Intramuscular pressure, tissue oxygenation and EMG fatigue measured during isometric fatigue-inducing contraction of the multifidus muscle

Lumbar multifidus layers stiffness at L5-S1 level in prone and sitting posture measured by shear wave elastography

BACKGROUND

Multifidus is an important lumbar muscle with distinct superficial and deep fibers responsible for torque production and stabilization, respectively. Its mechanical properties change when transitioning from lying to sitting positions, necessitating enhanced stability. It holds crucial clinical relevance to assess these layers separately, especially in the sitting posture, which demands increased neuromuscular control compared to the prone position.

OBJECTIVE

To compare lumbar multifidus stiffness in lying versus sitting postures, analyzing both superficial and deep layers.

METHODS

Supersonic Shear Imaging captured elastographic images from 26 asymptomatic volunteers in prone and seated positions.

RESULTS

Left multifidus shear modulus in lying: 5.98 ± 1.80/7.96 ± 1.59 kPa (deep/superficial) and sitting: 12.58 ± 4.22/16.04 ± 6.65 kPa. Right side lying: 6.08 ± 1.97/7.80 ± 1.76 kPa and sitting: 13.25 ± 4.61/17.95 ± 7.12 kPa. No side differences (lying p= 0.99, sitting p= 0.43). However, significant inter-postural differences occurred.

CONCLUSION

Lumbar multifidus exhibits increased stiffness in sitting, both layers affected, with superior stiffness in superficial versus deep fibers. Applying these findings could enhance assessing multifidus stiffness changes, for classifying tension-induced low back pain stages.

Can intermittent changes in trunk extensor muscle length delay muscle fatigue development?

Muscle length changes may evoke alternating activity and consequently reduce local fatigue and pain during prolonged static bending. The aim of this study was to assess whether a postural intervention involving intermittent trunk extensor muscle length changes (INTERMITTENT) can delay muscle fatigue during prolonged static bending when compared to a near-isometric condition (ISOMETRIC) or when participants were allowed to voluntarily vary muscle length (VOLUNTARY). These three conditions were completed by 11 healthy fit male participants, in three separate sessions of standing with 30 ± 3 degrees trunk inclination until exhaustion. Conventional and high-density electromyography (convEMG and HDsEMG, respectively) were measured on the left and right side of the spine, respectively. The endurance time for INTERMITTENT was 33.6% greater than ISOMETRIC (95% CI: [3.8, 63.5]; p = 0.027) and 29.4% greater than VOLUNTARY (95% CI: [7.0, 51.7]; p = 0.010), but not different between ISOMETRIC and VOLUNTARY. The convEMG and HDsEMG amplitude coefficient of variation was significantly greater for INTERMITTENT versus ISOMETRIC. The rate of change in convEMG and HDsEMG spectral content did not reveal significant differences between conditions as found in endurance time. Additional regression analyses between endurance time and rate of change in convEMG (p > 0.05) and HDsEMG (R2 = 0.39-0.65, p = 0.005-0.039) spectral content indicated that HDsEMG better reflects fatigue development in low-level contractions. In conclusion, imposed intermittent trunk extensor muscle length changes delayed muscle fatigue development when compared to a near-isometric condition or when participants were allowed to voluntarily vary muscle length, possibly due to evoking alternating activity between/within trunk extensor muscles.

