Search

We explore the effect of stress-recovery schedule on the cumulative creep response of lumbar tissues. Twelve participants performed a 48-minute protocol that consisted of 12 min of full trunk flexion and 36 min of upright standing. Two stress-recovery (work-rest) schedules were considered: a) three minutes of full trunk flexion followed by twelve minutes of upright standing (3:12), and b) one minute of full trunk flexion followed by four minutes of upright standing (1:4). Lumbar kinematics and EMG activity of erector spinae muscles were collected. Cumulative creep deformation was explored by considering the changes in peak lumbar flexion angles during full flexion and changes in the angles of flexion-relaxation (EMG-off) of the lumbar extensor musculature after the 48-minute protocol. The results of time-dependent lumbar flexion angle during full flexion revealed a noticeable creep response in both work-rest schedules, but the cumulative creep response was significantly greater in the 3:12 schedule (Δ3.5°) than in the 1:4 schedule (Δ1.6°). Similarly, the change in the EMG-off lumbar flexion angle in the 3:12 schedule was significantly greater than in the 1:4 schedule (Δ2.5° vs -Δ0.2°, respectively). These results indicate that the passive lumbar tissues recover their force producing capability more rapidly with shorter cycle times., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study aims to identify how spatial distribution of lumbar muscle activity is modulated by different fatigue tasks. Twenty healthy adults performed two different isometric trunk extension endurance tasks (the modified Sorensen test and the inverted modified Sorensen test) until exhaustion. During these tasks, bilateral superficial lumbar muscle activity was recorded using high-density electromyography. The spatial distribution of activation within these muscles was obtained using the centroid coordinates in the medio-lateral and cranio-caudal directions. The effects of task and endurance time (left and right sides) were investigated using repeated measures ANOVA. Results revealed a significant lateral shift of the centroid throughout the fatigue tasks on both sides and no difference between tasks. Significant task × time interaction effects were found for the cranio-caudal direction on both sides showing a significantly more caudal location of the centroid in the modified Sorensen test compared to the inverted test at the beginning of the tasks. Our findings suggest that spatial distribution of lumbar muscle activity is task-dependent in a pre-fatigue stage while an alternative but similar muscle recruitment strategy is used in both tasks to maintain performance in the later stages of muscle fatigue., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Viscoelastic creep of spine tissue, induced by submaximal spine flexion in sitting, can delay the onset of the flexion-relaxation phenomenon (FRP) and low back reflexes (LBR). Theoretically, these two outcome measures should be correlated; however, no studies have investigated this. This study aims to determine whether 30 min of near-maximal spine flexion will affect the onset of FRP and LBR in the lumbar erector spinae (LS) and lumbar multifidus (LM), and to examine the relation between these parameters. 15 participants were recruited (9F, 6M). Spine angle (between L1 and S2) was monitored synchronously with bilateral muscle activity in the LS (L1) and the LM (L4). FRP onset and LBR were measured in a randomized order before and after 30 min of slouched sitting. No significant difference was found for any muscle LBR onset time between pre and post-sitting (p > 0.05). A significant increase in FRP onset was found in the RLM (p = 0.016) following sitting. No significant correlation was found between the FRP and the LBR for any muscle. These results suggest that the LBR onset might not be as sensitive as an outcome measure to investigate shorter exposures of sitting as FRP., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Shear wave elastography (SWE) estimates shear modulus in muscle. This is interpreted as an index of muscle stiffness, but depends on muscle characteristics. This study evaluated relationship between shear modulus and myoelectric activity of lumbar multifidus and longissimus muscles to assess its validity. Intramuscular electromyography (EMG) of multifidus (deep [DM], superficial [SM] fibres) at L4/5, longissimus [LG] at L2, were recorded in nine healthy participants. Participants performed isometric trunk extension in side-lying from 0 to 30% maximal voluntary contraction (MVC) with EMG amplitude feedback. Using SWE, two regions of interest (ROI) were investigated in each muscle. Generally, shear modulus was moderately correlated with root mean squared (RMS) EMG (r = 0.50-0.78). Univariate and multiple regression analyses showed ultrasound/SWE features of 'B-mode quality' (24.5%), '%Void pixels' (17.9%) and 'Connective tissue' (16.2%) explained most variation in the shear modulus/EMG relationship. Regression prediction scores generated using imaging features were correlated with r-coefficients of shear modulus/EMG relationship. When analysis was restricted to high quality data (i.e., regression prediction score above an a priori defined threshold), the shear modulus/EMG relationship increased to r = 0.70-0.96. Although a linear relationship between shear modulus/EMG was confirmed, supporting validity of SWE measures in anatomically distinct back muscles, this depends on image quality., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study aimed to clarify the difference in the onset of EMG activity between eight trunk muscles, including the anterior (QL-a) and posterior (QL-p) layers of the quadratus lumborum during rapid shoulder joint abduction. Thirteen healthy men participated in this study. Electromyography of the QL-a, QL-p, transversus abdominis (TrA), internal oblique (IO), external oblique (EO), rectus abdominis (RA), lumbar multifidus (LMF), lumbar erector spinae (LES) on non-movement side, and middle deltoid (MD) on the movement side were measured. Subjects who were standing in a relaxed position performed rapid shoulder abduction with the dominant hand after light stimulus with or without a 3 kg wrist weight. Two-way ANOVA (muscles × weight conditions) was used to compare the onset of trunk muscles relative to that of MD. There was a significant main effect of the muscles. The onset of the QL-a, QL-p, and TrA was significantly earlier than that of the IO, EO, LMF, and LES (P < 0.01). This result suggests that the activities of the QL-a, QL-p, and TrA have a crucial role in controlling the center of mass within the base of support and stabilizing the lumbar spine in the coronal plane during shoulder abduction., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest. Koji Kaneoka is currently receiving a grant-in-aid for Scientific Research (C) from the Japan Society for the Promotion of Science. None of the remaining authors have received funding., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Abdominal bracing is a voluntary method of increasing spine stiffness to restrict spine displacement. Previous investigations of abdominal bracing have measured effects on whole lumbar motion; however, how this effect is distributed across the lumbar spine is unknown. Therefore, this study was designed to test the influence of abdominal bracing on spine intersegmental (T9/T10 to L5/S1) flexion, measured via skin surface markers, in response to sudden loading perturbations applied through the hands in 16 young healthy participants. Abdominal and back muscle activation responses were also measured. The results demonstrated that abdominal bracing significantly reduced sagittal plane motion at intersegmental levels T12/L1 to L4/L5, by 45% (0.74 degrees) at L4/L5 to 94% (0.71 degrees) at L1/L2 compared to control. L5/S1 experienced a 50% (0.36 degrees) reduction, but this was not statistically significant. Additionally, abdominal bracing resulted in greater baseline activation of all abdominal and back muscles, but did not affect onset times or response magnitudes of any of the back muscles acting counter to the perturbation. Therefore, the elevated baseline activation of trunk musculature during an abdominal brace serves to restrict flexion motion at the majority of the intersegmental lumbar spine (T12/L1 to L4/5) in response to sudden trunk flexion perturbations., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Clinically, sagittal spinal mobility is objectively assessed by forward bending range of motion (ROM) tests such as the modified-Schober test (m-Schober test). However, evidence comparing ROM during forward bending and daily activities is limited. In this study, a kinematic model including six spinal regions, pelvic/sacral and femur segment was used to characterize associations between m-Schober test and return from forward bending (RFB), and between RFB and lifting. No significant correlations were found between m-Schober test and lumbar ROM during RFB. Furthermore, we found significantly smaller ROM in all spinal regions during lifting compared to RFB, except in the upper thoracic spine, lumbosacral (L5/S1) and hip joints. However, we observed moderate to very strong correlations between the two movements tasks for all lumbar regions. Furthermore, cross-correlation between L5/S1 and lower lumbar spine regions showed no segmental redundancy of L5. These results suggest that an m-Schober test provides insufficient insight into lumbar mobility and that multi-segmental spine measurements should be introduced clinically. Furthermore, this study has demonstrated that RFB can be used as a reference for lumbar regions during lifting, with use of the current multi-segmental spine model and that the inclusion of L5/S1 provides more detailed information on lumbar kinematics., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Persons with low back pain (LBP) have demonstrated altered morphology and function of the deep multifidus (DM). This study examined the effects of postural cueing for increased lumbar lordosis on DM and longissimus thoracis (LT) activation during lumbar stabilization exercises (LSE) performed by persons with LBP. Nine adults with a history of chronic or recurrent LBP were recruited. Fine-wire EMG data was collected while participants performed 10 LSE's in neutral posture and with postural cueing. Percent maximum voluntary isometric contraction of L5 DM and T12 LT, and ratios of activation (DM/LT) were analyzed. There was a significant main effect for posture on DM activation (p < 0.001), indicating greater activation levels during exercises performed with postural cueing vs. neutral posture. LT activation did not increase significantly with postural cueing. Following a significant 1-way repeated measures ANOVA (p = 0.034) for the postural cueing condition, pairwise comparisons demonstrated significantly higher DM/LT activation ratios for prone leg lift, variable-angle Roman chair at 15°, bridging, and bilateral arm and leg lift. These results suggest postural cueing can be used across a range of LSE intensities to increase DM activation without a significant increase in LT activation in patients with chronic or recurrent LBP., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

