An in vivo assessment of the low back response to prolonged flexion: Interplay between active and passive tissues

Background Full flexion lumbar postures maintained over a prolonged period of time have been shown to lead to changes in the supporting passive structures of the spine and it has been hypothesized that this may lead to low back pain/disorders. However, the specific biomechanics and physiology of this link have not been fully developed. Of particular interest is the interplay between the active and passive extensor mechanisms and the role of rest break in this response. Methods Ten healthy participants performed a regimen of a 10-min full lumbar flexion followed by a 10-min upright standing, with a slow speed isokinetic lift every 2.5 min. Changes in the full lumbar flexion angle (system creep) and the electromyographic activity of back extensors in the isokinetic lifts were evaluated. Findings Results showed significant increases in the full flexion angle and increased activity of the extensor muscles in the prolonged flexion to compensate for the reduced extension moment producing capability of the passive tissues. A 30-s rest break in the middle of the flexion moderated these viscoelastic responses. Interpretation The results suggest that prolonged lumbar flexion results in the systematic transfer of an extension moment from passive tissues to active muscles. Heavy lifting or high force exertion of back muscles immediately after prolonged flexion could be a risk factor for low back disorders when the muscles lose their force generating capacity due to passive stretching. This study also indicated the importance of sufficient rest between consecutive full flexion tasks in reducing the risk. Article Outline 1. Introduction 2. Methods 2.1. Subjects 2.2. Apparatus 2.3. Experimental procedures 2.4. Experimental variables 2.5. Data processing and statistical analysis 3. Results 3.1. Full lumbar flexion angle 3.2. EMG of extensor muscles 4. Discussion References 4. You are not entitled to access the full text of this document Can activity within the external abdominal oblique be measured using real-time ultrasound imaging? Pages 972-979 E.K. John, I.D. Beith Close Preview Purchase PDF (281 K) | Related Articles AbstractAbstract | Figures/TablesFigures/Tables | ReferencesReferences Abstract Background Differences in the function of the anterolateral abdominal muscles have been the subject of much investigation, but primarily using electromyography. Recently changes in thickness of transversus abdominis and internal oblique measured from real-time ultrasound images have been shown to represent activity within these muscles. However it is still unclear if such a change in thickness in external oblique similarly represents activity within that muscle. The purpose of this study was to investigate the relationship between change in thickness and muscle activity in the external oblique using real-time ultrasound and surface electromyography. Methods Simultaneous measurements of electromyography and real-time ultrasound images of external oblique were studied in up to 24 subjects during two tasks compared to the muscle at rest (1) isometric trunk rotation and (2) drawing in the lower abdomen. Findings Changes in muscle thickness correlated significantly with electromyography during isometric trunk rotation in the majority of subjects but with a significant difference between subjects. In contrast, the relationship between change in thickness and electrical activity in the muscle when drawing in the lower abdomen was significant in less than 50% of subjects and the muscle often got thinner. Interpretation Thickness changes of external oblique can be used as a valid indicator of electromyography activity during isometric trunk rotation, though the relationship is not as good as previously published data for transversus abdominis. Thickness changes of external oblique measured during lower abdominal drawing in cannot be used to detect activity within this muscle.