Creep and fatigue development in the low back in static flexion

Bilateral Back Extensor Exosuit for multidimensional assistance and prevention of spinal injuries

Lumbar spine injuries resulting from heavy or repetitive lifting remain a prevalent concern in workplaces. Back-support devices have been developed to mitigate these injuries by aiding workers during lifting tasks. However, existing devices often fall short in providing multidimensional force assistance for asymmetric lifting, an essential feature for practical workplace use. In addition, validation of device safety across the entire human spine has been lacking. This paper introduces the Bilateral Back Extensor Exosuit (BBEX), a robotic back-support device designed to address both functionality and safety concerns. The design of the BBEX draws inspiration from the anatomical characteristics of the human spine and back extensor muscles. Using a multi-degree-of-freedom architecture and serially connected linear actuators, the device's components are strategically arranged to closely mimic the biomechanics of the human spine and back extensor muscles. To establish the efficacy and safety of the BBEX, a series of experiments with human participants was conducted. Eleven healthy male participants engaged in symmetric and asymmetric lifting tasks while wearing the BBEX. The results confirm the ability of the BBEX to provide effective multidimensional force assistance. Moreover, comprehensive safety validation was achieved through analyses of muscle fatigue in the upper and the lower erector spinae muscles, as well as mechanical loading on spinal joints during both lifting scenarios. By seamlessly integrating functionality inspired by human biomechanics with a focus on safety, this study offers a promising solution to address the persistent challenge of preventing lumbar spine injuries in demanding work environments.

Differential Back Muscle Flexion-Relaxation Phenomenon in Constrained versus Unconstrained Leg Postures

Previous studies examining the flexion-relaxation phenomenon (FRP) in back muscles through trunk forward flexion tests have yielded inconsistent findings, primarily due to variations in leg posture control. This study aimed to explore the influence of leg posture control and individual flexibility on FRP in back and low limb muscles. Thirty-two male participants, evenly distributed into high- and low-flexibility groups, were recruited. Activities of the erector spinae, biceps femoris, and gastrocnemius muscles, alongside the lumbosacral angle (LSA), were recorded as participants executed trunk flexion from 0° to 90° in 15° increments, enabling an analysis of FRP and its correlation with the investigated variables. The findings highlighted significant effects of all examined factors on the measured responses. At a trunk flexion angle of 60°, the influence of leg posture and flexibility on erector spinae activities was particularly pronounced. Participants with limited flexibility exhibited the most prominent FRP under constrained leg posture, while those with greater flexibility and unconstrained leg posture displayed the least FRP, indicated by their relatively larger LSAs. Under constrained leg posture conditions, participants experienced an approximate 1/3 to 1/2 increase in gastrocnemius activity throughout trunk flexion from 30° to 90°, while biceps femoris activity remained relatively constant. Using an inappropriate leg posture during back muscle FRP assessments can overestimate FRP. These findings offer guidance for designing future FRP research protocols.

Analysis of lumbar spine loading during walking in patients with chronic low back pain and healthy controls: An OpenSim-Based study

Low back pain (LBP) is one of the most prevalent and disabling disease worldwide. However, the specific biomechanical changes due to LBP are still controversial. The purpose of this study was to estimate the lumbar and lower limb kinematics, lumbar moments and loads, muscle forces and activation during walking in healthy adults and LBP. A total of 18 healthy controls and 19 patients with chronic LBP were tested for walking at a comfortable speed. The kinematic and dynamic data of the subjects were collected by 3D motion capture system and force plates respectively, and then the motion simulation was performed by OpenSim. The OpenSim musculoskeletal model was used to calculate lumbar, hip, knee and ankle joint angle variations, lumbar moments and loads, muscle forces and activation of eight major lumbar muscles. In our results, significant lower lumbar axial rotation angle, lumbar flexion/extension and axial rotation moments, as well as the muscle forces of the four muscles and muscle activation of two muscles were found in patients with LBP than those of the healthy controls (p < 0.05). This study may help providing theoretical support for the evaluation and rehabilitation treatment intervention of patients with LBP.

Measuring Muscle Activity in the Trunk, Pelvis, and Lower Limb Which Are Used to Maintain Standing Posture in Patients With Adult Spinal Deformity, With Focus on Muscles that Contract in the Compensatory Status

STUDY DESIGN

Prospective single-center study.

OBJECTIVE

This study aimed to investigate the muscle activity of the trunk, pelvis, and lower limb, which are used to maintain a standing posture in elderly patients with spinal deformities. We also elucidated the mechanism of compensation against spinal deformity in terms of muscle activity.

METHODS

Any patient scheduled to undergo surgery for adult spinal deformity was included. Surface electromyography and radiography were performed preoperatively. The following four representative alignments were defined as compensations: 1. pelvic retroversion, 2. reduction in thoracic kyphosis, 3. hyperextension of the lumbosacral junction, and 4. knee flexion. Individual muscle activity was compared with and without compensation. The patients were stratified into three groups according to the severity of spinal compensation, and differences in muscle activity were compared.

RESULTS

This study included 76 patients (7 men and 69 women, average age 69.4 years). Our results revealed that pelvic retroversion and knee flexion were compensations that required trunk muscle activity. In contrast, reduction of thoracic kyphosis and hyperextension of the lumbosacral junction did not require much trunk muscle activity. There was a significant difference in the muscle activity of the pelvis and lower limbs according to the severity of the deformity.

CONCLUSIONS

In terms of muscle activity, compensation for regional alignment changes in the adjacent spine is economical. However, extra-spinal compensations, such as pelvic retroversion and knee flexion, are non-economical. According to compensation recruitment, the muscle activity of the pelvis and lower limbs increased with the severity of the spinal deformity.

Creep deformation of viscoelastic lumbar tissue during sustained submaximal trunk flexion postures

Most in-vivo human experiments exploring creep deformation of viscoelastic lumbar tissue have used a maximum trunk flexion posture to engage the lumbar passive tissues. Recent evidence suggests that static trunk flexion tasks requiring submaximal trunk flexion can lead to gradual changes in the lumbar lordosis and this leads to our hypothesis that maintaining submaximal trunk flexion postures may lead to significant creep deformation of the viscoelastic lumbar tissues. Sixteen participants maintained a trunk flexion posture that was ten degrees less than the trunk flexion posture eliciting flexion-relaxation phenomenon for 12 min with breaks for a maximal trunk flexion protocol every three minutes. Trunk kinematic and extensor EMG measures were captured during the static, submaximal trunk flexion protocol as well as during the maximal trunk flexion protocol to provide evidence of creep development in the lumbar passive tissues. Results revealed that 12-minutes of submaximal trunk flexion led to significant increases in peak lumbar flexion angle (1.3°) and EMG-off lumbar flexion angle for L3/L4 paraspinals (2.9°). During the submaximal trunk flexion protocol, the changes in the lumbar flexion angle at 3-6 min and 6-9 min (average Δ5.4°) were significantly greater than at 0-3 min (Δ2.0°). The contribution of this study is the demonstration that sustained submaximal trunk flexion posture (i.e., constant global system) can lead to creep deformation of the viscoelastic lumbar tissue due to the increased lumbar flexion (i.e., altered local system) and may be attributed to a reduction in lumbar lordosis as the extensor muscles fatigue.

