Muscular Balance, Core Stability, Injury Prevention for
Middle – and Long-Distance Runners (and any motion of the body)
Michael Fredericson, MD, Tammara Moore, PTba
Department of Orthopaedic Surgery,
Division of Physical Medicine and Rehabilitation,
Stanford University School of Medicine,
3000 Pasteur Drive R105B, Stanford, CA 94305, USA
Sports and Orthopedic Leaders Physical Therapy, 5297A College Avenue,
Oakland, CA 94618, USA
Martial artists long have recognized the importance of well-developed
core musculature. One of the main differences between a novice practitioner
and a black belt is the black belt’s development and use of his core (called
‘‘center’’ or ‘‘Ki’’) to produce balanced, powerful, and explosive movements.
For middle- and long-distance runners whose chosen sport involves
balanced and powerful movements of the body propelling itself forward
and catching itself in complex motor patternsdthis stable core, as well as
a strong foundation of muscular balance, is essential. In many runners,
however even those at an Olympic level, this core musculature is not
developed fully. Weakness or lack of sufficient coordination in core
musculature can lead to less efficient movements, compensatory movement
patterns, strain, overuse, and injury. This article discusses the importance of
muscle balance and core stability for injury prevention and for improving
a distance runner’s efficiency and performance. It includes a detailed series
of core exercises that can be incorporated gradually into a runner’s training
program. The program starts with restoration of normal muscle length and
mobility to correct any muscle imbalances. Next, fundamental lumbo-pelvic
stability exercises are introduced which teach the athlete to activate the
deeper core musculature. When this has been mastered, advanced lumbopelvic stability
exercises on the physioball are added for greater challenge.
As the athlete transitions to the standing position, sensory motor training used to stimulate
the subcortex and provides a basis for functional
movement exercises that promote balance, coordination, precision, and
skill acquisition. The ultimate goal of core stabilization is to train
‘‘movements’’ and ‘‘positions’’ rather than muscles. Exercises are most
effective when they mirror the demands of the athlete’s sport.
The role of the core
In essence, the ‘‘core’’ can be viewed as a box with the abdominals in the
front, paraspinals and gluteals in the back, the diaphragm as the roof, and
the pelvic floor and hip girdle musculature as the bottom [1]. Within this box
are 29 pairs of muscles that help to stabilize the spine, pelvis, and kinetic
chain during functional movements. When the system works efficiently, the
result is appropriate distribution of forces; optimal control and efficiency of
movement; adequate absorption of ground-impact forces; and an absence of
excessive compressive, translation, or shearing forces on the joints of the
kinetic chain. This efficiency requires an integration of the myofascial,
articular, and neural systems, which, in turn, requires optimal functioning of
the muscles, including the muscles’ ability to contract in a coordinated
manner and with sufficient motor control and neuromodulation so the joints
receive adequate compression through the articular structures. This model
supports an integrated model of joint function [2] and leads to optimal
length-tension ratios and optimal force coupling of the muscles.
Additionally, this model sets the stage for optimal postural alignment, normal
movement patterns, and a minimal potential for joint dysfunction. Biomechanical
studies showed clearly that joint dysfunction anywhere from
the spine to the feet can lead to compromise elsewhere in the kinetic
chain [3].
The first stage in developing a stable core is to develop the abdominal
muscles. Richardson and coworkers [1] discovered that there are two
different types of muscles fibers (slow-twitch and fast-twitch) that comprise
the abdominal muscles; because of this different fiber composition, different
exercise regimens are required to train the abdominal muscles properly.
Slow-twitch fibers primarily make up the local muscle systemdthe muscles
of the deeper abdominal muscle layers. These muscles are closer to the
center of rotation of the spinal segments and, with their shorter muscle
lengths, are ideal for controlling intersegmental motion, maintaining
mechanical stiffness of the spine, and are best suited to respond to changes
in posture and extrinsic loads. The key muscles of this system include the
transversus abdominus, multifidi, internal oblique, deep transversospinalis,
and pelvic floor muscles. McGill [4] described a ‘‘hoop’’ around the
abdomen that consists of the abdominal fascia anteriorly, the lumbodorsal
fascia posteriorly, and the transverse abdominis and internal obliques
muscles laterally. In combination with the intra-abdominal pressure
mechanism, activation of this system serves to tension the hoop and
provide a stabilizing corset to the spine.
