POSTURAL VS. POSITIONAL NEUTRAL: ADDRESSING THE COMPLEXITIES OF MEASURING SPINAL FLEXION UNDER LOAD

INTRODUCTION

The ongoing discourse surrounding spinal flexion under load and its associated risks and benefits remains a significant topic of interest among contemporary coaches, therapists, trainers, and clinicians. The complexity inherent in this issue often leads to confusion, particularly when faced with assertive claims lacking empirical support. An academic exploration of this subject necessitates a comprehensive evaluation of all variables influencing research findings. Despite varying viewpoints, leading biomechanists acknowledge the substantial complexity involved in understanding spinal flexion dynamics. A key point of contention—especially within strength-based populations—is the accurate measurement of spinal flexion under load, which highlights the intricate challenges that arise in standardizing research methodologies across different studies.

DISCUSSION

The Neutral Zone

The concept of the spinal neutral zone remains elusive in both theoretical and practical contexts. Although it is acknowledged that the neutral zone is highly individual and can vary with several factors, including load,^1–3 the precise delineation of this zone is challenging. This variability is particularly pertinent when measuring spinal flexion in populations engaged in heavy lifting, where the elastic equilibrium of the joint system and its constituent structures play a critical role in defining the “neutral zone.”^1,2 Panjabi described the neutral zone as “a region of intervertebral motion around the neutral posture where little resistance is offered by the passive spinal column.”¹ Scannell and McGill defined the neutral zone as ‘the zone of lumbar positions of least tissue strain,’ reporting an approximate positional range from 0° to 40°, where 40° represents the natural lordotic curvature and 0° indicates a reduction of this curvature toward a more neutral or flexed posture.² (Figure 1)

Figure 1.Neutral Zone Approximate Values (data from Scanell and McGill 2003)²

Accurate measurement of the neutral zone is essential for contextualizing studies on spinal flexion kinematics under load, as it helps identify which spinal positions might be more susceptible to issues under repetitive stress or strain.² However, discrepancies in measuring and comparing neutral zones across studies are prevalent due to their highly individual and variable nature.^3,4

Recent claims that 60º-100º of maximal flexion is unavoidable during lifting are based on aggregating data from various studies, some of which did not address or report on neutral zones, had varied measurement protocols, and had a multitude of other factors that impact the outcomes.⁵ For instance, an analysis of studies by Bengtsson,⁶ Khoddam,⁷ McGill,⁸ Mawston,⁹ Holder,¹⁰ Potvin,¹¹ Ulrika,¹² and Williams¹³ reveals an average maximal flexion of 23.5º. Given an average spinal range of motion of 65º, this equates to approximately 36% of the total range, starkly contrasting with the 60-100% claims (Figure 2).

However, in practical terms, these generalized assertions do not align with the nuanced realities of spinal flexion measurement (including my above example). Using a flexion range or neutral zone measurement from a published study—essentially an average of a group—is not clinically relevant to a specific individual. Each person’s neutral zone, spinal stiffness, resistance to movement, and mechanical response to load are shaped by their unique tissue properties, loading history, and neuromuscular control. These variables create highly individualized stress and strain patterns that cannot be inferred from group means. So although they may be insightful, to interpret these biomechanical characteristics meaningfully, they must be assessed and calibrated within the context of the individual.

Figure 2.Lumbar Flexion Under Load Graph

Postural Neutral Vs. Positional-Discogenic Neutral (PDN)

The development of the secondary lumbar curve, or lordosis, typically begins in early childhood, usually within the first three years of life.¹⁴ This curve, which can vary significantly among individuals, generally ranges from -10° to -40° of lumbar lordosis, though specific values may vary according to different sources.¹⁵ In most studies, negative values indicate spinal extension, while positive values represent spinal flexion (but this can change depending upon the study).

When assessing spinal range of motion (ROM), the standard methodology involves measuring the baseline ROM in a standing position before evaluating the end range of flexion, often assessed by having the individual touch their toes. For instance, if an individual’s initial lordosis is -30° (postural neutral), the flexion measurement would track the movement from this lordotic position to the end range of, say, 60°. Consequently, the total observed flexion ranges from -30° (standing position) to 60° (fully flexed position), with 30° of this movement occurring through the lordotic curve. Thus, the total spinal flexion ROM is 90°, of which 60° is through positional flexion, while 30° involves flexion through lordosis.

