Background: Lumbar disc herniation (LDH) can cause distal lower-extremity weakness through nerve root compression. Specifically, compression of the L5 nerve root may cause weakness in great toe extension (GTE), ankle dorsiflexion (DF), and eversion (EV). Although magnetic resonance imaging (MRI)-derived disc height reflects structural degeneration, few studies have quantitatively examined the association between disc height and L5-innervated muscle strength in individuals with LDH. Objects: This study compared GTE, DF, and EV strength between individuals with LDH and healthy controls and examined the association between MRI-derived disc height and muscle strength within the LDH group. Methods: Thirty participants were divided into two groups: individuals with LDH (n = 15) and healthy controls (n = 15). GTE, DF, and EV strengths were measured using a digital dynamometer. In the LDH group, lumbar MRI was analyzed to measure anterior, middle, and posterior disc heights at both L4–5 and L5–S1. Results: GTE, DF, and EV strength were significantly lower in individuals with LDH than in healthy controls (all p < 0.001). After adjustment for visual analogue scale, the betweengroup differences in normalized GTE, DF, and EV strength remained significant. Within the LDH group, posterior disc height at L4–5 was positively correlated with GTE and DF strength, while posterior disc height at L5–S1 was positively correlated with EV strength (r = 0.532, 0.613, and 0.631, respectively; p < 0.001, respectively). Conclusion: Individuals with LDH showed significantly lower GTE, DF, and EV strength than healthy controls. Within the LDH group, posterior disc height was positively correlated with GTE and DF strength at L4–5 and with EV strength at L5–S1.

INTRODUCTION
MATERIALS AND METHODS
    1. Participants
    2. Procedure
    3. Measurement Methods
    4. Statistical Analysis
RESULTS
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Hyeok-jun Lee(Department of Physical Therapy, The Graduate School, Yonsei University, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University)
• Il-kyu Ahn(Department of Physical Therapy, The Graduate School, Yonsei University, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University)
• Oh-yun Kwon(Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University, Department of Physical Therapy, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea) Corresponding author