The influence of sedentary behaviour on lumbar-pelvic kinematics during squatting and forward bending among physically active students

Prolonged sitting may involve several mechanisms that make it a risk factor for low back pain. The aim of this study was to investigate lumbar-pelvic kinematics and multifidus muscle (MF) activity during squatting and forward bending in relation to the sedentary behaviour of physically active students. Sixty-three students were divided into two groups according to the time spent in a sitting position during the day: 'high' (>7 h/day); 'low' (≤7 h/day). Lumbar-pelvic ratios, ranges of motion, angular velocities, and MF flexion-relaxation phenomenon were investigated. Data were obtained using the optical motion analysis system, and surface electromyography. The results indicated that lumbar-pelvic ratios during both tasks and velocity of lumbar spine during squatting were significantly greater in the 'high' than in the 'low' sitting group. Muscle activity showed no differences between groups. Prolonged sitting can be considered a factor that slightly, but statistically significantly influences the lumbar-pelvic kinematics in physically active people.Practitioner summary: Lumbar-pelvic kinematics can be altered by prolonged sitting in physically active students. Lumbar-pelvic ratios during squatting and forward bending and lumbar spine velocity during squatting were significantly greater in the 'high' than in the 'low' sitting group. Sedentary behaviour should be considered during an assessment of movement patterns.Abbreviations: BMI: body mass index; ERR: extension-relaxation ratio; FRP: flexion-relaxation phenomenon; FRR: flexion-relaxation ratio; IPAQ: International Physical Activity Questionnaire; LBP: low back pain; METs: metabolic equivalent of tasks; MF: multifidus muscle; PA: physical activity; ROM: range of motion; sEMG: surface electromyography.

The Effects of an Acute Maximal Seated Lumbar Spine Flexion Exposure on Low Back Mechanical Pain Sensitivity

Viscoelastic creep generated in the lumbar spine following sustained spine flexion may affect the relationship between tissue damage and perceived pain. Two processes supporting this altered relationship include altered neural feedback and inflammatory processes. Our purpose was to determine how low back mechanical pain sensitivity changes following seated lumbar spine flexion using pressure algometry in a repeated-measures, cross-sectional laboratory design. Thirty-eight participants underwent a 10-minute sustained seated maximal flexion exposure with a 40-minute standing recovery period. Pressure algometry assessed pressure pain thresholds and the perceived intensity and unpleasantness of fixed pressures. Accelerometers measured spine flexion angles, and electromyography measured muscular activity during flexion. The flexion exposure produced 4.4° (2.7°) of creep that persisted throughout the entire recovery period. The perception of low back stimulus unpleasantness was elevated immediately following the exposure, 20 minutes before a delayed increase in lumbar erector spinae muscle activity. Women reported the fixed pressures to be more intense than men. Sustained flexion had immediate consequences to the quality of mechanical stimulus perceived but did not alter pressure pain thresholds. Neural feedback and inflammation seemed unlikely mechanisms for this given the time and direction of pain sensitivity changes, leaving a postulated cortical influence.

Effects of capacitive and resistive electric transfer therapy on pain and lumbar muscle stiffness and activity in patients with chronic low back pain

[Purpose] In this study, we investigated the therapeutic effects of capacitive and resistive electric transfer therapy in patients with chronic low back pain. [Participants and Methods] The study included 24 patients with chronic low back pain (12 patients each in the intervention and sham groups). Pain intensity, superficial and deep lumbar multifidus stiffness and maximum forward trunk flexion and associated activation level of the iliocostalis (thoracic and lumbar component) and lumbar multifidus muscles were measured. [Results] Post-intervention pain intensity and muscle stiffness were significantly lower than pre-intervention measurements in the intervention group. However, no between-group difference was observed in the muscle activation level at the end-point of standing trunk flexion. [Conclusion] Our findings highlight a significant therapeutic benefit of capacitive and resistive electric transfer therapy in patients with chronic low back pain and muscle stiffness.

Evaluation of trunk muscle activities in response to three breastfeeding positions utilised by women

BACKGROUND

High prevalence of breastfeeding (BF)-related musculoskeletal disorders (MSDs) in nursing mothers have been reported in previous studies. Studies are scarce on the biomechanical effects of the commonly utilized BF positions.

OBJECTIVE

This study evaluated the electromyographic (EMG) activities of the trunk muscles in response to three BF positions commonly utilized by mothers globally.

METHODS

20 non-pregnant nulliparous females participated in this experimental study. EMG activities from erector spinae (ES) and external oblique (EO) muscles were recorded bilaterally in three BF conditions: cradle (C1); cross-cradle (C2); football (FB). Data were analyzed using descriptive statistics and inferential statistics of one-way analysis of variance with alpha level set at 0.05.

RESULTS

The activity levels of right EO and ES muscles significantly increased during the C2 hold, while the left EO and ES muscles revealed significantly higher EMG levels in the C1 trial. Asymmetrical activity between the right and the left parts of the EO muscle was significantly higher during the C2 hold.

CONCLUSION

These findings suggest that compared to C2 and C1 holds, FB hold may be more biomechanically efficient relative to its decreased muscular demands. The physical stresses associated with BF may be higher with the adoption of C2 and C1 holds, especially for prolonged periods.

Changing the pattern of the back-muscle flexion-relaxation phenomenon through flexibility training in relatively inflexible young men

Although several studies have investigated the back-muscle flexion-relaxation phenomenon (FRP), the effect of individual flexibility on the FRP has been discussed infrequently, with very limited data on the influence of flexibility training on the FRP. This study thus examined the effect of flexibility training on the change of back-muscle FRP pattern in relatively inflexible young men. We collected and analyzed the valid data from 20 male participants (10 each with high and low flexibility included in the control and trained groups, respectively) when flexing their trunks at seven trunk flexion positions (0°-90°, in increments of 15°); their erector spinae and hamstring activation, pelvic tilt, and lumbosacral angle were then recorded. After 7 weeks of flexibility training for the low-flexibility group, no difference in flexibility was discovered between this group and the control (originally high-flexibility) group. The trunk flexion experiment was then repeated. The results showed that before the training stage, the low-flexibility group had lower erector spinae and higher hamstring activation, a larger pelvic tilt, and a smaller lumbosacral angle. By contrast, after training, the erector spinae and hamstring activation, pelvic tilt, and lumbosacral angle were significantly changed, and no intergroup differences were observed in FRP patterns. The study results suggest that flexibility training changes lumbopelvic movement and thereby reduces the degree of the back-muscle FRP when trunk flexion is performed.

