratios of the hip
concentric contraction of the adductor muscles occurs.         adductors at high velocity supports our hypothesis.
Regarding the eccentric abdominal/concentric adductor          The eccentric/concentric hip adductor strength ratio
ratio, as this ratio decreases, either the eccentric force     of 64% or lower shown in our study may be one of
has decreased compared to the concentric force or the          the greatest risk factors for OP.
concentric torque has increased compared to the eccentric          Neural control of the lengthening contraction can
torque. If one reconsiders the force-velocity relation-        be explained by two mechanisms: neural inhibition39 or
ship, the capacity of the abdominal muscles in the OP          incomplete voluntary activation.40 Duchateau, Enoka39
athletes to maintain eccentric torque production at the        suggested that during lengthening contractions, the
velocity used here was inadequate compared with the            augmented feedback from peripheral sensory receptors
concentric torque of the hip adductors. These findings         seems to be suppressed by centrally and peripherally
may help to explain the high incidence of OP and the           mediated presynaptic inhibition of Ia afferents, which
susceptibility of healthy soccer players to injury. This       may explain the depression of voluntary activation
observation may constitute the basis for the finding           that occurs during maximal lengthening contractions
that persons with OP have fracture lines described as          to prevent tissue damage. Additionally, this neural
tension stress fractures when their pubic symphysis            inhibitory control could be greatly reduced after a
is scanned using MRI. These fractures may have                 formal resistance training program, increasing the
been caused by excessive tensile or torsional stresses         chance for overuse injuries to occur in response to the
across the pelvis secondary to muscle imbalances,34            erratic pulling of eccentrically weak muscles. Serner,
which would then suggest that rehabilitation should            et al. concluded that specific hip adduction exercises
include not only concentric muscle strengthening but           can be used during different phases of groin injury
also eccentric muscle strengthening, particularly for          prevention and treatment in soccer players.
the abdominal muscles.                                                            CONCLUSION
    The eccentric PT values of hip muscles for OP
soccer players are unique to this study. However,                  This study revealed that eccentric/concentric ratios
several studies have reported PT values of hip adduc-          may help to predict the development of OP in soccer
tor muscles in normal athletes18,35–37 or the effects of       athletes. This information may help clarify the role of
specific training programs on the symptoms of OP.9 A           trunk and hip adductor muscles in the development
reduced eccentric/concentric hip adductor muscle ratio         of OP and may allow these muscle strength assess-
was observed in the OP cases in this study. Since the          ments to guide return-to-play decisions. Exercises that
magnitude of the moments produced by the concentric            increase the eccentric strength of the abdominal and
and eccentric modes are velocity dependent,27 the              adductor muscles should be included in rehabilitation
eccentric/concentric ratio is velocity dependent and           programs developed for patients with OP. Moreover,
increases proportionately to the test velocity, which          restoring the correct eccentric abdominal/concentric
is relevant to soccer given that it is a high-speed sport      adductor and eccentric/concentric hip adductor ratios
requiring sudden directional changes. The higher               might be an important measure for preventing pos-
eccentric strength in normal athletes may reflect the          sible muscle imbalances, consequent instability of the
role of hip adductor contraction during the backswing          pelvic region, and the subsequent risk of OP.
phase of kicking. In contrast, the reduced eccentric/                              DISCLOSURE
concentric ratio for the hip adductors in OP may be
related to impaired neuromotor control of the adductors            The authors have no conflicts of interest to declare.
or may be due to either selective inhibition of their          REFERENCES
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                                         J Mens Health Vol 14(3):e33-e40; June 18, 2018
                   This article is distributed under the terms of the Creative Commons Attribution-Non
                            Commercial 4.0 International License. Author Retained Copyright.
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