Examination of the flexion relaxation phenomenon in erector spinae muscles during short duration slumped sitting

[The effect of different working postures while felling a tree with a chain-saw on trunk muscles' activity]

PURPOSE

Many forestry workers who use chain-saws suffer from low back pain. Previous studies have reported that low back pain is related to the working postures while felling a tree with a using chain-saws. However, no previous study has investigated trunk muscle activities during work. The purpose of this study was to clarify the relationship between working postures while holding a chain-saw, and trunk muscles activities as measured by surface electromyography (EMG).

METHOD

Subjects were 10 males who were not forestry workers. Four task postures while holding a chain-saw were tested: standing, 30(o) trunk flexion, 90(o) trunk flexion and half-kneeling. EMG recordings were obtained bilaterally of the lumbar paraspinal (LP) muscles and rectus abdominis (RA) muscles. Raw EMG data were processed by integrating the EMG and normalizing them to %MVC. The paired t-test was used to detect statistical differences in the activities between the right and left LP muscles and RA muscles. One-factor repeated measures ANOVA was used to compare the bilateral LP and RA muscle activities among the 4 different postures. The significance level was set to less than 5%.

RESULTS

In the half-kneeling posture, the right LP muscle activity was 14.7% higher than the left LP muscle activity (p<0.05); however, there were no significant differences in muscle activities among the other postures. The right LP muscle activity of 30(o) trunk flexion posture was 25.6% higher than that of the standing posture, and 14.2% higher than that of half-kneeling posture (p<0.05). The bilateral LP muscle activities of the 90(o) trunk flexion posture were the highest of the 4 postures, 16.7% higher than the half-kneeling posture (p<0.05) right LP muscle activity. There was a tendency of increase in the left LP muscle activity when trunk flexion angle increased, but no significant differences among the 4 postures were found. The bilateral RA muscle activities were low and did not significantly differ among the 4 postures.

CONCLUSIONS

This study showed that when the trunk is flexed, the LP muscle activities change asymmetrically, with the right LP muscle activity increasing significantly compared to the standing posture and the half-kneeing posture, but there was no significant difference in the left LP muscle activity. These results suggest that working postures that involve trunk flexion while felling a tree with a holding chain-saw may lead to increased loading of the LP muscles.

Respiratory chest movement measurement as a chair quality indicator – preliminary observations

Regardless of the constantly increasing time man is spending in a sitting position, there is still a lack of objective chair quality assessment criteria. The aim of this paper is to find the answer to whether respiratory chest movement measurements can be a chair quality indicator. The study included 34 participants (mean 34.7 years ± 5.2). Their chest movements were assessed using respiratory inductive plethysmography while sitting on two subsequent chairs. Significant differences in chest movements depending on chair type were observed concerning the breathing duct (upper and lower) and breathing movement amplitude. The amplitude of the upper respiratory track in the first chair was higher (239.4 mV) compared with the second seat (207.3 mV) (p = .018). The analyzed parameters of respiratory chest movement may become a helpful indicator for design and selection of chairs which enable people to both work and relax in the most ergonomic conditions.

Etiology of lumbar lordosis and its pathophysiology: a review of the evolution of lumbar lordosis, and the mechanics and biology of lumbar degeneration

The goal of this review is to discuss the mechanisms of postural degeneration, particularly the loss of lumbar lordosis commonly observed in the elderly in the context of evolution, mechanical, and biological studies of the human spine and to synthesize recent research findings to clinical management of postural malalignment. Lumbar lordosis is unique to the human spine and is necessary to facilitate our upright posture. However, decreased lumbar lordosis and increased thoracic kyphosis are hallmarks of an aging human spinal column. The unique upright posture and lordotic lumbar curvature of the human spine suggest that an understanding of the evolution of the human spinal column, and the unique anatomical features that support lumbar lordosis may provide insight into spine health and degeneration. Considering evolution of the skeleton in isolation from other scientific studies provides a limited picture for clinicians. The evolution and development of human lumbar lordosis highlight the interdependence of pelvic structure and lumbar lordosis. Studies of fossils of human lineage demonstrate a convergence on the degree of lumbar lordosis and the number of lumbar vertebrae in modern Homo sapiens. Evolution and spine mechanics research show that lumbar lordosis is dictated by pelvic incidence, spinal musculature, vertebral wedging, and disc health. The evolution, mechanics, and biology research all point to the importance of spinal posture and flexibility in supporting optimal health. However, surgical management of postural deformity has focused on restoring posture at the expense of flexibility. It is possible that the need for complex and costly spinal fixation can be eliminated by developing tools for early identification of patients at risk for postural deformities through patient history (genetics, mechanics, and environmental exposure) and tracking postural changes over time.

The effects of backward adjustable thoracic support in wheelchair on spinal curvature and back muscle activation for elderly people

OBJECTIVES

To investigate the effects of backward adjustable thoracic support on spinal curvature and back muscle activation during wheelchair sitting.

METHODS

Twenty elderly people were recruited for this study. The backward adjustable thoracic support sitting posture was compared with the slumped, normal, and lumbar support sitting postures. Spinal curvatures (pelvic, lumbar, and thoracic angles) and muscle activations of 4 back muscles on both sides (maximal voluntary isometric contraction of the lumbar multifidus, lumbar erector spinae, iliocostalis lumborum pars thoracis, and thoracic erector spinae at T9) were measured and compared between the different sitting postures using one-way analysis of variance with repeated measures.

RESULTS

The backward adjustable thoracic support sitting posture showed a relatively neutral pelvic tilt (-0.32±4.80°) when compared with the slumped (22.84±5.27°) and lumbar support (-8.97±3.31°) sitting postures (P<0.001), and showed relatively higher lumbar lordosis (-23.38±6.50°) when compared with the slumped (14.77±7.83°), normal (0.44±7.47°), and lumbar support (-16.76±4.77°) sitting postures (P<0.05). It also showed relatively lower back muscle activity when compared with the normal and lumbar support sitting postures (P<0.05).

CONCLUSIONS

The backward adjustable thoracic support sitting concept was suggested because it maintains a more neutral pelvic tilt, higher lumbar lordosis, and lower back muscle activation, which may help maintain a better sitting posture and reduce the risk of back pain.

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.

Quantification of the lumbar flexion-relaxation phenomenon: comparing outcomes of lumbar erector spinae and superficial lumbar multifidus in standing full trunk flexion and slumped sitting postures

OBJECTIVE

The purpose of this study was to identify differences in flexion-relaxation outcomes in asymptomatic participants, with respect to both flexion-relaxation phenomenon (FRP) occurrence and spinal onset angles, as a function of posture and choice of muscle being examined.

