Changes in the flexion-relaxation response induced by hip extensor and erector spinae muscle fatigue

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.

Comparison of compensatory lumbar movement in participants with and without non-specific chronic low back pain: A cross-sectional study

BACKGROUND

Many studies have compared muscle length and muscle activity for low back pain. However, compensatory movement for non-specific low back pain has not yet been studied sufficiently.

OBJECTIVE

The purpose of this study was to compare the length of the hip flexor, lumbar extensor endurance and the muscle activity of the erector spinae and gluteus maximus during hip extension, and the compensatory movement of the lumbar in people with or without nonspecific chronic low back pain.

METHODS

In this case-control study, 16 participants with non-specific chronic LBP and 17 without LBP were included. Hip flexor length was assessed by the modified Thomas test. Lumbar extensor endurance was assessed by the modified Biering-Sorensen test. Muscle activity of the erector spinae and gluteus maximus during hip extension was measured using a Delsys-Trigno wireless EMG system. Compensatory lumbar movements during hip extension were measured using a digital inclinometer.

RESULTS

Muscle activity of the erector spinae and compensatory lumbar movements were significantly higher in the LBP group. (p< 0.05). Hip flexor length, muscle activity of the gluteus maximus and endurance of the lumbar extensor were significantly differences in the LBP group (p< 0.05).

CONCLUSIONS

Shortened hip flexors, low gluteus maximus activity, and high erector spinae activity during hip extension, lumbar extensor weak endurance, lumbar compensatory movement are potential factors for non-specific LBP.

The occurrence of flexion-relaxation phenomenon in elite cyclists during trunk forward bending

Flexion-relaxation phenomenon (FRP) is a well-known phenomenon in spinal extensor muscles. According to the literature, prolonged flexed posture leads to creep phenomenon and affects the active and passive neuromuscular control of the spinal column. The purpose of this study was to investigate FRP occurrence in elite cyclists that prolonged flexion posture is an integral part of their professional life. Their muscles' contraction pattern during forward bending was also compared. Electromyography (EMG) was recorded during flexion and extension from standing position in thoracic erector spinae (TES), lumbar erector spinae (LES) and gluteus maximus (Gluteus max) in 15 healthy male elite cyclists. In addition, the kinematic data related to the trunk angles were simultaneously recorded by a motion analysis system. Two-way ANOVA was used to assess the effects of muscle group and direction of movement on maximum amplitude of EMG activity. Among 15 cyclists, FRP was detectable in 60%, 87% and 73% of the participants in TES, LES and Gluteus max, respectively, and happened between 74% and 82% of the trunk flexion. There was no statistically significant difference in onset and offset of muscles FRP. Despite prolong hyper kyphotic posture, FRP was identifiable in TES, LES and Gluteus max muscles of elite cyclists.

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.

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.

The association of reactive balance control and spinal curvature under lumbar muscle fatigue

Background

Although low back fatigue is an important intervening factor for physical functioning among sedentary people, little is known about its possible significance in relation to the spinal posture and compensatory postural responses to unpredictable stimuli. This study investigates the effect of lumbar muscle fatigue on spinal curvature and reactive balance control in response to externally induced perturbations.

Methods

A group of 38 young sedentary individuals underwent a perturbation-based balance test by applying a 2 kg load release. Sagittal spinal curvature and pelvic tilt was measured in both a normal and Matthiass standing posture both with and without a hand-held 2 kg load, and before and after the Sørensen fatigue test.

Results

Both the peak anterior and peak posterior center of pressure (CoP) displacements and the corresponding time to peak anterior and peak posterior CoP displacements significantly increased after the Sørensen fatigue test (all at p < 0.001). A lumbar muscle fatigue led to a decrease of the lumbar lordosis in the Matthiass posture while holding a 2 kg load in front of the body when compared to pre-fatigue conditions both without a load (p = 0.011, d = 0.35) and with a 2 kg load (p = 0.000, d = 0.51). Also the sacral inclination in the Matthiass posture with a 2 kg additional load significantly decreased under fatigue when compared to all postures in pre-fatigue conditions (p = 0.01, d = 0.48). Contrary to pre-fatigue conditions, variables of the perturbation-based balance test were closely associated with those of lumbar curvature while standing in the Matthiass posture with a 2 kg additional load after the Sørensen fatigue test (r values in range from −0.520 to −0.631, all at p < 0.05).

