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

Abstract

Background: Inspite of common lifting advice to maintain a lordotic posture, there is debate regarding optimal lumbar spine posture during lifting. To date, the influence of lumbar posture on trunk muscle recruitment, strength and efficiency during high intensity lifting has not been fully explored.

Research question: How do differences in lumbar posture influence trunk extensor strength (moment), trunk muscle activity, and neuromuscular efficiency during maximal lifting?

Methods: Twenty-six healthy participants adopted three lumbar postures (maximal extension (lordotic), mid-range (flat-back), and fully flexed) in a free lifting position. Motion analysis and force measurements were used to determine the back extensor, hip and knee moments. Surface electromyography (EMG) of three trunk extensors and the internal obliques were recorded. Neuromuscular efficiency (NME) was expressed as a ratio of normalised extensor moment to normalised EMG.

Results: Significantly higher back extensor moments were exerted when moving from an extended to mid-range, and from a mid-range to fully flexed lumbar posture. This was accompanied by a decrease in activity across all three back extensor muscles (P < 0.001) resulting in a higher NME of these muscles in more flexed postures. Change in lumbar posture did not influence hip or knee moments or internal oblique activation.

Significance: A flexed-back posture is associated with increased strength and efficiency of the back muscles compared to a lordotic posture. These findings further question the manual handling advice to lift with a lordotic lumbar spine.

Keywords: Electromyography; Extensor moment; Low back pain; Lumbar spine; Trunk muscles.