Lumbar Multifidus and Erector Spinae Muscle Synergies in Patients with Nonspecific Low Back Pain During Prone Hip Extension: A Cross-sectional Study

Background: Prone hip extension is used to clinically assess movement control in patients with nonspecific low back pain (LBP). Excessive lumbopelvic movements and altered muscle activation patterns are common in patients with nonspecific LBP. However, no evidence exists regarding lumbar multifidus and lumbar erector spinae muscle synergy patterns in patients with nonspecific LBP during this clinical test. Objective; To determine the difference in lumbopelvic motion and change in muscle synergy between patients with nonspecific LBP and healthy individuals. Design: A cross-sectional study design. Setting: University physical therapy clinic and laboratory. Participants: Seven patients with nonspecific LBP (age [mean SD] 295 years, 43% female, body mass index [BMI] of 252 kg/m(2), Numeric Pain Rating Scale 62; Oswestry Disability Index 20%8%) and seven age-, sex-, and BMI-matched healthy individuals (mean age 28 +/- 5 years, 43% female, BMI of 22 +/- 2 kg/m(2)) were recruited. Methods: Each participant performed six repetitions of prone hip extension on each side; kinematic and electromyographic data were collected simultaneously. Main Outcome Measurements: Kinematic data were used to represent lumbopelvic motion, whereas electromyography (EMG) data were used to represent muscle activity. A paired t-test was used to determine the difference in lumbopelvic motion. Principal component analysis and two-way repeated-measures analysis of variance were used to extract muscle synergies and identify differences in muscle synergy patterns between and within groups. Results: Results demonstrated no significant group difference (P>.05) in amount of lumbopelvic motion. However, healthy individuals synergistically activate lumbar multifidus and lumbar erector spinae with 81.0% variance accounted for (VAF). Patients with nonspecific LBP had an altered synergy with independent activation of lumbar multifidus on the painful side with 32.0% VAF and the lumbar multifidus on the nonpainful side, and both lumbar erector spinae with 52.2% VAF synergistically activated. Conclusions: These findings suggest that clinicians should focus on muscle activation patterns rather than the amount of lumbopelvic motion during clinical observation of prone hip extension.