The relation between the flexion relaxation phenomenon onset angle and lumbar spine muscle reflex onset time in response to 30 min of slumped sitting

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.

Back Pain Related with Age, Anthropometric Variables, Sagittal Spinal Curvatures, Hamstring Extensibility, Physical Activity and Health Related Quality of Life in Male and Female High School Students

Spinal pain (SP) is widely extended among adolescents. The origin of SP can be multifactorial; thus, the present study aimed to estimate the prevalence and risk of SP in high school students and to determine the differences in sagittal spinal curvatures and pelvic tilt, hamstring extensibility, age, anthropometric variables and healthy lifestyle habits dependent on SP between sexes. Two hundred seventy-three teenagers took part in this cross-sectional study. Age, sagittal spinal curvatures, hamstring extensibility, physical activity, sedentary lifestyle, anthropometric variables and health related quality of life (HRQL) were recorded. SP was reported by 16.12% of adolescents. Differences were observed in the HRQL according to SP (p < 0.05). Participants without SP were less sedentary (22.12%) and younger (13.10 years old) than participants with SP (40.91% and 13.66, respectively) (p < 0.05). A logistic regression model showed that both variables were significantly collinear (VIF = 1.01; Durbin-Watson = 2.10). Subjects with low back pain (LBP) had a higher weight, body max index, and hip girth than subjects without pain (p < 0.05). A misalignment in the lumbar spine was associated with LBP for males (Cramer’s V = 0.204, p = 0.022). In conclusion, adolescents with SP were older and had a lower HRQL in all dimensions. SP could be predicted according to age and sedentary habits.

Influence of creep deformation on sub-regional lumbar spine motion during manual lifting

Prolonged or repetitive spine flexion induces creep deformation of posterior spine tissues allowing for increased intervertebral motion beyond 'normal' limits, which may influence sub-regional (intersegmental) spine motion during subsequent manual lifting tasks. Using spine skin-surface kinematics, intersegmental lumbar spine motion was recorded over 20 minutes of prolonged static spine flexion and a subsequent manual lifting task (2 lifts every 3 minutes, 30 minutes total) in 14 participants. Results demonstrated that mid to lower lumbar intersegmental levels (i.e. L₂/L₃ to L₄/L₅) experienced the greatest overall creep deformation and range of motion during both prolonged flexion and manual lifting; however, overall range of motion during manual lifting was unaffected. Additionally, creep deformation did not completely recover within 30 minutes. Future work should continue to investigate the influence of this residual creep, as well as how overall creep deformation impacts spine neuromuscular control and stability, and ultimately the development of low back disorders. Practitioner summary: Mid to lower lumbar spine levels (i.e. L₂/L₃ to L₄/L₅) experienced the greatest creep deformation and range of motion during both prolonged flexion and manual lifting. Repeated lifting following prolonged flexion may limit creep recovery; however, overall lifting kinematic motion remained unchanged.

Flexibility Measurement Affecting the Reduction Pattern of Back Muscle Activation during Trunk Flexion

Numerous studies have been conducted on lower back injury caused by deeper stooped posture, which is associated with the back muscle flexion–relaxation phenomenon (FRP). Individual flexibility also affects FRP; individuals with high flexibility have the benefit of delayed FRP occurrence. This study attempted to determine the most efficient measurement of flexibility for evaluating the occurrence and degree of FRP when participants flexed their trunk forward. We recruited 40 male university students who were grouped on the basis of three flexibility measurements (toe-touch test, TTT; sit-and-reach test, SRT; modified Schober’s test, MST) into three levels (high, middle and low). Muscle activation (thoracic and lumbar erector spinae, TES and LES, respectively; hamstring, HMS) and lumbosacral angle (LSA) were recorded when the trunk flexed forward from 0° (upright) to 15°, 30°, 45°, 60°, 75° and 90°. The results indicated that trunk angle had a significant effect on three muscle activation levels and LSA. The effects of muscles and LSA varied depending on flexibility measurement. TTT significantly discriminated LES electromyography findings between high and low flexibility groups, whereas MST and SRT distinguished between high and non-high flexibility groups. The TTT values positively correlated with the time of LES FRP occurrence, showing that the higher the TTT, the slower the occurrence of FRP. This is beneficial in delaying or avoiding excessive loading on the passive tissue of the lumbar spine when performing a deeper trunk flexion.

Hamstring extensibility differences among elite adolescent and young dancers of different dance styles and non-dancers

Background

Hamstrings have been analyzed extensively due to their tendency to shorten and their effect in the lumbo-pelvic dynamics and the sagittal position of the spine in trunk flexion with extended knees positions. It has been demonstrated that practicing a certain sport results in long-term changes in hamstring extensibility. Despite this, adequate extensibility of the hamstring musculature is essential for the dancer’s performance. Several studies have found differences in the extensibility of the hamstrings depending on the dance style, but none have compared ballet, Spanish dance and modern dance. The purpose of the present research was to analyze the differences in hamstring extensibility among professional dance students based on dance style practiced and non-dancers.

Methods

The sample was comprised of 210 students from the Professional Dance Conservatory (70 for ballet, 70 for Spanish dance and 70 for modern dance) and 70 non-dancers. For the assessment of hamstring extensibility, the angle in the passive and active straight leg raise (PSLR and ASLR, respectively) test, and the scores of the pelvic tilt in sit-and-reach (SR) test and the toe-touch (TT) test were randomly conducted.

Results

The results showed significant differences for all the tests according to group (p < 0.001). In the PSLR and ASLR test, for both legs, and in the pelvic tilt in the SR test, the ballet dancers showed greater ranges of hamstring extensibility than the modern dancers and Spanish dancers (p ≤ 0.001). In the distance in the SR test and in the pelvic tilt in the TT test, the ballet dancers obtained higher values than the Spanish dancers (p = 0.004 and p = 0.003, respectively). The modern dancers showed higher ranges of hip flexion than the Spanish dancers in the ASLR test for both legs and in the pelvic tilt in the SR test (p from 0.007 to <0.001). Dancers showed significantly higher hamstring extensibility than non-dancers in all the tests (p < 0.001).

