Comparison of Trunk Muscle Activities during Pressure Feedback Monitoring among Individuals With and Without Chronic Low Back Pain

Abstract

Background: Pressure biofeedback unit (PBU) is a widely used non-invasive device for the monitoring of transverse abdominals (TA) and multifidus (MF) muscles in patients with low back pain (LBP). There is little research that compared trunk muscle activities with pressure feedback during trunk muscle contraction in a seated position. The aim this study was to compare muscle activities between deep local trunk muscles (TA and MF) and different target pressures (50, 60 and 70mmHg) of PBU in individuals with and without cLBP. Methods: Twenty-two patients with chronic LBP (cLBP) and 24 age matched healthy individuals were recruited. Electromyography (EMG) signals were recorded from the TA and MF muscles while the TA and MF were contracted to achieve PBU pressure value of 50, 60 and 70mmHg in random order. The average EMG amplitude (AEMG) of 3 replicate trials was used in the analysis after normalization to %MVIC. %MVIC is defined as the mean of the three AEMG divided by the AEMG of MVIC. Two-way ANOVA was performed to assess the effects of groups (Healthy and cLBP) and the three different target pressures of PBU. Spearman’s correlation analysis was performed in the cLBP group to determine potential correlations between EMG activity, NPRS and ODI. Results: The %MVIC of the TA and MF in the cLBP group were statistically higher than the control group at each pressure value (P＜0.05). The slope of the %MVIC-pressure of the cLBP subjects was significantly steeper than the healthy subjects (TA: P=0.01, MF: P＜0.001). During maximal voluntary isometric contraction (MVIC) of TA and MF, compared with pain-free group, cLBP subjects showed a decrease in EMG amplitudes (P≤0.001). The MVIC of MF was negatively correlated with Numerical Pain Rating Scale (r = -0.48, P=0.024) and Oswestry Disability Index (r = -0.59, P=0.004). Conclusions: The study demonstrated the feasibility of using PBU to assess muscle contraction that corresponds with changes of muscle activity as measured by EMG. Clinicians may be able to confer PBU measurements with EMG recordings to estimate the level of muscle activities during MF and TA contraction exercise in patients with cLBP.