Fast-twitch fibers, conversely, primarily make up the global muscle
system (superficial or outer-layer muscles). These muscles possess long levers
and large moment arms that are capable of producing large outputs of
torque, with an emphasis on speed, power, and larger arcs of movement [5].
The main muscles in this layer are the erector spinae, external oblique, and
rectus abdominis muscles — the muscles that are strengthened by traditional
back and abdominal exercises and that assist with gross spinal movements.
Hodges and Richardson [6,7]showed that it is not simply that deep-layer
abdominal muscles are recruited during stabilization of the spine, but it is how
they are recruited that is important. The transverse abdominus, the innermost
of the four abdominal muscles, has fibers that run horizontally (except for the
most inferior fibers, which run in line with the internal oblique muscle). The
transverse abdominus and the multifidi are considered ‘‘stabilizing muscles’’
(muscles that are modulated continually by the central nervous system and
provide feedback about joint position), whereas the global and larger torque
producing muscles control acceleration and deceleration. The investigators
found that the cocontraction of the deeper-layer transverse abdominus and
multifidi muscle groups occurs before any movement of the limbs. They noted
that the transverse abdominus is active 30 milliseconds before movement of
the shoulder and 110 milliseconds before leg movement; this neuromuscular
stabilization may be delayed in individuals who have low back pain. It is
believed that these muscles anticipate dynamic forces that may affect the
lumbar spine and act to stabilize the spine before movement. In agreement
with this, Hides and colleagues [8] documented that patients who sustained
a low back injury had difficulty recruiting their transverse abdominus and
multifidi muscles early enough to stabilize the spine before movement.
For a more detailed discussion on the theoretic basis for core
strengthening, the reader is referred to a recent review article by Akuthota
and Nadler [9].
Muscle imbalances
Stability work should be started only after the athlete has achieved good
mobility, because adequate muscle length and extensibility are crucial to
proper joint function and efficiency. Also required is a proper relationship
between the prime movers, synergists, and stabilizers. A prime mover is the
muscle that provides most of the force during a desired body movement.
Stabilizers and synergists are muscles that assist in the motion by means of
control or neutralizing forces. Proper timing and coordinated effort of these
muscles is paramount to the runner, and the functional exercises included
here stress these relationships.
A thorough evaluation of the muscular system should include an
assessment of the muscles for overactivity, shortening, weakness, inhibition,
and quality of motion. This is accomplished best by using muscle-length
tests, strength tests, and tests for the efficiency of basic movement patterns
and neuromuscular control. A thorough postural observation and videotaping of
the athlete’s running gait will help in assessing and identifying any
movement imbalances. Muscles that are used frequently can shorten and become
dominant in a motor pattern. If a muscle predominates in a motor pattern, its antagonist
may become inhibited and cause a muscle imbalance. An example of this is
tightness in the iliopsoas muscledthe primary hip flexor that has its origins
at the anterolateral aspect of the lumbar vertebral bodies and its transverse
processes. When the iliopsoas muscle is tight or shortened, it is believed to
inhibit the deep abdominals and the primary hip extensordthe gluteus
maximus. Inhibition of the gluteus maximus muscles may result in
inadequate stabilization of the lumbar spine, with increased anterior shear
and extension forces on the lower lumbar vertebrae.
Muscles are divided into two types: postural and phasic (Box 1). Postural
muscles are used for standing and walking. Phasic muscles are used for
running; they propel the runner. Although 85% of the gait cycle is spent on
one leg when walking [10], when running, there is a double-float phase
during which both legs are off the ground — one at the beginning and one at
the end of swing phase. Running mechanics demand efficient firing patterns
from the postural muscles, whereas phasic muscles do the work of
propelling the runner forward. Because postural muscles are being activated
constantly in the human body to fight the forces of gravity, they have
a tendency to shorten and become tight. In runners, because of training and
prolonged use, certain postural muscles are particularly likely to tighten,
shorten, and become hypertonic. This occurs predominately in muscles that
cross more than one joint [11]. We commonly see this in the gastroc-soleus
(predominantly the soleus), rectus femoris, iliopsoas, tensor fascia lata,
hamstrings, adductors, quadratus lumborum, piriformis, and sartorius.