Despite this detailed breakdown, traditional measurements often classify the entire movement as flexion when evaluating flexion kinematics. This broad categorization can introduce inaccuracies, particularly when variations in the starting position affect the results. For this reason, it is crucial to differentiate between postural and positional nomenclature.

For example:

• Positional Extension (PE) is postural extension.

• Positional Lordosis (PL) is postural neutral.

• Positional Discogenic Neutral (PDN) is still considered postural flexion.

• Positional Flexion (PF) is postural flexion.

One may not be able to avoid flexing the lumbar spine when lifting, but it is possible to limit flexion to within one’s PL and PDN. Some argue that avoiding flexion is impossible, but they often include moving through the extension range as flexion (the lumbar spine’s lordosis). Alternatively, it could be argued that PL and PDN are approximate neutral positions that establish a zone through which movement can occur if required, and true flexion only occurs when the lumbar spine moves beyond the PDN into Positional Flexion (PF). In an upcoming case study, the participant’s neutral standing lumbar position was measured at -28°, and their maximum flexion was 31°, resulting in a Total Flexion Range of Motion (TFROM) of 59° (-28° + 31°). During a midway deadlift with a torso angle of 45°, the participant maintained minimal lumbar flexion, recorded at -17°, which represents 11° of flexion. This 11° of flexion accounts for 18.6% of the TFROM. However, under this hypothetical model, this flexion is only 11° of the PL, indicating that the participant effectively avoided true vertebral flexion under load and was within the neutral range. Positionally speaking, the participant’s lumbar spine was still in lordosis.¹³

To clarify, between postural neutral and positional-discogenic neutral, you have the neutral range (Figure 3).

These are our working terms for the vertebral position range of neutral.

Figure 3.Postural vs. Vertebral Positions¹⁹

Positional-Discogenic Neutral (Pdn)

When evaluating the risks associated with flexion under load, the intervertebral disc (IVD) emerges as a key concern, as literature consistently shows that repetitive flexion/extension combined with load can lead to injury.¹⁶ The IVD comprises a nucleus pulposus (NP) encased by 15–30 concentric collagen rings with oblique attachments. The disc’s response to load is hydraulic, with anterior pressure pushing the NP posteriorly and posterior pressure pushing it anteriorly.^17–19 For the disc to be in a neutral position, pressure differentials must be balanced, preventing excess movement of the NP into the annulus fibrosus (AF). The concept of parallel endplates implies a “neutral” disc state.

In the study by Byrne et al., dynamic radiographic imaging was used to examine lumbar intervertebral disc deformation in vivo as subjects transitioned between standing and flexion. Utilizing a dynamic stereo-X-ray system, the researchers captured real-time disc morphology changes. The results revealed that in the standing position, the posterior side of the disc showed reduced height, indicated by red coloration, and the nucleus pulposus (NP) shifted slightly anteriorly (figure 3). Similarly, in a flexed posture, there was reduced disc height on the anterior segment, with the NP moving posteriorly.²⁰ Furthermore, multiple studies have shown that in a standing postural neutral position, the lumbar facet joints bear up to 25% of the spine’s total load, with this load increasing as the spinal lordosis increases.²¹ These findings underscore that both standing and flexion create distinct deformations, suggesting that a postural neutral position (or standing) does not equate to a true neutral disc state, which would ideally exhibit less deformation, less concentrated posterior compression, and a centered NP. (Figure 4)

Additionally, during spinal flexion, the lumbar facets and discs handle approximately 200 N of anterior shear force, with increasing loads requiring greater posterior shear force from the extensor muscles to maintain stability.²² In a PL-PDN spinal position, the iliocostalis lumborum and longissimus thoracis muscles form an optimal angle of 25–45°, enhancing their ability to counteract shear forces. As spinal flexion reduces this angle, the muscles’ mechanical advantage diminishes. Thus, maintaining a neutral spine within this range is commonly advocated to maximize muscle leverage, enhance spinal stability, and minimize injury risk.²³

Figure 4.IVD pressure differentials (Bryne et al. (2019) CC BY 4.0) The graph depicts average normalized disc height (nDH) along the AP axis. Black-blue lines show nDH in the upright position, and black-red lines show it in a flexed position. Colored sections (blue or red) highlight nDH values from 0.95 to 1.05, indicating the nucleus pulposus area, with dashed lines showing NP movement across segments.¹⁹