High impact exercise can reduce postmenopausal bone loss, however stimulus frequency (loading cycles per second) can affect osteogenesis. We aimed to examine the effect of stimulus frequency on the mechanical loading of four common osteoporosis prevention exercises, measuring body acceleration and muscle activation with accelerometry and electromyography (EMG), respectively. Fourteen early postmenopausal women completed randomised countermovement jumps (CMJ), box-drops (BD), heel-drops (HD) and stamp (STP) exercises for continuous and intermittent stimulus frequencies. Sacrum accelerometry and surface electromyography (EMG) of four muscles were recorded. CMJ (mean ± SD: 10.7 ± 4.8 g & 10.0 ± 5.0 g), BD (9.6 ± 4.1 g & 9.5 ± 4.0 g) and HD (7.3 ± 3.8 g & 8.6 ± 4.4 g) conditions generated greater peak acceleration than STP (3.5 ± 1.4 g & 3.6 ± 1.7 g) across continuous and intermittent trials. CMJ and BD generated greater acceleration gradients than STP across continuous and intermittent trials. CMJ generated greater rectus femoris EMG than all other exercises, CMJ and BD generated greater semitendinosus and tibialis anterior EMG than HD across continuous and intermittent trials. CMJ and BD provide greater peak acceleration than STP and remain similar during different stimulus frequencies. CMJ, BD and HD may exceed STP in maintaining postmenopausal bone health., (Crown Copyright © 2018. Published by Elsevier Ltd. All rights reserved.)

This study investigated test-retest reliability of mechanomyography (MMG) on lumbar paraspinal muscles. Healthy male and female subjects (mean ± standard deviation, 25 ± 9.4 years, BMI 21.8 ± 2.99, n = 34) were recruited. Two test sessions (one week apart) consisted of MMG (laser displacement sensor (LDS)) muscle evaluations over the 10 lumbar facet joints, and 2 bilateral sacral sites, in anatomical extension and flexion. Two-way repeated measures ANOVA with Tukey's post hoc showed no significant differences between testing sessions for the same position (p > 0.05). The intra-class correlation coefficients (ICCs) in extension were classified as 'very good' (0.8-0.9) for maximal muscle displacement (Dmax), contraction time (Tc) and velocity of contraction (Vr). Half relaxation time (½Tr) and half relaxation velocity (½Vr) were 'poor' (0.4-0.5) and 'good' (0.7-0.8). In flexion, Dmax, Tc and Vr were 'excellent' (≥0.9) whilst ½Tr and ½Vr were 'fair' (0.6-0.7) and 'very good'. Comparing extension against flexion, significant (p < 0.05) differences in Dmax and ½Vr were found (L1/L2-L5/S1). Tc was significant (p < 0.05) for all sites whilst Vc was for L1/L2 on both sides (p < 0.05). ½Tr showed no significance (p > 0.05). Most MMG-derived parameters thus appear as reliable measures of muscle contractile properties in lumbar extension and flexion, with flexion providing more reliable results (ICCs)., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background: Low back pain (LBP) has been previously associated with delayed anticipatory postural adjustments (APAs) determined by trunk muscle activation. Lumbar stabilization exercise programs (LSEP) for patients with LBP may restore the trunk neuromuscular control of the lumbar spine, and normalize APAs. This exploratory study aimed at testing the reliability of EMG and kinematics-based postural adjustment measures over an 8-week interval, assessing their sensitivity to LBP status and treatment and examining their relationship with clinical outcomes., Methods: Muscle activation of 10 trunk muscles, using surface electromyography (EMG), and lumbar angular kinematics were recorded during a rapid arm-raising/lowering task. Patients with LBP were tested before and after an 8-week LSEP. Healthy controls receiving no treatment were assessed over the same interval to determine the reliability of the measures and act as a control group at baseline. Muscle activation onsets and reactive range of motion, range of velocities and accelerations were assessed for between group differences at baseline and pre- to post-treatment effects within patients with LBP using t-tests. Correlations between these dependent variables and the change of clinical outcomes (pain, disability) over treatment were also explored., Results: Kinematic-based measures showed comparable reliability to EMG-based measures. Between-group differences were found in lumbar lateral flexion ROM at baseline (patients < controls). In the patients with LBP, lateral flexion velocity and acceleration significantly increased following the LSEP. Correlational analyses revealed that lumbar angular kinematics were more sensitive to changes in pain intensity following the LSEP compared to EMG measures. These findings are interpreted in from the perspective of guarding behaviors and lumbar stability hypotheses., Conclusion: Future clinical trials are needed to target patients with and without delayed APAs at baseline and to explore the sensitivity of different outcome measures related to APAs. Different tasks more challenging to postural stability may need to be explored to more effectively reveal APA dysfunction., (Copyright © 2018. Published by Elsevier Ltd.)