METHODS

This was a cross-sectional study in a laboratory setting. Thirty asymptomatic participants performed standing full trunk flexion and slumped sitting postures while activation levels of the lumbar erector spinae and superficial lumbar multifidus were monitored. Two thresholds were used to define whether FRP was present in each muscle and, if present, at what trunk flexion angle it occurred. These outcomes were compared descriptively between muscles and between postures.

RESULTS

Most participants displayed FRP in both muscles during standing full flexion; occurrences were more variable in slumped sitting. On average, FRP during standing full flexion and slumped sitting occurred at approximately 80% and 52% of participants' maximum flexion value, respectively. Variability in the slumped sitting onset angles was greater than that in standing full flexion.

CONCLUSION

Outcomes for FRP during standing full flexion in asymptomatic participants appeared to be more robust and were not affected by the choice of either lumbar erector spinae or superficial lumbar multifidus. Conversely, during slumped sitting, FRP occurrence varied substantially depending on choice of muscle, although onset angles were relatively consistent between muscles. Although the choice of one muscle over the other may be warranted, it may be prudent to examine both muscles during FRP investigations in sitting postures, in order to fully characterize the behavior and activation patterns of the lumbar musculature.

Should a standing or seated reference posture be used when normalizing seated spine kinematics?

Currently in the literature there is no consensus on which procedure for normalizing seated spine kinematics is most effective. The objective of this study was to examine the changes in the range of motion (ROM) of seated posture trials when expressed as a percent of maximum standing and seated ROM. A secondary purpose was to determine whether the typical maximum planar calibration movements (flexion, lateral-bend, and axial twist) elicited the respective maximum ROM values for each spine region versus postures with specific movement instruction. Thirteen male participants completed seven different movement trials. These consisted of the maximum planar movement trials, with the remaining four postures being combinations of specific lumbar and thoracic movements. Global and relative angles for the upper-thoracic, mid-thoracic, lower-thoracic, and lumbar regions were calculated and normalized to both a seated and standing reference posture. When normalizing both global and relative angles the standing reference appears optimal for flexion, twisting and lateral bend angles in all spine regions, with the exception of relative flexion angle in the mid-thoracic region. The maximum planar movement trials captured the greatest ROM for each global angle, relative lower-thoracic angle and relative lumbar flexion angle, but did not for all other relative angles in the upper-thoracic, mid-thoracic, and lumbar regions. If future researchers can only collect one reference posture these results recommend that a standing reference posture be collected for normalizing seated spine kinematics, although a seated reference posture should be collected if examining relative flexion angles at the mid-thoracic region.

Improving Field Observation of Spinal Posture in Sitting

Observing seated posture is important for ergonomic assessment; proper chair fit and chair adjustment should be considered for the entire context of work demands. Recommending only one seated posture presumes that all seated work has a similar location of visual targets, shoulder reach distances, and support surfaces. The nature of work tasks may influence posture more than does chair adjustment, and field observation of sitting should focus specifically on lumbar spine posture when work may cause forward movement of the torso. I suggest that the position and movement of the pelvis in relation to the torso is a reasonable and important indicator of spinal posture.

Altered flexion-relaxation responses exist during asymmetric trunk flexion movements among persons with unilateral lower-limb amputation

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

Use of Kinetic and Kinematic Data to Evaluate Load Transfer as a Mechanism for Flexion Relaxation in the Lumbar Spine

Flexion relaxation (FR) in the low back occurs when load is transferred from the spine's extensor musculature to its passive structures. This study investigated the influence of added upper body mass on low back kinetics and kinematics at the FR onset. Sixteen participants (eight male, eight female) performed standing full forward spine flexion with 0%, 15%, and 30% of their estimated upper body mass added to their shoulders. Electromyographic data were obtained from the lumbar erector spinae. Ground reaction forces and kinematic data from the lower limbs, pelvis, and spine were recorded. Extensor reaction moments (determined using a bottom-up linked segment model) and flexion angles at the FR onset were documented along with the maximum spine flexion. The angle at the FR onset increased significantly with added mass (p < 0.05). Expressing the FR onset angle as a percent of the full range of trunk flexion motion for that condition negated any differences between the added mass conditions. These findings demonstrate that low back kinetics play a role in mediating FR in the lumbar spine.

Evaluation of methods for the quantification of the flexion-relaxation phenomenon in the lumbar erector spinae muscles

OBJECTIVES

There are various methods to quantify the flexion-relaxation phenomenon (FRP); however, there is little standardization. This study aimed to evaluate the performance of various quantification methods in terms of their ability to identify lumbar erector spinae flexion-relaxation during standing forward trunk flexion.

METHODS

The study was a cross-sectional design in a laboratory setting. Lumbar erector spinae activation levels were measured in 12 male participants performing full trunk flexion movements. Electromyographical signals were assessed using 16 criteria within 4 quantification methods (visual, statistical, threshold, ratio), and the sensitivity of each was assessed relative to the benchmark criterion (visual inspection of raw electromyography data).

RESULTS

Visual inspection and most of the threshold and ratio criteria displayed the highest sensitivity. On average (SD) across the 16 criteria, FRP was positively identified 21.6 (6.2) times of 24 data sets (12 participants, 2 muscles). The visual inspection criteria positively identified FRP in all 24 trials, whereas the statistical method did not identify FRP at all (P = .44 and P = .46 for the left and right sides, respectively). The threshold and ratio criteria positively identified FRP 23.2 (1.5) and 22.5 (3.7) times, on average, respectively. Results from criteria based on differences between upright and fully flexed muscle activation tended to be conservative in FRP identification. The methods were classified as reliable or nonreliable, based on their sensitivity when specific characteristics were evident in the electromyography signals.

CONCLUSIONS

Although many of the criteria identified FRP with 100% sensitivity, others produced unrealistic results. The latter may be suitable for other experimental designs or may require reevaluation regarding their ability to identify FRP. Although visual inspection, threshold, or ratio methods performed well and may be appropriate for either biomechanical or clinical research, the threshold method provided the optimal trade-off between performance, consistency, and feasibility for these data.

The Intra- and Inter-rater Reliabilities of the Forward Head Posture Assessment of Normal Healthy Subjects

[Purpose] Assessment of posture is an important goal of physical therapy interventions for preventing the progression of forward head posture (FHP). The purpose of this study was to determine the inter- and intra-rater reliabilities of the assessment of FHP. [Subjects and Methods] We recruited 45 participants (20 male subjects, 25 female subjects) from a university student population. Two physical therapists assessed FHP using images of head extension. FHP is characterized by the measurement of angles and distances between anatomical landmarks. Forward shoulder angle of 54° or less was defined as FHP. Intra- and inter-rater reliabilities were estimated using Kendall's Taub correlation coefficients. [Results] Intra-class correlation of intra-rater measurements indicated an excellent level of reliability (0.91), and intra-class correlation of inter-rater measurements showed a good level of reliability in the assessment of FHP (0.75). [Conclusion] Assessment of FHP is an important component of evaluation and affects the design of the treatment regimen. The assessment of FHP was reliably measured by two physical therapists. It could therefore become a useful method for assessing FHP in the clinical setting. Future studies will be needed to provide more detailed quantitative data for accurate assessment of posture.

