The fitness industry uses the word core exercise as a generic term, but two types of muscles comprise the abdominal and lumbopelvic region. Global muscles, also called mobilizers, sit at the most superficial layer of the abdominal region. Local muscles, also called stabilizers, sit deeper in the abdominal wall. True core exercise primarily engages the stabilizers.
Core Anatomy
Fitness presenter Paul Chek, of the Paul Chek Institute, refers to the local and global muscles as the inner and outer unit. The deep, intrinsic muscles such as transversus abdominis, the pelvic floor and the multifidus make up the inner unit, whereas the rectus abdominis and external obliques make up the outer unit. Most fitness enthusiasts are familiar with the mobilizing muscle groups. The rectus abdominus flexes the spine when performing crunches, and the obliques rotate the spine during oblique curls.
Core Muscle Function
During movement, the inner unit or core musculature provides a stable platform for the outer unit muscles, explains Chek. Most trainers, for example, tell their clients to exhale on the exertion phase of a movement. During exhalation, the transversus abdominis muscle presses against the diaphragm, creating a deep, spine-stabilizing abdominal contraction. Meanwhile, the multifidus, located close to your vertebrae, maintains posture by keeping your back in a straight alignment. Core stability exercises engage the inner unit and minimize rectus abdominus activity, explains Paul W. Marshall of the Department of Sport and Exercise Science at the University of Auckland. Marshall, in a 2005 article featured in the "Archives of Physical Medicine and Rehabilitation," describes the goal of core exercise as encouraging the synergistic relationship between the inner and outer abdominal units.
Core Stability Examples
Core stability exercises usually keep the spine extended and use only a minimal amount of movement. Begin on all fours; breathe in and draw your abdominal muscle toward your spine. Hold for 10 seconds; then relax and repeat. Next, have a partner place a dowel rod vertically along your spine. As you exhale, lift one palm a fraction of an inch from the floor, and lift the opposite knee to the same height. If your multifidus is engaged, your spine remains straight, and the dowel rod stays on your back. Repeat with the other hand.
Core Strength
Performing hundreds of crunches or oblique curls enhances outer core muscle endurance, but does not improve strength. To strengthen your global core muscles, you need to add challenge to the exercises. Examples include holding a weight while you perform the exercise, increasing the exercise range of motion and performing the exercise with both legs lifted from the floor. Using balance equipment such as stability balls imposes a balance challenge, which may require deeper core activity to maintain stability.
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