"Use your legs" is commonly perceived as sound advice to prevent lifting-related low-back pain and injuries, but there is limited evidence that this directive attenuates the concomitant biomechanical risk factors. Body segment kinematic data were collected from 12 men and 12 women who performed a laboratory lifting/lowering task after being provided with different verbal instructions. The main finding was that instructing participants to lift "without rounding your lower back" had a greater effect on the amount of spine flexion they exhibited when lifting/lowering than instructing them to lift "with your legs instead of your back" and "bend your knees and hips". It was concluded that if using verbal instructions to discourage spine flexion when lifting, the instructions should be spine- rather than leg-focused., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Introduction: Changes in movement variability and complexity may reflect an adaptation strategy to fatigue. One unresolved question is whether this adaptation is hampered by the presence of low back pain (LBP). This study investigated if changes in movement variability and complexity after fatigue are influenced by the presence of LBP. It is hypothesised that pain free people and people suffering from LBP differ in their response to fatigue., Methods: The effect of an isometric endurance test on lumbar movement was tested in 27 pain free participants and 59 participants suffering from LBP. Movement variability and complexity were quantified with %determinism and sample entropy of lumbar angular displacement and velocity. Generalized linear models were fitted for each outcome. Bayesian estimation of the group-fatigue effect with 95% highest posterior density intervals (95%HPDI) was performed., Results: After fatiguing %determinism decreased and sample entropy increased in the pain free group, compared to the LBP group. The corresponding group-fatigue effects were 3.7 (95%HPDI: 2.3-7.1) and -1.4 (95%HPDI: -2.7 to -0.1). These effects manifested in angular velocity, but not in angular displacement., Discussion: The effects indicate that pain free participants showed more complex and less predictable lumbar movement with a lower degree of structure in its variability following fatigue while participants suffering from LBP did not. This may be physiological responses to avoid overload of fatigued tissue, increase endurance, or a consequence of reduced movement control caused by fatigue., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Modeling the lumbar spine as a single rigid segment does not consider the relative contribution of regional or segmental motion that may occur during a task. The current study used a multi-segment model to measure three-dimensional (3D) upper and lower lumbar spine motion during walking and prone hip extension (PHE). The degree of segmental redundancy during these movements was assessed by calculating the cross-correlation of the segmental angle time series (R 0 ) and the correlation of the segmental ranges of motion (R ROM ). All correlation coefficients (R 0 , R ROM ) were interpreted as follows: very strong (0.80-1.00), strong (0.60-0.79), moderate (0.40-0.59), weak (0.20-0.39), and very weak (0.00-0.19). Strong/very strong positive R 0 were demonstrated between the two segments in all three planes during PHE and in the transverse plane during walking. Weak/moderate R 0 were demonstrated in the sagittal and frontal planes during walking. Strong/very strong positive R ROM were demonstrated in the transverse plane during PHE, and moderate positive R ROM was demonstrated in the sagittal plane during walking. Non-significant R ROM were demonstrated for all other planes and movements. These results suggest the motion patterns of the upper and lower lumbar regions during walking and PHE are sufficiently distinct to warrant the use a multi-segment model for these movements. It also appears that the degree of redundancy between the upper and lower lumbar regions may be task-dependent., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Musicians activate their muscles in different patterns, depending on their posture, the instrument being played, and their experience level. Bipolar surface electrodes have been used in the past to monitor such activity, but this method is highly sensitive to the location of the electrode pair. In this work, the spatial distribution of surface EMG (sEMG) of the right trapezius and right and left erector spinae muscles were studied in 16 violin players and 11 cello players. Musicians played their instrument one string at a time in sitting position with/without backrest support. A 64 sEMG electrode (16×4) grid, 10mm inter-electrode distance (IED), was placed over the middle and lower trapezius (MT and LT) of the bowing arm. Two 16×2 electrode grids (IED=10mm) were placed on the left and right erector spinae muscles. Subjects played each of the four strings of the instrument either in large (1bow/s) or detaché tip/tail (8bows/s) bowing in two sessions (two days). In each of two days, measurements were repeated after half an hour of exercise to see the effect of exercise on the muscle activity and signal stability. A "muscle activity index" (MAI) was defined as the spatial average of the segmented active region of the RMS map. Spatial maps were automatically segmented using the watershed algorithm and thresholding. Results showed that, for violin players, sliding the bow upward from the tip toward the tail results in a higher MAI for the trapezius muscle than a downward bow. On the contrary, in cello players, higher MAI is produced in the tail to tip movement. For both instruments, an increasing MAI in the trapezius was observed as the string position became increasingly lateral, from string 1 (most medial) toward string 4 (most lateral). Half an hour of performance did not cause significant differences between the signal quality and the MAI values measured before and after the exercise. The MAI of the left and right erector spinae was smaller in the case of backrest support, especially for violin players. Back muscles of violin and cello players were activated asymmetrically, specifically in fast movements (detaché tip/tail). These findings demonstrate the sensitivity and stability of the technique and justify more extensive investigation following this proof of concept., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Flexion relaxation (FR) is characterized by the lumbar erector spinae (LES) becoming myoelectrically silent near full trunk flexion. This study was designed to: (1) determine if decreasing the lumbar moment during flexion would induce FR to occur earlier; (2) characterize thoracic and abdominal muscle activity during FR. Ten male participants performed four trunk flexion/extension movement conditions; lumbar moment was altered by attaching 0, 5, 10, or 15lb counterweights to the torso. Electromyography (EMG) was recorded from eight trunk muscles. Lumbar moment, lumbar flexion and trunk inclination angles were calculated at the critical point of LES inactivation (CPLES). Results demonstrated that counterweights decreased the lumbar moment and lumbar flexion angle at CPLES (p<0.0001 and p=0.0029, respectively); the hypothesis that FR occurs earlier when lumbar moment is reduced was accepted. The counterweights did not alter trunk inclination at CPLES (p=0.1987); this is believed to result from an altered hip to spine flexion ratio when counterweights were attached. Lumbar multifidus demonstrated FR, similar to LES, while thoracic muscles remained active throughout flexion. Abdominal muscles activated at the same instant as CPLES, except in the 15lb condition where abdominal muscles activated before CPLES resulting in a period of increased co-contraction., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Purpose: Lumbar multifidus is a complex muscle with multi-fascicular morphology shown to be differentially controlled in healthy individuals during sagittal-plane motion. The normal behaviour of multifidus muscle regions during walking has only received modest attention in the literature. This study aimed to determine activation patterns for deep and superficial multifidus in young adults during walking at different speeds and inclination., Methods: This observational cohort study evaluated ten healthy volunteers in their twenties (three women, seven men) as they walked on a treadmill in eight conditions; at 2km/h and 4km/h, each at 0, 1, 5, and 10% inclination. Intramuscular EMG was recorded from the deep and superficial multifidus unilaterally at L5. Activity was characterized by: amplitude of the peak of activation, position of peak within the gait cycle (0-100%), and