Prevalence of low back symptoms and its consequences in relation to occupational group

BACKGROUND

The purpose of this study was to examine: (1) the prevalence of low back symptoms (LBS) and its consequences (reduced activities and absenteeism); (2) the association between occupational group and LBS; and (3) the association between LBS and its consequences.

METHODS

A self-administered questionnaire was used to determine the prevalence of LBS in 1,294 Indonesian coal mining workers. A Cox proportional hazards model was developed to quantify the 12-monthly hazard of LBS. Logistic regression models were developed to identify risk factors for reduced activity and absenteeism from the workplace.

RESULTS

The 12-month period prevalence for LBS, reduced activities, and absenteeism were 75%, 16%, and 13%, respectively. The 12-monthly hazard of LBS for blue-collar workers was 1.85 (95% CI: 1.06-3.25) times that of white-collar workers. LBS and smoking increased the risk of reduced activity and absenteeism.

CONCLUSIONS

Indonesian coal mining workers have a high prevalence of LBS. The findings imply that efforts to reduce LBS and in the workplace should focus on blue-collar workers. For smokers who report reduced activities and/or absenteeism, there should be a focus on rehabilitation and/or return-to-work programs.

What is slumped sitting? A kinematic and electromyographical evaluation

Slumped sitting is a commonly used reference posture when comparing effects of upright sitting in both clinical and non-clinical populations alike. The exact nature of slumped sitting has not been clearly defined, including regional differences within the posture, and how the passive nature of slumped sitting compares to an active-flexion posture. Kinematic and electromyographical (EMG) data were collected from 12 males during three repeats of slumped sitting and seated maximum forward flexion. Spine angles were defined in four regions (three thoracic and lumbar) as well as for the pelvis, and EMG was collected from eight muscles bilaterally. Kinematic data were expressed as a range of motion (in degrees), and as a percent of full forward flexion while seated (%SIT-FF) and standing (%STAND-FF). EMG data were normalized to a percent maximum contraction (%MVC). Results showed that slumped sitting is characterized by 10° posterior pelvis rotation, near end-range flexion of the mid- (90%SIT-FF) and lower- (81%SIT-FF) thoracic regions, and mid-range flexion of the upper-thoracic (51%SIT-FF) and lumbar (43%SIT-FF) regions. Comparison of slumped by %STAND-FF showed the upper- and mid-thoracic regions to have high variability and large values (over 100%STAND-FF). Muscle activation showed a significant 3%MVC reduction in the lower-thoracic erector spinae muscle when moving from upright to slumped sitting. These data highlight the postural differences occurring within different spine regions, and interpretations that could be drawn, depending on which normalization (sit or stand) method is used.

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.

Sustaining biological welfare for our future through consistent science

Physiological anthropology presently covers a very broad range of human knowledge and engineering technologies. This study reviews scientific inconsistencies within a variety of areas: sitting posture; negative air ions; oxygen inhalation; alpha brain waves induced by music and ultrasound; 1/f fluctuations; the evaluation of feelings using surface electroencephalography; Kansei; universal design; and anti-stress issues. We found that the inconsistencies within these areas indicate the importance of integrative thinking and the need to maintain the perspective on the biological benefit to humanity. Analytical science divides human physiological functions into discrete details, although individuals comprise a unified collection of whole-body functions. Such disparate considerations contribute to the misunderstanding of physiological functions and the misevaluation of positive and negative values for humankind. Research related to human health will, in future, depend on the concept of maintaining physiological functions based on consistent science and on sustaining human health to maintain biological welfare in future generations.

The effect of chair designs on sitting pressure distribution and tissue perfusion

OBJECTIVE

The aim of this study was to investigate the effect of five chair designs on interface pressure distribution and tissue perfusion in the buttock-thigh region.

BACKGROUND

Prolonged sitting has been found to contribute to the symptoms of work-related low back pain. Studies have found that chair design affects users' sitting posture and comfort. As sitting applies pressure to the user, it is necessary to investigate how chair design affects sitting pressure and tissue perfusion during sitting.

METHOD

We tested five chair designs (Suspension A, Suspension B, Foam A, Foam B, and bicompliant) on 15 young, healthy females. Sitting interface pressure and buttock-thigh tissue perfusion (in terms oftranscutaneous partial pressure of oxygen and carbon dioxide, tcPO2 and tcPCO2, respectively) were measured during 10-min sitting on each chair.

RESULTS

We found that chair design significantly affected the distribution of the sitting pressure (p < .001) and buttock-thigh tissue perfusion (p < .023). Average pressure and total contact area were found highest in both foam designs, and the average pressure was the lowest in one of the suspension designs. Across all tested chair designs, the anterior portion of the seat sustained the lowest contact pressure. It was also found that tcPO2 was the lowest (p < .003) and tcPCO2 was the highest (p < .001) in tissue around ischial tuberosity for all chair designs.

CONCLUSION

Chair design and materials of the seat significantly affect the sitting interface pressure distribution and tissue perfusion in sitting area. Further evaluation of these outcomes may provide useful information to correlate chair design with sitting comfort.

A comparative investigation of flexion relaxation phenomenon in healthy and chronic neck pain subjects

PURPOSE

The cervical flexion relaxation phenomenon (FRP) is a neck extensor myoelectric "silence" that occurs during complete cervical and lumbar flexion. In contrast to low back pain, the changes that occur during FRP in chronic neck pain (CNP) patients are still not clear. The aim of this study was to assess the characteristics of this phenomenon in the cervical region in CNP patients and controls.

METHODS

Twenty-two women (23 ± 2.62 years) with chronic non-specific neck pain and 21 healthy women (23.4 ± 1.68 years) participated in this study. They accomplished a cervical flexion and extension from neutral position. Neck angle and surface electromyographic activity of cervical erector spinae (CES) and upper trapezius muscles were recorded. Appearance, onset and offset angle of the FRP were analysed and compared between the two groups.

RESULTS

There were significant differences in the appearance of FRP between the two groups (P ≤ 0.001). The FRP in the CES muscles was observed in 85.7 % of healthy subjects and in 36.3 % of CNP patients, and no FRP was observed in the upper trapezius. Results of this study show that the onset and offset of FRP parameters were significantly different between the two groups (P ≤ 0.001).

CONCLUSIONS

The results of the present study indicate that FRP in CNP patients was seen less than the healthy subjects, and moreover the FRP period was reduced in CNP patients. Our results also suggest that the changes in FRP of CNP patients may be due to the increased CES activity in these patients.

