Trunk Dynamic Stability Assessment for Individuals With and Without Nonspecific Low Back Pain During Repetitive Movement.

OBJECTIVE: This study aimed to employ nonlinear dynamic approaches to assess trunk dynamic stability with speed, symmetry, and load during repetitive flexion-extension (FE) movements for individuals with and without nonspecific low back pain (NSLBP). BACKGROUND: Repetitive trunk FE movement is a typical work-related LBP risk factor contingent on speed, symmetry, and load. Improper settings/adjustments of these control parameters could undermine the dynamic stability of the trunk, hence leading to low back injuries. The underlying stability mechanisms and associated control impairments during such dynamic movements remain elusive. METHOD: Thirty-eight male volunteers (19 healthy, 19 NSLBP) enrolled in the current study. All participants performed repetitive trunk FE movements at high/low speeds, in symmetric/asymmetric directions, with/without a wearable loaded vest. Trunk instantaneous rotation angle was computed for each trial to be assessed in terms of local and orbital stability, using maximum finite-time Lyapunov exponents (LyEs) and Floquet multipliers (FMs), respectively. RESULTS: Both groups demonstrated equivalent competency in terms of trunk control and stability, suggesting functional adaptation strategies may be used by the NSLBP group. Wearing the loaded vest magnified the effects of trunk control impairment for the NSLBP group. The combined presence of high-speed and symmetrical FE movements was associated with least trunk local stability. CONCLUSION: Nonlinear dynamic techniques, particularly LyE, are potentially effective for assessing trunk dynamic stability dysfunction for individuals with NSLBP during various activities. APPLICATION: This work can be applied toward the development of quantitative personalized spinal evaluation tools with a wide range of potential occupational and clinical applications.

The effect of whole-body vibration training on the lower extremity muscles' electromyographic activities in patients with knee osteoarthritis.

Background: Whole-Body Vibration Training (WBVT) is a novel neuromuscular training method that has been recently developed as a rehabilitation tool. The purpose of this study was to determine whether WBVT is effective on electromyographic activity of the muscles of the lower limbs in patients with knee osteoarthritis. Methods: The study was designed as a single blinded randomized clinical trial (IRCT201601171637N5), 45 patients with knee osteoarthritis were randomly assigned to three groups; WBVT (n = 15) receiving 12 sessions vibration therapy, control group (n =15) doing two exercise in the home and placebo (n =15) doing exercise like WBVT group on-off vibration system. Electromyographic activities of vastus lateralis and vastus medialis, semitendinosus, gastrocnemius and soleus were evaluated pre and post intervention. The pairedsamples t-test and ANOVA were applied respectively to determine the differences in each group and among the groups (P≤0.05). Results: The RMS value of vastus medialis in semi squat position in placebo group (p=0.024), vastus lateralis in SLR position in WBVT group (p=0.037), soleus in knee flexion in WBVT group (p=0.018), semitendinosus in knee flexion in WBVT group (p=0.007) and RMS response of Semitendinosus in ankle plantar flexion in control group (p=0.047) were revealed significant differences between the pre- and post- intervention. The ANOVA test confirmed the significant differences between the studied groups according to the EMG activity of vastus medialis in semi squat position (p=0.045), semitendinosus in semi squat position (p=0.046) and in plantar flexion position (p=0.015) and also soleus in plantar flexion position (p=0.003). Conclusions: The findings of this study showed the beneficial effects of WBVT in the improvement of the muscles RMS values in the patients with knee OA especially muscles' progression rates in a four-week period.

Effects of unstable load and unstable surface ontrunk muscles activation and postural control in healthy subjects.

Exercise with an unstable load is considered a new training method to activate the core muscles. Research has shown consistency regarding an unstable surface but has not provided comprehensive findings about the effect of an unstable load. The study aimed to examine the impact of an unstable load and unstable surfaces on core muscle activation and postural control during lifting. Thirty-eight participants lifted a load equivalent to 10 % of their body weight under three conditions: a stable load on an unstable surface, a stable load on a stable surface, and an unstable load on a stable surface. The center of pressure (COP) displacement and electromyography activity of abdominal and back extensor muscles were measured during lifting. The results indicated that lifting on an unstable surface activated the lumbar erector spinae and multifidus muscles more than in a stable condition (P<0.05). However, there was no significant difference in the level of thoracic erector spinae muscle activity between the unstable load and unstable surface conditions. The stable condition increased activity in the internal oblique muscle (1.37 times) compared to the unstable conditions. The analysis of postural control revealed that lifting the load on an unstable surface significantly decreased COP displacement in the anteroposterior direction (P<0.05), while holding the load on the unstable surface significantly increased COP displacement in the anteroposterior direction compared to the other conditions. These findings could be valuable for future rehabilitation research, learning appropriate lifting techniques, and setting specific training goals in sports.