Conclusions

The systematic practice of dance, regardless of the style, seems to lead to high ranges of hamstring extensibility. Ballet dancers have the greatest hamstring extensibility.

The new "Tehran Back Belt": Design then testing during a simulated sitting task improved biomechanical spine muscle activity

Background: Spinal load and muscle activity in occupation settings is an area of increasing concern. Regarding technological advancements, in diverse occupations the spinal loads have increased through constrained seated postures. Back belts are consequently used in prophylactic and conservative management of occupational low back pain (LBP) in two distinct settings, prevention in industry, and treatment in LBP management. Industrial sites utilize belts for LBPprophylaxis on a large scale with their design and user experience (UE) influencing both the effectiveness and the workers’ compliance. This pilot study aims at determining the effectiveness of the new Tehran Back Belt (TBB) and assesses both UE and biomechanical effect (BE) on para-spinal muscle activity in healthy subjects.

Methods: A pretest-posttest study. Stage-1, design and fabrication of the TBB. Stage-2, the UE of the designed belt evaluated in healthy volunteers (n=30) via a checklist. The BE was determined from the level of lumbar extensor and trunk flexor muscle activity gauged during two test conditions of sitting posture (with and without belt) over 35-minute periods.

Results: Most subjects (>90%) reported high ‘ease of use’ and ‘comfort’ while wearing the TBB.The BE statistical analysis showed significantly reduced EMG activity levels for the longissimus(P = 0.012, η²=0.24), rectus abdominis (P=0.024, η²=0.18) and internal oblique (P=0.001,η²=0.44) muscles in belt-use conditions.

Conclusion: Decreased muscle activity while using the TBB is potentially advantageous for workers as spinal muscle activity is significantly reduced. Further investigations for longer duration effects and during real work office-based activities are warranted.

Back Muscle Function in Older Women With Age-Related Hyperkyphosis: A Comparative Study

OBJECTIVE

The purpose of this study was to compare static maximal back extensor muscle force, endurance, and characteristics of flexion relaxation phenomenon (FRP) in older women with and without age-related hyperkyphosis.

METHODS

Maximum back extensor force and endurance measured in a sitting position with a designed load cell setup; appearance, onset, and offset angles of FRP; and extension relaxation ratio (ERR) during a dynamic flexion-extension task were compared between 24 older women with hyperkyphosis (thoracic kyphosis angle ≥50°), mean age 65 ± 4.4 years, and 24 older women without hyperkyphosis (thoracic kyphosis angle ≪50°), mean age 63 ± 4.3 years. Variables of force, endurance, angles of FRP, and ERR were analyzed using an independent sample t test. A χ² test was used to identify differences between groups in FRP appearance.

RESULTS

Static back extensor force and endurance were significantly lower among those with versus those without hyperkyphosis (P ≪ .001). Although the 2 groups did not differ in FRP appearance and ERR in the superficial erector spinal muscles (P ≫ .05), FRP in the hyperkyphosis group started sooner and ended later than in the group without hyperkyphosis (P ≪ .05).

CONCLUSION

Our study indicates that women with age-related hyperkyphosis had decreased static maximal force and endurance of the back extensor muscles and prolonged myoelectrical silence of the superficial erector spinal muscles. Reduced endurance of the superficial erector spinal muscles may trigger early onset of FRP and prolonged relaxation of these muscles.

Are hybrid sit-stand postures a good compromise between sitting and standing?

Potential alternatives for conventional sitting and standing postures are hybrid sit-stand postures (i.e. perching). The purposes of this study were (i) to identify where lumbopelvic and pelvic angles deviate from sitting and standing and (ii) to use these breakpoints to define three distinct postural phases: sitting, perching, and standing, in order to examine differences in muscle activations and ground reaction forces between phases. Twenty-four participants completed 19 1-min static trials, from sitting (90°) to standing (180°), sequentially in 5°trunk-thigh angle increments. The perching phase was determined to be 145-175° for males and 160-175° for females. For both sexes, knee extensor activity was lower in standing compared to perching or sitting (p < .01). Anterior-posterior forces were the highest in perching (p < .001), requiring ∼15% of body-weight. Chair designs aimed at reducing the lower limb demands within 115-170° trunk-thigh angle may improve the feasibility of sustaining the perched posture. Practitioner summary: Individuals who develop low back pain in sitting or standing may benefit from hybrid sit-stand postures (perching), yet kinematic and kinetic changes associated with these postures have not been investigated. Perching can improve lumbar posture at a cost of increased lower limb demands, suggesting potential avenues for chair design improvement. Abbreviations: A/P: anterior-posterior; M/L: medial-lateral; LBP: low back pain; EMG: electromyography; TES: thoracic erector spinae; LES: lumbar erector spinae; VMO: vastus medialis obliquus; MVC: maximum voluntary contraction; ASIS: anterior superior iliac spine; PSIS: posterior superior iliac spine; BW: body weight; RMSE: root mean square error; SD: standard deviation; ROM: range of motion.

Acute muscle stretching and the ability to maintain posture in females with adolescent idiopathic scoliosis

BACKGROUND

Physiotherapy scoliosis specific exercises include exercises to attain and maintain proper posture, as well as flexibility movements such as stretching.

OBJECTIVE

To examine the effect of prior muscle stretching on the performance of posture exercise in females with adolescent idiopathic scoliosis (AIS).

METHODS

Eighteen females with AIS were randomly assigned to perform a posture maintenance task for three minutes preceded by either stretching protocol (group A) or no-stretching (group B). A second session was carried out after three days, where the same procedure was repeated in a reverse order between groups. During each session, three outcomes were tested: the ability to complete the task, the ability to maintain postural body alignment, and the perceived effort.

RESULTS

All participants completed the task in both sessions. Subjects' ability to preserve the required lower trunk alignment decreased following stretching compared to no-stretching. Lower-trunk angle changed toward flexion by 10∘ and 4.3∘ respectively, p= 0.032. There was no difference in perceived effort.

CONCLUSIONS

Prior muscle stretching has a negative effect on the ability to preserve body positional alignment during posture exercise. The present findings should be considered by practitioners when designing protocols for scoliosis-specific exercises. Stretching immediately prior to posture maintenance exercises should be avoided.