Posture-related stiffness mapping of paraspinal muscles

The paraspinal compartment acts as a bone-muscle composite beam of the spine. The elastic properties of the paraspinal muscles play a critical role in spine stabilization. These properties depend on the subjects' posture, and they may be drastically altered by low back pain. Supersonic shear wave elastography can be used to provide quantitative stiffness maps (elastograms), which characterize the elastic properties of the probed tissue. The aim of this study was to challenge shear wave elastography sensitivity to postural stiffness changes in healthy paraspinal muscles. The stiffness of the main paraspinal muscles (longissimus, iliocostalis, multifidus) was measured by shear wave elastography at the lumbosacral level (L3 and S1) for six static postures performed by volunteers. Passive postures (rest, passive flexion, passive extension) were performed in a first shear wave elastography session, and active postures (upright, bending forward, bending backward) with rest posture for reference were performed in a second session. Measurements were repeated three times for each posture. Sixteen healthy young adults were enrolled in the study. Non-parametric paired tests, multiple analyses of covariance, and intra-class correlations were implemented for analysis. Shear wave elastography showed good to excellent reliability, except in the multifidus at S1, during bending forward, and in the multifidus at L3, during bending backward. Yet, during bending forward, only poor quality was recorded for nine volunteers in the longissimus. Significant intra- and inter-muscular changes were observed with posture. Stiffness significantly increased for the upright position and bending forward with respect to the reference values recorded in passive postures. In conclusion, shear wave elastography allows reliable assessment of the stiffness of the paraspinal muscles except in the multifidus at S1 and longissimus, during bending forward, and in the multifidus at L3, during bending backward. It reveals a different biomechanical behaviour for the multifidus, the longissimus, and the iliocostalis.

Determining Physiological and Psychological Predictors of Time to Task Failure on a Virtual Reality Sørensen Test in Participants With and Without Recurrent Low Back Pain: Exploratory Study

BACKGROUND

Sørensen trunk extension endurance test performance predicts the development of low back pain and is a strong discriminator of those with and without low back pain. Performance may greatly depend on psychological factors, such as kinesiophobia, self-efficacy, and motivation. Virtual reality video games have been used in people with low back pain to encourage physical activity that would otherwise be avoided out of fear of pain or harm. Accordingly, we developed a virtual reality video game to assess the influence of immersive gaming on the Sørensen test performance.

OBJECTIVE

The objective of our study was to determine the physiological and psychological predictors of time to task failure (TTF) on a virtual reality Sørensen test in participants with and without a history of recurrent low back pain.

METHODS

We recruited 24 individuals with a history of recurrent low back pain and 24 sex-, age-, and body mass index-matched individuals without a history of low back pain. Participants completed a series of psychological measures, including the Center for Epidemiological Studies-Depression Scale, Pain Resilience Scale, Pain Catastrophizing Scale, Tampa Scale for Kinesiophobia, and a self-efficacy measure. The maximal isometric strength of trunk and hip extensors and TTF on a virtual reality Sørensen test were measured. Electromyography of the erector spinae, gluteus maximus, and biceps femoris was recorded during the strength and endurance trials.

RESULTS

A two-way analysis of variance revealed no significant difference in TTF between groups (P=.99), but there was a trend for longer TTF in females on the virtual reality Sørensen test (P=.06). Linear regression analyses were performed to determine predictors of TTF in each group. In healthy participants, the normalized median power frequency slope of erector spinae (beta=.450, P=.01), biceps femoris (beta=.400, P=.01), and trunk mass (beta=-.32, P=.02) predicted TTF. In participants with recurrent low back pain, trunk mass (beta=-.67, P<.001), Tampa Scale for Kinesiophobia (beta=-.43, P=.01), and self-efficacy (beta=.35, P=.03) predicted TTF.

CONCLUSIONS

Trunk mass appears to be a consistent predictor of performance. Kinesiophobia appears to negatively influence TTF for those with a history of recurrent low back pain, but does not influence healthy individuals. Self-efficacy is associated with better performance in individuals with a history of recurrent low back pain, whereas a less steep median power frequency slope of the trunk and hip extensors is associated with better performance in individuals without a history of low back pain.

Organization of the fascia and aponeurosis in the lumbar paraspinal compartment

PURPOSE

The thoracolumbar fascia (TLF) and the erector spinae aponeurosis (ESA) play significant roles in the biomechanics of the spine and could be a source of low back pain. Attachment, collagen fiber direction, size and biomechanical properties of the TLF have been well documented. However, questions remain about the attachment of the TLF and ESA in relation to adjoining tissues in the lumbosacral region. Moreover, quantitative data in relation to the ESA have rarely been examined. The aim of this study was to further investigate the anatomical features of the TLF and ESA and to determine the attachments and sliding areas of the paraspinal compartment through dissection.