Trunk muscle activity during holding two types of dynamic loads in subjects with nonspecific low back pain.

BACKGROUND: Chronic low back pain due to manual lifting continues to be one of the significant common public health challenges in modern societies despite increased automation. While there are extensive studies on the biomechanics of lifting as associated with LBP, the role of unstable and time-varying dynamic loads, quite common in industrial lifting and daily life, remains elusive. OBJECTIVES: The present study aimed to investigate the response of trunk muscles in subjects with chronic non-specific low back pain (CNLBP) while holding unstable dynamic loads. METHODS: Twelve male patients with CNLBP and twelve healthy controls participated in this cross-sectional study. The subjects held static and dynamic loads in neutral positions. Normalized EMG data of the trunk muscles were captured and analyzed by repeated-measures ANOVA test. RESULTS: The low back pain group demonstrated significantly higher activation levels of the internal and external abdominal oblique muscles while holding dynamic loads (p < 0.05). CONCLUSION: Our results suggest that the neuromusculoskeletal system in low back patients holding dynamic loads may invoke a motor control strategy that significantly increases muscle co-activation leading to higher joint stiffness at the expense of higher compressive loads on the lumbar spine. Importantly, the type of load plays a critical role in terms of external perturbations that may lead to spinal injury in CNLBP patients and must, therefore, be considered in the risk prevention and assessment of lifting and other manual material handling tasks.

Amplitude of Electromyographic Activity of Trunk and Lower Extremity Muscles during Oscillatory Forces of Flexi-Bar on Stable and Unstable Surfaces in People with Nonspecific Low Back Pain.

Background: Recently, the oscillatory bar has been proposed as a new and effective rehabilitation tool in people with nonspecific low back pain (NSLBP), although its effects on muscular control in this population have not been well documented, especially in lower extremity muscles and different support surface conditions. Objective: This study aimed to evaluate and compare the effects of flexi-bar use on stable and unstable surfaces on electromyographic activity of trunk and lower extremity muscles in healthy persons and those with NSLBP. Material and Methods: 18 healthy men and 18 men with NSLBP participated in this cross-sectional study. The root mean square value of electromyographic activity was calculated in the trunk and lower extremity muscles during 4 different task conditions: quiet standing (QS) or flexi-bar use on a rigid or foam support surface. A repeated measures test was used for statistical analysis. Results: The results showed that the amplitude activity of almost all muscles was significantly greater during flexi-bar use than in the QS condition (P<0.05). The rectus femoris, tibialis anterior, and gastrocnemius demands were significantly greater on the foam than the rigid surface (P<0.05). Conclusion: This study showed that oscillatory forces caused by flexi-bar use can increase muscle activation in multiple segments (hip and ankle in addition to trunk muscles) that are crucial for postural stability. Furthermore, the foam surface appeared to target the rectus femoris in addition to the ankle muscles. Using a flexi-bar may be helpful in NSLBP rehabilitation, and exercising on a foam surface may enhance additive hip muscle activity in people with NSLBP.

Trunk extensor muscle fatigue influences trunk muscle activities.

BACKGROUND: Trunk muscles fatigue is one of the risk factors in workplaces and daily activities. Loads would be redistributed among active and passive tissues in a non-optimal manner in fatigue conditions. Therefore, a single tissue might be overloaded with minimal loads and as a result the risk of injury would increase. OBJECTIVE: The goal of this paper was to assess the electromyographic response of trunk extensor and abdominal muscles after trunk extensor muscles fatigue induced by cyclic lifting task. METHODS: This was an experimental study that twenty healthy women participated. For assessing automatic response of trunk extensor and abdominal muscles before and after the fatigue task, electromyographic activities of 6 muscles: thorasic erector spine (TES), lumbar erector spine (LES), lumbar multifidus (LMF), transverse abdominis/ internal oblique (TrA/IO), rectus abdominis (RA) and external oblique (EO) were recorded in standing position with no load and symmetric axial loads equal to 25% of their body weights. RESULTS: Statistical analysis showed that all the abdominal muscles activity decreased with axial loads after performing fatigue task but trunk extensor activity remained constant. CONCLUSIONS: Results of the current study indicated that muscle recruitment strategies changed with muscle fatigue and load bearing, therefore risks of tissue injury may increase in fatigue conditions.

