Low back stiffness can be caused by a role reversal between the outer unit and inner unit muscles.
What are outer unit and inner unit muscles?
Outer unit muscles (also referred to as global muscles) are superficial to the deep inner unit muscles. A few examples of global muscles are, the quads, lats and external obliques. Global muscles are gross stabilizers of the spine and function properly by responding proportionately to a given amount of stimulus. Back pain often arises when global muscles are constantly turned on (medically known as being in a facilitated state) while the inner unit muscles are inhibited. For example, many people hold tension in their neck (upper trapezius) and experience upper neck discomfort from the muscle responding excessively disproportionate to the given stimulus.
To give you an example in my studio, many people come to me for the first time and when I show then a pulling exercise they feel the neck activate instead of the rhomboids or lats. It takes time to retrain my client to recruit the proper muscles and learn to relax the facilitated upper neck musculature.
The inner unit muscles need to be activated at all times to serve their function properly. The medical term for these inner unit muscles are called tonic muscles. Deep/tonic muscles play a larger role in stabilization of the spine for light to moderate loads. In low back stability, the multifidus plays a crucial role. According to (Hides et al 1994, Danneels et al 2000, O’sullivan 2000, Hungerford 2002, Moseley et al 2002) noticed a high correlation to low back pain and pelvic pain patients and the multifidus muscle fibers becoming shut off (or inhibited) alongside muscle atrophy.
Why should you do more multifidus training?
As stated above, the multifidus is a stabilizing muscle of the spine. Many people with low back pain have a lumbar spine that is excessively mobile and not stable. For example, one reason why golfers (or many rotation sports for that matter) have higher incidences of low back pain is due to a lack of strength in the stabilizers and and increased/disproportionate strength in the global muscles that drive the golf club.
Example of the Lower Back and Pelvic Stability – The Sprinter
If you look at a professional sprinter from behind, you’ll notice very little movement in the low back and pelvis and a lot of movement in the extremities (the legs and arms are moving like crazy!) A sprinter with good pelvic stability must have great core strength and proper inner unit activation to stabilize the legs and upper body.
Which exercises are best for conditioning the multifidus for low back injury prevention or treatment?
Below are a couple great exercises for conditioning the multifidus muscle.
The Prone Cobra – Beginner
Simply lie face down on an exercise mat and lift your torso up from the mat while externally rotating your arms so the thumbs are facing the ceiling. Hold your neck in a neutral position (do not look up or tuck your chin). Retract your shoulder blades together to activate the rhomboids (strengthening the rhomboids is a great way to improve posture).
The Prone Cobra Intermediate – see images below. Lie face down on an exercise mat and position yourself exactly like you would in the beginner cobra. Advance the exercise by placing your arms at a 45 degree angle towards your head and hold the thumbs up toward the ceiling. The prone cobra intermediate will work your multifidus and your thoracic extensors as well as your mid traps (all great postural muscles to work).
Have a personal trainer or a workout partner stabilize your ankles and roll out onto the ball until your hips are close to the apex of the ball. The further your workout partner rolls you out onto the ball the more difficult the exercise becomes. At some point you can roll out too far, which will recruit more of the hamstrings and glutes. To keep the exercise in the back/multifidus converse with your partner and let them know which muscles you feel being worked.
This important exercise for back injury prevention can be done anywhere! Start out by performing 10 sets of 10 seconds on 10 seconds off. When ready gradually progress to holding prone cobra exercise for up to 1-4 minutes (depending upon the demands of your work, sport or life environment).
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