Lifting Posture: The Controversy Whether Lordotic or Kyphotic Posture Should be Maintained While Lifting.
Which type of posture is safer for the spine when lifting things? There has been much controversy in the scientific literature as to the preferred strategy for lifting. This may actually come as some surprise to many of you who believe that lifting with a flat or arched back (lordotic posture) is unequivocally the safer and more efficient way to lift things. The proponents of the rounded back (kyphotic posture) lifting theory, most prominently Serge Gracovetsky and Harry Farfan, argue that the back muscles are not strong enough to properly support the spine and that when lifting naturally (without being coached how to lift) we round our backs and rely on the posterior ligaments to support our spine. Gracovetsky and Farfan claim that lifting with an arched back is dangerous, since contraction of the erector spinae muscles increases the compressive load on the spine.(1,2,3)
In fact, a central problem in spinal biomechanics has been to explain how it can be that when the theoretical forces about the spine are computed when bending over and lifting a moderately heavy weight that the calculated compressive load on the spine, taking into account the compression imposed by contraction of the erector spinae muscles, is greater than that which the spine can withstand. Aspden writes, "A fundamental problem in spinal mechanics...[is] that of explaining why the vertebrae [or discs] are not crushed during the lifting of even relatively small loads."(4) This problem has been wrestled with by spinal experts for years.
Gracovetsky and Farfan attempt to solve this problem partially by proposing a model of the spine where lifting occurs without great involvement of the back muscles. They argue that lifting with a rounded back (kyphotic lifting posture) is safer since this results in less contraction of the erector spinae (lower back) muscles, instead relying on the passive bracing of the posterior ligamentous system and the thoraco-lumbar fascia (TLF) of the spine for support. They claim that this lifting posture/strategy is to be preferred, since it results in less spinal compression and less tendency for shear forces in the spine.
Gracovetsky argues that the lower back muscles are not located posterior enough to the spine to be able to exert very much extensor torque. Instead, he argues that these muscles are located very close and lateral to the spine, which is an indication that these muscles were never intended to generate much power. (5) Because these muscles are located so close to the center of the discs, contraction of these erector muscles results in increased spinal disc compression. He also argues that studies reveal that the erector spinae muscles are actually too small to handle the necessary load to support the trunk.(6)
Gracovetsky and Michael Adams have both argued (in separate papers) that the posterior ligaments, esp. the supraspinous and interspinous, and the thoracolumbar fascia, have longer lever arms than the lumbar muscles due to their posterior location (spinous process attachment).(3,7,8) They also claim that these ligaments produce a posterior shear force, which helps to counter the tendency for L5 to slide forwards (anterior shear) that occurs during lifting. Therefore it is more efficient to round the back when lifting in order to engage the posterior ligaments to support the spine. This also allows us to utilize the gain of the TLF abdominal support mechanism. Gracovetsky goes so far as to state that maintaining lordosis while lifting "always results in an increase of the compressive force of the spine" (9) and "is dangerous and places the spine at risk."(10) He goes on to state that when in doubt, "it is safer to overflex one's spine." (11)
Gracovetsky claims that farm and industrial workers instinctively bend over and round their backs when lifting since they are instinctively using the safest and most efficient method of lifting. Mayer also notes that healthy industrial workers who are not instructed to lift a certain way lift with a rounded back.(12) Such a strategy conserves energy by shifting some of the load to the passive ligamentous structures. It could not be the case that we instinctively bend and lift in a way that is destructive to our spines.
Adams notes that his studies have shown that even when trained individuals tried to lift weights with a full lordosis, they actually rounded their backs, averaging 57% flexion.(13) He claims that while 100% flexion may lead to disc injury, 60 to 80% of full flexion is the ideal posture while lifting heavy objects. Adams points out that advising patients to keep their back flat or arched while lifting is good advice, however, it probably just serves to reduce flexion to 60 to 80% of full flexion (which Adams considers to be ideal).