Restricted extensibility of muscles also can lead to decreased circulation and
ischemia, which contributes to overuse injury [12].
In comparison, phasic muscles (the more global muscles) typically may
remain in an elongated state. It was shown that elongated muscles may lack
force in shortened-range test positions[13]. Weak phasic muscles might allow
excessive motion to occur at the joints upon which they act. In our experience,
common phasic muscles that have a tendency to develop weakness or become
inhibited in runners are the tibialis anterior; peronei; vastus medialis; long
thigh adductors; and the gluteus maximus, medius, and minimus.
Beginning a core strengthening program
The first step in a preventive or performance-enhancing program is to
assess which muscles have become tight and shortened. These deficits can be
addressed with stretching exercises and soft tissue mobilization techniques.
Following this, the clinician should seek to activate inhibited, or strengthen
any weak, muscle groups. The challenge for the clinician is to design an
individualized program that addresses these imbalances.
Preliminary stretches for shortened, predominant muscles should include
proprioceptive neuromuscular facilitation–type or contract-relax stretches
that strive for isometric contraction, followed by end-range stretching. These
are effective techniques for maintaining muscle length and joint mobility.
Active Release Techniques [12], (a specialized method for soft tissue
mobilization) when used in conjunction with stretching techniques, have
shown great promise in restoring muscle length and soft tissue extensibility.
Athletes also can do self-mobilization with the use of a foam roll. One example
of this technique targets the iliotibial band, is shown in Fig. 1.
Middle-distance runners have unique and specific training programs that
demand strength, power, and endurance. These runners place terrific
demands for balance and precise functioning of structures all the way from
the core to the feet. Specific exercises for the runner should progress from
mobility to stability, reflexive motor patterning, acquiring the skills of
fundamental movement patterns, and finally, progressive strengthening.
These sequences may not be applicable to all athletes; therefore, the key is to
analyze the individual in each exercise category and then to tailor an exercise
regimen that will best suit that runner’s needs. For example, it was shown
that runners who are prone to iliotibial band syndrome often have weakness
in their hip abductors that predisposes them to increased stress on the
iliotibial band [14]. Thus, a preventative training program for runners who
have this syndrome must target the hip abductors, particularly the posterior
aspect of the gluteus medius that assists external rotation or in decelerating
adduction of the hip. Other muscles that prove weak or inhibited on
evaluation also should be strengthened on a case-by-case basis.
The stages of core training
Warm-up
Before beginning the basic core strengthening exercises, the athlete
should warm-up the spine with the Cat-Camel motion (Fig. 2).
Fundamental lumbo-pelvic stability
The purposes of the fundamental core stabilization exercises are to gain
stability, but more importantly, to gain coordination and timing of the deep
abdominal wall musculature. It is extremely important to do these basic
exercises correctly because they are the foundation of all other core exercises
and movement patterns. These basic exercises emphasize maintaining the
lumbar spine in a neutral position (which is the midrange position between
lumbar extension and flexion.) This alignment allows for the natural
curvature of the spine. All of these exercises are best done with light loads
and high repetitions.
This first stage of core stability training begins with the athlete learning to
stabilize the abdominal wall. Proper activation of these muscles is considered crucial
in the first stages of a core stability program, before progressing to more dynamic and
multiplanar activities. We recommend the abdominal bracing technique as described
by McGill (Fig. 3) [4].
The exercise program should progress sequentially through the initial
fundamental movements as detailed inFigs. 4 through 8. These fundamental
exercises are to be performed three times a week to maximize results. The
athlete begins with two sets of 15 repetitions and progresses to three sets of
15 to 20 repetitions to develop fully the requisite muscle endurance for
higher level performance. Initially, these exercises are taught in a supine,
hook-lying position or an all-fours quadruped position. The athlete can
progress to more functional standing exercises as control is developed.
Important concepts that are taught at this stage include not tilting the pelvis
or flattening the spine. We also emphasize normal rhythmic breathing.
