Historically, back exercises took the form of sit-ups and crunches, or partial sit-ups. Trainers, physical therapists and others would often differentiate between “upper” and “lower” abdominals when prescribing exercises for their clients and patients. However, this differentiation is misleading, because the abdominals are one group from top to bottom. Therefore, it may be more appropriate to consider each of the four abdominal muscles as being either superficial or deep, depending on where they lie.
The superficial layer of muscles, consisting of the rectus abdominus and external obliques, are considered “global” muscles because they act across multiple joints of the spine. They consist of type II, or fast-twitch muscle fibers, which help in torque-producing activities such as swinging a golf club or tennis racquet. Nevertheless, they are poor stabilizers of the spine.
The deep abdominals consists of the transversus abdominus and internal obliques. Together with the quadratus lumborum at the sides of the trunk, and the lumbar multifidus, or segmental muscles of the spine, they compose the “core” muscles. The core muscles are type I, or postural muscles. They are tonic, or endurance muscles, working at only a small portion of their maximum voluntary contraction over long periods of time. Since they are deeper and lie closer to the spinal joints, they are considered better stabilizers of the spine than the global muscles. They also attach to a very important structure, the thoracolumbar fascia. When the core muscles work in conjunction with the thoracolumbar fascia, this creates a great deal of tension in the trunk, thus further stabilizing each segment of the spine and protecting it from injury during torqueing and twisting activities.
When the spine is injured, there is a loss of self-stabilization. This can be due to damage to the spinal discs, the supporting ligaments, joint capsules or the muscles. In fact, it has been found that two core muscles, the transversus abdominus and lumbar multifidus, atrophy quickly after injury to the spine and often fail to regain their function. The incidence of prolonged core muscle weakness among chronic LBP sufferers could be as high as 80% according to some studies. Many experts agree that this could be one contributing factor to the presence of recurrent back pain.
Proper exercise prescription takes into consideration the elements of frequency, duration, intensity, and specificity. Core stabilization can be achieved through performance of a series of specific exercises aimed at training the deep trunk muscles. These exercises are initiated isometrically. They must be done frequently and at about 30% of maximal voluntary contraction in order to train the endurance function of the muscles. Also, in the beginning phases of exercise, isolating the core without contracting the global muscles is emphasized.
As an example, the transversus abdominus, a muscle active in forced expiration and flattening of the abdominal wall, can be strengthened by slowly pulling the navel towards the spine without contracting the rectus abdominus (the “six pack”) muscles. This should be done in different positions (lying down, on all fours, and sitting, for example) throughout the day. A difficult skill to learn, this takes a lot of practice at first. Once mastered, co- contraction of opposing core muscles is the next level of training. Co-contraction is the way that your musculoskeletal system reacts in order to prevent sheer forces from damaging the spine when twisting at high speeds.
When co-contraction becomes second nature, sport-specific training can be initiated. Sport-specific exercise can be as simple as swinging a weighted golf club or tennis racquet, or could include medicine ball training, the use of exercise tubing to mimic different phases of a stroke, or videotape analysis while incorporating core principles with proper tennis or golf form. At this point the program is limited only by the creativity of the trainer or therapist!
Because of the skill and complexity involved in setting up a core stabilization program, supervision by a physical therapist, athletic trainer, or a certified strength and conditioning specialist is usually necessary. It is always recommended that a physician’s evaluation and referral be obtained prior to beginning an exercise program, especially if there is a history of back pain. Making the time and effort to incorporating core stabilization into any athlete’s fitness program can be a key to enhanced performance and pain-free competition.
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