In contrast to Gracovetsky, Farfan, and Adams, we argue that it is much safer to lift with a flat or slightly arched lower back. The erector muscles are maximally activated and can generate greater force to protect the spine when lordosis is maintained.(14) It is strategically sounder to rely upon our back muscles rather than our ligaments to support our spine while lifting. Ligaments are obviously designed to check excess motion or stress at joints but our muscles are designed for handling most of the stress on a regular basis. Muscles can contract and shorten or lengthen via nervous system input to react to various stresses and forces at joints, whereas ligaments cannot contract to react to changing forces. In fact, if ligaments are loaded for any time period they deform or creep, i.e. they stretch out. The kyphotic lifting strategy, where you end up hanging on your ligaments is likely to lead to such creep and eventually to spinal instability. Research has correlated lifting with knees straight and the back bent with an increased risk of disc herniation.(15,16)
Injury to spinal ligaments such as the annulus of the disc, is even more likely to occur if there has been a previous injury. Previously injured ligaments are not capable of withstanding as much loading without failing (tearing). Since the exact anatomical cause of low back pain is usually indeterminable, it is not known who has previously suffered an injury to a spinal ligament. Therefore, we feel that hanging on a ligamentous structure with an uncertain tissue tolerance level is like playing Russian roulette.
The muscles also have a plentiful blood supply and can heal fairly rapidly from injury, whereas ligaments have a poor blood supply and have very limited capacity for healing from injury. Therefore, if you rely on the back muscles and suffer an injury to the muscles, healing from such an injury would likely involve a shorter recovery period than healing from a ligament injury.
The posterior ligaments of the spine are not as strong as Gracovetsky presumed. For one thing, the supraspinous ligament rarely extends below L4, which means that one of the key ligaments cannot help to stabilize the most vulnerable segments of the spine--L4/5 and L5/S1.(17) Recent investigation also indicates that this ligament is composed of a loose collagen structure interspersed with loose, fatty tissue, which means that it lacks tensile stiffness.(18) The supraspinous ligament, then is only able to offer limited resistance to flexion. One of the other key ligaments--the interspinous ligament--may also not be as strong or as helpful as supposed. Careful dissection studies have revealed that the fibers of this ligament do not run parallel but rather run somewhat obliquely. Thus, the interspinous ligament may not be as efficient at resisting flexion forces as first thought.(19) And the fibers of this ligament run in such a direction (from the anterior part of the spinous of the vertebra below to the posterior portion of the spinous process of the vertebra above) that pulling on this ligament actually produces rather than resists anterior shear forces as Gracovetsky had hypothesized.(20,21) In fact, Potvin hypothesizes that a possible mechanism for back injury would be the increased anterior shear created by the interspinous ligament if lifting occurred while maximally flexing the spine.(17) And Bogduk maintains that much of what appears to be the interspinous ligament is actually tendons of the back muscles.(22)
While the ligaments are not as strong as Gracovetsky thought, the erector spinae muscles are actually quite a bit larger and stronger than estimated by him. The studies relied upon by Gracovetsky used cadavers of older individuals, whose muscles are much smaller than those of young, active subjects. More recent studies using CT scans found that the erector muscles of young, healthy males to be capable of more than the twice the force that Gracovetsky estimated.(23) We speculate that the back muscles of experienced weight lifters and bodybuilders are capable of generating significantly more force than this. Can you imagine comparing the erector spinae muscles of Mr. Olympia Dorian Yates to those of a dead 60 year old sedentary man?! And these lumbar erector muscles are capable of producing significantly more posterior shear forces on the lower spine than Gracovetsky had supposed. The substantial posterior shear forces produced by the lumbar erector muscles help to balance the tendency towards anterior shear that occurs while lifting. This is achieved to the greatest extent when lordosis is maintained while lifting, since this facilitates activation of these muscles. Therefore, lifting with a flat or arched back will help to prevent injuries by using the erector muscles to prevent the anterior shear that is exacerbated by the interspinous ligaments when lifting with a rounded back.(24)
1. Gracovetsky, The Spinal Engine,
Springer-Varlag: New York, 1988, p.152.