duration relative to the full gait cycle., Results: Across all conditions superficial multifidus showed higher normalised EMG amplitude (p<0.01); superficial multifidus peak amplitude was 232±115% higher when walking at 4km/h/10%, versus only 172±77% higher for deeper region (p<0.01). The percentage of the gait cycle where peak EMG amplitude was detected did not differ between regions (49±13%). Deep multifidus duration of activation was longer when walking at the faster vs slower speed at all inclinations (p<0.01), which was not evident for superficial multifidus (p<0.05). Thus, a significantly longer activation of deep multifidus was observed compared to superficial multifidus when walking at 4km/h (p<0.05)., Conclusions: Differential activation within lumbar multifidus was shown in young adults during walking. The prolonged, more tonic activation of deep relative to superficial regions of multifidus during gait supports a postural function of deeper fibres., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The purpose of this study was to clarify the effectiveness of expiration and abdominal bracing maneuvers in response to sudden trunk loading in healthy subjects. Fifteen healthy male subjects were anteriorly loaded under different experimental conditions. Tests were conducted at rest and while performing each of the stabilization maneuvers (expiration and abdominal bracing) at 15% of the maximal voluntary isometric contraction of the internal oblique muscle. Subjects had no knowledge of the perturbation timing. An electromyographic biofeedback system was used to control the intensity of internal oblique muscle activation. Muscular pre-activation of three trunk muscles (internal oblique, external oblique, and L3 erector spinae muscles) and lumbar acceleration in response to loading were measured. The expiration and abdominal bracing maneuvers promoted torso co-contraction, reduced the magnitude of lumbar acceleration, and increased spinal stability compared to the resting condition. There were no differences between the expiration and abdominal bracing maneuvers in the pre-activation of the three trunk muscles or in lumbar acceleration in response to loading. It appears that both expiration and abdominal bracing maneuvers are effective in increasing spinal stability in response to sudden anterior loading., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Flexion relaxation (FR), a myoelectric silence of extensor muscles near end range of lumbar flexion, is commonly reported as the lumbar flexion angle at the instant the extensor muscles become silent. However, lumbar flexion angle alone is insufficient to characterize mechanisms that modulate FR. As FR requires the moment generated by passive lumbar extensor tissues to equilibrate the moment due to gravity, the inter-relationships between lumbar moment, flexion angle, and myoelectrical silence will provide added information in the understanding of FR. The purpose of this study was to examine the relationship between lumbar moment and flexion angle throughout various flexion manoeuvres. It was hypothesized that lumbar moment and flexion angle would not be linearly related and would be affected by lower limb position, range of motion, and the addition of mass to the torso. Eleven participants performed four different lumbar flexion trials. Results showed that lumbar flexion was correlated with the lumbar moment (r = 0.92); however an analysis of residuals found that these measures were not linearly related. The moment was, however, correlated (r = 0.99) and linearly related to the sine of trunk inclination (T12 rigid body with respect to global horizontal). Future studies of FR could use trunk inclination as a simple kinematic measure to predict relative changes in lumbar moment with flexion., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Trunk extension exercises are used to train endurance and strength of the trunk extensor muscles. Appropriate exercise dosage is crucial to achieve specific training effects, however literature describing the relation between the predetermined exercise intensity and the actual trunk extensors activity is scarce and inconclusive. To examine whether the actual activity of the thoracic and lumbar extensors during extensions exercises correspond with the predetermined intensity, electromyographic evaluation of the trunk extensors was performed during trunk extension exercises at various intensities expressed as percentages of 1-RM. The 1-RM was predetermined using 2 different methods: (1) through direct estimation by determining the maximum isometric force produced during semi-seated trunk extension on a Tergumed rehabilitation device, (2) through indirect estimation calculated based on the relation between the maximum number of repetitions of trunk extension from prone lying on a variable angle chair and the submaximal resistance at which the repetitions were performed as presented on the Holten-diagram. The total trunk muscle activity during extension exercises performed semi-seated on a rehabilitation device or from prone lying corresponds with the predetermined dosage using both estimation methods. The indirect estimation method more accurately predicts the actual trunk extensor activity for low load training than for high load training. However, the direct estimation method is suitable to closely predetermine the load and actual trunk extensors activity during high load exercises. A shift from a differential recruitment between the thoracic and lumbar extensors at low intensities to a more homogenous recruitment at high intensities is observed during semi-seated trunk extension exercises. During prone extension exercises both muscle groups equally contribute to the total muscle work regardless of the exercise intensity. Based on these findings suggestions regarding the appropriate choice of estimation and performance method are made., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Intramuscular electromyography (EMG) is commonly used to quantify activity in the trunk musculature. However, it is unclear if the discomfort or fear of pain associated with insertion of intramuscular EMG electrodes results in altered motor behavior. This study examined whether intramuscular EMG affects locomotor speed and trunk motion, and examined the anticipated and actual pain associated with electrode insertion in healthy individuals and individuals with a history of low back pain (LBP). Before and after insertion of intramuscular electrodes into the lumbar and thoracic paraspinals, participants performed multiple repetitions of a walking turn at self-selected and controlled average speed. Low levels of anticipated and actual pain were reported in both groups. Self-selected locomotor speed was significantly increased following insertion of the electrodes. At the controlled speed, the amplitude of sagittal plane lumbo-pelvic motion decreased significantly post-insertion, but the extent of this change was the same in both groups. Lumbo-pelvic motion in the frontal and axial planes and thoraco-lumbar motion in all planes were not affected by the insertions. This study demonstrates that intramuscular EMG is an appropriate methodology to selectively quantify the activation patterns of the individual muscles in the paraspinal group, both in healthy individuals and individuals with a history of LBP., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this study, we aimed to compare the intrarater reliability and validity of muscle thickness measured using ultrasonography (US) and muscle activity via electromyography (EMG) during manual muscle testing (MMT) of the external oblique (EO) and lumbar multifidus (MF) muscles. The study subjects were 30 healthy individuals who underwent MMT at different grades. EMG was used to measure the muscle activity in terms of ratio to maximum voluntary contraction (MVC) and root mean square (RMS) metrics. US was used to measure the raw muscle thickness, the ratio of muscle thickness at MVC, and the ratio of muscle thickness at rest. One examiner performed measurements on each subject in 3 trials. The intrarater reliabilities of the % MVC RMS and raw RMS metrics for EMG and the % MVC thickness metrics for US were excellent (ICC=0.81-0.98). There was a significant difference between all the grades measured using the % MVC thickness metric (p<0.01). Further, this % MVC thickness metric of US showed a significantly higher correlation with the EMG measurement methods than with the others (r=0.51-0.61). Our findings suggest that the % MVC thickness determined by US was the most sensitive of all methods for assessing the MMT grade., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