To determine the true elastic equilibrium of a joint system, it is essential to consider the capacity of each tissue component.² For an accurate assessment of neutral positions, we must consider what constitutes equilibrium for the disc, specifically whether it achieves true elastic equilibrium with endplates aligned parallel and a position close to 0º. Researchers often use cadaveric intervertebral discs to test mechanical properties in isolation. These discs are typically positioned in a “neutral position” during testing (Figure 5), with endplates aligned parallel to normalize data and minimize variables.^24–27 However, the concept of intervertebral disc elastic equilibrium can vary by spinal level, as some joints naturally assume more neutral positions than others. Additionally, individual differences and genetic variability further complicate the assessment.^28–32

Figure 5.Mechanical jig loading IVD specimens

Loaded Neutral

When an axial load is applied to the spine, the demand for stability increases as the body adjusts to maintain a more stable and aligned posture under the load. Aasa et al. (2022) found that the average lordosis in an unloaded neutral position was 25 degrees; however, under load, the starting lordosis was significantly reduced, ranging from -6.6º to -13.8º. This reduction indicates a substantial shift in spinal alignment due to the load.³³ Similarly, Bengtsson et al. reported a 45%–78% decrease in lordosis when comparing unloaded standing neutral to loaded neutral positions prior to performing a squat with a load at 70% of maximum capacity.³⁴ This reduction in lordosis is likely a result of the body recalibrating to a more neutral and secure posture to better handle the compressive forces. Research shows that unloaded postural neutral and loaded standing neutral positions are different, with the degree of spinal range of motion decreasing as the spine is loaded, moving closer to a more neutral alignment (PDN).³⁵ This adjustment helps in stabilizing the spine under load.

Furthermore, studies on loaded spinal alignment in lifters have often used unloaded lumbar positions to infer conclusions about loaded spinal flexion. This approach can be problematic as it does not account for the differences between unloaded and loaded neutral positions. Those who lift intuitively understand that unloaded and loaded spinal alignments are distinct. It is common practice among powerlifters to avoid excessive lordosis, or spinal extension, during loaded squats. Strength coaches have long emphasized the importance of pressurizing the core—through techniques like breathing and bracing—and optimizing ribcage and pelvis positioning to enhance spinal stability. This approach is based on the understanding of the torso as a cylinder, where anatomical positioning, musculature, and intra-abdominal pressure are crucial for stabilizing the spine while under load.

World strength expert Chris Duffin of Kabuki Strength said, "A lot of people think of it as being spinal protective (excessive lumbar extension in a squat); it is not; you’re destabilizing all of this stuff (spine and associated structures). A lot of people seem to coach that in the squat…we’re arched up, boom, we’re ready to squat! Well, I tell you what, that bar is going to come right the hell through you."³⁵

Impact of Postural Variability on Spinal Alignment Measurements

Understanding the nuances of spinal alignment in different postural states is crucial because it significantly affects the accuracy of biomechanical assessments and interventions. Using unloaded postural neutral as the starting point for measurements can skew results due to several factors. Day-to-day variations in spinal alignment can be influenced by numerous variables, including chronic or acute injuries, tight muscles, previous training adaptations, treatments such as stretching, manipulation, or massage, as well as factors like sleep quality and hydration.³⁶

Buchman-Pearle et al. reported that 44% of participants had standing lumbar angles outside the neutral zone, highlighting significant variability in spinal alignment.³⁷ Similarly, Scannell and McGill found that participants in a hyperlordotic pre-training group stood outside their neutral zone before training but demonstrated improved alignment after exercise, with lordosis changing from approximately -43º to -24º.² This indicates that initial lordosis and spinal alignment can be highly variable and affected by multiple factors.

If unloaded postural neutral is used as a baseline, these variations can lead to less accurate calculations of total spinal flexion and other metrics. Therefore, relying solely on unloaded postural data can provide incomplete insights into spinal mechanics and stability. It is essential to consider these variables and use comprehensive measures to ensure more accurate and applicable results in spinal assessments and interventions.

Challenges in Comparing Spinal Flexion Across Different Studies And Conditions

To accurately compare spinal flexion across different studies, it is important to recognize that such comparisons can be misleading when the studies involve differing populations, conditions, and measurement protocols. Caution must be exercised when interpreting research in this area. Due to considerable variability in methods, definitions, and study-specific variables, it becomes exceedingly difficult to normalize the data and draw robust conclusions. Metrics such as “neutral spine” are defined differently across studies; some offer alternative interpretations of the neutral zone, while others omit these measurements altogether. In addition, inconsistencies in how flexion range of motion is measured — including variations in starting positions, total flexion assessed, and the calculations used — further complicating cross-study comparisons.

