The Effect of Low Back Pain History on Multifidus Co-contraction During Common Lumbosacral Voluntary Stabilizing Contractions
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Nearly all individuals will experience a low back pain episode within their lifetime. Despite pain remission, individuals who experience one low back pain episode are four times more likely to experience another low back pain episode within the next year. As a result, low back pain is often viewed as a cyclical condition characterized by periodic pain followed by remission. Low back pain has been shown to relate to multifidus morphological and sensorimotor control changes that tend to persist despite pain remission, thus potentially increasing the likelihood of pain reoccurrence. The abdominal drawing in maneuver and abdominal bracing maneuver are two common clinical strategies used to provide spinal protection, improve multifidus morphology, and improve sensorimotor control in hopes to prevent low back pain reoccurrence. Although it was commonly believed that these strategies result in multifidus co-contraction, it was not until Matthijs et al (2014) empirically demonstrated superficial multifidus cocontraction during both abdominal contraction strategies in subjects without low back pain. Since these strategies are commonly used in a clinical population, it is important to identify whether these strategies result in deep and superficial multifidus co-contraction in patients with a history of low back pain as well as healthy controls. Therefore, the purposes of this dissertation were to determine: 1) if deep and superficial multifidus fibers demonstrate different co-contraction patterns during volitional abdominal contractions; 2) the effect of a LBP history on the ability of lumbar stabilizing muscles to co-contract with abdominal muscle activation compared to individuals without a LBP history; and 3) if co-contraction differences exist among abdominal activation strategies and common positions used in clinical practice. Muscular activity was assessed using surface EMG for the internal oblique, external oblique, superficial multifidus, and the longissimus thoracis as well as fine wire EMG for deep multifidus. Subjects were asked to perform abdominal drawing in maneuvers and abdominal bracing maneuvers in a standing and quadruped position. Each condition was repeated three times. Additionally, subjects were asked to perform a quadruped hip extension and hold exercise while holding an abdominal drawing in maneuver for additional data analysis at a later time. Baseline data were compared using a t-test while comparisons between groups, strategies, muscles, and positions were compared using ANOVAs. Post-hoc pairwise comparisons were used to locate significant differences. Study 1 used data from the 30 subjects (18 male and 12 female) between the ages of 18 and 65 (37.8 ± 14.46) years old without a recent history of LBP. Robust ANOVAs were completed to look for interactions and main effects of multifidus depth and abdominal contraction strategy. No significant differences were observed in cocontraction between deep and superficial multifidus fiber depth during any of the three abdominal activation strategies in either standing or quadruped positions. Both ADIM and ABM resulted in greater co-contraction in both the deep and superficial multifidus when compared to the resting condition. No multifidus co-contraction was found between ADIM and ABM. Study 2 use data from 30 subjects with a recent LBP history (36.83 ± 13.79 years of age) and 30 subjects without a recent history of low back pain (37.8 ± 14.46 years of age). Between-group differences in baseline variables were assessed using t-tests. Robust ANOVAs were calculated to identify differences in multifidus co-contraction between groups. Additionally, robust ANOVAs were calculated within the HxLBP group for main effects of multifidus fiber depth, abdominal activation strategy, and position. Interactions within all ANOVAs were also assessed. No significant differences were found between group for the demographic variables of sex, age, height, weight, and BMI. However, the history of LBP group had significantly higher scores for TSK, ODI, and the LSIQ. No significant interactions were identified between any variable combination examined. No difference in multifidus co-contraction was found between the HxLBP group and controls. Within the HxLBP group, inconsistent significant differences between deep and superficial multifidus fiber co-contraction were identified with small effect sizes. Both ADIM and ABM contraction resulted in greater multifidus co-contraction compared to the resting condition while no differences were observed between the ADIM and ABM co-contractions. A significant main effect for position was observed with all three abdominal contraction states resulting in greater multifidus co-contraction while in the standing position compared to the quadruped position. These results show the ADIM and ABM contractions do in fact cause multifidus co-contraction. Three possible explanations that may explain why this multifidus cocontraction occurs are: 1) ABM and ADIM contractions include multifidus contraction within the motor program and it is inherently part of the contraction, 2) an anatomical connection between the abdominal muscles and the multifidus muscles requires cocontraction for efficient stabilization, and 3) in order to maintain a static position, forces on each side of the motion segment axis must be balanced. Additionally, this study found that the amount of co-contraction may not be different between the deep and superficial multifidus fibers. The contraction activities in this study were static and may not have challenged individuals to a degree required to observe consistent differences between the superficial and deep multifidus fibers. This study also found that HxLBP subjects experienced similar multifidus co-contraction as control subjects, suggesting that those individuals with a history of LBP can utilize either the ADIM or ABM to stabilize the spine. Lastly, this study found significantly greater multifidus co-contraction during all three abdominal contraction states when in standing compared to the same contraction states in quadruped. This difference could be due to a difference in the direction of gravitational forces acting on the spine combined with the body having contact with the stable both cranial and caudal to the spine. Clinically, this demonstrates that both the ADIM and ABM contraction strategies can be used to stabilize the spine in preparation for a potentially painful functional activity. Furthermore, clinicians interested in educating patients on abdominal contractions to stabilize the spine during these activities can choose either the ADIM or ABM strategies based on which strategy the patient prefers to use.