Offering proper feedback to control for out-of-plane lumbar moments influences the activity of trunk muscles during unidirectional isometric trunk exertions

Biofeedback Sensor vs. Physiotherapist Feedback During Core Stabilization Training in Patients with Chronic Nonspecific Low Back Pain

Core stabilization training utilizes principles of motor learning to retrain control of the trunk muscles and lead to improvements in chronic non-specific low back pain (CNLBP). To compare the effects of biofeedback sensor and conventional physiotherapist (PT) feedback during core stabilization and activity training in patients with CNLBP. Thirty-eight patients with CNLBP were randomly assigned to Biofeedback (n = 19) or PT feedback (n = 19) groups. Patients continued 12 sessions of combined core stabilization and activity training. An auditory and tactile biofeedback was given using a validated tilt sensor integrated with an application in the Biofeedback group. An experienced PT provided verbal and tactile feedback to maintain the neutral position in the PT Feedback group. The outcomes were; disability (Revised Oswestry Disability Index-RODI), muscle activity (m.transversus abdominis and m.multifidus), pain (Visual Analog Scale-VAS), proprioception error of the trunk, patient beliefs (Fear Avoidance Beliefs Questionnaire-FABQ) and presence of depressive symptoms (Beck Depression Index-BDI), and quality of life (Short Form (SF)-36). The main effect of time were statistically significant on VAS, RODI, m.transversus abdominis and m.multifidus muscle activities, flexion, and extension proprioception error of the trunk, FABQ, BDI, and SF-36 scores in Biofeedback and PT feedback groups (p < 0.05 for all). The time X group interaction was significant on flexion and extension proprioception error of the trunk PT feedback group (consecutively; p = 0.004, p = 0.022). Biofeedback sensor or PT feedback during core stabilization training equally improves pain, disability, muscle activity, depressive symptoms, patient beliefs, and quality of life in patients with CNLBP.

Comparative evaluation of different spinal stability metrics

Direct in vivo measurements of spinal stability are not possible, leaving computational estimations (such as dynamic time series and structural analyses) as the feasible option. However, differences between different stability assessment approaches and metrics remain unclear. To explore this, we asked 32 participants to perform 35 cycles of repetitive lifts with and without load (4/2.6 kg for males/females). EMG signals and 3D kinematics were collected via 12 surface electrodes and 17 inertial sensors, and three dynamical stability measures were computed: short and long temporal and conventional maximum Lyapunov exponents (LyE) and maximum Floquet multipliers (FM). A dynamic subject-specific EMG-assisted musculoskeletal model computed four structural stability measures (critical muscle stiffness coefficient at which spine becomes unstable, average spine stiffness, minimum and geometric average of Hessian matrix eigenvalues). Across cycles, dynamical and structural stability outcomes varied noticeably. Temporal short-term LyE and all structural stability measures were more influenced by the cycle percentage (posture factor) than by phase (lifting, lowering) or load factor. The effect of all factors were non-significant for FM and long LyE, except for the posture on LyE-L with a small effect size. Pearson's correlations revealed a weak to moderate, or non-existent, correlation between structural and dynamical stability metrics, with small shared variances, underscoring their distinct and independent nature and theoretical foundations. Moreover, the low sensitivity of dynamic measures to posture and load factors, found in this study, calls for further examination. Considering the limitations and shortcomings of both dynamical and structural stability assessment approaches, there is a need for the development of improved musculoskeletal stability evaluation techniques.

Validation of an EMG submaximal method to calibrate a novel dynamic EMG-driven musculoskeletal model of the trunk: Effects on model estimates

BACKGROUND

Multijoint EMG-assisted optimization models are reliable tools to predict muscle forces as they account for inter- and intra-individual variations in activation. However, the conventional method of normalizing EMG signals using maximum voluntary contractions (MVCs) is problematic and introduces major limitations. The sub-maximal voluntary contraction (SVC) approaches have been proposed as a remedy, but their performance against the MVC approach needs further validation particularly during dynamic tasks.