Comparing lower lumbar kinematics in cyclists with low back pain (flexion pattern) versus asymptomatic controls--field study using a wireless posture monitoring system

The aim of this study was to examine lower lumbar kinematics in cyclists with and without non-specific chronic low back pain (NS-CLBP) during a cross-sectional cycling field study. Although LBP is a common problem among cyclists, studies investigating the causes of LBP during cycling are scarce and are mainly focussed on geometric bike-related variables. Until now no cycling field studies have investigated the relationship between maladaptive lumbar kinematics and LBP during cycling. Eight cyclists with NS-CLBP classified as having a 'Flexion Pattern' (FP) disorder and nine age- and gender-matched asymptomatic cyclists were tested. Subjects performed a 2 h outdoor cycling task on their personal race bike. Lower lumbar kinematics was measured with the BodyGuard™ monitoring system. Pain intensity during and after cycling was measured using a numerical pain rating scale. The NS-CLBP (FP) subjects were significantly more flexed at the lower lumbar spine during cycling compared to healthy controls (p = 0.018), and reported a significant increase in pain over the 2 h of cycling (p < 0.001). One-way repeated measures ANOVA revealed a significant main effect for group (p = 0.035, F = 5.546) which remained just significant when adding saddle angle as a covariate (p = 0.05, F = 4.747). The difference in posture between groups did not change over time. These findings suggest that a subgroup of cyclists with NS-CLBP (FP) demonstrate an underlying maladaptive motor control pattern resulting in greater lower lumbar flexion during cycling which is related to a significant increase in pain.

Gender differences in work-related risk factors associated with low back symptoms

The prevalence of low back symptoms (LBS) in many working populations is high and differences in prevalence between genders are inconsistent. However, gender-specific risk factors for LBS have seldom been examined. Hence, the aim of the present study was to indicate gender-specific LBS risk factors. A sample of 3003 people was interviewed by telephone to get information about current workplace exposure and LBS. The risk of LBS for the whole population increased with work in awkward/tiring positions (OR 1.37, 95% CI 1.12-1.68) and very/extremely stressful jobs (OR 1.46, 95% CI 1.05-2.03). None of the explanatory variables were significantly associated with LBS for males but working in awkward/tiring positions (OR 1.51, 95% CI 1.04-2.20), dissatisfaction with contact and cooperation with management (OR 1.68, 95% CI 1.02-2.78) and finding their job to be very/extremely stressful (OR 2.27, 95% CI 1.46-3.52) were significantly associated with LBS for females. Interventions to reduce LBS in workplaces should focus on reducing working in awkward/tiring positions, improving contact and cooperation with management, and reducing stressful jobs, especially amongst females.

PRACTITIONER SUMMARY

Strategies to prevent or reduce LBS should focus on reducing exposure to awkward or tiring positions at work, improving contact and cooperation with management, and reducing stressful jobs, especially for females.

Association of spinal muscle composition and prevalence of hyperkyphosis in healthy community-dwelling older men and women

BACKGROUND

Older adults with hyperkyphosis are at increased risk of falls, fractures, and functional decline. Modifiable risk factors for hyperkyphosis have not been well studied. Our objective was to determine whether spinal muscle area and density are associated with hyperkyphosis, independent of age, race, sex, bone mineral density, and trunk fat.

METHODS

Using data from the Pittsburgh site of the Health, Aging, and Body Composition study, we performed a baseline cross-sectional analysis. Participants were black and white men and women 70-79 years old (N = 1172), independent in activities of daily living and able to walk &frac14; mile and up 10 steps without resting. We measured Cobb's angle of kyphosis from supine lateral scout computed tomography scans, and categorized hyperkyphosis as Cobb's angle >40°. Axial images from lateral scout computed tomography scans assessed spinal extensor muscle cross-sectional area and density (proxy for fat infiltration).

RESULTS

In our sample, 21% had hyperkyphosis. Prevalence in black men was 11%; in white men, 17%; in black women, 26%; and in white women, 30%. In multivariate analysis, each standard deviation increase in muscle density was associated with a 29% reduction in the odds of hyperkyphosis, independent of covariates. Muscle area was not significantly associated with hyperkyphosis.

CONCLUSIONS

Lower spinal muscle density is associated with hyperkyphosis in healthy community-dwelling older adults. This potentially modifiable risk factor could be targeted in exercise interventions. Randomized trials are needed to determine whether an exercise program targeting spinal muscle density reduces hyperkyphosis and in turn improves health outcomes.

Changes in craniocervical and trunk flexion angles and gluteal pressure during VDT work with continuous cross-legged sitting

OBJECTIVES

This study investigated changes in craniocervical and trunk flexion angles and gluteal pressure on both sides during visual display terminal (VDT) work with continuous cross-legged sitting.

METHODS

The gluteal pressures of ten VDT workers, who were recruited from laboratories, were measured using a Teckscan system and videotaped using a single video camera to capture the craniocervical and trunk flexion angles during VDT work at 30 s, 10, 20 and 30 min.

RESULTS

The craniocervical angle was significantly increased at 10 and 20 min compared with the initial angle (p<0.05). The trunk flexion angle was significantly decreased at 30 s, 10, 20 and 30 min (p<0.05). The gluteal pressure of the crossed-leg side significantly increased at 30 s, 10 and 20 min (p<0.05). The gluteal pressure of the uncrossed-leg side significantly decreased at 30 s (p<0.05).

CONCLUSION

We found that cross-legged sitting during VDT work may exert disadvantageous postural effects resulting from craniocervical and trunk flexion angles and gluteal pressure. Therefore, this posture could not be recommended during long-term VDT work.

The reliability and accuracy of an electromagnetic motion analysis system when used conjointly with an accelerometer

The effect of an accelerometer driven electronic postural monitor (Spineangel®) placed within the electromagnetic measurement field of the Polhemus Fastrak™ is unknown. This study assessed the reliability and accuracy of Fastrak™ linear and angular measurements, when the Spineangel® was placed close to the sensor(s) and transmitter. Bland Altman plots and intraclass correlation coefficient (2,1) were used to determine protocol reproducibility and measurement consistency. Excellent reliability was found for linear and angular measurements (0.96, 95% CI: 0.90-0.99; and 1.00, 95% CI: 1.00-1.00, respectively) with the inclusion of Spineangel®; similar results were found, without the inclusion of Spineangel®, for linear and angular measurements, (0.96, 95% CI: 0.89-0.99; and 1.00, 95% CI: 1.00-1.00, respectively). The greatest linear discrepancies between the two test conditions were found to be less than 3.5 mm, while the greatest angular discrepancies were below 3.5°. As the effect on accuracy was minimal, these findings support the conjoint use of the Fastrak™ during validation studies of the Spineangel® device. STATEMENT OF RELEVANCE: Although previous studies have used the Fastrak™ as the gold standard measurement system, the influence of an accelerometer driven postural monitor on accuracy has not been reported. The strength of the present study has been to determine the effect of accelerometer placement within the electromagnetic field on the reliability and accuracy of the Fastrak™.

