Flexion relaxation of erector spinae response to spinal shrinkage

Enhancing understanding: Back muscle strength and individual flexibility impact on the flexion-relaxation phenomenon in the lumbar erector spinae

The flexion-relaxation phenomenon (FRP) refers to the deactivation of back muscles during deep forward trunk bending. This study examined the effects of back muscle strength, individual flexibility, and trunk angle on FRP in the back muscles. Forty male participants were classified into four groups according to toe-touch flexibility and back muscle strength. Lumbar erector spinae (LES) activity and the lumbosacral angle (LSA) were measured at incremental trunk flexion angles (0°-90°, with increments of 15°) to analyze FRP. Results indicated significant effects of back muscle strength, flexibility, and trunk angle on LES activity (all p < 0.001). Flexibility (p < 0.05) and trunk angle (p < 0.001) also influenced LSA. Additionally, an interaction between flexibility and trunk angle impacted LES activation (p < 0.001). Flexibility mainly determined FRP onset, while back muscle strength influenced efforts during moderate trunk flexion (30°-60°). These findings indicate that differences in lower back load among individuals with varying back muscle strengths become apparent even at relatively small trunk flexion angles (approximately 30°). When prolonged static trunk flexion in workplace settings places considerable strain on the lower back, we recommend utilizing toe-touch flexibility and back muscle strength assessments as practical screening tools for identifying early and subtle indicators of the FRP in workers.

Comparison of flexion relaxation phenomenon between female yogis and matched non-athlete group

BACKGROUND

Trunk flexion is a common exercise during daily activities. Flexion relaxation phenomenon (FRP) occurs during forward bending in which there is a sudden silence of erector spinae (ES) muscles. The pattern of forward bending differs in yoga practitioners. This learned pattern probably predisposes yogis to injuries. The hypothesis of this study was that FRP differs in yogis in comparison to non-yogis individuals.

METHODS

This observational cross-sectional study was performed on 60 women assigned into yogis and non-athlete groups. Each participant was asked to bend forward and then return to the initial position. ES activity was recorded at L3 level, 4 cm from mid line during the trial. Trunk inclination and lumbar flexion angles were calculated at FRP onset and cessation moments.

RESULTS

The FRP occurred in 80% of yoga practitioners in comparison to 96.7% in the control group. Trunk inclination angle was significantly greater at FRP initiation in yogis compared to control group. Lumbar flexion angle was not different between the groups.

CONCLUSIONS

It is concluded that the altered pattern of forward bending observed in yogis may change patterns of ES muscles activity if it becomes part of a person's daily lifestyle which might predispose these muscles to fatigue and subsequent injuries; however, further studies are warranted for clarification.

Assessing aberrant muscle activity patterns via the analysis of surface EMG data collected during a functional evaluation

BACKGROUND

Surface electromyographic (EMG) recordings collected during the performance of functional evaluations allow clinicians to assess aberrant patterns of muscle activity associated with musculoskeletal disorders. This assessment is typically achieved via visual inspection of the surface EMG data. This approach is time-consuming and leads to accurate results only when the assessment is carried out by an EMG expert.

METHODS

A set of algorithms was developed to automatically evaluate aberrant patterns of muscle activity. EMG recordings collected during the performance of functional evaluations in 62 subjects (22 to 61 years old) were used to develop and characterize the algorithms. Clinical scores were generated via visual inspection by an EMG expert using an ordinal scale capturing the severity of aberrant patterns of muscle activity. The algorithms were used in a case study (i.e. the evaluation of a subject with persistent back pain following instrumented lumbar fusion who underwent lumbar hardware removal) to assess the clinical suitability of the proposed technique.

RESULTS

The EMG-based algorithms produced accurate estimates of the clinical scores. Results were primarily obtained using a linear regression approach. However, when the results were not satisfactory, a regression implementation of a Random Forest was utilized, and the results compared with those obtained using a linear regression approach. The root-mean-square error of the clinical score estimates produced by the algorithms was a small fraction of the ordinal scale used to rate the severity of the aberrant patterns of muscle activity. Regression coefficients and associated 95% confidence intervals showed that the EMG-based estimates fit well the clinical scores generated by the EMG expert. When applied to the clinical case study, the algorithms appeared to capture the characteristics of the muscle activity patterns associated with persistent back pain following instrumented lumbar fusion.

CONCLUSIONS

The proposed approach relies on EMG-based measures to generate accurate estimates of the severity of aberrant patterns of muscle activity. The results obtained in the case study suggest that the proposed technique is suitable to derive clinically-relevant information from EMG data collected during functional evaluations.

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.