2. Farfan HF, Mechanical Disorders of the Low Back, Philadelphia: Lea and Febiger, 1973.
3. Gracovetsky S, Farfan H, Lamy C, "The Mechanism of the Lumbar Spine", Spine, 1981, 6: 249-262.
4. Aspden RM, "Intra-abdominal Pressure and its Role in Spinal Mechanics," Clinical Biomechanics, 1987, 2: 168-174.
5. Gracovetsky, The Spinal Engine, p.107.
6. Gracovetsky, The Spinal Engine, p.122.
7. Gracovetsky S, Farfan H, Helleur C. "The Abdominal Mechanism," Spine, 1985, 10: 317-324.
8. Adams MA, Dolan P, "Posture and Spinal Mechanisms During Lifting," in The Integrated Function of the Lumbar Spine and Sacroiliac Joint, 1995, eds. by Vleeming A, Mooney V, Dorman T, Snijders C: 19-28.
9. Gracovetsky, The Spinal Engine, p.152.
10. Gracovetsky, The Spinal Engine, p.122.
11. Gracovetsky, The Spinal Engine, p.153.
12. Mayer TG, Barnes D, Kishino ND, et al., "Progressive Isoinertial Lifting Evaluation 1. A Standardized Protocol and Normative Database." Spine, 1988, 13: 993-7.
13. Adams MA, Dolan P, "Posture and Spinal Mechanisms During Lifting," in The Integrated Function of the Lumbar Spine and Sacroiliac Joint, 1995, eds. by Vleeming A, Mooney V, Dorman T, Snijders C: p.23.
14. Holmes JA, Damaser MS, Lehman SL, "Erector Spinae Activation and Movement Dynamics About the Lumbar Spine in Lordotic and Kyphotic Squat-Lifting," Spine, 1992, 17: 327-334.
15. Kelsey JL, et al, "An Epidemiologic Study of Lifting and Twisting on the Job and Risk for Acute Prolapsed Lumbar Intervertebral Disc", Journal of Orthopaedic Research, 1984, 2: 61-66.
16. Mundt DJ, Githens PB, White AA, et al., "An Epidemiological Study of Non-Occupational Lifting as a Risk Factor for Herniated Lumbar Intervertebral Disc," Spine, 1993, 18, 595-602.
17. Bogduk N, Twomey LT. Clinical Anatomy of the Lumbar Spine. 2nd ed. (Churchill Livinstone: New York, 1991), p.40.
18. Hukins DWL, Kirby MC, Sikoryn TA, Aspden RM, Cox AJ, "Comparison of Structure, Mechanical Properties, and Functions of Lumbar Spinal Ligaments, Spine, 1990, 15: 787-795.
19. Heylings DJA, "Supraspinous and Interspinous Ligaments of the Human Lumbar Spine," J. Anatomy, 1978, 125: 127-131.
20. McGill SM, "Estimation of Force and Extensor Moment Contributions of the Disc and Ligaments at L4/5," Spine, 1988, 13: 1395.
21. Potvin JR, Norman RW, McGill SM, "Reduction in Anterior Shear Forces on the L4/5 Disc by the Lumbar Musculature" Clin Biomech, 1991, 6: 88-96.
22. Bogduk N, "The Anatomical Basis for Spinal Pain Syndromes" JMPT, 1995, 8: 603.
23. McGill SM, Patt N, Norman RW. "Measurement of the Trunk Musculature Of Active Males Using CT Scan Radiography: Implications for Force and Moment Generating Capacity about the L4/5 Joint." J Biomech, 1988, 21: 329-41.
24. Potvin JR, Norman RW, McGill SM, "Reduction in Anterior Shear Forces on the L4/5 Disc by the Lumbar Musculature" Clin Biomech, 1991, 6: 95.