Introduction:
Adaptations in lumbar sensory-motor control relate to the evolution of Low Back Pain (LBP) [1]. 
Factors influencing the lumbar motor output have been extensively studied, while less attention has been given to the possibly compromised lumbar proprioceptive input leading to a loss of trunk control and contributing to LBP chronification [2].  
Muscle spindles represent the main proprioceptive receptors and its dominant kinestetic role can be highlighted by the illusion of limb movement induced by muscular vibration [3]. 

Aim:
Examine the contribution of the lumbar muscle spindles on trunk control in LBP versus asymptomatic control (Control), measuring the trunk repositioning error with and without vibration of the lumbar portion of the erector spinae.

Methods:
Seventeen Control (age: 29.8 ± 4.1 years) and seventeen LBP (age: 37.1 ± 9.1 years, average pain: 5.7 ± 2.1/10 see Table 1) participated. 
An inertial motion sensor attached to the 3rd thoracic spinous process measured the accuracy in adopting and returning to a trunk neutral position after a sagittal movement (50 deg flexion). 
Lumbar vibration was randomly applied during trials. Three trials were executed for each condition (Vibration, No Vibration). 
The mean trunk repositioning error (TRE) was calculated and statistically evaluated using a repeated-measure analysis of variance (ANOVA) within the two vibration conditions.

Results:
Vibration significantly increased TRE in the LBP group (F(1,12)=7.221, P=0.02) but had no significant effect on the control group (F(1,14) =0.985, P=0.34).

Discussion:
The increased muscle spindles input caused by vibration, giving an illusion of muscles lengthening, resulted in an increased TRE and overestimation of the neutral trunk position (excessive trunk extension). 
The results show that people with LBP are unable to compensate, as happens in the Control group, such paradoxical proprioceptive input exploiting other available sensory information. 
This study highlights the pivotal importance of lumbar muscle spindles in controlling trunk motion accuracy.

TRUNK CONTROL IN PEOPLE WITH LOW BACK PAIN: THE IMPORTANCE OF MUSCLE SPINDLES INPUT ORIGINATING FROM THE LUMBAR PORTION OF THE ERECTOR SPINAE