Motor adaptations to trunk perturbation: effects of experimental back pain and spinal tissue creep

In complex anatomical systems, such as the trunk, motor control theories suggest that many motor solutions can be implemented to achieve a similar goal. Although reflex mechanisms act as a stabilizer of the spine, how the central nervous system uses trunk redundancy to adapt neuromuscular responses under the influence of external perturbations, such as experimental pain or spinal tissue creep, is still unclear. The aim of this study was to identify and characterize trunk neuromuscular adaptations in response to unexpected trunk perturbations under the influence of spinal tissue creep and experimental back pain. Healthy participants experienced a repetition of sudden external trunk perturbations in two protocols: 1) 15 perturbations before and after a spinal tissue creep protocol and 2) 15 perturbations with and without experimental back pain. Trunk neuromuscular adaptations were measured by using high-density electromyography to record erector spinae muscle activity recruitment patterns and a motion analysis system. Muscle activity reflex attenuation was found across unexpected trunk perturbation trials under the influence of creep and pain. A similar area of muscle activity distribution was observed with or without back pain as well as before and after creep. No change of trunk kinematics was observed. We conclude that although under normal circumstances muscle activity adaptation occurs throughout the same perturbations, a reset of the adaptation process is present when experiencing a new perturbation such as experimental pain or creep. However, participants are still able to attenuate reflex responses under these conditions by using variable recruitment patterns of back muscles. NEW & NOTEWORTHY The present study characterizes, for the first time, trunk motor adaptations with high-density surface electromyography when the spinal system is challenged by a series of unexpected perturbations. We propose that the central nervous system is able to adapt neuromuscular responses by using a variable recruitment pattern of back muscles to maximize the motor performance, even under the influence of pain or when the passive structures of the spine are altered.

Changes in Lumbopelvic Movement and Muscle Recruitment Associated with Prolonged Deep Squatting: A Pilot Study

This study examined the changes in spinal kinematics and muscle recruitment of the lumbopelvic region associated with prolonged squatting. Eight subjects with chronic nonspecific low back pain (LBP) and eight asymptomatic subjects (AS) performed squat-to-stand and reverse movements, before and immediately after 15 min deep-squatting. Within-group and between-group differences in lumbopelvic kinematics and electromyographic activity acquired in lumbar erector spinae (ES), gluteus maximus (GM), and vastus lateralis (VL) were analyzed. During squat-to-stand after squatting, the LBP group showed slower then faster lumbar movement in the second and third quartiles, respectively. In the second quartile, the AS group moved with a significantly greater lumbar angle. However, significantly greater bilateral GM activity (+4–4.5%) was found in the LBP group only. A more profound decrease in bilateral ES activity (−10%) was also shown in the LBP group, yet this was nonsignificant compared to the AS group (−4%). In the third quartile, only the LBP group moved with a significantly greater lumbar angle, together with a significant increase in bilateral ES (+6–8%) and GM muscle (+2–3%) activity. The findings of the altered pattern of joint kinematics and recruitment of the key lumbopelvic muscles displayed in the LBP group inform on the possible mechanisms that may contribute to the increased risk of developing lumbar dysfunctions for people who work in prolonged squatting postures.

Case Studies in Neuroscience: A dissociation of balance and posture demonstrated by camptocormia

Upright stance in humans requires an intricate exchange between the neural mechanisms that control balance and those that control posture; however, the distinction between these control systems is hard to discern in healthy subjects. By studying balance and postural control of a participant with camptocormia - an involuntary flexion of the trunk during standing that resolves when supine - a divergence between balance and postural control was revealed. A kinematic and kinetic investigation of standing and walking showed a stereotyped flexion of the upper body by almost 80° over a few minutes, and yet the participant's ability to control center of mass within the base of support and to compensate for external perturbations remained intact. This unique case also revealed the involvement of automatic, tonic control of the paraspinal muscles during standing and the effects of attention. Although strength was reduced and MRI showed a reduction in muscle mass, there was sufficient strength to maintain an upright posture under voluntary control and when using geste antagoniste maneuvers or "sensory tricks" from visual, auditory, and haptic biofeedback. Dual tasks that either increased or decreased the attention given to postural alignment would decrease or increase the postural flexion, respectively. The custom-made "twister" device that measured axial resistance to slow passive rotation revealed abnormalities in axial muscle tone distribution during standing. The results suggest that the disorder in this case was due to a disruption in the automatic, tonic drive to the postural muscles and that myogenic changes were secondary. NEW & NOTEWORTHY By studying an idiopathic camptocormia case with a detailed biomechanical and sensorimotor approach, we have demonstrated unique insights into the neural control of human bipedalism 1) balance and postural control cannot be considered the same neural process, as there is a stereotyped abnormal flexed posture, without balance deficits, associated with camptocormia, and 2) posture during standing is controlled by automatic axial tone but "sensory tricks" involving sensory biofeedback to direct voluntary attention to postural alignment can override, when required.

Spasm and flexion-relaxation phenomenon response to large lifting load during the performance of a trunk flexion-extension exercise

BACKGROUND

The flexion relaxation phenomenon (FRP) has been widely investigated. Nevertheless, no study has been reported on the FRP as well as spasm response to large lifting load. The aim of this study was to evaluate the effect of large lifting load on the FRP response and spasm during execution of a flexion-extension exercise.

METHODS

Twenty-two healthy male university students without low back pain history participated this study. Subjects randomly performed three trials of trunk flexion-extension cycles of 5 s flexion and 5 s extension in each of 4 conditions (three large lifting loads of 15, 20 and 25 kg and one lifting load of 0 kg for comparison). Surface EMG from bilateral erector spinae was recorded during the performance of a trunk anterior flexion-extension exercise. The relaxation phase was determined through the onset of electromyography (EMG) signals. Spasm was evaluated in the relaxation period. The mean normalized electromyography (NEMG) was derived from the raw EMG.

RESULTS

Spasm was observed in more than 45% of the individuals and the intensity of muscle activation was increased by more than 78% in the relaxation phase.

CONCLUSIONS

A large lifting load could lead to a high prevalence of spasms as well as a high intensity of muscle activations on erector spinae muscle in the relaxation period, which may be associated with the development of low back disorder during the performance of a flexion-extension exercise.

Changes of lumbar posture and tissue loading during static trunk bending

Static trunk bending is an occupational risk factor for lower back pain (LBP). When assessing relative short duration trunk bending tasks, existing studies mostly assumed unchanged spine biomechanical responses during task performance. The purpose of the current study was to assess the biomechanical changes of lumbar spine during the performance of relatively short duration, sustained trunk bending tasks. Fifteen participants performed 40-s static trunk bending tasks in two different trunk angles (30° or 60°) with two different hand load levels (0 or 6.8 kg). Results of the current study revealed significantly increased lumbar flexion and lumbar passive moment during the 40 s of trunk bending. Significantly reduced lumbar and abdominal muscle activities were also observed in most conditions. These findings suggest that, during the performance of short duration, static trunk bending tasks, a shift of loading from lumbar active tissues to passive tissues occurs naturally. This mechanism is beneficial in reducing the accumulation of lumbar muscle fatigue; however, lumbar passive tissue creep could be introduced due to prolonged or repetitive exposure.