Conclusion

These findings indicate that lumbar muscle fatigue causes changes in the lumbar spinal curvature and this is functionally relevant in explaining the impaired ability to maintain balance after externally induced perturbations. This emphasizes the importance for assessing both spinal posture and reactive balance control under fatigue in order to reveal their interrelations in young sedentary adults and predict any significant deterioration in later years.

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.

Short-Term Effects of Kinesio Taping® on Electromyographic Characteristics of Paraspinal Muscles, Pain, and Disability in Patients With Lumbar Disk Herniation

Context: Kinesio taping® (KT) is a therapeutic modality frequently used in the clinical practice for the treatment of various musculoskeletal disorders. It is often applied in patients with chronic low back pain to decrease pain and improve functional capacity. However, it is not known, whether thoracolumbar fascia KT technique can decrease back pain, restore normal activity of paraspinal muscles, and improve functional capacity in patients with lumbar disk herniation (LDH). Objective: To evaluate the impact of 7-day new KT stabilizing application on lumbar paraspinal muscles function, pain perception, and disability in patients with LDH. Design: A randomized controlled trial. Setting: Human Performance Laboratory. Patients: A number of 38 patients with LDH were randomized into KT (n = 19) and placebo taping (n = 19) groups. Interventions: Both groups received the same "x" type application running over the back along fibers of superficial lamina of the posterior layer of thoracolumbar fascia. Main Outcome Measures: The primary outcome measures were flexion-relaxation and extension-relaxation ratios calculated from electromyographic activity of lumbar multifidus and longissimus thoracic muscles. Pain intensity rating (Quadruple Visual Analogue Scale), pressure pain thresholds of the lower back, Roland-Morris Disability Questionnaire score, back extension force, and flexion range of motion (ROM) were among secondary outcomes. Results: KT application did not affect the lumbar multifidus and longissimus thoracic muscles flexion-relaxation and extension-relaxation ratios, lower back pressure pain thresholds, back flexion ROM, and back extension force (no group × time interaction [GTI]). KT and placebo taping comparably decreased disability level (time effect: F1,36 = 22.817, P < .001; GTI: F1,36 = 0.189, P = .67), average pain (time effect: F1,36 =39.648, P < .001; GTI: F1,36 = 2.553, P = .12), and the worst pain (time effect: F1,36 = 36.039, P < .001; GTI: F1,36 = 0.003, P = .96) intensity. Conclusion: Seven-day KT does not normalize lumbar paraspinal muscle function and is not superior to placebo in reducing disability and pain intensity in patients with LDH.

The Ratio of Lumbar to Hip Motion during the Trunk Flexion in Patients with Mechanical Chronic Low Back Pain According to O'Sullivan Classification System: A Cross-sectional Study

BACKGROUND

Static and dynamic postures of lumbopelvic in low back pain (LBP) are considered as two important aspects of clinical assessment and management of LBP. Thus, the focus of the current study was to compare the posture and compensatory strategy of hip and lumbar region during trunk flexion between LBP subgroupsand health subjects. LBP cases are subdivided into active extension pattern (AEP) and flexion pattern (FP) based on O'Sullivan's classification system (OCS).

METHODS

This work was a cross-sectional study involving 72 men, 21 low back pain patients with FP and 31 low back pain patients with AEP and 20 healthy groups. Lumbar and hip angles during trunk flexion were measured by a 3D motion analysis system in neutral standing posture and end-range of trunk flexion. The participants were asked to full bend without any flexion of the knees. The bending speed was preferential. Hip and lumbar ranges of motion were divided into four quartiles (Q). The quartiles were compared between groups. Data analysis was performed using one-way analysis of variance (ANOVA) and independent t-test.