METHODS

To compare model outcomes between MVC and SVC approaches, nineteen healthy subjects performed a dynamic lifting task with two loading conditions.

RESULTS

Results demonstrated that these two approaches produced highly correlated results with relatively small absolute and relative differences (<10 %) when considering highly-aggregated model outcomes (e.g. compression forces, stability indices). Larger differences were, however, observed in estimated muscle forces. Although some model outcomes, e.g. force of abdominal muscles, were statistically different, their effect sizes remained mostly small (η_G² ≤ 0.13) and in a few cases moderate (η_G² ≤ 0.165).

CONCLUSION

The findings highlight that the MVC calibration approach can reliably be replaced by the SVC approach when the true MVC exertion is not accessible due to pain, kinesiophobia and/or the lack of proper training.

The effect of extensible and non-extensible lumbosacral orthoses on anticipatory postural adjustments in participants with low back pain and healthy controls

BACKGROUND

Wearing a lumbosacral orthosis (LSO) is known to influence spine mechanics, but less is known about how LSOs affect motor control. Whether the use of a LSO can negatively affect motor control of the lumbar spine is still under debate.

OBJECTIVE

The current study examined the immediate effects of two flexible LSOs (extensible and non-extensible) on the anticipatory postural adjustments that prepare the spine for a predictable perturbation.

DESIGN

A comparative study using a repeated measures design in a laboratory setting.

METHODS

Healthy controls (n = 20) and participants with low back pain (n = 40) performed a rapid arm flexion/extension cycle with and without these LSOs. The latency between the activations of the shoulder and different back (iliocostalis lumborum) and abdominal (rectus abdominis, internal and external obliques) muscles, as measured with surface electromyography, was used as the outcome.

RESULTS

The effects, which were comparable between groups and between LSOs, were mixed, with some muscles showing significantly (p ˂ 0.05) earlier activation and others showing delayed activation with the use of a LSO, relative to the control condition. The corresponding effect sizes were low to average (Hedges's g range: 0.17-0.48).

CONCLUSIONS

These findings suggest a change in the motor program before task initiation, which might be generalizable to other activities of daily living or work. However, none of the effects were large, making it difficult to provide clear conclusions with regard to their clinical relevance. It remains to be tested whether these immediate adaptations in motor planning can induce long term detrimental effects to the control of lumbar stability.

Maintaining Lumbar Spine Stability: A Study of the Specific and Combined Effects of Abdominal Activation and Lumbosacral Orthosis on Lumbar Intrinsic Stiffness

BACKGROUND

Two potential interventions for enhancing lumbar stability are to actively increase abdominal muscle activity, either through the abdominal drawing-in maneuver (ADIM) or bracing, and passively increase lumbar stiffness using a lumbosacral orthosis (LSO).

OBJECTIVE

To compare the increase in lumbar stiffness after 2 active interventions (ADIM versus bracing) and 1 passive intervention (LSO), and to evaluate the combined effect of active (abdominal bracing) and passive interventions.

METHODS

In this experimental and comparative study, lumbar stiffness, a surrogate measure of lumbar stability, was estimated in 25 healthy individuals during 7 trunk perturbation conditions: (1) control, (2) ADIM, (3) bracing at 5% of right external oblique maximal voluntary activation (5% bracing), (4) bracing at 10% of right external oblique maximal voluntary activation (10% bracing), (5) LSO, (6) LSO plus 5% bracing, and (7) LSO plus 10% bracing. Electromyographic biofeedback of the external oblique was provided on a monitor, while ultrasound was used for the ADIM to ensure a sustained contraction of the transversus abdominis.

RESULTS

The ADIM, 5% bracing, and 10% bracing active interventions generated comparable lumbar stiffness. However, considering that bracing can range from 10% to 20%, it may be superior to hollowing, as further estimated with a mixed-effect statistical model. Combining bracing and an LSO resulted in an additive effect on lumbar stiffness.