Repeated end range spinal movement while seated abolishes the proprioceptive deficit induced by prolonged flexed sitting posture. A study assessing the statistical and clinical significance of spinal position sense

BACKGROUND

Sustained spinal flexion has been proposed to affect the properties of spinal tissues, increase postural muscle's activation latency and act detrimentally on proprioception.

OBJECTIVES

This study evaluated the effect of flexed posture (FP) on spinal proprioception and assessed the immediate effect of spinal movement on the presumable flexion-induced proprioceptive deficit.

DESIGN

Clinical measurement study.

METHODS

Marker-based kinematic analyses of the head, spine, and pelvis were conducted on 50 individuals. Subjects were educated in a lordotic sitting posture (IOSP) that they reproduced immediately; after 10 and 30 min in FP; and after sagittal spinal movement. Nine sagittal angles were calculated. Absolute error (AE) and constant error (CE) were used to evaluate repositioning accuracy. Repeated measures ANOVA was used to test for significant differences in angles obtained among postures, as well as for the AE and CE calculated from the trials.

RESULTS

No significant differences were found in reposition error (RE) after immediate reproduction of IOSP (all p > 0.0083). Following FP AEs presented significant differences for head (4.1°), head protraction (1.9°), head tilt (2.1°), lumbar (3.2°) and pelvis angle (2.1°). CEs revealed significant differences for head protraction (-1.8°) and lumbar angle (-3.5°). No significant differences were found for AE and CE after spinal sagittal movement (all p > 0.0083).

CONCLUSIONS

Prolonged FP can affect spinal position sense, but sagittal spinal movement can abolish the proprioceptive deficit. The significant differences documented, may be of limited clinical utility given their magnitude, and the reliability data presented may be of use in reinterpreting previously documented proprioceptive analyses.

Combined effect of low back muscle fatigue and passive tissue elongation on the flexion-relaxation response

Previous literature has documented the alterations in the flexion-relaxation response of the lumbar extensor musculature to passive tissue elongation (PTE) and muscle fatigue (MF). There is no study, however, that has explored this response as a function of the combined effect of both PTE and MF, which is often seen in occupational settings. Twelve participants performed three experimental protocols on three different days to achieve (1) PTE, (2) MF and (3) PTE&MF (combined). Trunk kinematics and muscle activities were monitored to assess the effects of these protocols on the peak lumbar flexion angle and the lumbar angle of the flexion-relaxation of the trunk extensor muscles. Results showed responses to the uni-dimensional stresses (PTE and MF) consistent with those seen in the previous literature, while the combined protocol elicited responses that more closely matched the PTE protocol.

Stooping, crouching, and standing - Characterizing balance control strategies across postures

BACKGROUND

While stooping and crouching postures are critical for many activities of daily living, little is known about the balance control mechanisms employed during these postures. Accordingly, the purpose of this study was to characterize the mechanisms driving net center of pressure (COP_Net) movement across three postures (standing, stooping, and crouching) and to investigate if control in each posture was influenced by time.

METHODS

Ten young adults performed the three postures for 60s each. Kinetic signals were collected via a force platform under each foot. To quantify mechanisms of control, correlations (Correl_LR) were calculated between the left and right COP trajectories in the anterior-posterior (AP) and medio-lateral (ML) directions. To examine the potential effects of time on balance control strategies, outcomes during the first 30s were compared to the last 30s.

RESULTS

Correl_LR values did not differ across postures (AP: p = 0.395; ML: p = 0.647). Further, there were no main effects of time on Correl_LR (AP: p = 0.976; ML: p = 0.105). A significant posture-time interaction was observed in the ML direction (p = 0.045) characterized by 35% decreases in Correl_LR over time for stooping (p = 0.022).

CONCLUSION

The dominant controllers of sway (i.e., AP: ankle plantar/dorsi flexors; ML: hip load/unload mechanism) are similar across quiet stance stooping, and crouching. Changes in ML control strategies over time suggests that fatigue could affect prolonged stooping more so than crouching or standing.

Effects of Muscle Fatigue, Creep, and Musculoskeletal Pain on Neuromuscular Responses to Unexpected Perturbation of the Trunk: A Systematic Review

Introduction: Trunk neuromuscular responses have been shown to adapt under the influence of muscle fatigue, as well as spinal tissue creep or even with the presence of low back pain (LBP). Despite a large number of studies exploring how these external perturbations affect the spinal stability, characteristics of such adaptations remains unclear.

Aim: The purpose of this systematic review was to assess the quality of evidence of studies investigating trunk neuromuscular responses to unexpected trunk perturbation. More specifically, the targeted neuromuscular responses were trunk muscle activity reflex and trunk kinematics under the influence of muscle fatigue, spinal creep, and musculoskeletal pain.

Methods: A research of the literature was conducted in Pubmed, Embase, and Sport-Discus databases using terms related to trunk neuromuscular reflex responses, measured by electromyography (baseline activity, reflex latency, and reflex amplitude) and/or trunk kinematic, in context of unexpected external perturbation. Moreover, independent variables must be either trunk muscle fatigue or spinal tissue creep or LBP. All included articles were scored for their electromyography methodology based on the “Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM)” and the “International Society of Electrophysiology and Kinesiology (ISEK)” recommendations whereas overall quality of articles was scored using a specific quality checklist modified from the Quality Index. Meta-analysis was performed on reflex latency variable.

Results: A final set of 29 articles underwent quality assessments. The mean quality score was 79%. No effect of muscle fatigue on erector spinae reflex latency following an unexpected perturbation, nor any other distinctive effects was found for back muscle fatigue and reflex parameters. As for spinal tissue creep effects, no alteration was found for any of the trunk reflex variables. Finally, the meta-analysis revealed an increased erector spinae reflex latency in patients with chronic LBP in comparison with healthy controls following an unexpected trunk perturbation.

Conclusion: The literature provides some evidence with regard to trunk adaptions in a context of spinal instability. However, most of the evidence was inconclusive due to a high methodological heterogeneity between the studies.

Working position influences the biomechanical demands on the lower back during dental hygiene

This investigation monitored the biomechanical demands on the lower back during simulated dental hygiene work. A total of 19 female, registered dental hygienists performed 30 continuous minutes of manual scaling (plaque removal) of a manikin's teeth while seated. We monitored the working location and orientation of the dental hygienists, with respect to the manikin, along with their spine kinematics, spine extensor muscle activities and seat pressure, throughout the 30 min. A clock representation was used to express the working location. The location significantly influenced the dental hygienists' pelvic orientation with respect to the manikin, spine posture, erector muscle activity and pressure distribution. Findings from this study suggest that the prevalence of lower back pain amongst dental hygienists may be directly related to low-level tonic activity of the spine's extensor musculature, and the combined flexed and axially rotated spine postures. Practitioner Summary: Low back pain (LBP) is prevalent in dental hygienists, yet occupational demand on the low back has not been investigated. Posture, muscle activity and seat pressure were monitored. Combined spine rotation and flexion, and tonic activity of the extensor musculature may be related to LBP in dental hygienists.

