Dynamic adjustments of walking behavior dependent on noxious input in experimental low back pain

Neuromuscular adaptations to experimentally induced pain in the lumbar region: systematic review and meta-analysis

ABSTRACT

Experimental pain models are frequently used to understand the influence of pain on the control of human movement. In this systematic review, we assessed the effects of experimentally induced pain in the lumbar region of healthy individuals on trunk muscle activity and spine kinematics. Databases were searched from inception up to January 31, 2022. In total, 26 studies using either hypertonic saline injection (n = 19), heat thermal stimulation (n = 3), nociceptive electrical stimulation (n = 3), or capsaicin (n = 1) were included. The identified adaptations were task dependent, and their heterogeneity was partially explained by the experimental pain model adopted. Meta-analyses revealed an increase of erector spinae activity (standardized mean difference = 0.71, 95% confidence interval [CI] = 0.22-1.19) during full trunk flexion and delayed onset of transversus abdominis to postural perturbation tasks (mean difference = 25.2 ms, 95% CI = 4.09-46.30) in the presence of pain. Low quality of evidence supported an increase in the activity of the superficial lumbar muscles during locomotion and during voluntary trunk movements during painful conditions. By contrast, activity of erector spinae, deep multifidus, and transversus abdominis was reduced during postural perturbation tasks. Reduced range of motion of the lumbar spine in the presence of pain was supported by low quality of evidence. Given the agreement between our findings and the adaptations observed in clinical populations, the use of experimental pain models may help to better understand the mechanisms underlying motor adaptations to low back pain.

An index to quantify deviations from normal trunk mobility: Clinical correlation and initial test of validity

BACKGROUND

In case of people suffering from chronic low back pain, specific movements of the hip, pelvis, and trunk are associated with pain. Comparing range of motion measurements for multiple planes and from different segments and lines in reference to those of healthy individuals seems interesting but present interpretations challenge in relation to important number of variables and correlation with clinical data.

METHODS

The proposed index is based on using principal component analysis to quantify differences in trunk mobility between patients with chronic low back pain and a control group. Kinematic data were recorded for the cervical and thoracic vertebrae, the lumbar spine, and the pelvic and scapular belts during repeated trials (hip flexion and extension, hip bending, and trunk twists). Angular motion values were calculated. Principal component analysis was used to convert 10 discrete variables (kinematical data) extracted from control data into 10 independent variables.

FINDINGS

The proposed index comprises the sum of the variables. Initial demonstration of its clinical utility and statistical tests of this index validity were revealed. It establishes correlations between the psychosocial impact of chronic low back pain, trunk mobility (as summarized by the index) and the positive effects of functional restoration program.

INTERPRETATION

This index let to assess the absolute potential benefits of rehabilitation in term of kinematic motion. Functional restoration program promotes the physical functioning of patients by increasing their range of motion. This index uses kinematic motion to assess the potential benefits of such rehabilitation program.

A prospective investigation of changes in the sensorimotor system following sports concussion. An exploratory study

BACKGROUND

Sports concussion is a risk for players involved in high impact, collision sports. Post-concussion, the majority of symptoms subside within 7-10 days, but can persist in 10-20% of athletes. Understanding the effects of sports concussion on sensorimotor systems could inform physiotherapy treatment.

OBJECTIVE

To explore changes in sensorimotor function in the acute phase following sports concussion.

DESIGN

Prospective cohort study.

METHODS

Fifty-four players from elite rugby union and league teams were assessed at the start of the playing season. Players who sustained a concussion were assessed three to five days later. Measures included assessments of balance (sway velocity), vestibular system function (vestibular ocular reflex gain; right-left asymmetry), cervical proprioception (joint position error) and trunk muscle size and function.

RESULTS

During the playing season, 14 post-concussion assessments were performed within 3-5 days of injury. Significantly decreased sway velocity and increased size/contraction of trunk muscles, were identified. Whilst not significant overall, large inter-individual variation of test results for cervical proprioception and the vestibular system was observed.