To assess the electromyographic (EMG) activation of trunk muscle during exertions performed in one primary plane (sagittal, frontal, transverse), we previously proposed a protocol allowing minimizing out-of-plane efforts (coupled moments - CMs) with the use of a static dynamometer combined with a visual feedback system. The aims of this study were to go further by testing motor learning and reliability issues related to such a protocol. Three identical sessions were conducted, where maximal voluntary contractions and submaximal ramp contractions were performed in six different directions while standing in the dynamometer. Two feedback conditions were tested, the simple 1D-feedback in the primary plane and the full 3D-feedback in all planes simultaneously. Surface EMG signals were collected from back and abdominal muscles and EMG amplitude and CMs were computed during the ramp contractions. Providing a 3D feedback to minimize CMs did not improve EMG reliability or in other words, did not reduce the within-subject variability. Providing three assessment days had practically no effect (no learning) on CMs and EMG variables. Overall, the reliability of EMG was at best moderate. However, although this limits its use on an individual basis, it still allows within- and between-group comparisons for research applications., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The aim of this study was to investigate the relation between variability in muscle activity and fatigue during a sustained low level contraction in the lumbar muscles. Twenty-five healthy participants (13 men 12 women) performed a 30min sitting task with 5 degrees inclination of the trunk. Surface electromyographic (EMG) signals were recorded bilaterally from the lumbar muscles with 2 high density surface EMG grids of 9×14 electrodes. Median frequency (MDF) decrease, amplitude (RMS) increase and the rating of perceived exertion (RPE) were used as fatigue indices. Alternating activation and spatial and temporal variability were computed and relations with the fatigue indices were explored. During sitting, the mono- and bipolar RMS slightly increased while the MDF remained unchanged indicating no systematic muscle fatigue, although the average RPE increased from 6 to 13 on a scale ranging between 6 and 20. Higher frequency of alternating activation between the left and right side was associated with increased RPE (p=0.03) and decreased MDF (p=0.05). A tendency in the same direction was seen between increased spatial and temporal variation within the grids and increased RPE and decreased MDF. Present findings provide evidence for a relationship between variability in muscle activity and fatigue., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The aim of the current study was to analyze the activation characteristics and potential compartmentalization of the latissimus dorsi (LD) muscle during common maximal voluntary isometric contractions (MVICs) and functional dynamic tasks. Surface electromyography (sEMG) was used to measure activation magnitudes from four electrode sites (referenced to the T10, T12, L1 & L4 LD vertebral origins) across the fanning muscle belly of the LD. In addition, EMG waveforms were cross-correlated to study temporal activation timing between electrode sites (T10-T12, T12-L1, L1-L4 & T10-L4). The MVICs that were tested included a humeral adduction, humeral adduction with internal rotation, a chest-supported row and a humeral extension. Dynamic movements included sagittal lift/lowers from the floor to knee, knee to hip and hip to shoulder. No magnitude-based (p=0.6116) or temporal-based differences were observed between electrode sites during the MVIC trials. During dynamic movements no temporal-based, but some magnitude-based differences between electrode sites were observed to be present; these differences were small in magnitude and were observed for both the maximum (p=0.0002) and mean (p=0.0002) EMG magnitudes. No clear pattern of compartmentalization was uncovered in the contractions studied here. In addition to these findings, it was determined that the most effective MVIC technique for LD EMG normalization purposes was a chest-supported row MVIC, paired with a T12 electrode site., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Repetitive exposures to altered gait and movement following lower-limb amputation (LLA) have been suggested to contribute to observed alterations in passive tissue properties and neuromuscular control in/surrounding the lumbar spine. These alterations, in turn, may affect the synergy between passive and active tissues during trunk movements. Eight males with unilateral LLA and eight non-amputation controls completed quasi-static trunk flexion-extension movements in seven distinct conditions of rotation in the transverse plane: 0° (sagittally-symmetric), ±15°, ±30°, and ±45° (sagittally-asymmetric). Electromyographic (EMG) activity of the bilateral lumbar erector spinae and lumbar kinematics were simultaneously recorded. Peak lumbar flexion and EMG-off angles were determined, along with the difference ("DIFF") between these two angles and the magnitude of peak normalized EMG activities. Persons with unilateral LLA exhibited altered and asymmetric synergies between active and passive trunk tissues during both sagittally-symmetric and -asymmetric trunk flexion movements. Specifically, decreased and asymmetric passive contributions to trunk movements were compensated with increases in the magnitude and duration of active trunk muscle responses. Such alterations in trunk passive and active neuromuscular responses may result from repetitive exposures to abnormal gait and movement subsequent to LLA, and may increase the risk for LBP in this population., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The purpose of this study was to quantify the load on the lumbar spine of subjects when they are asked to adjust from a slouched sitting posture into an upright posture with one of three different strategies: "free" (no instruction) and two coached patterns: "lumbopelvic" dominant and "thoracic" dominant. The activity of selected muscles and kinematic data was recorded from 20 volunteers while performing the three movement patterns to adjust sitting posture. Moments and forces at the lumbar spine were computed from an anatomically detailed model that uses kinematics and muscle activation as input variables. The lumbopelvic pattern produces less joint moment on the lumbar spine (on average 31.2±3.9Nm) when compared to the thoracic pattern (43.8±5.8Nm). However, the joint compression force was similar for these two patterns, but it was smaller in the free pattern, when no coaching was given (lumbopelvic: 1279±112N, thoracic: 1367±(125N, free: 1181±118N). Lower thoracic erector muscle activity and higher lumbar erector activity were measured in the lumbopelvic pattern in comparison with the other two. In summary the lumbopelvic pattern strategy using predominantly the movement of anterior pelvic tilt results in smaller joint moments on the lumbar spine and also positions the lumbar spine closest to the neutral posture minimizing passive tissue stress. This may be the strategy of choice for people with low back flexion intolerance., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The aim of this study was to compare the activity of the erector spinae (ES) and hamstring muscles and the amount and onset of lumbar motion during standing knee flexion between individuals with and without lumbar extension rotation syndrome. Sixteen subjects with lumbar extension rotation syndrome (10 males, 6 females) and 14 healthy subjects (8 males, 6 females) participated in this study. During the standing knee flexion, surface electromyography (EMG) was used to measure muscle activity, and surface EMG electrodes were attached to both the ES and hamstring (medial and lateral) muscles. A three-dimensional motion analysis system was used to measure kinematic data of the lumbar spine. An independent-t test was conducted for the statistical analysis. The group suffering from lumbar extension rotation syndrome exhibited asymmetric muscle activation of the ES and decreased hamstring activity. Additionally, the group with lumbar extension rotation syndrome showed greater and earlier lumbar extension and rotation during standing knee flexion compared to the control group. These data suggest that asymmetric ES muscle activation and a greater amount of and earlier lumbar motion in the sagittal and transverse plane during standing knee flexion may be an important factor contributing to low back pain., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