Muscle Activity Adaptations to Spinal Tissue Creep in the Presence of Muscle Fatigue

Aim

The aim of this study was to identify adaptations in muscle activity distribution to spinal tissue creep in presence of muscle fatigue.

Methods

Twenty-three healthy participants performed a fatigue task before and after 30 minutes of passive spinal tissue deformation in flexion. Right and left erector spinae activity was recorded using large-arrays surface electromyography (EMG). To characterize muscle activity distribution, dispersion was used. During the fatigue task, EMG amplitude root mean square (RMS), median frequency and dispersion in x- and y-axis were compared before and after spinal creep.

Results

Important fatigue-related changes in EMG median frequency were observed during muscle fatigue. Median frequency values showed a significant main creep effect, with lower median frequency values on the left side under the creep condition (p≤0.0001). A significant main creep effect on RMS values was also observed as RMS values were higher after creep deformation on the right side (p = 0.014); a similar tendency, although not significant, was observed on the left side (p = 0.06). A significant creep effects for x-axis dispersion values was observed, with higher dispersion values following the deformation protocol on the left side (p≤0.001). Regarding y-axis dispersion values, a significant creep x fatigue interaction effect was observed on the left side (p = 0.016); a similar tendency, although not significant, was observed on the right side (p = 0.08).

Conclusion

Combined muscle fatigue and creep deformation of spinal tissues led to changes in muscle activity amplitude, frequency domain and distribution.

Differences in lumbopelvic rhythm between trunk flexion and extension

BACKGROUND

Trunk flexion and extension have already been found to have different characteristics, such as those in lumbopelvic rhythm. Although a more advanced method of quantifying such rhythm, lumbopelvic continuous relative phase and phase variability have not been used to explore the differences between trunk flexion and extension motions. This information is important since abnormal lumbopelvic coordination patterns increase the risk of low back pain. The current study investigated the differences in lumbopelvic rhythm between trunk flexion and extension, and how the rhythm changed within each of the two motions.

METHODS

Thirteen subjects performed pace-controlled trunk flexion/extension motions in the sagittal plane while lumbar and pelvis kinematics data were recorded, such that the lumbopelvic continuous relative phase and phase variability could be calculated to quantify lumbopelvic rhythm.

FINDINGS

Trunk extension motion had significantly smaller lumbopelvic continuous relative phase and phase variability than flexion motion, which indicated a more in-phase and stable rhythm. Additionally, the lumbopelvic rhythm within trunk extension motion changed from a more in-phase and stable pattern to a more out-of-phase and unstable pattern; by contrast, the opposite change (from out-of-phase and unstable to in-phase and stable) was observed in trunk flexion.

INTERPRETATION

Findings of the current study provided important information about the differences in lumbopelvic rhythm between trunk flexion and extension motions. Quantifying these patterns provides the means for identifying abnormal patterns in a clinical setting, and could serve as normative benchmarks during low back pain rehabilitation plans.

Use of antagonist muscle EMG in the assessment of neuromuscular health of the low back

BACKGROUND

Non-specific low back pain (LBP) has been one of the most frequently occurring musculoskeletal problems. Impairment in the mechanical stability of the lumbar spine has been known to lower the safety margin of the spine musculature and can result in the occurrence of pain symptoms of the low back area. Previously, changes in spinal stability have been identified by investigating recruitment patterns of low back and abdominal muscles in laboratory experiments with controlled postures and physical activities that were hard to conduct in daily life. The main objective of this study was to explore the possibility of developing a reliable spine stability assessment method using surface electromyography (EMG) of the low back and abdominal muscles in common physical activities.

METHODS

Twenty asymptomatic young participants conducted normal walking, plank, and isometric back extension activities prior to and immediately after maintaining a 10-min static upper body deep flexion on a flat bed. EMG data of the erector spinae, external oblique, and rectus abdominals were collected bilaterally, and their mean normalized amplitude values were compared between before and after the static deep flexion. Changes in the amplitude and co-contraction ratio values were evaluated to understand how muscle recruitment patterns have changed after the static deep flexion.

RESULTS

Mean normalized amplitude of antagonist muscles (erector spinae muscles while conducting plank; external oblique and rectus abdominal muscles while conducting isometric back extension) decreased significantly (P < 0.05) after the 10-min static deep flexion. Normalized amplitude of agonist muscles did not vary significantly after deep flexion.

CONCLUSIONS

Results of this study suggest the possibility of using surface EMG in the evaluation of spinal stability and low back health status in simple exercise postures that can be done in non-laboratory settings. Specifically, amplitude of antagonist muscles was found to be more sensitive than agonist muscles in identifying changes in the spinal stability associated with the 10-min static deep flexion. Further research with various loading conditions and physical activities need to be performed to improve the reliability and utility of the findings of the current study.

Comparison of trunk muscle reflex activation patterns between active and passive trunk flexion-extension loading conditions

The aim of the present study was to determine the effects of trunk flexion-extension loading on the neuromuscular reflexive latencies and amplitude responses of the trunk musculature. Eighteen male and female subjects (18-27yrs) participated in active and passive trunk flexion extension, performed ∼7days apart. Subjects performed 60 trunk flexion-extension repetitions. Surface electromyography (EMG) was collected bilaterally from paraspinal and abdominal muscles. In the active condition, subjects volitionally moved their trunks, while in the passive condition the dynamometer controlled the movements. The trunk was perturbed before and immediately after 30 repetitions. Latency of muscle onset, latency of first peak, latency of maximum peak, and peak EMG amplitude were evaluated. No differences between conditions, sides, or perturbation session were apparent. Overall latencies were shorter in females (p<.05) and abdominal muscles compared to paraspinals (p<.05). Thoracic paraspinal muscle amplitudes were greater than all other muscles (p<.05). Based upon the present results, the neuromuscular system engages trunk flexor muscles prior to the paraspinals in order to provide possible stabilization of the trunk when flexor moments are generated. Overall, the results indicate no difference in response of the neuromuscular system to active or passive repetitive loading.

