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Purpose <p>Symptomatic lumbar spinal stenosis (sLSS) is associated with sagittal imbalance and degeneration of paraspinal muscles. While morphological changes are well documented, the functional relationships between electromyographic paraspinal fatigability, endurance, and global imbalance remain unclear. This study aimed to examine these relationships in preoperative patients with sLSS.</p> Methods <p>In this cross-sectional study, 109 preoperative patients with sLSS underwent magnetic resonance imaging, EOS radiography, and a modified Biering-Sørensen test with bilateral surface electromyography (EMG) of the longissimus, iliocostalis and multifidus muscles. Paraspinal muscle fatigability was defined by three EMG-based indices: slope of median frequency (MDF) decline (Hz/s), normalized slope (%/s), and absolute MDF decrease (Hz). Endurance was defined as the duration of the modified Biering-Sørensen test. Global spinal imbalance was quantified using the Full Balance Integrated (FBI) score. Associations between fatigability, endurance, and FBI were assessed using Pearson correlation and stepwise multiple regression analyses.</p> Results <p>Valid EMG data were available for 90 of the 109 patients who performed the modified Biering-Sørensen test. Greater absolute MDF decreases (but not MDF slopes) were significantly associated with lower FBI scores (<i>r</i> = -0.38, <i>p</i> &lt; 0.001). Longer endurance times correlated with both lower FBI scores (<i>r</i> = -0.41, <i>p</i> &lt; 0.001) and greater absolute MDF decreases (<i>r</i> = 0.40, <i>p</i> &lt; 0.001). Regression analysis revealed that absolute MDF decrease (β = -0.3, <i>p</i> = 0.004), endurance time (β = -0.1, <i>p</i> = 0.005), and age (β = 0.31, <i>p</i> &lt; 0.001) independently predicted FBI, explaining 35% of its variance. Mediation analysis confirmed that the association between absolute MDF decrease and FBI was predominantly direct (71%) and only partially mediated through endurance time.</p> Conclusion <p>In preoperative patients with sLSS, both reduced paraspinal endurance and lower absolute MDF decrease were independently associated with greater global spinal imbalance. The association between absolute MDF decrease and imbalance was only partially mediated through endurance time, indicating that these two measures capture complementary aspects of paraspinal muscle function. Since lower absolute MDF decrease coincided with shorter endurance times, reduced electromyographic fatigability in this population likely reflects diminished physiological reserve rather than enhanced neuromuscular efficiency.</p>

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Reduced paraspinal muscle endurance and electromyographic fatigability are associated with greater global spinal imbalance in symptomatic lumbar spinal stenosis

  • 期刊论文

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  • 发表日期：

    2026年7月1日

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  • David Koch,
  • Sifang Li,
  • Stefan Schären,
  • Stephen J. Ferguson,
  • Annegret Mündermann,
  • Corina Nüesch,
  • Cordula Netzer

摘要

Purpose

Symptomatic lumbar spinal stenosis (sLSS) is associated with sagittal imbalance and degeneration of paraspinal muscles. While morphological changes are well documented, the functional relationships between electromyographic paraspinal fatigability, endurance, and global imbalance remain unclear. This study aimed to examine these relationships in preoperative patients with sLSS.

Methods

In this cross-sectional study, 109 preoperative patients with sLSS underwent magnetic resonance imaging, EOS radiography, and a modified Biering-Sørensen test with bilateral surface electromyography (EMG) of the longissimus, iliocostalis and multifidus muscles. Paraspinal muscle fatigability was defined by three EMG-based indices: slope of median frequency (MDF) decline (Hz/s), normalized slope (%/s), and absolute MDF decrease (Hz). Endurance was defined as the duration of the modified Biering-Sørensen test. Global spinal imbalance was quantified using the Full Balance Integrated (FBI) score. Associations between fatigability, endurance, and FBI were assessed using Pearson correlation and stepwise multiple regression analyses.

Results

Valid EMG data were available for 90 of the 109 patients who performed the modified Biering-Sørensen test. Greater absolute MDF decreases (but not MDF slopes) were significantly associated with lower FBI scores (r = -0.38, p < 0.001). Longer endurance times correlated with both lower FBI scores (r = -0.41, p < 0.001) and greater absolute MDF decreases (r = 0.40, p < 0.001). Regression analysis revealed that absolute MDF decrease (β = -0.3, p = 0.004), endurance time (β = -0.1, p = 0.005), and age (β = 0.31, p < 0.001) independently predicted FBI, explaining 35% of its variance. Mediation analysis confirmed that the association between absolute MDF decrease and FBI was predominantly direct (71%) and only partially mediated through endurance time.

Conclusion

In preoperative patients with sLSS, both reduced paraspinal endurance and lower absolute MDF decrease were independently associated with greater global spinal imbalance. The association between absolute MDF decrease and imbalance was only partially mediated through endurance time, indicating that these two measures capture complementary aspects of paraspinal muscle function. Since lower absolute MDF decrease coincided with shorter endurance times, reduced electromyographic fatigability in this population likely reflects diminished physiological reserve rather than enhanced neuromuscular efficiency.