Lumbar Flexion Angle Research Articles

Effects of prolonged sitting on the passive flexion stiffness of the in vivo lumbar spine

Background context Prolonged sitting may alter the passive stiffness of the lumbar spine. Consequently, performing full lumbar flexion movements after extended periods of sitting may increase the risk of low back injury. Purpose The purpose was to quantify time-varying changes in the passive flexion stiffness of the lumbar spine with exposure to prolonged sitting and to link these changes to lumbar postures and trunk extensor muscle activation while sitting. A secondary objective was to determine whether men and women responded differently to prolonged sitting. Study design Passive lumbar flexion moment-angle curves were generated before, during and after 2 hours of sitting. Lumbar flexion/extension postures and extensor muscle activation levels were measured while sitting. Sample Twelve (6 men, 6 women) university students with no recent low back pain were studied. Outcome measures Quantified changes in the shapes of the passive flexion moment-angle curves (slopes, breakpoints and maximum lumbar flexion angles) were the outcome measures. While sitting, average lumbar flexion/extension angles, the distribution of lumbar flexion/extension postures, average electromyogram (EMG) amplitude, the number and average length of EMG gaps, and trunk extensor muscle rest levels were measured. Methods Participants performed deskwork for 2 hours while sitting on the seat pan of an office chair. Moment-angle relationships for the lumbar spine were derived by pulling participants through their full voluntary range of lumbar flexion on a customized frictionless table. Results Lumbar spine stiffness increased in men after only 1 hour of sitting, whereas the responses of women were variable over the 2-hour trial. Men appeared to compensate for this increase in stiffness by assuming less lumbar flexion in the second hour of sitting. Conclusions Changes in the passive flexion stiffness of the lumbar spine may increase the risk of low back injury after prolonged sitting and may contribute to low back pain in sitting.

Precision of estimates of mean and peak spinal loads in lifting

A bootstrap procedure was used to determine the statistical precision of estimates of mean and peak spinal loads during lifting as function of the numbers of subjects and measurements per subject included in a biomechanical study. Data were derived from an experiment in which 10 subjects performed 360 lifting trials each. The maximum values per lift of the lumbar flexion angle, L5S1 sagittal plane moment, and L5S1 compression force were determined. From the data set thus compiled, 3000 samples were randomly drawn for each combination of number of subjects and number of measurements considered. The coefficients of variation of mean and peak (defined as mean plus 2 standard deviations) spinal loads across these samples were calculated. The coefficients of variation of the means of the three parameters of spinal load decreased as a linear function of the number of subjects to a power of about −0.48 and number of measurements to a power of about −0.06, while the corresponding powers for peak loads were about −0.44 and −0.11.

Variability of Lifting Technique of Experienced Women Lifters across Light, Medium and Heavy Loads

The purpose of this study was to examine the variability in lifting technique kinematics within and between 35 female subjects when lifting light, medium and heavy loads. Each female performed five lifts in a free-style from floor to shoulder-height of a box (37times;29times;27 cm) with handles at three weights: 5, 10 and 15 kg. Polhemus Fastrak™, 3D electromagnetic sensors placed on the wrist, T***I, L***I and S***I spinous processes revealed spinal kinematics that showed increasing variability with heavier loads at the T***I sensor, L***I sensor, thoracic flexion angle, lumbar flexion angle and trunk flexion displacements. The velocity profiles provided similar results of variability for the T***I sensor, L***I sensor, S***I sensor, thoracic and lumbar flexion velocities. In addition, differences in technique were examined between loads using knee bend, box to body distance and trunk mean angles.

Passive tissues help the back muscles to generate extensor moments during lifting

We examined the possibility that passive tissues can help the erector spinae to generate large extensor moments during lifting. One hundred and forty-nine healthy men and women participated in the study. Subjects pulled upwards with steadily increasing force on a floor-mounted load cell, while EMG activity was recorded from electrodes overlying the erector spinae at L3 and T10. Extensor moment was calculated from the load cell data, and was plotted against the full-wave rectified and averaged EMG signal. The relationship was linear with an intercept on the extensor moment axis ( I) which indicated the flexion moment resisted by ‘passive’ (electrically silent) tissues. The dependence of I on lumbar flexion angle was studied by repeating the isometric pulls between 6 and 12 times, with the subject positioned in varying amounts of flexion, as measured by the ‘3-Space Isotrak’. Subjects then lifted weights of up to 20 kg from the floor, using ‘stoop’, ‘squat’ and ‘freestyle’ techniques, while lumbar flexion and EMG activity were recorded at 28 Hz. The isometric pulls showed that, on average, I increased from 25 Nm in lordotic postures to 120 Nm (for men) and 77 Nm (for women), in full flexion. During the lifts, peak extensor moment was generated with the lumbar spine flexed by 78–97% of the range between erect standing and full flexion. Comparisons with the static calibrations showed that between 16 and 31% of the peak extensor moment generated during lifting was unrelated to EMG activity in the erector spinae. Comparisons with cadaveric data suggested that less than a quarter of this ‘passive’ extensor moment was due to the intervertebral discs and ligaments.