MATERIALS AND METHODS

In 10 fresh cadavers (6 females, 4 males, mean age: 77 ± 10 years), we determined (1) the gross anatomy of the ESA and the TLF (attachments and sliding areas) and (2) the structure of the ESA and the TLF (thickness, width, orientation of collagen fibers). The pennation angle between the axis of the ES muscle fibers and the axis of the collagen fibers of the ESA were also measured.

RESULTS

The TLF is an irregular dense connective tissue with a mean thickness of 0.95 mm. The distance between the spinous processes line and the site where the neurovascular bundles pierced the TLF, depending on the vertebral level, ranged from 29 mm at L1 to 75 mm at L3. The ESA constituted a band of regular longitudinally oriented connective fibers (mean thickness: 1.85 mm). Muscles fibers of the ES were strongly diagonally attached to the ESA (mean pennation angle 8° for the iliocostalis and 14° for the longissimus). To a lesser extent, the superficial multifidi were attached to the ESA at the lumbar level close to the midline and at the sacral level.

CONCLUSION

The ESA, at twice the thickness of the pTLF, was the thickest dense connective tissue of the paraspinal compartment. The ESA and the TLF circumscribed subcompartments and sliding areas between the TFL and the lumbar paraspinal muscles, between the ES and the multifidus, and between the longissimus and the iliocostalis.

Low Back Pain in Patients with Lumbar Spinal Stenosis-Hemodynamic and electrophysiological study of the lumbar multifidus muscles

Introduction

Several studies have demonstrated improvement in low back pain (LBP) after decompression surgery for lower extremity symptoms in lumbar spinal stenosis (LSS); however, the influence of neuropathic disorders on LBP is uncertain. Aim of this study is to identify the features of motion-induced and walking-induced LBP in patients with LSS and to assess whether neuropathic LBP develops.

Methods

In total, 234 patients with LSS including L4/5 lesion were asked to identify their LBP. Subjects were classified into three groups: walking-induced LBP that aggravated during walking (W group), motion-induced LBP that aggravated during sitting up (M group), and no LBP (N group). Cross-sectional areas of the dural sac, lumbar multifidus, and the erector spinae were measured. Intramuscular oxygenation was evaluated with near-infrared spectrophotometer. Surface electromyography (EMG) and mechanomyography (MMG) were performed on the lumbar multifidus. Morphological, hemodynamic, and electrophysiological differences in the onset of LBP were evaluated.

Results

The prevalence of W, M, and control groups was 31.2%, 32.1%, 36.8%, respectively. Concordance between the laterality of LBP and leg symptoms including pain and numbness was 86.3% in the W group and 47.0% in the M group. Dural sac area was lower in the W group than in the M and control groups. In the hemodynamic evaluation, the oxygenated hemoglobin level was significantly lower in the W group than in the M and N groups. In electrophysiological evaluation of lumbar multifidus, the mean power frequency in EMG was significantly higher in the W group than in the N group. Amplitude in MMG was significantly lower in the W group than in the N group.

Conclusions

Neurologic disturbance in patients with LSS may be attributed to “neuropathic LBP.” Neuropathic multifidus disorder plays a role in walking-induced LBP.

Multispectral opto-acoustic tomography of exercised muscle oxygenation

Unlike near-infrared spectroscopy, multispectral opto-acoustic tomography (MSOT) has the potential to offer high-resolution imaging assessment of hemodynamics and blood saturation levels in muscle. However motion artifacts impede the real-time applications of the technique. We developed fast-MSOT with motion tracking that reduces motion artifacts. We used this algorithm to follow blood oxygenation level changes associated with muscle exercise in the muscle and the skin of healthy volunteers.

Creation of an asymmetrical gradient of back muscle activity and spinal stiffness during asymmetrical hip extension

BACKGROUND

Low back pain is often associated with increased spinal stiffness which thought to arise from increased muscle activity. Unfortunately, the association between paraspinal muscle activity and paraspinal stiffness, as well as the spatial distribution of this relation, is unknown. The purpose of this investigation was to employ new technological developments to determine the relation between spinal muscle contraction and spinal stiffness over a large region of the lumbar spine.