RESULTS

There was no statistically significant difference in lumbar lordosis in standing and full trunk flexion positions between the healthy groups and heterogeneous LBP groups. In addition, there was not any statistically significant difference between the healthy group and the homogenous LBP group (FP and AEP). Moreover, no statistically significant difference was observed in hip angles during standing between the healthy group and the heterogeneous LBP group, and between the healthy group and the homogenous LBP group (FP and AEP). In full trunk flexion position, there was statistically significant difference in hip angles between the healthy group and the heterogeneous LBP group (P=0.026). In this position, the difference in hip angles between the healthy group and FP group was statistically significant (P<0.05). In the second Q, there was no significant difference between the healthy group and the heterogeneous LBP group (P=0.062), however, there was a significant difference between FP group and the healthy group in the fourth Q of the total hip range of motion. There was no statistically significant difference between the healthy group and the heterogeneous LBP group (P=0.054) but there was a difference between FP group and the healthy group. Lumbar/hip motion ratio (L/H ratio) was different between and within the subgroups in the second Q.

CONCLUSION

This study supported the subgrouping of LBP and showed that the difference between subgroups could be determined effectively through subdividing the total range of lumbar and hip motions into smaller portions. It is possible that the neuromuscular system selects different strategies to compensate and prevent further injury of the chain components (muscle, joint, nerve and etc.).

LEVEL OF EVIDENCE

IV.

Muscle Shear Moduli Changes and Frequency of Alternate Muscle Activity of Plantar Flexor Synergists Induced by Prolonged Low-Level Contraction

During prolonged low-level contractions, synergist muscles are activated in an alternating pattern of activity and silence called as alternate muscle activity. Resting muscle stiffness is considered to increase due to muscle fatigue. Thus, we investigated whether the difference in the extent of fatigue of each plantar flexor synergist corresponded to the difference in the frequency of alternate muscle activity between the synergists using muscle shear modulus as an index of muscle stiffness. Nineteen young men voluntarily participated in this study. The shear moduli of the resting medial and lateral gastrocnemius muscles (MG and LG) and soleus muscle (SOL) were measured using shear wave ultrasound elastography before and after a 1-h sustained contraction at 10% peak torque during maximal voluntary contraction of isometric plantar flexion. One subject did not accomplish the task and the alternate muscle activity for MG was not found in 2 subjects; therefore, data for 16 subjects were used for further analyses. The magnitude of muscle activation during the fatiguing task was similar in MG and SOL. The percent change in shear modulus before and after the fatiguing task (MG: 16.7 ± 12.0%, SOL: −4.1 ± 13.9%; mean ± standard deviation) and the alternate muscle activity during the fatiguing task (MG: 33 [20–51] times, SOL: 30 [17–36] times; median [25th–75th percentile]) were significantly higher in MG than in SOL. The contraction-induced change in shear modulus (7.4 ± 20.3%) and the alternate muscle activity (37 [20–45] times) of LG with the lowest magnitude of muscle activation during the fatiguing task among the plantar flexors were not significantly different from those of the other muscles. These results suggest that the degree of increase in muscle shear modulus induced by prolonged contraction corresponds to the frequency of alternate muscle activity between MG and SOL during prolonged contraction. Thus, it is likely that, compared with SOL, the alternate muscle activity of MG occurs more frequently during prolonged contraction due to the greater increase in fatigue of MG induced by the progression of a fatiguing task.

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.

Impact of Fatigue on Maintenance of Upright Posture: Dynamic Assessment of Sagittal Spinal Deformity Parameters After Walking 10 Minutes

STUDY DESIGN

Retrospective analysis of prospectively collected data.

OBJECTIVE

To assess global and regional spinal sagittal radiographic parameters in adults with loss of lumbar lordosis ("flatback") before and after walking 10 minutes.

