• Williams B

• Biomechanical Phenomena
• Open Access Document
• Posture

Objective: To examine the validity of claims suggesting that 60°–100° of maximal spinal flexion is unavoidable during lifting and to critique the conceptual and methodological inconsistencies in defining and measuring spinal neutral and flexion, particularly under load. This commentary proposes a refined framework for interpreting vertebral position during lifting tasks.

Methods: This analysis synthesizes and critiques existing literature on spinal flexion biomechanics, with a focus on how the concepts of postural neutral, positional neutral, and loaded neutral are defined and applied. Case examples and comparative data from published studies are evaluated to illustrate inconsistencies in measurement, variability in individual neutral zones, and the effects of axial load on spinal positioning. A novel working model of vertebral position nomenclature (PE, PL, PDN, PF) is proposed to refine terminology and facilitate clearer interpretation.

Results: Findings demonstrate substantial variation in spinal flexion measurement, influenced by individual anatomy, loading conditions, and baseline postural positions. For example, a reanalysis of key studies reports an average of 23.5° of spinal flexion during lifting—approximately 36% of the lumbar spine’s available ROM—not the 60–100% often cited. The commentary emphasizes the importance of distinguishing between postural and positional neutral to assess flexion and potential injury risk. It introduces the concept of a positional range of neutral (PL-PDN) as a biomechanical zone rather than a fixed point, noting that the elastic equilibrium of the intervertebral disc (IVD) and associated musculature shifts dynamically under load.

Conclusion: Generalized claims about spinal flexion during lifting often overlook the complexities of measurement, loading effects, and individual variability. Recognizing and differentiating postural, positional, and loaded neutral is essential for accurate biomechanical assessment and injury prediction. Future research should focus on refining measurement models and standardizing definitions to support evidence-based and individualized lifting recommendations.

Author keywords: Spine; Load; Posture

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