Introduction:
Near-infrared spectroscopy (NIRS) has become an extensively used, non-invasive method for real-time monitoring of microvascular tissue oxygenation in skeletal muscles. The lumbar multifidus muscle plays an important role in spinal control. Impairment of the multifidus has previously been associated with segmental instability and the pathogenesis of LBP. However, the role of hemodynamic properties of the multifidus in LBP is still unclear. Only few studies have investigated this, mainly focusing on the erector spinae using protocols towards maximal fatigue, instead of also including more functional tasks. Therefore, we aim to explore lumbar multifidus oxygenation in functional, daily life postures in people with and without non-specific low back pain (NSLBP).
Methods:
A pair of NIRS (NX200 Hamamatsu Photonics) probe was used to evaluate multifidus fractional Tissue Oxygenation Index (%TOI) during a functional, low load protocol including baseline (prone), sitting, standing and forward bending (B25°) postures in 11 people with recurrent NSLBP and 12 healthy controls. Each posture was maintained for three minutes.
First, we determined multifidus %TOI in people with and without NSLBP. Secondly, %TOI data for each posture was expressed as changes from prone (baseline) position. %TOI data were compared within and between groups (i.e., NSLBP vs Healthy) using a two-tailed paired and unpaired t-tests, respectively.
Results:
In people with NSLBP, multifidus %TOI significantly decreased only during bending forward (Baseline= 80.3%; sit= 80.6%, p= 0.73; stand= 76.9%, p= 0.06; B25°= 72.4%, p= 0.002). In healthy controls, multifidus %TOI was significantly decreased in all postures compared to baseline (Baseline= 79.1%; sit= 70.6%, p= 0.011; stand= 68.8%, p= 0.017; B25°= 63.1%, p= 0.005).
In addition, healthy controls showed significantly larger decrease in multifidus %TOI compared to people with NSLBP for sitting (sit (NSLBP, change in TOI)= 2.1%; sit (controls, change in TOI)= 8.5%, p= 0.02) and standing (stand (NSLBP, change in TOI)= 3.3%; stand (controls, change in TOI)= 10.3%, p= 0.024), with a trend during bending forward (B25° (NSLBP, change in TOI)= 7.5%; B25° (controls, change in TOI)= 15.9%, p= 0.057).
Discussion:
We observe that people with NSLBP presented a diminished multifidus oxygen utilization in daily tasks such as sitting and standing, while healthy controls demonstrated a more task-appropriate multifidus oxygen use. Future studies are needed to evaluate the mechanism/s of this different oxygenation pattern of the multifidus muscle as well as the effect of exercise training on lumbar muscle oxygenation in daily tasks.