A comparison of low back kinetic estimates obtained through posture matching, rigid link modeling and an EMG-assisted model

This study examined errors introduced by a posture matching approach (3DMatch) relative to dynamic three-dimensional rigid link and EMG-assisted models. Eighty-eight lifting trials of various combinations of heights (floor, 0.67, 1.2 m), asymmetry (left, right and center) and mass (7.6 and 9.7 kg) were videotaped while spine postures, ground reaction forces, segment orientations and muscle activations were documented and used to estimate joint moments and forces (L5/S1). Posture matching over predicted peak and cumulative extension moment (p < 0.0001 for all variables). There was no difference between peak compression estimates obtained with posture matching or EMG-assisted approaches (p = 0.7987). Posture matching over predicted cumulative (p < 0.0001) compressive loading due to a bias in standing, however, individualized bias correction eliminated the differences. Therefore, posture matching provides a method to analyze industrial lifting exposures that will predict kinetic values similar to those of more sophisticated models, provided necessary corrections are applied.

The mechanical effect of anterior pelvic tilt taping on slump sitting by seated workers

The objectives of this study were to determine whether there is a change in the pelvic inclination after about 30 min of slump sitting by seated workers, and if so, to determine whether these changes can be prevented by the application of anterior pelvic tilt taping (APTT). The subjects who consented to participate in the experiment were randomly allocated to two groups: no-APTT group and APTT group. The no-APTT group performed slump sitting for 30 min, and the both pelvic inclinations were remeasured. In the APTT group, the both pelvic inclinations were measured immediately after the application of the APTT, and then again after 30 min of slump sitting. The both pelvic inclinations in the no-APTT group were significantly decreased (p<0.05) after they returned to the upright standing posture. The both pelvic inclinations in the APTT group were significantly increased immediately after the APTT (p<0.05), and this increase was maintained when returning to the upright standing posture after 30 min of slump sitting (p>0.05). We suggest that APTT can be applied as an auxiliary treatment method for preventing changes in pelvic inclination and musculoskeletal problems of low back area by awkward sitting posture in the seated worker.

Effects of a Visual Feedback Device for Hip Adduction on Trunk Muscles and Sitting Posture in Visual Display Terminal Workers

This study was designed to identify the effects of a visual feedback device for hip adduction on trunk muscles and sitting posture when working at a visual display terminal. The forward head and trunk flexion angles of 20 workers were analyzed using a motion analysis system, and the activities of the lower trapezius, external abdominal oblique, internal abdominal oblique, and L5 paraspinal muscles were analyzed using a electromyography system. The statistical significance of differences between using and not using a visual feedback device was assessed by paired t tests. Using the visual feedback device during Visual Display Terminal work significantly decreased the forward head and trunk flexion angles, and significantly increased the activities of the external abdominal oblique, internal abdominal oblique, and L5 paraspinal muscles. The authors suggest that the visual feedback device for hip adduction promotes the adoption of standard spine and pelvic postures, which might be effective in preventing poor sitting postures.

Ultrasound assessment of the anatomical validity of T3 and L4 as sEMG recording sites

The accuracy of surface EMG measurement is dependent upon minimizing potential crosstalk from other muscles. Although they are deeply situated, in places the erector spinae are covered with electrically silent aponeuroses rather than active muscle tissue. Theoretically these aponeuroses can serve as windows for sEMG recordings. A recent anatomical study concluded that T3 and L4 are ideal sites for recording the ES because the superficial muscle aponeuroses are wide at these sites. The aim of this prospective study was to investigate these sites in vivo using real time ultrasound. Ultrasound images from 20 subjects (10<30 years and 10>70 years; equal numbers of males and females in each group) were acquired during rest and in prone extension with the arms in three different positions. The most superficial aponeurosis widths were measured. The mean T3 aponeurosis width reduced significantly in extension from 4.4±4.7mm at rest to 1.8±2.6mm in extension (p<0.0001). Males had significantly smaller T3 aponeurosis widths than females (p=0.049). The mean L4 aponeurosis width also significantly decreased in extension from 35.5±7.0mm at rest to 29.9±7.2mm in extension (p<0.0001) due to 'doming' of the aponeurosis. Our results demonstrate that T3 is not a reliable site over which to record the ES because the aponeurosis width is too narrow. L4 is a good site if the electrodes are placed no more than 20mm from the midline.

Características biomecânicas, ergonômicas e clínicas da postura sentada: uma revisão

A posição sentada é a mais adotada nos ambientes de trabalho, na escola e nas atividades de lazer. Porém, a manutenção prolongada dessa posição ocasiona a adoção de posturas inadequadas e sobrecarrega as estruturas do sistema musculoesquelético, o que pode acarretar dor e lesão na coluna lombar. A presente revisão teve como objetivo identificar os fatores biomecânicos, ergonômicos e clínicos envolvidos na sustentação da postura sentada. Para isso, foram consultadas as bases de dados ISI Web of Knowledge, Medline, Pubmed e EBSCO Host, sendo selecionados 72 artigos publicados entre 1965 e 2010. Foi possível identificar que na posição sentada não existe uma postura ideal a ser sustentada, mas algumas posturas são mais recomendadas do que outras, tal como a postura sentada ereta e a postura lordótica. As cadeiras influenciam o padrão da posição sentada: conforme seu design, pode permitir maior variedade de posturas. Modificações na cadeira e a utilização de exercícios para o aumento da resistência muscular e da propriocepção, bem como a reeducação postural, são intervenções úteis para reduzir o impacto causado pela posição sentada prolongada no sistema musculoesquelético.

Flexion-relaxation ratio in sitting: application in low back pain rehabilitation

STUDY DESIGN

A multiple-comparative study between normal and low back pain (LBP) patients before and after rehabilitation.

OBJECTIVE

To examine whether there is a change in flexion-relaxation phenomenon in sitting in LBP patient following a rehabilitation treatment.

SUMMARY OF BACKGROUND DATA

There is an association between LBP and seated spine posture. Previous study has reported an absence of flexion-relaxation phenomenon in LBP patients during sitting. However, it is unknown whether there is a difference in flexion-relaxation phenomenon in sitting in LBP patients before and after rehabilitation treatment.

METHODS

A total of 20 normal subjects and 25 chronic LBP patients who underwent a 12 weeks rehabilitation program were recruited. Surface electromyography recordings during upright sitting and flexed sitting were taken from the paraspinal muscles (L3) bilaterally from the normal subjects, and in the LBP patients before and after the rehabilitation treatment. The main outcome measures for patients include the visual analogue scale, Oswestry disability index, subjective tolerance for sitting, standing and walking, trunk muscle endurance, lifting capacity, and range of trunk motion in the sagittal plane. Flexion-relaxation phenomenon in sitting, expressed as a ratio between the average surface electromyography activity during upright and flexed sitting, was compared between normal and patients; and in LBP patients before and after rehabilitation.

