Goal of the Study?
In this cross-sectional laboratory design article from the Journal of Applied Biomechanics1 the authors’ goal was to determine how sustained lumbar spine flexion affects the pain sensitivity of young healthy adults.
Why are they doing this study?
Sustained lumbar spine flexion creep, which is defined as a gradual length change under a constant load, appears to disrupt the collagen connectivity and reduce the load tolerance strength within ligaments and other soft tissue about the spine. This damage to surrounding tissues can cause localized low back pain. Longer exposures can cause spinal creep and have been associated with a higher risk of pain development; this finding is not universal. This study is an attempt to understand how viscoelastic creep generated in the lumbar spine following sustained spine flexion affects the relationship between tissue damage and perceived pain.
What was done?
Thirty-eight healthy young individuals; 19 men and 19 women, were recruited. Inclusion criteria were no history of lower back pain in the last 12 months and currently not taking any pain medications. They were also not allowed to consume any alcohol, caffeine, high fat foods or vitamin supplements in the last 24 hours. Each participant was exposed to ten minutes of sustained seated maximal spine flexion followed by a 40-minute standing recovery period. Lumbar spine flexion was measured by triaxial accelerometers and an average and maximum flexion angle was measured. A pressure algometer, which applied a one square centimetre pressure point at a rate of four millimetres per second provided three measures of mechanical pain sensitivity ; (1) pressure pain thresholds; (2) perceptions of subthreshold stimulus unpleasantness and (3) perceptions of subthreshold stimulus intensity. For pressure pain thresholds, participants were told to release the switch as soon as the pressure became painful. Five dependent variables assessed were; pressure pain thresholds, subthreshold stimulus intensity and unpleasantness, maximum lumbar spine flexion angles and surface Electromyography (EMG) of the erector spinae muscle bulk at the L3 level.
What did they find?
The study presented evidence that seated sustained lumbar spine flexion can affect pain processing but does not appear to alter local pressure pain thresholds. Spinal flexion creep, induced by a ten-minute sustained spinal flexion exposure does not appear to trigger an obvious neural or inflammatory-based mechanism to alter pain sensitivity. Pain sensitization appears to be altered through some other means. The authors postulate that it may be cortically influenced. The study data also supported previous research that female participants, in general, find fixed pressures to be more intense than men. Additional stratification by age indicates that this difference dissipates in older adults.
Why do these findings matter?
Postures involving sustained lumbar spine flexion, such as stooped forward bending or slumped sitting alter afferent neural feedback from the tissues within the lower back. These afferent signals can influence pain processing pathways within the brain and spinal cord, increasing pain sensitivity. Lumbar spine flexion has been related to low back pain but the mechanism is not entirely understood.
At Dynamic Disc Designs, we have developed realistic lumbar modelling that can help demonstrate the act of lumbar flexion on a spinal motion segment. If flexion is suspected as a mechanism for someone’s low back pain pain, our models can help teach this movment and help the practitioner construct a plan to alieviate their pain.