Diagnostic methods: Original Research
Effects of tactile feedback on lumbar multifidus muscle activity in asymptomatic healthy adults and patients with low back pain

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Abstract

Background

Reduced lumbar multifidus (LM) muscle contraction has been observed in patients with low back pain (LBP). Clinicians often use various strategies to ensure LM activation, including tactile feedback and verbal instruction. However, the effects of tactile feedback on muscle activation have not been studied previously. Therefore, the purpose of this study was to investigate whether or not tactile feedback would increase LM muscle activity in adults with and without LBP.

Methods

Twenty asymptomatic adults and 20 patients with existing LBP completed the study. Two electromyographic (EMG) electrodes were applied to both sides of the LM at the L5 segment. EMG activity was collected three times at rest with and without tactile feedback, then five times during contralateral arm lifts with and without tactile feedback. The tactile feedback was applied by direct and continuous hand contact to the bilateral LM over the lumbosacral area. Lastly, two 5-second trials of maximum voluntary isometric contraction (MVIC) during a bilateral arm lift were performed. EMG activity collected at rest and during contralateral arm lifts was normalized to that collected during MVIC. Normalized EMG values of the right side of the asymptomatic group and the painful side of the LBP group were used for data analysis.

Results

Statistical analysis showed significantly decreased LM EMG activity with tactile feedback both at rest and during contralateral arm lifts compared to LM EMG activity without tactile feedback. There was no difference in LM EMG between the asymptomatic and the LBP groups.

Conclusions

The results of the study showed that adding tactile stimulation to verbal instruction appeared to provide an inhibitory effect on LM activity in both asymptomatic healthy adults and patients with LBP. Contrary to common belief, tactical feedback via direct hand contact may reduce LM muscle recruitment, and may lessen the desired treatment effect.

Introduction

The function of the lumbar multifidus muscle for spinal stabilization has been well-recognized due to its anatomic proximity to the spine, particularly for the lumbar segments (Bogduk, 2005, MacDonald et al., 2006). In an ultrasonographic imaging study of patients with acute unilateral low back pain (LBP), the size of the lumbar multifidus muscle was significantly smaller on the painful side than on the un-involved side, even though the patients had significant pain reduction at the 10-week follow-up (Hides et al., 1996). Decreased lumbar multifidus muscle size at the painful segments also was found in patients in subacute and chronic stages of LBP (Hides et al., 1994, Hides et al., 2008, Wallwork et al., 2009). In addition, a higher amount of fatty infiltration (i.e. muscle atrophy) in the lumbar multifidus muscle is positively correlated to a lower level of physical activity in patients with LBP (Le Cara et al., 2014). Therefore, improving this muscle's function is considered to be crucial to restoring physical function in rehabilitation of LBP. Moreover, the ability to activate the lumbar multifidus muscle was identified as a predictor for clinical success with a spinal stabilization exercise program (Hebert et al., 2010). Consequently, clinicians routinely include muscle activation training specific to the lumbar multifidus muscle in spinal stabilization exercise programs for treating patients with LBP (Hicks et al., 2005, O'Sullivan et al., 1997).

Many strategies have been employed clinically to facilitate activation of the lumbar multifidus muscle. A pressure biofeedback unit has been advocated to encourage lumbar stabilization or co-contraction of the lumbar multifidus and deep abdominal muscles during spinal stabilization exercise (Richardson et al., 2004, Cynn et al., 2006). However, a pressure biofeedback unit has been shown to be a more useful tool for identifying lumbopelvic stability impairments than for improving treatment effectiveness (Cairns et al., 2000, Mills et al., 2005). The evidence suggests ultrasound imaging to be a useful visual feedback tool for recruiting the lumbar multifidus and deep abdominal muscles in patients with LBP (Henry and Westervelt, 2005, Lee et al., 2016, Van et al., 2006). However, this mode of feedback is rarely used in clinical settings because of the high cost of ultrasound imaging machines. In contrast, verbal instructions are quick and easy to implement in clinics, and several verbal instructions have been found to be useful to activate the lumbar multifidus muscle (Van et al., 2006, Wallwork et al., 2009, Wang-Price et al., 2017). However, verbal instructions require patients to be able to understand the meaning of the instruction to perform the exercise properly.

Because the depth of the lumbar multifidus muscle limits the clinician's ability to observe muscle activation, tactile feedback often is added to verbal instruction in order to confirm or further facilitate contraction of this muscle (Van et al., 2006, Wallwork et al., 2009). Tactile feedback using taping was shown to improve posture sway when adhesive tape was applied to the ankle and heel (Matsusaka et al., 2001) and to improve muscle activity when a piece of kinesiotape was applied over the pectoral muscle (Gusella et al., 2014). Although taping has positive effects on muscle recruitment, the most common form of tactile feedback technique used by clinicians is direct hand contact (i.e. palpation) over the target muscle (Henry and Westervelt, 2005, Wallwork et al., 2009, Vega Toro et al., 2016). Despite the routine practice of tactile feedback by clinicians using direct hand contact for muscle recruitment, the effect of hand contact on lumbar multifidus muscle activation has not been studied previously. Therefore, the purposes of this study were (1) to examine the effect of tactile feedback on lumbar multifidus muscle activity at rest, and (2) to compare the added effect of tactile feedback to verbal instruction during a contralateral arm lift, in adults with and without LBP.

Section snippets

Participants

This study was approved by the investigator's affiliated Institutional Review Board and registered with ClinicalTrials.gov (NCT02836860). Before data collection began, a power analysis was performed using G*Power 3.1.3 to estimate an adequate sample size (Faul et al., 2007). Using a medium effect size of 0.25 and an alpha level of 0.025, a total of 42 participants, 21 in each group, were required to reach a power of 0.80. Forty-four eligible participants, 20 asymptomatic adults and 24 patients

Results

Forty-two participants were enrolled in the study and 40 participants completed the study. One participant had to leave for another medical appointment and was not able to complete the study. EMG recording from one participant was incomplete because an unexpected software problem occurred. Both drop outs were in the LBP group. Table 1 illustrates the characteristics of participants, including age, gender, height, weight and, the OSW scores of both groups, and the NPRS score and duration of pain

Discussion

All of the participants with or without LBP demonstrated decreased lumbar multifidus muscle activity by 2–3% of MVIC with tactile feedback at rest and during the contralateral arm lift. The results suggest that when tactile feedback is applied via continuous hand contact over the lumbar multifidus muscle, the hand contact appeared to produce an inhibitory or relaxing effect, rather than a facilitating effect, on lumbar multifidus muscle activity in both asymptomatic healthy adults and patients

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Acknowledgement

We would like to show our gratitude to Zak Mitchell, Yousef Alshehre, and Khalid Alkhathami for their assistance in data collection and Jim Price for his comments and edits on this manuscript.

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