To coordinate the muscle activity required for both dynamic and static spinal stability the central nervous system requires accurate feedback from the sensors that provide information on things such as joint position, the tension on connective tissues and the force applied by muscles. It has been speculated that inaccurate such information affects the central nervous system’s ability to coordinate this stability and is a causative and perpetuating factor in many pain syndromes. A recent study investigated one such parameter- the ability to accurately judge and control muscular force. They compared those with lower back pain to normal controls, plus investigated the effect of fatigue and the application of localised vibration to the muscles.
Subjects were tested using a high tech exercise machine designed to exercise the lumbar extensor muscles. The subjects were able to practice developing a force equal to 60% of maximum while monitoring their effort on the gauge. Once this was done subjects were asked to reproduce this force using their judgement alone. To assess variation several such readings were taken. This was repeated again testing the effects of fatigue and of the application of vibration to the lumbar erector spinae muscles.
Those with no back pain were able to reproduce this force quite accurately, with minimal variation between measurements. On the other hand, those with lower back pain were far less accurate and had greater variation between attempts. When vibration was applied to those with back pain they became far more accurate and less varied. Fatigue was shown to reduce accuracy in both controls and those with low back pain. As occurred with non-fatigue testing, vibration was show to improve accuracy.
Major issues with the study
The study shows that those with pain syndromes have abnormal sensory feedback impairing the ability of the central nervous system to provide the accurate control of muscles needed for the coordination of movement and stability. This is likely an important cause and perpetuating factor in pain syndromes. Furthermore, this is a serious consideration with regard to the prescription of rehabilitation exercises. Do we really want clients/patients performing rehabilitation exercises with the same abnormal coordination that causes problems in the first place??? However, there are serious issues with the solution suggested by the author.
Short term only
The post vibration testing was done immediately after the application of 30 seconds of vibration. Indeed, when further testing was done after 30 seconds of no vibration the results were back to where they were previously. If the vibration protocol used was implemented as suggested by the authors it would mean those undergoing rehabilitation would need to have the vibration applied immediately before each set of exercises, which is highly impractical.
They played “neurological tricks” rather than address the cause of abnormal feedback
In a previous study the authors tested the same vibration protocol on normal subjects. Rather than help them it made their sensory motor function less accurate.
This is what this author believes happened. The vibration frequency used was 80hz. This frequency is used by TENS machines to interfere with nerve transmission to create a pain block. In those with lower back pain feedback from sensors providing inaccurate information was interfered with, resulting in an improvement. When accurate information from the sensors in normal subjects was interfered with control worsened.
Some clinical guidance
Yes, we need to address this issue, but by restoring normal feedback from the sensors rather than blocking them. To this author’s knowledge research has not caught up to this one yet. However, in his clinic vibration and other therapies are used, and functional and sensorimotor testing is regularly performed. While the ability to accurately reproduce force is not used as a clinical test feedback from these sensors is a key element of many manual muscle tests and other functional testing. These same sensors have been implicated in the perpetuation of myofascial trigger points and other clinical issues. Pre and post testing seems to indicate that lower frequency vibration penetrates and “re-sets” these sensors. Importantly, though further applications may be needed to resolve an issue these results are not just temporary as the study protocol was.
When developing the author’s DrGraeme Massagers prototypes were built able to deliver vibration greater then 70hz. This was found to be uncomfortable and not very effective. Excellent penetration and effects were found using around 50hz and lower. It is for this reason the production machines were built using a custom built motor with high torque but limited to deliver up to approximately 55hz.
We are ahead of the scientific research here, but when used sensibly vibration massage is inexpensive, easy to use, incredibly safe, and the effects easily monitored. Clinicians are encouraged to evaluate this use their training and skills.
Boucher J-A, Abboud J, Nougarou F,
Normand MC, Descarreaux M (2015) The Effects of
Vibration and Muscle Fatigue on Trunk Sensorimotor
Control in Low Back Pain Patients. PLoS ONE 10(8):
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