RESULTS

Flexion-relaxation ratio in sitting in normal subjects (Left: 6.83 +/- 3.79; Right: 3.45 +/- 2.2) presented a significantly higher (Left: P < 0.001; Right: P < 0.05) value than LBP patients (Left: 3.04 +/- 2.36; Right: 2.02 +/- 1.49). An increase in flexion-relaxation ratio in sitting was observed in LBP patients after rehabilitation (Left: 4.69 +/- 3.94, P < 0.05; Right: 3.58 +/- 2.97, P < 0.001), together with a significant improvement (P < 0.05) in subjective tolerance in sitting and standing, abdominal and back muscle endurance, lifting capacity, and range of motion. There were no significant changes in disability and pain scores, and subjective tolerance in walking.

CONCLUSION

Flexion-relaxation ratio in sitting has demonstrated its ability to discriminate LBP patients from normal subjects, and to identify changes in pattern of muscular activity during postural control after rehabilitation.

Directed attention alters the temporal activation patterns of back extensors during trunk flexion-extension in individuals with chronic low back pain

In chronic low back pain patients (CLBP), neuromuscular and pain intensity have been identified as contributing factors in the disability of the individual. However, it is unclear whether pain intensity influences neuromuscular activation and if directed attention mediates this relationship. Thus, the purpose of this study was to determine the effect of directed attention in individuals with different pain intensities on back extensor activation profiles. Fifty-four CLBP patients were separated into either high- or low-pain groups. Surface electromyograms were recorded from back muscles while the subjects performed a trunk flexion motion for four different attention conditions. Pattern recognition and repeated measures ANOVAs were used to examine the effect of sex, attention and pain intensity on temporal muscle activation patterns. The results showed that there was a significant sex x attention x pain interaction. The largest changes in muscle timing were observed in the low-pain group when their attention was focused on their pain, but the pattern of muscle activation differed between sexes. For males, a rapid decline in activation at mid-extension occurred, whereas females showed delayed activation at the beginning of extension. Overall, this study demonstrated that directed attention on pain had an effect on trunk muscle temporal recruitment, and that this relationship differed between sexes and pain groups. This suggests that sex-specific mechanisms may alter the neuromuscular control of the spine in CLBP patients for different pain levels.

Creep and fatigue development in the low back in static flexion

STUDY DESIGN

In vivo measurements of low back flexion posture and muscle activity before, during, and after static flexion.

OBJECTIVE

To identify the occurrence of creep and muscle fatigue development in the low back during static upper body deep flexion that resembled an above ground work posture.

SUMMARY OF BACKGROUND DATA

Static lumbar flexion has been related to the development of low back disorders, and its injury mechanism has been focused on the changes in passive spinal tissues. Potential influences of muscle fatigue of extensor muscles have not been explored.

METHODS

A total of 20 asymptomatic subjects performed submaximal isometric trunk extension exertions and an isokinetic trunk flexion before and immediately after 5-minute static flexion while the trunk sagittal flexion angle and the myoelectric activities (electromyography [EMG]) of back extensor muscles were recorded simultaneously. Changes in the flexion-relaxation onset angle, maximum flexion angle, muscle activity level, and the median power frequency of EMG associated with the static flexion were evaluated.

RESULTS

Flexion-relaxation onset angle in isokinetic flexion and EMG amplitude of isometric extension were significantly greater after static flexion, indicating creep of spinal tissues in static flexion. Median power frequency of lumbar erector spinae EMG during isometric extension was significantly lower after static flexion, suggesting the development of muscle fatigue. Consistent but low level of EMG was observed together with sporadic muscle spasms during the static flexion period.

CONCLUSION

Fatigue of low back extensor muscles may occur in static flexion due to prolonged passive stretching of the muscles. Low back extensor muscles are required to generate more active forces in weight holding or lifting after static flexion to compensate for the reduced contribution of creep deformed passive tissues in maintaining spinal stability and the posture. The degraded force generating capacity of the fatigued muscles can be a significant risk factor for low back pain.

Trunk muscle activation patterns and spine kinematics when using an oscillating blade: influence of different postures and blade orientations

OBJECTIVE

To compare trunk muscle activation patterns and trunk kinematics when using an oscillating blade in standing and unsupported sitting postures, and with different orientations of the blade.

DESIGN

A cross-sectional survey of trunk muscle activities and lumbar motion.

SETTING

Biomechanics research laboratory.

PARTICIPANTS

Healthy men (N=13).

INTERVENTIONS

An oscillating blade was held with 2 hands and oscillated with vertical and horizontal orientations of blade. These exercises were performed both in an erect standing position and in an erect sitting position.

MAIN OUTCOME MEASURES

Surface electromyography from 14 trunk and 2 shoulder muscles, together with lumbar angular displacement in the 3 planes of motion, were measured while subjects used an oscillating blade at different performance variations. Electromyographic signals were normalized to isometric maximal voluntary contraction (MVC) amplitudes.

RESULTS

With the exception of internal oblique and anterior deltoid for the horizontal condition, and erector spinae at L5 level for the vertical condition, the subject's posture had no effect on trunk muscular recruitment when using the oscillating blade. The vertical blade orientation resulted in higher amplitudes of spine rotation on the horizontal plane and produced the greatest activation levels of the internal oblique (47% MVC), pectoralis major (33% MVC), and external oblique (23% MVC). On the other hand, the horizontal orientation resulted in the greatest activation levels of erector spinae at T9 level (28% MVC), latissimus dorsi (26% MVC), and rectus abdominis (17% MVC).

CONCLUSIONS

Muscle activation and spine motion from using an oscillating blade were not affected by the standing or sitting posture of the subject. The choice of blade orientation was more important, because it defined the main group of muscles recruited during the exercise.

The association between back pain and trunk posture of workers in a special school for the severe handicaps

Background

The present study aims to determine the time spent in different static trunk postures during a typical working day of workers in a special school for the severe handicaps.

Methods

Eighteen workers with low back pain (LBP) and fifteen asymptomatic workers were recruited. A cross-sectional design was employed to study the time spent in different static trunk postures which was recorded by a biaxial accelerometer attached to the T₁₂ level of the back of the subjects.

Results

The results of ANCOVA revealed that subjects with LBP spent significantly longer percentage of time in static trunk posture when compared to normal (p < 0.05). It was also shown that they spent significantly longer time in trunk flexion for more than 10° (p < 0.0125).

Conclusion

An innovative method has been developed for continuous tracking of spinal posture, and this has potential for widespread applications in the workplace. The findings of the present investigation suggest that teachers in special schools are at increased risk of getting LBP. In order to minimise such risk, frequent postural change and awareness of work posture are recommended.