The effects of stance width and foot posture on lumbar muscle flexion-relaxation phenomenon

BACKGROUND

Characterizing the lumbar muscle flexion-relaxation phenomenon is a clinically relevant approach in understanding the neuromuscular alternations of low back pain patients. Previous studies have indicated that changes in stance posture could directly influence trunk kinematics and potentially change the lumbar tissue synergy. In this study, the effects of stance width and foot posture on the lumbar muscle relaxation responses during trunk flexion were investigated.

METHODS

Thirteen volunteers performed trunk flexion using three different stance widths and 'toe-forward' or 'toe-out' foot postures (six conditions in total). Lumbar muscle electromyography was collected from the L3 and L4 level paraspinals; meanwhile three magnetic motion sensors were placed over the S1, T12, and C7 vertebrae to track lumbar and trunk kinematics. The lumbar angle at which muscle activity diminished to a near resting level was recorded. At the systemic level, the boundary where the internal moment started to shift from active to passive tissues was identified.

FINDINGS

For the L3 paraspinals, the flexion relaxation lumbar angle reduced 1.3° with the increase of stance width. When changed from 'toe-forward' to 'toe-out' foot posture, the flexion relaxation lumbar angle reduced 1.4° and 1.1° for the L3 and L4 paraspinals respectively. However, the active and passive lumbar tissue load shifting boundary was not affected.

INTERPRETATION

Findings of this study suggest that changes in stance width and foot posture altered the lumbar tissue load sharing mechanism. Therefore, in a clinical setting, it is critical to maintain consistent stance postures when examining the characteristics of lumbar tissue synergy.

The changes of lumbar muscle flexion-relaxation response due to laterally slanted ground surfaces

Lifting tasks performed on uneven ground surfaces are common in outdoor industries. Previous studies have demonstrated that lifting tasks performed on laterally slanted ground surfaces influence lumbar muscle activation and trunk kinematics. In this study, the effect of laterally slanted ground surfaces on the lumbar muscle flexion-relaxation responses was investigated. Fourteen participants performed sagittal plane, trunk flexion-extension tasks on three laterally slanted ground surfaces (0° (flat ground), 15° and 30°), while lumbar muscle activities and trunk kinematics were recorded. Results showed that flexion-relaxation occurred up to 6.2° earlier among ipsilateral lumbar muscles with an increase in laterally slanted ground angle; however, the contralateral side was not affected as much. Our findings suggest that uneven ground alters the lumbar tissue load-sharing mechanism and creates unbalanced lumbar muscle activity, which may increase the risk of low back pain with repeated exposure to lifting on variable surfaces.

PRACTITIONER SUMMARY

Uneven ground surfaces are ubiquitous in agriculture, construction, fishing and other outdoor industries. A better understanding of the effects of laterally slanted ground surfaces on the interaction between passive and active lumbar tissues during lifting tasks could provide valuable knowledge in the design of preventive strategies for low back injuries.

Low back pain development response to sustained trunk axial twisting

PURPOSE

To investigate if there is an effect of sustained trunk axial twisting on the development of low back pain.

METHODS

Sixteen male pain-free university students volunteered for this study. The trunk axial twisting was created by a torsion moment of 50 Nm for 10-min duration. The axial rotational creep was estimated by the transverse camera view directly on the top of the head. The visual analog scale in low back area was examined both in the initial and at the end of twisting. Each performed three trials of lumbar flexion-extension with the cycle of 5 s flexion and 5 s extension in standing before and after twisting. Surface electromyography from bilateral erector spinae muscles as well as trunk flexion performance was recorded synchronously in video camera. A one-way ANOVA with repeated measures was used to evaluate the effect of twist.

RESULTS

The results showed that there was a significant (p < 0.001) twist creep with rotational angle 10.5° as well as VAS increase with a mean value 45 mm. The erector spinae was active in a larger angle during flexion as well as extension after trunk axial twisting.

CONCLUSIONS

Sustained trunk axial twisting elicits significant trunk rotational creep. It causes the visual analog scale to have a significant increase, and causes erector spinae muscles to become active longer during anterior flexion as well as extension, which may be linked to the decrease of the tension ability of passive tissues in low back area, indicating a higher risk in developing low back pain.

Load-relaxation properties of the human trunk in response to prolonged flexion: measuring and modeling the effect of flexion angle

Experimental studies suggest that prolonged trunk flexion reduces passive support of the spine. To understand alterations of the synergy between active and passive tissues following such loadings, several studies have assessed the time-dependent behavior of passive tissues including those within spinal motion segments and muscles. Yet, there remain limitations regarding load-relaxation of the lumbar spine in response to flexion exposures and the influence of different flexion angles. Ten healthy participants were exposed for 16 min to each of five magnitudes of lumbar flexion specified relative to individual flexion-relaxation angles (i.e., 30, 40, 60, 80, and 100%), during which lumbar flexion angle and trunk moment were recorded. Outcome measures were initial trunk moment, moment drop, parameters of four viscoelastic models (i.e., Standard Linear Solid model, the Prony Series, Schapery's Theory, and the Modified Superposition Method), and changes in neutral zone and viscoelastic state following exposure. There were significant effects of flexion angle on initial moment, moment drop, changes in normalized neutral zone, and some parameters of the Standard Linear Solid model. Initial moment, moment drop, and changes in normalized neutral zone increased exponentially with flexion angle. Kelvin-solid models produced better predictions of temporal behaviors. Observed responses to trunk flexion suggest nonlinearity in viscoelastic properties, and which likely reflected viscoelastic behaviors of spinal (lumbar) motion segments. Flexion-induced changes in viscous properties and neutral zone imply an increase in internal loads and perhaps increased risk of low back disorders. Kelvin-solid models, especially the Prony Series model appeared to be more effective at modeling load-relaxation of the trunk.

Putting proficiency: contributions of the pelvis and trunk

Putting proficiency is a key determinant of golfing success and yet minimal biomechanical research has been published on this important skill. Little is known about the motion and coordination of the pelvis and trunk during the putting motion. The purpose of this study was to present detailed three-dimensional (3D) kinematic profiles of the pelvis and trunk during the putting motion, and to determine if differences in kinematics exist between proficient and non-proficient golfers. A 3D analysis (100 Hz) was conducted on 10 single figure handicap golfers using a six-camera motion capture system. Participants completed 18 putts (2 m) towards a cup in an indoor facility and were subsequently divided into two groups based on putting proficiency (Proficient: >79%; Non-proficient: <79%). Variables assessed were the linear movements of the centre of mass (COM) and head, and the angular movements of the pelvis and trunk. Effect size statistics showed that the Proficient putters tended to move predominantly in the frontal plane (towards the target), while the non-proficient putters moved more sagittally. In addition, the Non-proficient putters recorded greater movement variability. The implications of this study suggest that putting proficiency is enhanced when the COM moves towards the target.