To understand the effects of a resistive vibration exercise (RVE) countermeasure on changes in lumbo-pelvic muscle motor control during prolonged bed-rest, 20 male subjects took part in the Berlin Bed-Rest Study (in 2003-2005) and were randomised to a RVE group or an inactive control group. Surface electromyographic signals recorded from five superficial lumbo-pelvic muscles during a repetitive knee movement task. The task, which required stabilisation of the lumbo-pelvic region, was performed at multiple movement speeds and at multiple time points during and after bed-rest. After excluding effects that could be attributed to increases in subcutaneous fat changes and improvements in movement skill, we found that the RVE intervention ameliorated the generalised increases in activity ratios between movement speeds (p⩽0.012), reductions in lumbo-pelvic extensor and flexor co-contraction (p=0.058) and increases in root-mean-square electromyographic amplitude (p=0.001) of the lumbar erector spinae muscles. Effects of RVE on preventing increases in amplitude-modulation (p=0.23) of the lumbar erector spinae muscles were not significant. Few significant changes in activation-timing were seen. The RVE intervention during bed-rest, with indirect loading of the spine during exercise, was capable of reducing some, but not all, motor control changes in the lumbo-pelvic musculature during and after bed-rest., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Estimates of the amount of force exerted by a muscle using electromyography (EMG) rely partially upon the accuracy of the reference point used in the normalization technique. Accurate representations of muscle activities are essential for use in EMG-driven spinal loading models. The expected maximum contraction (EMC) normalization method was evaluated to explore whether it could be used to assess individuals who are not capable of performing a maximum exertion such as a person with a low back injury. Hence, this study evaluated the utility of an EMG normalization method (Marras and Davis, A non-MVC EMG normalization technique, Part 1, method development. Journal of Electromyography and Kinesiology 2000) that draws upon sub-maximal exertions to determine the reference points needed for normalization of the muscle activities. The EMC normalization technique was compared to traditional MVC-based EMG normalization by evaluating the spinal loads for 20 subjects (10 males and 10 females) performing dynamic lifts. The spinal loads (estimated via an EMG-assisted model) for the two normalization techniques were very similar with differences being <8%. The model performance variables indicated that both normalization techniques performed well (r(2)>0.9 and average error below 6%) with only the muscle gain being affected by normalization method as a result in different reference points. Based on these results, the proposed normalization technique was considered to be a viable method for EMG normalization and for use in EMG-assisted models. This technique should permit the quantitative evaluation of muscle activity for subjects unable to produce maximum exertions.