Muscular Activation Pattern of Bilateral Extensors Response to Asymmetric Hand Lifting During Trunk Flexion-extension Performance

The authors' purpose was to test the effect of asymmetric hand lifting on muscular activation patterns of 3 bilateral extensors. Eighteen male university students without back pain were volunteered. Each performed flexion-extension randomly with conditions of right lifting, left lifting, and nonlifting. Surface electromyography from bilateral thoracic, lumbar erector spinae, and hamstring was recorded. The cross-correlation and relative intensity in paired muscles of bilateral extensors was calculated in flexion as well as extension period. The results showed that the cross-correlation coefficient was decreased and the phase lag as well as the relative intensity of bilateral extensors was increased significantly in thoracic level. The phase lag as well as the relative intensity of bilateral extensors was increased significantly in lumbar level. It was concluded that asymmetric lifting has a significant effect on muscular activation of bilateral extensors in thorax level, which causes the ipsilateral extensor to activate larger and longer. Asymmetric lifting also has some effect on muscular activation of bilateral extensors in lumbar level but with less extent than in thorax level, which causes contralateral extensor to activate larger and longer. Asymmetric lifting seems to have no significant effect on muscular activation of bilateral hamstring.

Evaluation of the lumbar kinematic measures that most consistently characterize lumbar muscle activation patterns during trunk flexion: a cross-sectional study

OBJECTIVE

The purpose of this study was to determine which kinematic measure most consistently determined onset and cessation of the flexion-relaxation response.

METHODS

The study was a cross-sectional design in a laboratory setting in which 20 asymptomatic university-aged (19.8-33.3 years old) participants were tested. Muscle activation was measured for the lumbar erector spinae, and 3-dimensional motion was recorded. Flexion-relaxation onset and cessation occurrences were determined for 10 standing maximum voluntary flexion trials. The lumbar and trunk angles at both events were expressed as unnormalized (°) and normalized (%Max: percentage of maximum voluntary flexion) measures. Intraclass correlation coefficients and coefficients of variation were calculated to determine within- and between-participant reliability, respectively.

RESULTS

Mean (SD) unnormalized flexion-relaxation angles ranged from 46.28° (11.63) (lumbar onset) to 108.10° (12.26) (trunk cessation), whereas normalized angles ranged from 71.31%Max (16.44) (trunk onset) to 94.83%Max (lumbar cessation). Intraclass correlation coefficients ranged from 0.905 (normalized lumbar, left side, onset) to 0.995 (unnormalized lumbar, both sides, cessation). Coefficients of variation ranged from 3.56% (normalized lumbar, right side, cessation) to 26.02% (unnormalized trunk, left side, onset).

CONCLUSIONS

The data suggest that, for asymptomatic individuals, unnormalized and normalized lumbar kinematics most consistently characterized flexion-relaxation angles within and between participants, respectively. Lumbar measures may be preferential when the flexion-relaxation response is investigated in future clinical and biomechanical studies.

Effect of leg support on muscle cross-correlation of bilateral erector spinae during trunk flexion-extension performance

Investigations corresponding to the affected factors of the cross-correlation of pair muscles are limited though muscle activation patterns of bilateral erector spinae (ES) during trunk flexion-extension performance in standing have been utilized as an indicator in the evaluation of low back pain condition. The purpose of the study is to evaluate the effect of leg support on the cross-correlation of bilateral ES, and to test if the average of bilateral ES could weaken this effect. Twenty male university students volunteered for this study. Each performed the trunk flexion-extension in three leg support conditions randomly with the condition of single left leg support, double leg support and single right leg support, respectively. Each condition included three trials of trunk flexion-extension with the cycle of 5s flexion and 5s extension in standing. Surface electromyography from the right ES muscle as well as from the left one was recorded. The cross-correlation both in pair muscle of right-left ES and in pair muscle of right-average of bilateral ES was calculated in the flexion as well as extension period. A one-way ANOVA with repeated measures was used. The results showed that leg support has some effect on cross-correlation of bilateral ES, which causes the absolute value of phase lag to be significantly larger in flexion period. It is suggested that this effect could be weakened by the average of bilateral ES through significantly increasing the cross-correlation coefficient, and decreasing the absolute value of phase lag.

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.

Does prolonged seated deskwork alter the lumbar flexion relaxation phenomenon?

Sustained maximum lumbar spine flexion can increase the angle at which the low back flexion relaxation phenomenon (FRP) is observed. This adaptation has been hypothesized to have implications for the control of lumbar spine stability and increase the potential for low back injury. The objective of this study was to investigate if similar changes in the FRP would occur from sub-maximal spine flexion induced by an extended continuous duration of seated office deskwork. Twenty-three participants (12 male and 11 female) performed three bouts of full forward spine flexion interspersed with two 1-h periods of seated deskwork. Lumbar spine angular kinematics and electromyographic activity from the lumbar erector spinae were obtained throughout all trials. The angles at which myoelectric silence occurred (FRP onset) were documented. Lumbar flexion at FRP onset increased by 1.3±1.5° after 1-h of sitting (p<0.05) with no further increase after 2-h. However, when the angle at the FRP onset was normalized to the total range of flexion, there was no difference in the FRP onset. These results suggest that the seated posture may induce residual deformation in the viscoelastic passive tissues of the low back; this could increase the challenge of controlling spine motion and reduce the load-bearing capacity of the lumbar spine system during activities performed following extended bouts of sitting.