LIMITATIONS

The number of players who sustained a concussion was not large, but numbers were comparable with other studies in this field. There was missing baseline data for vestibular and cervical proprioception testing for some players.

CONCLUSIONS

Preliminary findings post-concussion suggest an altered balance strategy and trunk muscle control with splinting/over-holding requiring consideration as part of the development of appropriate physiotherapy management strategies.

Reorganized Trunk Muscle Activity During Multidirectional Floor Perturbations After Experimental Low Back Pain: A Comparison of Bilateral Versus Unilateral Pain

Low back pain changes trunk muscle activity after external perturbations but the relationship between pain intensities and distributions and their effect on trunk muscle activity remains unclear. The effects of unilateral and bilateral experimental low back pain on trunk muscle activity were compared during unpredictable multidirectional surface perturbations in 19 healthy participants. Pain intensity and distribution were assessed using a visual analogue scale (VAS) and pain drawings. Root mean square (RMS) of the electromyographic (EMG) signals from 6 trunk muscles bilaterally after each perturbation was extracted and averaged across perturbations. The difference (ΔRMS-EMG) and absolute difference (absolute ΔRMS-EMG) RMS from baseline conditions were extracted for each muscle during pain conditions and averaged bilaterally for back and abdominal muscle groups. Bilateral compared with unilateral pain induced higher VAS scores (P < .005) and larger pain areas (P < .001). Significant correlation was present between VAS scores and muscle activity during unilateral (P < .001) and bilateral pain (P < .001). Compared with control injections ΔRMS-EMG increased in the back (P < .03) and abdominal (P < .05) muscles during bilateral and decreased in the back (P < .01) and abdominal (P < .01) muscles during unilateral pain. Bilateral pain caused greater absolute ΔRMS-EMG changes in the back (P < .01) and abdominal (P < .01) muscle groups than unilateral pain.

PERSPECTIVE

This study provided novel observations of differential trunk muscle activity in response to perturbations dependent on pain intensity and/or pain distribution. Because of complex and variable changes the relevance of clinical examination of muscle activity during postural tasks is challenged.

Effect of Nonspecific Chronic Low Back Pain on Walking Economy: An Observational Study

The authors investigated the effects of chronic low back pain (LBP) and walking speed (WS) on metabolic power and cost of transport (CT). Subjects with chronic nonspecific LBP (LBP group [LG]; n = 9) and healthy (control group [CG]; n = 9) were included. The test battery was divided into 3 blocks according to WS as follows: preferred self-selected speed (PS), and lower and higher than the PS. In each block, the volunteers walked 5 min, during which oxygen consumption was measured. Although without differences between groups, the LG had CT lower in slower speeds than in faster speeds. Walking speed affected CT only in the LG, which the group had the greatest walking economy at slower speeds.

Does insertion of intramuscular electromyographic electrodes alter motor behavior during locomotion?

Intramuscular electromyography (EMG) is commonly used to quantify activity in the trunk musculature. However, it is unclear if the discomfort or fear of pain associated with insertion of intramuscular EMG electrodes results in altered motor behavior. This study examined whether intramuscular EMG affects locomotor speed and trunk motion, and examined the anticipated and actual pain associated with electrode insertion in healthy individuals and individuals with a history of low back pain (LBP). Before and after insertion of intramuscular electrodes into the lumbar and thoracic paraspinals, participants performed multiple repetitions of a walking turn at self-selected and controlled average speed. Low levels of anticipated and actual pain were reported in both groups. Self-selected locomotor speed was significantly increased following insertion of the electrodes. At the controlled speed, the amplitude of sagittal plane lumbo-pelvic motion decreased significantly post-insertion, but the extent of this change was the same in both groups. Lumbo-pelvic motion in the frontal and axial planes and thoraco-lumbar motion in all planes were not affected by the insertions. This study demonstrates that intramuscular EMG is an appropriate methodology to selectively quantify the activation patterns of the individual muscles in the paraspinal group, both in healthy individuals and individuals with a history of LBP.