The purpose of this study was to determine, for different back muscles, if the median frequency (MF) of the electromyographic (EMG) power spectrum changes according to the position of the time window during a 5 s step contraction. Twenty males with no known back problems were standing upright in a dynamometer allowing lower limb and pelvis stabilization. Trunk extension efforts were performed by pushing on a force platform positioned at the T4 level while the extension moment at L5/S1 was displayed as visual feedback. The EMG signals from four homologous back muscles (multifidus at L5, ilicostalis lumborum at L3, and longissimus at L1 and T10) were collected using active surface electrodes during two 5 s static step contractions performed at five force levels (10, 20, 40, 60 and 80% of the maximal voluntary contraction). The root mean square (RMS) and MF values of the EMG signals corresponding to three 250 ms time windows (beginning, middle and end of each step contraction) were computed. The RMS values of several back muscles increased from the first to the third time window for contractions performed at high force levels only. However, a concomitant decrease in the MF values was observed only for the left multifidus muscle. It was concluded that muscle fatigue does not generally manifest itself during 5 s step contractions through the EMG signal. However, it is recommended to use step contractions lasting less than 5 s and to choose a time window located in the first 1-3 s to completely eliminate the possible effects of fatigue.

Normalization of muscle activity has been commonly used to determine the amount of force exerted by a muscle. The most widely used reference point for normalization is the maximum voluntary contraction (MVC). However, MVCs are often subjective, and potentially limited by sensation of pain in injured individuals. The objective of the current study was to develop a normalization technique that predicts an electromyographic (EMG) reference point from sub-maximal exertions. Regression equations predicting maximum exerted trunk moments were developed from anthropometric measurements of 120 subjects. In addition, 20 subjects performed sub-maximal and maximal exertions to determine the necessary characteristic exertions needed for normalization purposes. For most of the trunk muscles, a highly linear relationship was found between EMG muscle activity and trunk moment exerted. This analysis determined that an EMG-moment reference point can be obtained via a set of sub-maximal exertions in combination with a predicted maximal exertion (expected maximum contraction or EMC) based upon anthropometric measurements. This normalization technique overcomes the limitations of the subjective nature for the MVC method providing a viable assessment method of individuals with a low back injury or those unwilling to exert an MVC as well as could be extended to other joints/muscles.

Background: It is important to evaluate the reliability of common used methods of examining muscle fatigue from the lower back since the methods are used in patient evaluation., Methods: To establish between-days reliability, ten subjects without lower-back pain performed a Sorensen test, a prone test for back extensor muscles against gravity, on three separate days. EMG was recorded from the L1 and L5 of the back extensor muscles. Fatigue was subjectively rated using a Borg CR-10 scale. Intraclass correlation coefficient, standard error of measurement and coefficient of variation were calculated from a one-way ANOVA. Percent agreement was also calculated., Results: The study revealed good reliability for the slope for the total time (ICC 0.65-0.90), the initial and end median frequency (ICC 0.75-0.89), median frequencies at Borg ratings of three (ICC 0.63-0.88), five (ICC 0.62-0.84) and seven (ICC 0.67-0. 87), endurance time (ICC 0.89). The Borg ratings of the first minute agreed better than those of the second and the third. The Borg ratings at the second and the third test agreed to 40-80%, indicating a need for a practice session., Conclusion: The protocol used for assessing fatigue in the back extensor muscles proved to be reliable and is recommended for further use.

The objective of this study was to determine the frequency profile, median frequency (MF) and mean power frequency (MPF) of trunk muscles in an isometric graded maximal voluntary contraction (MVC) in isometric axial trunk rotation from a neutral upright seated posture. Twelve young healthy subjects (seven males, five females) were instrumented with surface electrodes on their external obliques, internal obliques, rectus abdominis, pectoralis, latissimus dorsi and erector spinae at T10 and L3 levels bilaterally. These subjects were stabilized in seated posture in an axial rotation tester (AROT) and asked to perform a graded isometric contraction of their maximal value to both right and left directions from a neutral posture within a period of 10s. EMG from all 14 channels were sampled at 1 kHz at 10% intervals of MVC from 10% to MVC. These samples were subjected to fast Fourier transform analysis. The frequency profile plots demonstrated the power of muscles involved in agonistic and antagonistic activity. However, the frequency composition showed little difference between them. The MF was higher in agonists of the same muscle. The MPF was always higher than MF. Both values were generally insignificantly different between different levels of contraction. However, with increasing level of contraction there was increase in power.

Many low-back patients undergo electromyography (EMG)-based evaluations of muscle performance but present to the clinic after being prescribed muscle relaxants. The question that needed to be addressed was, do centrally acting muscle relaxants (methocarbamol; Robaxin) affect the EMG spectral indices of muscle fatigue that are often used to assess muscle performance. Participants performed an isometric spine extension protocol involving a 30 s fatigue exertion trial, then 1 min rest, and finally a 10 s long repeat exertion trial, at a 60% maximum voluntary contraction (MVC) level of exertion. Seven men were tested on two separate days (approximately 3-7 days apart), one day while medicated (six doses) with Robaxin and on another while not medicated. Specifically, the following parameters were studied in the bilateral multifidus (L5), lower erector spinae (L3) and upper erector spinae (T9): the slope of median power frequencies (MPFs) over the duration of the trial and the initial y-intercept of the MPF. The results generally suggest that methocarbamol (Robaxin) does not have any significant affect on the EMG median power frequency of the extensors during a fatiguing contraction followed by a repeat exertion, at least in normal people (one exception was observed--one side of multifidus at L5). However, given that this appears to be the first study of its kind, and that a relatively small number of subjects were used in this study, further investigation is needed to make a definitive conclusion about the effects of this drug on the several features of the electromyogram, over a broad spectrum of the clinical population performing a wider variety of tasks.

This study investigated the trunk kinematics and electromyographic (EMG) activity of eight trunk muscles when "expected" and "unexpected" loads were applied directly to the torso. Twenty individuals (mean age: 25.1 yr; range 20-33 yr) participated in this mixed model study in which gender was the between-subjects factor, and expectancy and symmetry of the applied load were within-subject factors. The sudden load was delivered to the subject via a cable attached to a thoracic harness and motion was restricted to the lumbar spine by strapping the pelvis to a rigid fixation apparatus. Surface EMG was recorded bilaterally from the longissimus thoracis (LGT), erector spinae (ERS), rectus abdominis (RAB) and the external obliques (EXO). Trunk kinematics were measured with a Lumbar Motion Monitor. During expected loading conditions, the peak muscle activity was reduced for the RAB and EXO bilaterally, and for the ERS(R) (p < 0.01) relative to the unexpected conditions. Conversely, the normalized area of EMG activity prior to the onset of load was increased for the ERS and EXO bilaterally, and for the RAB(R) (p < 0.05) during an expected loading event. Trunk motion in the sagittal and frontal planes was reduced during expected loading. Activation of the trunk muscles just prior to a rapid loading event increases trunk stiffness, decreasing trunk displacement and peak muscle activity.