Evidence of a pelvis-driven flexion pattern: are the joints of the lower lumbar spine fully flexed in seated postures?

BACKGROUND

Seated postures are achieved with a moderate amount of lumbo-sacral flexion and sustained lumbo-sacral spine flexion has been associated with detrimental effects to the tissues surrounding a spinal joint. The purpose of this study was to determine if the lower intervertebral joints of the lumbo-sacral spine approach their end ranges of motion in seated postures.

METHODS

Static sagittal digital X-ray images of the lumbo-sacral region from L3 to the top of the sacrum were obtained in five standing and seated postures from 27 participants. Vertebral body bony landmarks were manually digitized and intervertebral joint angles were calculated for the three lower lumbo-sacral joints.

FINDINGS

In upright sitting, the L5/S1 intervertebral joint was flexed to more than 60% of its total range of motion. Each of the lower three intervertebral joints approached their total flexion angles in the slouched sitting posture. These observations were the same regardless of gender. The results support the idea that lumbo-sacral flexion is driven by rotation of the pelvis and lower intervertebral joints in seated postures.

INTERPRETATION

This is the first study to quantitatively show that the lower lumbo-sacral joints approach their total range of motion in seated postures. While not directly measured, the findings suggest that there could be increased loading of the passive tissues surrounding the lower lumbo-sacral intervertebral joints, contributing to low back pain and/or injury from prolonged sitting.

Back posture and low back muscle activity in female computer workers: a field study

BACKGROUND

Few studies have investigated sitting posture and low back muscle activity in occupational settings. This study aims to determine back posture and its influence on low back muscle activity in computer workers, and to investigate whether the work situation is associated with exacerbation of low back pain.

METHODS

Twenty-one female computer workers participated. Surface electromyographic activity was recorded from lumbar multifidus, longissimus, and iliocostalis throughout the workday. Simultaneous inclinometer recordings from pelvis, upper trunk, and left thigh were used to determine back posture and identify periods with sitting, standing, and walking. Low back pain intensity was recorded by visual analogue scale every hour throughout the work and leisure periods.

FINDINGS

All subjects adopted a markedly flexed back posture while seated at work. Surface electromyographic activity was very low for all muscles during sitting (group median <1.4% of root-mean-square-detected response at maximal voluntary contraction). Back posture moderately influenced electromyographic activity, accounting for 19% (sitting) to 38% (standing) of intra-individual variation in muscle activity. Subjects reporting aggravating low back pain (n=10) during the workday were not distinguished by duration of sitting, sitting posture, or low back muscle activity. Low back pain was markedly reduced from the last hour of work to the first hour of leisure, accompanied by an increase in low back muscle activity.

INTERPRETATION

Low back muscle activity was very low during seated posture, presumably due to the flexion-relaxation phenomenon. Sustained stretch of passive lumbar structures in combination with essentially silent muscles may exacerbate low back pain in sedentary workers.

Lumbar-pelvic coordination in the sitting position

This study assessed the relationship of each movement direction on the lumbar spine and on the pelvis in regards to lumbar-pelvic coordination in the sitting position. Lumbar and pelvic motions were recorded using a flexible electrogoniometer in 12 healthy subjects during two different tasks in the sitting position. The coordination of the lumbar spine and pelvis was evaluated using the ratio of lumbar and pelvic angles (L/P ratio hereafter) in three motion phases. There were significant differences in the L/P ratio values between during the "forward bending" and "rising from a forward flexed position" phases (P<0.01). The L/P ratio value ( approximately -0.7) was consistent during the movement from an erect to a slumped sitting position as the lumbar spine and pelvis moved in opposing directions. This study shows that lumbar-pelvic coordination occurs in the sitting position. Lumbar-pelvic coordination is confirmed even if the movement tasks are different in the sitting position, and these findings show that aspects of a particular movement are dependent on the given movement task. These findings may provide greater insight into the kinematic changes involved in lumber-pelvic coordination, and help clinicians implement sitting exercises conducive to the independence of the patient.

Effects of a proximity-sensing feedback chair on head, shoulder, and trunk postures when working at a visual display terminal

INTRODUCTION

This study was designed to identify the effects of feedback from a proximity-sensing chair on head, shoulder, and trunk postures when working at a visual display terminal (VDT).

METHODS

Twenty healthy adults were asked to perform VDT work, and their forward head, forward shoulder, and trunk flexion angles were analyzed using a 3-D motion analysis system. The statistical significance of differences between without and with an auditory feedback device was tested by paired t-tests, with the significance cutoff set at alpha=0.05.

RESULTS

The forward head, forward shoulder, and trunk flexion angles significantly decreased during VDT work when using the proximity sensor with auditory feedback.

CONCLUSION

We suggest that a feedback device promotes the adoption of beneficial postures, which may be effective in preventing VDT-work-related neck and upper-limb disorders.

Effect of different upright sitting postures on spinal-pelvic curvature and trunk muscle activation in a pain-free population

STUDY DESIGN

A normative within-subjects single-group study.

OBJECTIVE

To compare spinal-pelvic curvature and trunk muscle activation in 2 upright sitting postures ("thoracic" and "lumbo-pelvic") and slump sitting in a pain-free population.

SUMMARY OF BACKGROUND DATA

Clinical observations suggest that both upright and slump sitting postures can exacerbate low back pain. Little research has investigated the effects of different upright sitting postures on trunk muscle activation.

METHODS

Spinal-pelvic curvature and surface electromyography of 6 trunk muscles were measured bilaterally in 2 upright (thoracic and lumbo-pelvic) sitting postures and slump sitting in 22 subjects.

RESULTS

Thoracic, compared to lumbo-pelvic, upright sitting showed significantly greater thoracic extension (P < 0.001), with significantly less lumbar extension (P < 0.001) and anterior pelvic tilt (P = 0.03). Furthermore, there was significantly less superficial lumbar multifidus (P < 0.001) and internal oblique (P = 0.03) activity, with significantly higher thoracic erector spinae (P < 0.001) and external oblique (P = 0.04) activity in thoracic upright sitting. There was no significant difference in superficial lumbar multifidus activity between thoracic upright and slump sitting.

CONCLUSIONS

Different upright sitting postures resulted in altered trunk muscle activation. Thoracic when compared to lumbo-pelvic upright sitting involved less coactivation of the local spinal muscles, with greater coactivation of the global muscles. These results highlight the importance of postural training specificity when the aim is to activate the lumbo-pelvic stabilizing muscles in subjects with back pain.

Evaluation of the flexion relaxation phenomenon of the trunk muscles in sitting

STUDY DESIGN

A normative, single-group study was conducted.

OBJECTIVE

To investigate the flexion relaxation phenomenon in the thoraco-lumbopelvic muscles among a pain-free population when moving from an upright to a slump sitting posture.