SUMMARY OF BACKGROUND DATA

While routine activities of daily living may exacerbate functional disability of spinal sagittal-plane deformity, there is limited understanding of how sagittal parameters and compensatory mechanisms are affected by activity.

METHODS

Consecutive adults with "flatback" at a single institution who previously had full-length standing spinal radiographs before and after walking 10 minutes were reviewed. Changes in spinal deformity sagittal parameters before and after walking were evaluated for two groups: Compensated Sagittal Deformity ("Compensated": sagittal vertical axis [SVA] ≤4 cm and pelvic tilt [PT] >20°) and Decompensated Sagittal Deformity ("Decompensated": SVA>4 cm and PT>20°). Intra-group radiographic comparisons were performed with paired Student t tests.

RESULTS

One hundred fifty-seven patients (143 females, 14 males; average age 67.9 ± 5.9 yr) met inclusion criteria. Initial average SVA was 1.7 ± 1.2 cm for "Compensated" and 11.5 ± 6.4 cm for "Decompensated." After walking 10 minutes, significant deteriorations in average SVA were observed for all "Decompensated" patients and 84.6% of "Compensated" patients. For both groups, this was accompanied by significant decreases in PT and LL and increases in PI-LL (P <0.01). Thoracic kyphosis increased after walking for only "Decompensated" (P <0.01). For "Compensated," the change in SVA was determined by decreases in PT and LL, while changes in SVA for "Decompensated" were correlated to worsening of all sagittal parameters.

CONCLUSION

After walking, compensatory mechanisms to maintain sagittal balance in adults with spinal deformity are less pronounced than when the patient initially presents. This results in significant sagittal decompensation, irrespective of the initial SVA. As we postulate that loss of compensatory mechanisms is due to fatigue on pelvic and spinal extensor muscles, sagittal parameters can be re-evaluated with radiographs obtained after patients walk 10 minutes to unmask a hidden sagittal imbalance in compensated deformities.

LEVEL OF EVIDENCE

3.

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.

Postural strategy and trunk muscle activation during prolonged standing in chronic low back pain patients

Prolonged standing has been associated with development and aggravation of low back pain (LBP). However, the underlying mechanisms are not well known. The aim of the present study was to investigate postural control and muscle activation during and as a result of prolonged standing in chronic LBP (cLBP) patients compared to healthy controls (HCs). Body weight shifts and trunk and hip muscle activity was measured during 15 min standing. Prior and after the standing trial, strength, postural sway, reposition error (RE), flexion relaxation ratio (FRR), and pain were assessed and after the prolonged standing, ratings of perceived exertion. During prolonged standing, the cLBP patients performed significantly more body weight shifts (p<.01) with more activated back and abdominal muscles (p=.01) and similar temporal variability in muscle activation compared to HCs, while the cLBP patients reported more pain and perceived exertion at the end of prolonged standing. Moreover, both groups had a similar change in strength, postural sway, RE and FRR from before to after prolonged standing, where changes in HC were towards pre-standing values of cLBP patients. Thus, despite a more variable postural strategy, the cLBP patients did not have higher muscle activation variability, but a general increased muscle activation level. This may indicate a reduced ability to individually deactivate trunk muscles. Plausibly, due to the increased variable postural strategy, the cLBP patients could compensate for the relatively high muscle activation level, resulting in normal variation in muscle activation and normal reduction in strength, RE and FRR after prolonged standing.

Age and gender related neuromuscular changes in trunk flexion-extension

BACKGROUND

The root mean square surface electromyographic activity of lumbar extensor muscles during dynamic trunk flexion and extension from a standing position and task specific spine ranges of motion objectively assess muscle function in healthy young and middle age individuals. However, literature on neuromuscular activation and associated spine and hip kinematics in older individuals is sparse. This cross sectional study sought to examine the sex and age (<40 versus >60 years) related differences in the neuromuscular activation profiles of the lumbar extensors and the related spine and hip kinematics from healthy individuals during a standardized trunk flexion-extension task.