[Possible changes in energy-minimizer mechanisms of locomotion due to chronic low back pain - a literature review]

One goal of the locomotion is to move the body in the space at the most economical way possible. However, little is known about the mechanical and energetic aspects of locomotion that are affected by low back pain. And in case of occurring some damage, little is known about how the mechanical and energetic characteristics of the locomotion are manifested in functional activities, especially with respect to the energy-minimizer mechanisms during locomotion. This study aimed: a) to describe the main energy-minimizer mechanisms of locomotion; b) to check if there are signs of damage on the mechanical and energetic characteristics of the locomotion due to chronic low back pain (CLBP) which may endanger the energy-minimizer mechanisms. This study is characterized as a narrative literature review. The main theory that explains the minimization of energy expenditure during the locomotion is the inverted pendulum mechanism, by which the energy-minimizer mechanism converts kinetic energy into potential energy of the center of mass and vice-versa during the step. This mechanism is strongly influenced by spatio-temporal gait (locomotion) parameters such as step length and preferred walking speed, which, in turn, may be severely altered in patients with chronic low back pain. However, much remains to be understood about the effects of chronic low back pain on the individual's ability to practice an economic locomotion, because functional impairment may compromise the mechanical and energetic characteristics of this type of gait, making it more costly. Thus, there are indications that such changes may compromise the functional energy-minimizer mechanisms.

An experimental study investigating the effect of pain relief from oral analgesia on lumbar range of motion, velocity, acceleration and movement irregularity

Background

Movement alterations are often reported in individuals with back pain. However the mechanisms behind these movement alterations are not well understood. A commonly cited mechanism is pain. The aim of this study was to investigate the effect of pain reduction, from oral analgesia, on lumbar kinematics in individuals with acute and chronic low back pain.

Methods

A prospective, cross-sectional, experimental repeated-measures design was used. Twenty acute and 20 chronic individuals with low back pain were recruited from General Practitioner and self-referrals to therapy departments for low back pain. Participants complained of movement evoked low back pain. Inertial sensors were attached to the sacrum and lumbar spine and used to measure kinematics. Kinematic variables measured were range of motion, angular velocity and angular acceleration as well as a determining movement irregularity (a measure of deviation from smooth motion). Kinematics were investigated before and after administration of oral analgesia to instigate pain reduction.

Results

Pain was significantly reduced following oral analgesia. There were no significant effects on the kinematic variables before and after pain reduction from oral analgesia. There was no interaction between the variables group (acute and chronic) and time (pre and post pain reduction).

Conclusion

The results demonstrate that pain reduction did not alter lumbar range of motion, angular velocity, angular acceleration or movement irregularity questioning the role of pain in lumbar kinematics.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-304) contains supplementary material, which is available to authorized users.

Effect of therapeutic infra-red in patients with non-specific low back pain: a pilot study

The purpose of this study was to investigate the effect of infra-red (IR) in patients with chronic non-specific low back pain (NSLBP). Ten patients with NSLBP (5 men and 5 women) and disease duration of 21.7 ± 11.50 months participated in this pilot study. Patients had a mean age of 36.40 ± 10.11 years (range = 25-55). Patients were treated with infra-red (IR) for 10 sessions, each for 15 min, 3 days per week, for a period of 4 weeks. Outcome measures were the Numerical Rating Scale (NRS), the Functional Rating Index (FRI), the Modified-Modified Schober Test (MMST), and the Biering-Sorensen test to assess pain severity, disability, lumbar flexion and extension range of motion (ROM), and back extensor endurance, respectively. Data were collected at: baseline - study entry (T0); end of 5th treatment session after 2 weeks (T1); and end of the treatment after 4 weeks (T2). The results of the ANOVA demonstrated a statistically significant main effect of IR on all outcomes of pain, function, lumbar flexion-extension ROM, and back extensor endurance. The treatment effect sizes ranged from large to small. IR was effective in improving pain, function, lumbar ROM, and back extensor endurance in a sample of patients with NSLBP. Treatment effect sizes ranged from large to small indicating clinically relevant improvements primarily in pain and function for patients with NSLBP.