Advanced lumbo-pelvic stability
Once the athlete demonstrates good stability with all static core exercises,
they can be replaced with more advanced exercises as detailed in Figs. 9
through 14. The use of the physioball requires the athlete to work on
proprioception and higher level core stabilization. These exercises should be
performed two to three times weekly to maximize results. Again, the athlete
begins with one or two sets of 15 repetitions and progresses to three sets of
15 to 20 repetitions. Quality is more important than quantity. Make sure
that the lumbar spine does not go into extension or the cervical/thoracic
spine into flexion and maintain the spine in perfect alignment.
As the athlete progresses through a core exercise program, the emphasis
always should be on correct postural alignment as athletes challenge
themselves with a variety of movement patterns in the three planes of
movement: sagittal, frontal, and transverse. Although runners move
predominately in the sagittal plane, there still is body movement in the
transverse and frontal planes that must be controlled adequately by the
neuromuscular system. During midstance of the running gait cycle, the foot
and ankle unlock to allow absorption of ground reaction forces. During this
phase, the body is challenged most to control excessive or aberrant motion
in the frontal and transverse planes. Functional exercises on one leg are used
to best simulate the neuromuscular demands of running. The athlete is
trained with increasingly challenging functional patterns, with continued
emphasis on postural control and core stabilization. The ultimate goal of
core stabilization is to train ‘‘movements’’ and ‘‘positions,’’ rather than
muscles. Exercises are most effective when they mirror the demands of the
athlete’s sport.
Development of balance and motor control
The following movements require reflexive control. The athlete can
accomplish this control by using the numerous proprioceptors in the soles of
the feet and the exteroceptors of the skin, and by activating the neck
muscles; these are highly contributory to postural regulation. This sensory motor
stimulation is an attempt to provide the subcortex with a basis for
movement that is progressively more challenging. It involves exercises that
stimulate balance, coordination, precision, and skill acquisition.
The following exercises should be performed while standing (Figs. 15–
17). We instruct the athlete to control the feet, pelvis, and head consciously,
with the goal of making sure that the feet are aligned properly.
These exercises use a rocker board. A rocker board is a board with
a hemisphere underneath that allows single-plane rocking. (The board was
designed by Dr. Vladimer Janda to promote balance and stability of the
spine, www.optp.com).
Common errors or abnormal compensations to look for when attempting
these exercises include increased anterior pelvic tilt, increased lumbar
lordosis, increasing internal rotation of the hip, excessive valgus at the knee,
and hyperpronation at the foot. Therefore, when teaching these exercises, it
is imperative to instruct the athlete on proper spinal alignment. To aid in
this, we recommend initiating the abdominal bracing technique before
performing the stepping forward-and-backward motions of any of these
exercises (which train correct weight transfer over the feet). Additionally, it
is important to instruct the athlete on proper gait. The focus here should be
on controlling the initial heel strike in a supinated position on the lateral
edge of the foot, into pronation on the medial aspect of the foot, with flexion
of the first metatarsal head and toes. Continuing proper gait instruction, we
teach a falling-forward position into a lunge (with perfect control). The
athlete then progresses to jumps on one or two legs, assuring that there is no
increased lumbar lordosis or increased valgus moment at the knee. This
stimulates vestibular and cerebellar activity, which, in turn, leads to
automatic postural controldan important part of our training. (Readers
will note the increased muscle activity of the ankles and muscles that control
the lower extremity chain and spine.) The athlete can progress to standing
on one leg, with alternating arm movements.
Various devices are useful to challenge balance progressively, moving the
athlete from conscious to subconscious control of the muscles that are
responsible for postural maintenance and gait. These devices include
a balance board (a whole sphere underneath the board, which creates
multiplanar instability) or a rocker board (a curved surface underneath the
board, which allows single-plane motion). Dynamic foam rollers are an
inexpensive alternative to the boards that also can be used to challenge
balance, proprioception, and stability. These include half-rollers and fullsized rollers.
Two other items that are invaluable to challenge balance and
core stability and aid proprioceptive training in the standing position are the
Bosu Balance Trainer and the Dyna Disk (these can be used interchangeably). T
he Bosu has two functional surfaces that integrate dynamic balance
with sports-specific or functional training: the domed surface is convex, the
other side is flat and can be used for less challenge. The Dyna Disk is an air-
filled plastic disc that can be inflated firmly. It has a smaller diameter than
the Bosu and can be used like the Bosu Trainer because it creates an
increased proprioceptive challenge to the athlete while standing on it. The
Dyna Disk is unstable and does not have a base like the Bosu Trainer.