SUMMARY OF BACKGROUND DATA

The presence of the flexion relaxation phenomenon (FRP) of the back muscles is well documented at end-range spinal flexion when standing. This phenomenon is commonly found disrupted in low back subjects. However, whether FRP occurs in sitting remains controversial.

METHODS

The sample consisted of 24 healthy pain-free adults. Surface electromyography was used to measure activity in the superficial lumbar multifidus (SLM), the thoracic erector spinae (TES), and the transverse fibers of the internal oblique (IO) muscles while subjects moved from an erect to a slump sitting posture. An electromagnetic motion-tracking device simultaneously measured thoracolumbar kinematics during this task.

RESULTS

There was a significant decrease in both the SLM and the IO activity when moving from an erect to a slump sitting posture (P = 0.001 and P = 0.004, respectively), indicating the presence of FRP. TES activity was highly variable. While 13 subjects exhibited an increase in activity (P = 0.001), 11 demonstrated a decrease in activity (P = 0.001), indicating the presence of FRP. FRP occurred in the mid-range of spinal flexion for the SLM, IO and TES when present.

CONCLUSION

The findings show that the SLM and the IO are facilitated in neutral lordotic sitting postures and exhibit FRP at mid range flexion while moving from upright sitting to slump sitting. These findings show that FRP in sitting differs from that in standing. Variable motor patterns (activation or FRP) of the TES were observed. These findings suggest that sustaining mid to end-range flexed sitting spinal postures result in relaxation of the spinal stabilizing muscles.

Altered patterns of superficial trunk muscle activation during sitting in nonspecific chronic low back pain patients: importance of subclassification

STUDY DESIGN

A cross-sectional comparative study between healthy controls and two subgroups of nonspecific chronic low back pain (LBP) patients.

OBJECTIVES

To determine differences in trunk muscle activation during usual unsupported sitting.

SUMMARY OF BACKGROUND DATA

Patients with LBP commonly report exacerbation of pain on sitting. Little evidence exists to confirm that subgroups of patients with nonspecific chronic LBP patients use different motor patterns in sitting than pain-free controls.

METHODS

A total of 34 pain-free and 33 nonspecific chronic LBP subjects were recruited. Two blinded clinicians classified nonspecific chronic LBP patients into two subgroups (active extension pattern and flexion pattern). Surface electromyography (sEMG) was recorded from five trunk muscles during subjects' unsupported "usual" and "slumped" sitting.

RESULTS

No differences in trunk muscle activity were observed between healthy controls and nonspecific chronic LBP groups for usual sitting. When the classification system was applied, differences were identified. Compared with no-LBP controls, the active extension pattern group presented with higher levels of cocontraction of superficial fibers of lumbar multifidus (12%), iliocostalis lumborum pars thoracis (36%) and transverse fibers of internal oblique (43%). while the flexion pattern group showed a trend toward lower activation patterns (lumbar multifidus, -7%; iliocostalis lumborum pars thoracis, -6%, and transverse fibers of internal oblique, -5%). The flexion relaxation ratio of the back muscles was lower for nonspecific chronic LBP (superficial lumbar multifidus: t = 4.5; P < 0.001 and iliocostalis lumborum pars thoracis:t = 2.7; P < 0.001), suggesting a lack of flexion relaxation for the nonspecific chronic LBP.

CONCLUSION

Subclassifying nonspecific chronic LBP patients revealed clear differences in sEMG activity during sitting between pain-free subjects and subgroups of nonspecific chronic LBP patients.

Intramuscular hemodynamics in bilateral erector spinae muscles in symmetrical and asymmetrical postures with and without loading

BACKGROUND

Although attention has been paid to the relationship between the changes in blood circulation in erector spinae muscles and back pain, little is known about their hemodynamics in several various comparable postures with and without loading. Studies on hemodynamics of erector spinae muscles using near-infrared spectroscopy have been performed on subjects and patients mainly in forward flexion positions.

METHODS

Two near-infrared spectroscopes were used to measure oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin in bilateral erector spinae muscles at L2-3 in subjects in 9 postures, and holding no load, 10 kg or 20 kg in maximum flexed and lateral bending. Those three values in each posture and loading condition were expressed as a percentage of their corresponding values obtained in the standing upright position, and designated and statistically analyzed as %Oxy-Hb, %Deoxy-Hb and %Total-Hb, respectively.

FINDINGS

%Total-Hb and %Oxy-Hb in maximum flexion were the most decreased. In maximum lateral bending, %Oxy-Hb only in the contralateral erector spinae muscles was decreased. When the load was 20 kg, the decreases in %Oxy-Hb were the largest in maximum flexion and lateral bendings.

INTERPRETATION

Using two near-infrared spectroscopes allowed us to measure simultaneously the hemodynamics of bilateral muscles. They demonstrated different responses in each side. Asymmetrical posture and loading were accompanied by asymmetrical changes of the bilateral erector spinae muscles. Stretched muscle had less blood volume and oxygenation, both of which decreased with increasing load. These results showed that these postures and conditions might lead to fatigue of the ES muscles.

The effects of lumbar massage on muscle fatigue, muscle oxygenation, low back discomfort, and driver performance during prolonged driving

An increasing dependence of society on automobiles for both work and leisure and the corresponding increase in time spent seated in the car has been correlated with a greater risk of low back pain and absence from work (Porter and Gyi 2002). This study examined the effects of three types of lumbar massage units on seating comfort, muscle fatigue, muscle oxygenation, muscle blood flow and driving performance during a 1 h simulated driving task. Electromyographic (EMG) signals were recorded from the right and left thoracic and lumbar erector spinae musculature. Average EMG (AEMG), mean power frequency (MPF), gaps and amplitude probability distribution function (APDF) parameters were analysed from the three massage seats and compared to a control seat. Near infrared spectroscopy (NIRS) and skin temperature from the right thoracic and lumbar erector spinae were used as an indication of muscle oxygenation and blood flow throughout the driving task. Ratings of perceived discomfort were used to assess driver discomfort, and driving performance was assessed by calculating mean lap times for the duration of each driving trial. The results showed statistically significant increases in skin temperature compared with the control seat after 60 min of driving. The NIRS results reflected these trends although the results were not statistically significant. AEMG and MPF measures showed no significant differences between the seats. MPF measures were found to increase over time, effects attributed to increases in muscle temperature. Gaps and APDF analyses revealed greater rest times and lower activation levels, respectively, with the control seat, which could result in increased loading of passive structures. This study demonstrated the beneficial effects of lumbar massage systems in increasing muscle blood flow and oxygenation. Although EMG parameters were not significantly different, the trends support the significant blood flow results. Future research should include longer driving times and adjustments in EMG measures to account for the effects of increasing muscle temperature on AEMG and MPF measures.