Flexed lumbar spine postures are associated with greater strength and efficiency than lordotic postures during a maximal lift in pain-free individuals

Key points

1. 01Participants produced their highest back-extensor moment in a fully flexed posture and their lowest in the extended (lordotic) posture.
2. 02More flexed postures needed less muscle activity for more force, raising neuromuscular efficiency about 25% from extended to mid-range and roughly three-fold from mid-range to full flexion.
3. 03An extended, standing-like lumbar posture could not actually be maintained during lifting; even the 'extended' attempt still held about 22.7 degrees of flexion.
4. 04Hip and knee moments and internal oblique (abdominal) activity did not change with lumbar posture.
5. 05Findings are mechanical only (force and EMG in pain-free people); the authors caution flexion may increase anterior shear and, if repeated, creep on the lower spine.

How it was conducted

Design

Experimental, repeated-measures study of maximal voluntary isometric trunk extension in a symmetrical lifting position

Participants

26 healthy, pain-free adults (13 male, 13 female; mean age 23.4 years), no low back pain in the prior 12 months

Conditions

Three lumbar postures held by each person, randomly ordered: fully flexed, mid-range (flat-back), and maximal extension (lordotic/arch)

Measures

Motion analysis and force plates for back-extensor, hip and knee moments; surface EMG of upper and lower erector spinae, multifidus, and internal oblique

Primary outcomes

Normalised back-extensor moment, normalised muscle activity, and neuromuscular efficiency (NME, the ratio of normalised moment to normalised EMG)

What they found

• Normalised extensor moment showed a significant main effect of posture (P < 0.0001), with post-hoc differences between flexed and mid-range (P = 0.003), mid-range and extended (P = 0.016), and flexed and extended (P = 0.0001).
• Back-extensor muscle activity decreased by 10.9% (95% CI 3.9% to 17.9%, P = 0.001) from extended to mid-range, and by a further 26.8% (95% CI 17.1% to 36.4%, P = 0.001) from mid-range to flexed.
• Neuromuscular efficiency rose about 25%, from a mean of 1.26 (95% CI 1.14 to 1.38) in the extended posture to 1.65 (95% CI 1.41 to 1.9) at mid-range (P = 0.012), then roughly tripled to 3.73 (95% CI 2.81 to 4.65) at full flexion (P = 0.007).
• Back-extensor activity was about 75% of MVIC in the extended posture versus about 40% of MVIC at full flexion.
• Internal oblique activity was low (approximately 6% to 12% MVIC) and did not differ significantly between postures.
• Lumbar posture had no effect on hip or knee moments (P > 0.05).
• Mean peak lumbar flexion was 56.2 degrees (95% CI 51.4 to 61.1) in the flexed condition, while the 'extended' posture still retained about 22.7 degrees of flexion (95% CI 18.3 to 27.2).

Limitations

• Small single study of 26 healthy, young, pain-free adults, so results may not generalise to older workers or people with back pain.
• Used static maximal isometric exertions in a controlled position, not real dynamic lifting of loads.
• Outcomes were mechanical surrogates (force, muscle activity, efficiency), not pain, injury, or long-term spinal health.
• The authors note the efficient flexed posture may increase anterior shear forces and, if repeated, spinal creep, a potential downside not captured by the strength and efficiency measures.

Why it matters

For patients

If lifting with a slightly rounded back feels stronger and more natural than forcing a straight arch, that matches what this study found, though it does not prove rounding is risk-free.

For clinicians

This adds in vivo mechanical evidence questioning blanket advice to lift with a lordotic spine, while still flagging that flexion increases shear loading and that pain and injury were not measured.

For readers

The familiar rule to 'lift with a straight back' is not well supported by strength and efficiency data, but the science here is about mechanics in healthy people, not proof of what prevents injury.