METHODS

Twenty five older (13 females, 60-90 years) and 24 younger (12 females, 18-40 years) healthy individuals performed trunk flexion-extension testing by holding static positions at half-flexion way and full range of motion between standing and maximum trunk flexion. The associated lumbar extensor muscle activity was derived from measurements at standing, half, and maximum flexion positions. The range of motion at the hip and lumbar spine was recorded using 3d accelerometers attached to the skin overlying the multifidus and semispinalis thoracis muscles lateral to the L5 and T4 spinous processes, respectively. Statistical calculations were performed using a permutation ANOVA with bootstrap confidence intervals.

RESULTS

The muscle activity in the half related to the maximum flexion position (half flexion relaxation ratio) was significantly smaller in older males when compared with younger males. Moreover, measurements revealed smaller activity changes from standing to the half and from half to the maximum flexion position in older compared to younger individuals. Older males displayed smaller gross trunk range of motion from standing to maximum flexion than any other group.

CONCLUSIONS

Gender and normal aging significantly affect both the activation patterns of the lumbar extensor muscles and the kinematics of the trunk during a standardized trunk flexion-extension task. Measurement results from healthy young and middle age individuals should not be used for the assessment of individuals older than 60 years of age.

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.

Effects of noxious stimulation and pain expectations on neuromuscular control of the spine in patients with chronic low back pain

BACKGROUND CONTEXT

Alterations of the neuromuscular control of the lumbar spine have been reported in patients with chronic low back pain (LBP). During trunk flexion and extension tasks, the reduced myoelectric activity of the low back extensor musculature observed during full trunk flexion is typically absent in patients with chronic LBP.

PURPOSE

To determine whether pain expectations could modulate neuromuscular responses to experimental LBP to a higher extent in patients with chronic LBP compared with controls.

STUDY DESIGN

A cross-sectional, case-control study.

PATIENT SAMPLE

Twenty-two patients with nonspecific chronic LBP and 22 age- and sex-matched control participants.

METHODS

Trunk flexion-extension tasks were performed under three experimental conditions: innocuous heat, noxious stimulation with low pain expectation, and noxious stimulation with high pain expectation. Noxious stimulations were delivered using a contact heat thermode applied on the skin of the lumbar region (L4-L5), whereas low or high pain expectations were induced by verbal and visual instructions.

OUTCOME MEASURES

Surface electromyography of erector spinae at L2-L3 and L4-L5, as well as lumbopelvic kinematic variables were collected during the tasks. Pain was evaluated using a numerical rating scale. Pain catastrophizing, disability, anxiety, and fear-avoidance beliefs were measured using validated questionnaires.

RESULTS

Two-way mixed analysis of variance revealed that pain was significantly different among the three experimental conditions (F2,84=317.5; p<.001). Increased myoelectric activity of the low back extensor musculature during full trunk flexion was observed in the high compared with low pain expectations condition at the L2-L3 level (F2,84=9.5; p<.001) and at the L4-L5 level (F2,84=3.7; p=.030). At the L4-L5 level, this effect was significantly more pronounced for the control participants compared with patients with chronic LBP (F2,84=3.4; p=.045). Pearson correlation analysis revealed that increased lumbar muscle activity in full flexion induced by expectations was associated with higher pain catastrophizing in patients with chronic LBP (r=0.54; p=.012).

CONCLUSIONS

Repeated exposure to pain appears to generate rigid and less variable patterns of muscle activation in patients with chronic LBP, which attenuate their response to pain expectations. Patients with high levels of pain catastrophizing show higher myoelectric activity of lumbar muscles in full flexion and exhibit greater neuromechanical changes when expecting strong pain.

Pilot study of the impact sacroiliac joint manipulation has on walking kinematics using motion analysis technology

OBJECTIVE

The purpose of this study was to evaluate the feasibility of engaging in a series of larger studies measuring the effect of sacroiliac joint manipulation on walking kinematics using motion analysis technology.

