Core Training Series, 2

In part 1, I detailed the basic muscles of the body's core and their basic function. To begin understanding the complexity of our core and how it relates to overall function we must address the inner unit and the outer unit. These two units work together to allow the athlete to function at the highest levels.

The Inner Unit

The inner unit provides joint stabilization for the spine. If the inner unit does not activate properly, the athlete's spine, pelvis and joint structures are placed in a position that will lead to injuries.

The inner unit consists of the transversus abdominis, multifidus, internal obliques, lumbar transversospinalis, pelvic floor and diaphragm. Although I will cover the transversus abdominis, multifidus and pelvic floor in detail, the other muscles in the inner unit are also at work.



In Part 1, I detailed how the transversus abdominis is the deepest layer of all abdominal muscles and it is considered your body's internal weight belt. When it contracts, it causes hoop tension around your mid section like a girdle. When the transversus abdominis is working properly, it contracts before the extremities will move.

Bracing your torso will activate the transversus abdominis. If this muscle does not contract, the spine and pelvis is unstable and at high risk of injury. When the spine is unstable, the central nervous system will not recruit the extremity muscles correctly. The extremity muscles assist with functional movement patterns.

For example, if you bend over to lift a heavy load, your transverse abdominis needs to activate in order to stabilize your spine. When it doesn't activate and stabilize, you are at high risk for a low back injury.

When you make a habit of not recruiting the transversus abdominis to stabilize your spine, the joints will begin early degeneration.

The multifidus lies deep to the spine crossing over three joint segments. It works to provide joint stabilization at each segmental level. The vertebrae need stability to work correctly and reduce degeneration of joint structures.

The pelvic floor covers the area under the pelvis. The pelvic floor is critical for the inner unit to work properly. Sometimes, operations for sports hernias cause damage because the inner unit muscles have been cut. Core exercises can rehabilitate, strengthen and tone these muscles.

The Outer Unit

The muscles of the outer unit are: rectus abdominis, external obliques, erector spinae, quadratus lumborum, adductor complex, quadriceps, hamstrings and gluteus maximus.

The transversospinalis group, erector spinae, quadratus lumborum and latissimus dorsi are critical lumbar spine muscles. The other muscles in the outer unit also play a role in core stabilization to dynamically produce force (concentric), stabilize force (isometric) and reduce force (eccentric) in all 3 planes of motion.

If the muscles of the inner unit and outer unit work in isolation, they can not stabilize the athlete's lumbo-pelvic-hip complex effectively. And, this will of course lead to injuries.

In Part 3, I will write about what research has to say about core stabilization techniques.

See Core Training Series, 1

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Mark Dilworth, BA, PES
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