METHODS

Thirty-two male subjects performed graded isometric prone right hip extension at four different exertion levels (0%, 10%, 25% and 50% of the maximum voluntary contraction) to induce asymmetric back muscle activity. The corresponding stiffness and muscle activity over bilateral paraspinal lumbar regions was measured by indentation loading and topography surface electromyography, respectively. Paraspinal stiffness and muscle activity were then plotted and their correlation was determined.

FINDINGS

Data from this study demonstrated the existence of an asymmetrical gradient in muscle activation and paraspinal stiffness in the lumbar spine during isometric prone right hip extension. The magnitude and scale of the gradient increased with the contraction force. A positive correlation between paraspinal stiffness and paraspinal muscle activity existed irrespective of the hip extension effort (Pearson correlation coefficient, range 0.566-0.782 (P<0.001)).

INTERPRETATION

Our results demonstrate the creation of an asymmetrical gradient of muscle activity and paraspinal stiffness during right hip extension. Future studies will determine if alterations in this gradient may possess diagnostic or prognostic value for patients with low back pain.

Muscle oxygenation and intramuscular pressure related to posture and load in back muscles

BACKGROUND CONTEXT

There is little information about the simultaneous changes of intramuscular pressure (IMP) and oxygen saturation (StO(2)) of the paraspinal muscle under various conditions of posture and load.

PURPOSE

To measure simultaneously and compare IMP and StO(2) across a range of static trunk postures commonly observed during normal work tasks.

STUDY DESIGN

A prospective study using a repeated-measure design in clinical setting.

PATIENT SAMPLE

Sixteen healthy young men with no history of back pain.

OUTCOME MEASURES

Simultaneous measurements of IMP by a flexible slit catheter and StO(2) by near infrared spectroscopy of the multifidus muscle were performed.

METHODS

The two measures were taken in six static posture tasks: standing upright and bending forward with and without load (20kg), bending backward and during a sustained isometric contraction (ie, Sorensen test). To compare the influence of the tasks on IMP and StO(2) variables, a one-way variance analysis with repeated measures was used. Spearman's rank correlation coefficient (rho) was determined between the two variables for each posture task.

RESULTS

We observed only a moderate but significant correlation between IMP and StO(2) values in upright standing and a trend in bending forward positions with load (p<.05). IMP increased in the bending backward position and showed the greatest increase during the Sorensen test. StO(2) decreased significantly during the Sorensen test, in the bending forward position with and without load bearing but did not in bending backward.

CONCLUSION

The simultaneous recording of IMP and StO(2) of the multifidus muscle allows a deeper insight of physiological events during various trunk postures. In the mutifidus muscle, there is no evident linear relationship between IMP and StO(2) values in various static postures of the trunk in young males. This preliminary study shows that IMP may play a role on StO(2) only in some circumstances, such as a prolonged endurance test or in a bending forward position with a significant load bearing.

Low-level activity of the trunk extensor muscles causes electromyographic manifestations of fatigue in absence of decreased oxygenation

This study was designed to determine whether trunk extensor fatigue occurs during low-level activity and whether this is associated with a drop in muscle tissue oxygenation. Electromyography (EMG) feedback was used to impose constant activity in a part of the trunk extensor muscles. We hypothesized that electromyographic manifestations of fatigue and decreased oxygenation would be observed at the feedback site and that EMG activity at other sites would be more variable without fatigue manifestations. Twelve volunteers performed 30-min contractions at 2% and 5% of the maximum EMG amplitude (EMGmax) at the feedback site. EMG was recorded from six sites over the lumbar extensor muscles and near-infrared spectroscopy was used to measure changes in oxygenation at the feedback site (left L3 level, 3 cm paravertebral). In both conditions, mean EMG activity was not significantly different between electrode sites, whereas the coefficient of variation was lower at the feedback site compared to other recording sites. The EMG mean power frequency (MPF) decreased consistently at the feedback site only. At 5% EMGmax, the decrease in MPF was significant at the group level at all sites ipsilateral to the feedback site. These results suggest that the limited variability of muscle activity at the EMG feedback site and at ipsilateral locations enhances fatigue development. No decreases in tissue oxygenation were detected. In conclusion, even at mean activity levels as low as 2% EMGmax, fatigue manifestations were found in the trunk extensors. These occurred in absence of changes in oxygenation of the muscle tissue.