A comparison of abdominal muscle thickness changes after a lifting task in subjects with and without chronic low-back pain.

OBJECTIVE: Using ultrasound imaging, the abdominal muscles' response to the back extensor muscle fatigue was assessed in subjects with chronic low-back pain (CLBP). BACKGROUND: Lumbar muscle fatigue is a common occurrence among workers. Alteration in motor coordination is one consequence of muscular fatigue. According to previous studies, CLBP subjects use their back and abdominal muscles in different ways, but questions remain about abdominal muscle responses to back muscle fatigue in CLBP patients. METHOD: Thirteen CLBP patients and 15 healthy subjects participated in this study. The thickness of abdominal muscles-including transverse abdominis (TrA), internal oblique abdominis (IO), and external oblique abdominis (EO) muscles-was measured in standing position with and without axial loads before and after a lifting fatigue task. RESULTS: The results reveal a significant difference for the main effects of group on percentage of change in TrA thickness (F = 8.9, p = .004). Percentage of change in thickness of TrA was 10% greater in the CLBP group. Although IO thickness displayed greater percentage of change in the CLBP group, the difference between groups was not significant. CONCLUSION: Abdominal muscle behavior changes with back-muscle fatigue in both healthy and CLBP subjects, but responses were more exaggerated in CLBP patients. APPLICATION: Ultrasound imaging technique can provide critical information about the effect of fatigue on spinal muscle activation and consequently about the stability of the spine. As a more applicable and easy technique, ergonomists can use ultrasound imaging in musculoskeletal system assessment in worker populations in future studies.

A Mechanical model for flexible exercise bars to study the influence of the initial position of the bar on lumbar discs and muscles forces.

A single-degree-of-freedom model is considered for flexible exercise bars based on the lumped-element approach. By considering the side segment of a flexible bar as a cantilever beam with an equivalent mass at the free end, its free-vibration response, as well as the forced response under the excitation of the grip, are expressed parametrically. Experiments are performed on a particular flexible bar (FLEXI_BAR) in order to obtain numerical values for quantifying the model's parameters. The model is also computationally simulated to study the response of the flexible bar to various excitations. The results are imported into a multi-segment musculoskeletal software (AnyBody), where the effect of different initial hand positions on the lumbar disc and back muscle forces is investigated (including Longissimus, Iliocostalis, and Transversus) during up-down exercises. The results show that all intervertebral discs and muscles forces are more sensitive to the horizontal position of the bar as compared to its vertical position.

Validation of a musculoskeletal model of lifting and its application for biomechanical evaluation of lifting techniques.

BACKGROUND: Lifting methods, including standing stance and techniques have wide effects on spine loading and stability. Previous studies explored lifting techniques in many biomechanical terms and documented changes in muscular and postural response of body as a function of techniques .However, the impact of standing stance and lifting technique on human musculoskeletal had not been investigated concurrently. METHODS: A whole body musculoskeletal model of lifting had been built in order to evaluate standing stance impact on muscle activation patterns and spine loading during each distinctive lifting technique. Verified model had been used in different stances width during squat, stoop and semi-squat lifting for examining the effect of standing stance on each lifting technique. RESULTS: The model muscle's activity was validated by experimental muscle EMGs resulting in Pearson's coefficients of greater than 0.8. Results from analytical analyses show that the effect of stance width on biomechanical parameters consists in the lifting technique, depending on what kind of standing stance was used. CONCLUSIONS: Standing stance in each distinctive lifting technique exhibit positive and negative aspects and it can't be recommended either one as being better in terms of biomechanical parameters.

The study of the variability of anticipatory postural adjustments in patients with recurrent non-specific low back pain.

