Introduction: Low back pain (LBP) is prevalent worldwide and is affecting even more individuals as the population ages. There has recently been an increase in production of low back pain (LBP) vibration modality belts that apply localized vibration to the lumbar region of the spine as it has shown to reduce pain. However, vibration is also known to perturb muscle spindles and thus interfere with proprioception. If a LBP vibration modality causes a proprioceptive deficit in the trunk lumbar region it could potentially increase an individual’s risk of injury due to poor postural control. Therefore, the effects of a LBP vibration modality on trunk motor control needed to be investigated further.
Methods: 15 participants who had not experienced LBP for longer than 3 days in the previous year were recruited to partake in a control and experimental day approximately one week apart from each other. Each day consisted of 3 conditions including; previbration, post-vibration, and vibration ON. Between each condition participants sat on a standard chair for 15 minutes while wearing the vibration belt and the belt was also worn during the last vibration ON condition. On the control day the vibration belt was worn but not turned on between conditions or during the last vibration ON condition. Each condition consisted of 4 sudden unexpected trunk perturbations following by 3 half- and 3 full-trunk flexion repositioning tasks. Electromyography (EMG) was collected from several trunk muscles to analyze changes in trunk postural control and motion capture was collected to analyze changes in lumbar spine movement.
Results: The magnitude of lumbar flexion caused from the sudden trunk perturbation decreased after sitting for 15-minutes and was exacerbated by vibration. No other significant differences in the variables measured after wearing the vibration belt for 15- minutes were found. However, profound differences were found during the vibration ON condition. Bilaterally the LES (p<0.0001), LEO (p=0.03), and REO (p=0.002) displayed significantly delayed muscle activation onset latencies. Bilaterally the LES (p<0.0001), LTES (p=0.01), RTES (p<0.0001), EO (p<0.0001), LRA (p<0.0001), and RRA (p=0.0001) all showed significant increases in resting muscle activation pre-perturbation. The LLES (p=0.0002), RLES (p=0.0003), LTES (p=0.0008), RTES (p=0.03), LRA (p=0.02), and RRA (p=0.01) also all displayed significantly reduced muscle activation magnitudes post-perturbation.
Discussion and Conclusion: The increased resting muscle activation pre-perturbation caused from the vibration can be explained as the tonic vibration reflex (TVR) because of vibrations stimulatory effect on Ia afferents. The delayed muscle activation onset latencies that were observed while wearing the vibration belt most likely occurred because of the ability for vibration to create a ‘busy line’ or vibration-locked discharge of the muscle spindles. Proper muscle spindle function is essential for providing critical proprioceptive information on body awareness and functions as a protective mechanism against injury. Additionally, the TVR can also lead to fatigue and subsequent altered trunk motor control. The findings of the current study reveal that impaired trunk motor control when wearing a LBP vibration modality belt needs to be considered due to the potentially greater risk for experiencing an injury to the low back or LBP.