Functional movement training
Functional movements require acceleration, deceleration, and dynamic
stabilization. Figs. 18 through 24 present an array of functional, diagonal
exercises for the trunk and extremities that are essential for runners.
Exercises should be safe, challenging, and stress multiplanar motions. These
training exercises encourage functional strength, which depends on the
neuromuscular system’s ability to produce dynamic eccentric, concentric,
and isometric contractions during movement patterns.
A functional exercise regimen that is specific to the demands of running
includes single-leg drills, three-dimensional lunges, resistive diagonal
patterns of the upper and lower extremities, drills that involve plyometrics,
and triplanar movement sequences. Athletes can progress through the three
planes of motion by performing similar exercises on balance boards, the
Dyna Disk, or Bosu-type trainers, after static trunk and core stability have
been mastered.
Summary
This article is intended to provide an understanding of the importance of
core musculature to runners and to offer exercises that will help them
achieve desired mobility, stability, muscular balance, and neuromuscular
control. Please see Table 1 for an example of how to incorporate these
exercises into a periodized training program. It is highly recommended,
however, that athletes consult a skilled practitioner to address individual
needs and maximize results from a program of this nature.
References
[1] Richardson C, Jull G, Hodges P, et al. Therapeutic exercise for spinal stabilization and low
back pain: scientific basis and clinical approach. Edinburgh (Scotland): Churchill Livingstone; 1999.
[2] Lee D. An integrated model of ‘‘joint’’ function and its clinical application. Fourth
Interdisciplinary World Congress on Low Back and Pelvic Pain. Montreal, Canada, p. 138.
[3] Nicholas JA, Strizak AM, Veras G. A study of thigh muscle weakness in different
pathological states of the lower extremity. Am J Sports Med 1976;4:241–8.
[4] McGill S. Ultimate back fitness and performance. Waterloo: Wabuno Publishers; 2004.
[5] Comerford MJ, Mottram SL. Movement and stability dysfunction–contemporary developments. Man Ther 2001;6:15–26.
[6] Hodges PW, Richardson CA. Altered trunk muscle recruitment in people with low back pain
with upper limb movement at different speeds. Arch Phys Med Rehabil 1999;80:1005–12.
Table 1
Periodization of core training program
Summer/Falldbase training Winterdsport specific Spring/Summerdcompetition
(3 /wk, 3 sets of 15–20
repetitions for each exercise)
(2–3 /wk, 2–3 sets of 10–15
repetitions for each exercise)
(1–2 /wk, 2–3 sets of 8–12
repetitions for each exercise)
Restore mobility/address
any muscle imbalances
Advanced core stability
exercises
Similar to sports specific
training with addition of
Fundamental core stability plyometric exercises
exercises
Functional movement
training
Sensory motor stimulation
688 FREDERICSON & MOORE[7] Hodges PW, Richardson CA. Inefficient muscular stabilization of the lumbar spine
associated with low back pain. A motor control evaluation of transversus abdominis. Spine
1996;21:2640–50.
[8] Hides JA, Richardson CA, Jull GA. Multifidus muscle recovery is not automatic after
resolution of acute, first-episode low back pain. Spine 1996;21:2763–9.
[9] Akuthota V, Nadler SF. Core strengthening. Arch Phys Med Rehabil 2004;85:S86–92.
[10] Janda V. On the concept of postural muscles and posture in man. Aust J Physiother 1983;29:
83–4.
[11] Kendall F, McCreary E, Provance P. Muscle testing & function. Baltimore: Williams and
Wilkins; 1993.
[12] Schiottz-Christensen B, Mooney V, Azad S, et al. The role of active release manual therapy
for upper extremity overuse syndromes-a preliminary report. J Occup Rehabil 1999;9:
201–11.
[13] Sahrmann S. Diagnosis and treatment of movement impairment syndromes. St. Louis:
Mosby; 2000.
[14] Fredericson M, Cookingham CL, Chaudhari AM, et al. Hip abductor weakness in distance
runners with iliotibial band syndrome. Clin J Sport Med 2000;10:169–75.
