downward, whereas contraction of the lower fibers pulls the pelvis upward toward the chest. Combined contraction of both the upper and lower fibers rolls the trunk into a ball.
The muscles of the two lateral groups are arranged into three layers. The external oblique forms the most superficial layer. From its attachment on the external surface of ribs 5 through 12, the fibers run obliquely (diagonally) to attach at the midline of the body along the linea alba and pelvis. If you were to think of your fingers as the fibers of this muscle, the fibers would run in the same direction as your fingers do when you put your hand into the front pocket of a pair of pants. Unilateral (single-sided) contraction of the muscle results in trunk rotation to the opposite side, meaning that contraction of the right external oblique rotates the trunk to the left. Bilateral contraction results in trunk flexion.
The next layer is formed by the internal oblique. The orientation of its fibers is perpendicular to those of the external oblique. This muscle originates from the upper part of the pelvis and from a structure known as the thoracolumbar fascia, which is a broad band of dense connective tissue that attaches to the spine in the upper- and lower-back region. From its posterior attachment, the internal oblique wraps around to the front of the abdomen, inserting at the linea alba and pubis. Unilateral contraction rotates the trunk to the same side, and bilateral contraction leads to trunk flexion. The deepest of the three layers is formed by the transversus abdominis, so named because the muscle fibers run transversely (horizontally) across the abdomen. The transversus abdominis arises from the internal surface of the cartilage of ribs 5 through 12, the upper part of pelvis, and the thoracolumbar fascia. The muscle joins with the internal oblique to attach along the midline of the body at the linea alba and pubis. Contraction of the transversus abdominis does not result in significant trunk motion, but it does join the other muscles of the lateral group to function as a core stabilizer. An analogy that often helps people grasp the core- stabilizing function of the muscles of the lateral group is to think of them as a corset that, when tightened, holds the core in a stabilized position.
Note that other muscles, including the serratus anterior and hip flexors, can be recruited along with the abdominal muscles when many of the exercises in this chapter are performed. The serratus anterior commonly functions as a stabilizer of the scapula, as described in chapter 3, but it is also activated during many of the exercises that target the external and internal obliques. The two primary hip flexors are the rectus femoris and the iliopsoas. As described in chapter 7, these muscles can either flex the hip or flex the lower trunk, depending on whether the lower extremity or trunk is stabilized.
The role of the core abdominal muscles in swimming can be easily broken down according to their roles as trunk flexors, trunk rotators, and trunk stabilizers. Through their ability to flex the trunk, the rectus abdominis, external oblique, and internal oblique all play important roles in the movements that take place during swimming. For example, flexion of the trunk during flip turns is initiated by the upper fibers of the rectus abdominis, sustained by the lower fibers of the rectus abdominis, and helped to completion by both obliques. The trunk flexors are also important contributors to the wavelike, or undulating, body roll that takes place during butterfly, breaststroke, and underwater dolphin kicking. Besides contributing to flexion of the trunk, the obliques are responsible for trunk rotational movements. Strong obliques are vital to enhancing the speed of open turns performed during butterfly and breaststroke. The obliques are active during the body-rolling movements that take place during freestyle and backstroke, functioning to link the movements of the arms with the movements of the hips and legs. As previously mentioned, through their ability to function like a corset, the abdominal muscles are central to stabilizing the trunk. Trunk stability is one of the keys to efficient movement through the water, because it ensures a firm base of support upon which the arms and legs can generate their propulsive forces.
When incorporating abdominal strengthening exercises into the dryland program, you must understand the importance of focusing on correct technique. The focal point of correct technique begins with the conscious recruitment of the abdominal muscles, often referred to as setting, or locking in, the core, as described in the sidebar on page 13 of chapter 2. Setting the core first involves using the abdominal muscles to control the positioning of the hips and low back. This is best done by lying on the back, as pictured in the starting position for the first exercise of this chapter, the hollow hold. In this position, contraction of the abdominal muscles rolls the hips backward, pressing the low back against the floor. Conversely, contraction of the hip flexors rolls the hips forward, causing the low back to arch. After becoming comfortable with rolling the hips forward and backward, attention should be switched to holding the low back and pelvis in a neutral, fixed position. A useful approach to maintaining this neutral position is to visualize all the abdominal muscles as a corset and to focus consciously on contracting the abdominal muscles in this manner. You should perform the process of setting the core at the start of every abdominal exercise, and it should remain the underlying focus while you execute the entire exercise. The most common indicators that you are not setting the core are excessive arching of the low back and, if you are performing an exercise while facing the ground, excessive rounding of the low back and the hips rising toward the ceiling. Either of these compensatory movements is an indication that you are relying on your stronger hip flexors (rectus femoris and iliopsoas) to hold the body position instead of your abdominal musculature.
Hollow Hold
Execution
1. Lie face up on the floor with your arms by your sides, knees bent, and feet on the floor.
2. Tighten the abdominal muscles like a corset to set your core.
3. Lift your shoulders 6 inches (15 cm) off the ground, making sure to keep the low back in a stable and fixed position.
4. While lifting the shoulders, reach your arms toward the tops of your knees.
5. Hold this position for 60 seconds or until you are unable to keep the low back in the set position.
Muscles Involved
Primary:Rectus abdominis (upper fibers)
Secondary:External oblique, internal oblique, transversus abdominis, serratus anterior
Swimming Focus
This exercise is a good way to learn how to use your abdominal musculature to position the hips for correct technique and to stabilize the low back. In the starting position, you can experiment with contracting and relaxing your abdominal musculature to roll your hips forward and backward. Practicing these movements will help you gain a feel for the positioning of your hips. Gaining this feel will help you detect when you haven fallen out of the proper positioning for the exercise. A partner can monitor your positioning by testing whether he or she can slide a hand under your low back. If your partner can slide a whole hand under your low back, then you have fallen out of the proper position. When you lift your shoulders off the ground, look down your arms and past your knees to increase recruitment of the upper fibers of the rectus abdominis.
Direct benefits include strengthening of the core musculature, which will carry over to a tighter streamline and a reduction in the risk of injury. By targeting the upper fibers of the rectus abdominis, this exercise helps with the initiation of trunk flexion during freestyle and backstroke flip turns.
VARIATION
Hollow Hold With Feet Elevated
Incorporation of the legs will make the exercise significantly more challenging. Again, the key to performing the exercise properly is maintaining contact between the low back and the ground.