Each joint operates within its elastic equilibrium, or neutral zone, which varies individually and is influenced by several factors.^1,2 This neutral zone is defined by each joint’s stress/strain curve and its capacity for load before reaching a failure point, which can lead to injury if exceeded. Since the neutral zone is highly individual and can change with load, measuring it accurately requires accounting for all relevant structures involved in spinal movement—such as ligaments, tendons, muscles, bones, cartilage, the annulus fibrosus (AF), and the nucleus pulposus (NP)—and their reactions under specific conditions. Given these complexities, relying on varying studies without considering these individual and contextual factors can lead to inaccurate conclusions about spinal flexibility and neutral zones.

The practice of combining the lowest average end-range flexion value from one source with the highest reported value from another constitutes a significant oversimplification. Such pairing risks distorting the data and may result in conclusions that are more reflective of a desired narrative than of the evidence itself.

Determining the Optimal Starting PointfFor Measuring Spinal Alignment in Weightlifting Populations

When evaluating spinal alignment in weightlifting populations, selecting the appropriate starting measurement point is critical as it impacts the results of data analysis. Measurements can be taken from an unloaded neutral spinal position (postural lordosis—PL) or a loaded neutral spinal position (closer to positional-discogenic neutral—PDN). Using the loaded position requires establishing a consistent and standardized testing protocol to ensure accurate and comparable results across different individuals. This approach ensures that the data reflects true spinal alignment under typical lifting conditions and accounts for individual variations effectively.

Case Studies

In the case study “Measuring Lumbar Flexion and Neutral Spine Under Load—Part 1,” we assessed the lumbar spine positions of an elite powerlifter with a load of 150 kg. We reported the standing lumbar position as -35°, but for the study, we adjusted the lifter to a neutral 0° position before the lift to simulate a loaded neutral spine (PDN). We did not record the neutral zone, so the total “unloaded” spinal flexion range of motion (ROM) was 104°, while the flexion from the loaded 0° position ranged from 65° to 69°. The lifter managed to maintain 29° of flexion with an inclined torso, avoiding an additional 40° of potential flexion and retaining 42% of his total flexion capacity from the calibrated starting point.³⁸ While this measurement approach may be subject to critique, it represents an alternative to conventional methods and serves as an opportunity to further explore the topic. (Figure 6)

In part 2 of this published case study, as mentioned above, a separate participant (this time a weightlifter) was able to avoid flexion quite successfully, even under load and in a 45º incline torso angle mid-deadlift. After undergoing a warm-up, the participant only flexed 11°, which was 18.6% of his total max end range flexion. The participant was still in a lumbar lordotic posture, and here we are faced with the reality of “flexing” and “flexion.”¹³

Figure 6.Effect of Structured Warm-Up on Lumbar Flexion During Deadlift

We Can Avoid Flexion

Based on the summary of data gathered above (albeit an inaccurate method as explained), the average person approximately flexes 23° when squatting or deadlifting (this range would be heavily dependent upon experience, skill, and technique). The average standing lordosis is around 20-45°.³⁹ So one’s neutral range between their PL and PDN is likely around 30°~. In addition to this, those with experience may be able to avoid positional flexion altogether, only flexing through part of their neutral range (lordotic curve).

So yes, you can avoid VPF.

You cannot avoid flexing, but you can avoid flexion.

CONCLUSION

Accurately measuring the spinal neutral zone is crucial for assessing spinal alignment, especially in weightlifting. Variability in neutral zones due to factors like load and individual differences underscores the need for standardized measurement methods. Research shows significant differences between unloaded and loaded spinal positions, highlighting the importance of distinguishing these states. While completely avoiding lumbar flexion under load is challenging, effective techniques can minimize excessive flexion and enhance spinal stability. Proper measurement and understanding of spinal alignment are key to obtaining accurate assessments.

Acknowledgements

The author wishes to express heartfelt gratitude to the late Dr. Andrew Lock, whose mentorship, wisdom, and passion for musculoskeletal rehabilitation left a profound impact on this work. Dr. Lock’s insights and encouragement were instrumental in shaping the foundation of this study. His legacy continues to inspire through the countless clinicians and patients whose lives he touched. This work is dedicated, in part, to his memory—with deep respect and appreciation.