BACKGROUND AND OBJECTIVES: Intrinsic variability is present in all actions, including repetitive tasks. The aim of this study was to evaluate the variability of anticipatory postural adjustments (APAs) of trunk muscles in participants with low back pain (LBP). MATERIAL AND METHOD: The study included 21 participants with recurrent non-specific LBP (15 men, 6 women) and 21 healthy volunteers. Standard deviation of electromyographic activity of the external oblique (EO), transverse abdominis/internal oblique (TrA/IO), and erector spinae (ES) muscles onset relative to deltoid muscle onset was recorded in 75 rapid arm flexions, and the correlation with the participants' avoidance belief (the FABQ score) and disability (the Roland-Morris Questionnaire score) was statistically analyzed. RESULTS: participants with LBP exhibited less variability in timing of APAs of the TrA/IO muscle compared with the control group (P=0.047). The timing of APAs of the TrA/IO muscle was significantly correlated with the FABQ score (P=0.006). There was no significant correlation between this variable and disability (P=0.09). Decrease in variability of the timing of APA of the EO (P=0.45) and ES (P=0.6) muscles was not significant. CONCLUSION: The variability of the postural responses of participants with LBP decreased. Restoring variability in postural control responses might be a goal in rehabilitating these patients.

Evaluation of trunk muscle activity in chronic low back pain patients and healthy individuals during holding loads.

OBJECTIVES: Low back pain after load-carrying is the most important disorder in musculoskeletal system and a cause of dysfunction and economic problems. Holding materials can disturb spinal stability; nevertheless, there are few researches about the pattern of trunk muscle recruitment in patients with chronic low back pain (CLBP) during load holding. METHODS: Ten female patients with CLBP and ten matched healthy subjects participated in this study. Normalized electromyography activation of trunk muscles during holding loads was analyzed. RESULTS: The low back pain group demonstrated significantly higher activation levels of the External oblique abdominis muscle during loading 12 kg in flexed trunk position and lower activation levels of the Internal oblique abdominis muscle during loading 6 and 12 kg in neutral trunk position than the control group. With the highest external load and trunk flexion, the electrical activity of back muscles increased significantly in both groups. With increasing load, the activation of Rectus abdominis muscle in patients with CLBP and the activation of Rectus abdominis and Internal oblique muscles were increased significantly in healthy subjects. CONCLUSION: Higher activation of global and lower activation of local abdominal muscles in patients with CLBP may represent that pain changes neuromuscular control systems. The increased activity of extensor muscles during trunk flexion is probably needed for stability and controlling of flexion.

Effects of micro-amperage direct current stimulation on injury potential and its relation to wound surface area in guinea pig.

INTRODUCTION: it is believed that the exogenous electrical stimulation via improving the natural endogenous bioelectric current, accelerate the wound healing. Up to now, this hypotheses has not been researched in acute surgically wounds. MATERIALS AND METHODS: Thirty-nine male guinea pigs were randomly divided into one control and two experimental groups (DC anodal group and DC cathodal group). A full thickness skin incision, length of 2.5 cm, was made on the dorsum of each animal The differential surface skin potential was measured before and immediately after the injury and also through the healing process until 21st days. RESULTS: Only in anodal group, there was not significant difference between the basal initial potential and the wound potential on days of 17, 19 and 21 (p>0.05). On days of 19 and 21, the wound potential decreased higher in anodal group than in control group (p<0.05). Wound surface area in two experimental groups decreased higher in 3rd weeks with respect to control group (p<0.05). DISCUSSION AND CONCLUSION: Anodal micro-amperage direct current can accelerate bioelectric events of skin wound and return more rapidly the wound potential to its before injury natural level.

Evaluation of spinal internal loads and lumbar curvature under holding static load at different trunk and knee positions.

A study was performed to investigate how different trunk and knee positions while holding static loads affect the lumbar curvature and internal loads on the lumbar spine at L4-L5. Ten healthy male subjects participated in this study. Two inclinometers were used to evaluate the curvature of lumbar spine, lordosis, while a 3D static biomechanical model was used to predict the spinal compression and shear forces at L4-L5. Eighteen static tasks while holding three level of load (0, 10 and 20 kg), two levels of knee position (45 and 180 degrees of flexion) and three levels of trunk position (neutral, 15 and 30 degree of flexion) were simulated for 10 healthy male subjects. The results of this study revealed that the lordosis of lumbar spine changed to kyphosis with increasing weight of load from 0 to 20 kg in trunk flexion position (p<0.05), but in squatting position (45 degrees knee full flexion) the higher load did not affect the curvature. The results of this study suggested, at a more flexed trunk and standing position with higher loads both external moment and internal loads increased significantly at L4-L5 level but with 45 knee flexion external moment and compression force increased and shear force decreased significantly (p < 0.05). Subjects made more effort to maintain stability of the body in squat position. The highest external moment and compression force were computed at flexed knee and trunk position with highest loads. Hence holding weight in this position must be avoided by implementing ergonomic change to the workplace.