In a biomechanical model we described that for stability of the flat sacroiliac joints (SIJ) muscle forces are required which press the sacrum between the two hip bones (self-bracing). Shear loading of these joints is caused by gravity and longitudinally oriented muscles. Protection against shearing can come from transversely oriented muscles like the internal oblique (OI) abdominal muscles. For validation we used standing postures with significantly more or less OI activity compared to activity in a standardized erect standing reference posture. OI activity decreased significantly when (a) resting on one leg (the contralateral), as can be observed at bus stops, (b) tilting the pelvic backward and (c) applying a pelvic belt. We explain this decrease of OI activity by, respectively, decrease of gravity load, decrease of load from the psoas major muscles, and a substitute of self-bracing. The outcome of this study is in line with the biomechanical model on SIJ stability. Clinical relevance of this study regards aspecific low back pain and is found in the effect of the use of a pelvic belt, of a trunk position as adopted when wearing a small rucksack and of the benefit of exercising trunk muscles in extension and torsion.

Axial twisting of the torso has been identified via epidemiologic studies as a significant risk factor for occupationally-related low back disorders. However, only recently have biomechanical studies been able to describe how twisting is accomplished through the use of the trunk musculature. These studies have been performed on subjects whose torso twists were performed in an upright posture. In this study, the electromyographic activity of ten trunk muscles was observed while 12 subjects performed twisting exertions in three different trunk postures. These postures included upright twisting, twisting while the trunk was flexed in the sagittal plane, and twisting while the trunk was flexed and rotated asymmetrically. In addition, twisting velocity and direction of motion were changed under the experimental conditions. Under upright twisting conditions, the twisting torque was generated easily and relatively efficiently through the employment of the oblique (internal and external) and latissimus dorsi muscles. When the trunk was flexed the activity of erector spinae muscles increased (about 10-15%) while the external oblique activity decreased (about 3-5%). Twisting while in asymmetric bent postures was accomplished with a reduction in oblique and latissimus dorsi muscle activities (approximately 5%) while the erector spinae muscle activity remained elevated. The change in muscle activity needed to balance the torso during twisting while bending also increased the amount of lateral torque that was produced by the trunk. These findings suggest that studies observing trunk muscle activities and trunk loading while subjects were in upright postures should be interpreted with caution when evaluating the activity of the trunk during occupational activities. Since many occupational twisting tasks are performed in awkward, asymmetric postures, application of results from upright twisting studies might underestimate the risk of these activities.

Axial rotation of the trunk is commonly associated with back injury and pain. However, the behaviour of trunk muscles in axial rotation is poorly understood. The objective of this study was to measure spectral parameters from the EMG of erector spinae at T10 and L3 levels, latissimus dorsi, external and internal oblique, rectus abdominis and pectoralis major muscles bilaterally in a standardized repeatable axial rotation at 60% MVC to fatigue. Twelve young and healthy subjects were recruited after screening for musculoskeletal disorders. Surface electrodes were applied to the named seven trunk muscles bilaterally. Subjects were seated in the device called Axial Rotation Tester and stabilized such that they could rotate only their thoracolumbar spine. Other motions were prevented. Subjects held 60% of their MVC for a period of 2 min. Samples (2.1 s) were obtained at every 10 s interval at a sampling frequency of 1 KHz. Samples were subjected to FFT analysis. The total power and the median frequencies were analyzed. The median frequency for different muscles were different (p < 0.001). The slopes of decline of the median frequencies of the agonists were different for different muscles (p < 0.001). This differential fatiguing rate could conceivably create a force imbalance potentiating back injury.

A ligamento-muscular protective reflex in the lumbar spine was demonstrated in a feline model. Stimulating electrodes were applied to the supraspinous ligament between several lumbar vertebra (L1 to L6) while recording myoelectric discharge from the paraspinal muscles at the L3, L4 and L5, bilaterally. Electromyographic (EMG) activity was present in the paraspinal muscles bilaterally, upon stimulation of the supraspinous ligament, in six preparations. The EMG discharge was strongest in the muscles one level below that of the stimulated ligament, whereas weaker EMG signals were recorded from as far as two levels above and below. The mean time delay between the application of the stimulus to the ligament to the resulting EMG ranged from 2.52 to 2.77 ms at all levels. Stimulation of the supraspinous ligament in the L6 segment resulted in a weak reflex response, and stimulation in the L7 segment did not produce any EMG activity. It was concluded that mechanoreceptors in the supraspinous ligament at the L1/6 levels may initiate sensory signals upon strain of the ligament, during flexion. This, in turn, causes contraction of the paraspinal muscles, bilaterally, to extend the spine and prevent possible damage to the ligament while maintaining stability. The results may add to the understanding of low back pain, and to the formulation of surgical procedures which could spare the neural supply of the ligament, allowing advanced physiotherapeutic modalities to be implemented for post-surgical rehabilitation.

A new approach to estimating the frequency compression of the surface EMG signal during cyclical dynamic exercise is described. The basic properties of the method are first developed using simulated EMG signals. Spectral compression is measured by defining the instantaneous median frequency from time-frequency representations of the signal derived from a transformation of the Cohen class. The technique is then used to process real EMG signals from paraspinal muscles during repetitive lifting. Our purpose was to use this new procedure to identify (a) whether changes in the instantaneous median frequency among concurrently active paraspinal muscles during repetitive trunk extension produces a 'fatigue pattern' that is indicative of normal functioning, and (b) whether this pattern is different when the subject produces a sustained isometric trunk extension. Four healthy subjects (26 +/- 4 years; 3 males, 1 female) were tested in both a Back Analysis System, for the production of a sustained static isometric contraction, and a LIDO-Lift Controller (Loredan), for repetitive lifting and lowering of a weighted box. EMG signals were recorded concurrently from six bilateral lumbar paraspinal regions during these tasks. The results demonstrate that static and dynamic tasks result in very different patterns of EMG spectral changes, suggestive of differences in load-sharing and underlying metabolic fatigue processes. Unlike the linear decrease in median frequency observed for static contractions, during dynamic contractions instantaneous median frequency behavior is non-linear and more complex. Examples are provided in which distinct periods of instantaneous median frequency decay are followed by periods of recovery during a single trial of repetitive lifting. It is hypothesized that this difference reflects a complex strategy of utilizing muscle load-sharing during strenuous dynamic exercise to provide periods of metabolic recovery that limit localized fatigue. New analysis procedures to characterize this complex behavior are needed to enhance the technique for assessment of impairment in patients with lower back pain.