METHODS

Twelve college students engaged in a baseline 90-second gait analysis at 1.5 mph using infrared VICON cameras. Following this, they underwent a prone heel comparison test for functional leg length inequality. Upon examination, participants were then classified as follows: left short leg, right short leg, or no short leg. Participants in each of the 2 short leg branches of this study were then randomized to receive either chiropractic manipulative therapy to the posterior superior iliac spine on the short limb side or no manipulation. Recruitment was ongoing for this pilot study until 1 participant was recruited in each of the following 5 comparative study groups: left short leg-manipulation, left short leg-no manipulation (control 1), right short leg-manipulation, right short leg-no manipulation (control 2), and no short leg (control 3). All participants then underwent another 90-second gait analysis. Data were then grouped and submitted to a blinded biomechanist to determine if there were any unique biomechanical differences between the groups.

RESULTS

No statistically significant differences were measured because of this being a pilot study with a small sample size.

CONCLUSIONS

The data from this study indicate that a series of larger studies with this design is feasible.

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 influence of acute back muscle fatigue and fatigue recovery on trunk sensorimotor control

OBJECTIVE

The aim of this study was to evaluate trunk repositioning sense after an acute muscle fatigue protocol and during a 30-minute recovery period.

METHODS

Twenty healthy participants were asked to reproduce a 20° and 30° angle in trunk extension. Participants were tested before and after a Biering-Sorensen fatigue protocol was performed. Movement time, peak angle variable error, constant error and absolute error in peak angle were calculated and compared between 4 temporal conditions in both 20° and 30° extensions.

RESULTS

The statistical analysis revealed a main effect of angle between 20° and 30° extension condition for variable error, absolute error, and movement time. A main effect of time was also found and was characterized by a significant increase in variable error between the prefatigue condition and the first postfatigue condition. During recovery, a significant decrease in variable error was observed between the first postfatigue condition and the 30-minute postfatigue condition, indicating that the variable mean scores were similar to initial values.

CONCLUSION

Lower back muscle fatigue induced changes in trunk repositioning sense indicators immediately after the fatigue protocol. However, the observed changes did not last for more than a few minutes.

Short term modulation of trunk neuromuscular responses following spinal manipulation: a control group study

Background

Low back pain (LBP) is one of the most frequent musculoskeletal conditions in industrialized countries and its economic impact is important. Spinal manipulation therapy (SMT) is believed to be a valid approach in the treatment of both acute and chronic LBP. It has also been shown that SMT can modulate the electromyographic (EMG) activity of the paraspinal muscle. The purpose of this study was to investigate, in a group of patients with low back pain, the persistence of changes observed in trunk neuromuscular responses after a spinal manipulation (SMT).

Methods

Sixty adult participants with LBP performed a block of 5 flexion-extension movements. Participants in the experimental group (n=30) received lumbar SMT whereas participants in the control group (n=30) were positioned similarly for the treatment but did not receive SMT. Blocks of flexion-extension movements were repeated immediately after the manipulation as well as 5 and 30 minutes after SMT (or control position). EMG activity of paraspinal muscles was recorded at L2 and L5 level and kinematic data were collected to evaluate the lumbo-pelvic kinematics. Pain intensity was noted after each block. Normalized EMG, pain intensity and lumbo-pelvic kinematics were compared across experimental conditions.

Results

Participants from the control group showed a significant increase in EMG activity during the last block (30 min) of flexion-extension trials in both flexion and full-flexion phases at L2. Increase in VAS scores was also observed in the last 2 blocks (5 min and 30 min) in the control group. No significant group x time interaction was seen at L5. No significant difference was observed in the lumbo-pelvic kinematics.

Conclusion

Changes in trunk neuromuscular control following HVLA spinal manipulation may reduce sensitization or muscle fatigue effects related to repetitive movement. Future studies should investigate short term changes in neuromuscular components, tissue properties and clinical outcomes.