CONCLUSION

Bracing and ADIM produced comparable lumbar stiffness, as they were performed at the same overall abdominal activation levels (5% and 10% maximal voluntary activation). The independent effects of bracing and LSO raises the possibility of combining these interventions in some circumstances. J Orthop Sports Phys Ther 2019;49(4):262-271. Epub 18 Jan 2019. doi:10.2519/jospt.2019.8565.

Trunk musculoskeletal response in maximum voluntary exertions: A combined measurement-modeling investigation

Maximum voluntary exertion (MVE) tasks quantify trunk strength and maximal muscle electromyography (EMG) activities with both clinical and biomechanical implications. The aims here are to evaluate the performance of an existing trunk musculoskeletal model, estimate maximum muscle stresses and spinal forces, and explore likely differences between males and females in maximum voluntary exertions. We, therefore, measured trunk strength and EMG activities of 19 healthy right-handed subjects (9 females and 10 males) in flexion, extension, lateral and axial directions. MVEs for all subjects were then simulated in a subject-specific trunk musculoskeletal model, and estimated muscle activities were compared with EMGs. Analysis of variance was used to compare measured moments and estimated spinal loads at the L5-S1 level between females and males. MVE moments in both sexes were greatest in extension (means of 236 Nm in males and 190 Nm in females) and least in left axial torque (97 Nm in males and 64 Nm in females). Being much greater in lateral and axial MVEs, coupled moments reached ∼50% of primary moments in average. Females exerted less moments in all directions reaching significance except in flexion. Muscle activity estimations were strongly correlated with measurements in flexion and extension (Pearson's r = 0.69 and 0.76), but the correlations were very weak in lateral and axial MVEs (Pearson's r = 0.27 and 0.13). Maximum muscle stress was in average 0.80 ± 0.42 MPa but varied among muscles from 0.40 ± 0.22  MPa in rectus abdominis to 0.99 ± 0.29 MPa in external oblique. To estimate maximum muscle stresses and evaluate validity of a musculoskeletal model, MVEs in all directions with all coupled moments should be considered.

Variations in trunk muscle activities and spinal loads following posterior lumbar surgery: A combined in vivo and modeling investigation

BACKGROUND

Iatrogenic injuries to paraspinal muscles during posterior lumbar surgery cause a reduction in their contractile cross-sectional area and thus presumably their postoperative activation. This study investigates the effect of such intraoperative injuries on postoperative patterns of muscle activations and spinal loads during various activities using a combined modeling and in vivo MR imaging approach.

METHODS

A three-dimensional, multi-joint, musculoskeletal model was used to estimate pre- and postoperative muscle forces and spinal loads under various activities in upright and flexed postures. According to our in vivo pre- and postoperative (~6 months) measurements in six patients using a 3-Tesla-MR scanner, physiological cross-sectional areas of multifidus and erector spinae were reduced in the postoperative model by 26 and 11%, respectively.

FINDINGS

Postoperative trunk extension strength was predicted to decrease by ~23% from 215 Nm in the intact model to 165 Nm in the postoperative model. Postoperative force in multifidus fascicles decreased by ~21-40% in flexion tasks and by ~14-35% in upright tasks. In contrast, the sum of the forces in all other intact and less injured extensor muscles slightly increased (by <6%) in the postoperative model. Postoperative L5-S1 compressive and shear loads varied slightly (by ~3%).

INTERPRETATION

Intraoperative injuries induced a shift in load-sharing from the most injured muscle (multifidus) toward other less injured and intact muscles during all simulated activities. Postoperative rehabilitation programs should therefore strengthen and facilitate (while avoiding muscle imbalance) not only the injured multifidus but also other intact and less injured trunk muscles that play a compensatory role after the operation.