Effects of exercise-induced low back pain on intrinsic trunk stiffness and paraspinal muscle reflexes

The purpose of this study was to (1) compare trunk neuromuscular behavior between individuals with no history of low back pain (LBP) and individuals who experience exercise-induced LBP (eiLBP) when pain free, and (2) investigate changes in trunk neuromuscular behavior with eiLBP. Seventeen young adult males participated including eight reporting recurrent, acute eiLBP and nine control participants reporting no history of LBP. Intrinsic trunk stiffness and paraspinal muscle reflex delay were determined in both groups using sudden trunk flexion position perturbations 1-2 days following exercise when the eiLBP participants were experiencing an episode of LBP (termed post-exercise) and 4-5 days following exercise when eiLBP had subsided (termed post-recovery). Post-recovery, when the eiLBP group was experiencing minimal LBP, trunk stiffness was 26% higher in the eiLBP group compared to the control group (p=0.033) and reflex delay was not different (p=0.969) between groups. Trunk stiffness did not change (p=0.826) within the eiLBP group from post-exercise to post-recovery, but decreased 22% within the control group (p=0.002). Reflex delay decreased 11% within the eiLBP group from post-exercise to post-recovery (p=0.013), and increased 15% within the control group (p=0.006). Although the neuromuscular mechanisms associated with eiLBP and chronic LBP may differ, these results suggest that previously-reported differences in trunk neuromuscular behavior between individuals with chronic LBP and healthy controls reflect a combination of inherent differences in neuromuscular behavior between these individuals as well as changes in neuromuscular behavior elicited by pain.

The influence of pain distribution on walking velocity and horizontal ground reaction forces in patients with low back pain

Objective. The primary purpose of this paper was to evaluate the influence of pain distribution on gait characteristics in subjects with low back problems (LBP) during walking at preferred and fastest speeds. Design. Cross-sectional, observational study. Setting. Gait analysis laboratory in a health professions university. Participants. A convenience age- and gender-matched sample of 20 subjects with back pain only (BPO), 20 with referred leg pain due to back problems (LGP), and 20 pain-free individuals (CON). Methods and Measures. Subjects completed standardized self-reports on pain and disability and were videotaped as they walked at their preferred and fastest speeds along a walkway embedded with a force plate. Temporal and spatial gait characteristics were measured at the midsection of the walkway, and peak medial, lateral, anterior, and posterior components of horizontal ground reaction forces (hGRFs) were measured during the stance phase. Results. Patients with leg pain had higher levels of pain intensity and affect compared to those with back pain only (t = 4.91, P < .001 and t = 5.80, P < 0.001, resp.) and walking had an analgesic effect in the BPO group. Gait velocity was highest in the control group followed by the BPO and LGP group and differed between groups at both walking speeds (F(2.57) = 13.62, P < .001 and F(2.57) = 9.09, P < .001, for preferred and fastest speed condition, resp.). When normalized against gait velocity, the LGP group generated significantly less lateral force at the fastest walking speed (P = .005) and significantly less posterior force at both walking speeds (P ≤ .01) compared to the control group. Conclusions. Pain intensity and distribution differentially influence gait velocity and hGRFs during gait. Those with referred leg pain tend to utilize significantly altered gait strategies that are more apparent at faster walking speeds.

Postural recovery following voluntary arm movement is impaired in people with chronic low back pain

STUDY DESIGN

Recovery of postural equilibrium following bilateral voluntary arm movement was evaluated using a case-control study, with 13 subjects with chronic LBP and 13 age- and gendermatched control subjects.

OBJECTIVES

To evaluate control of the centre-of-pressure (COP), as a marker of the quality of control of postural equilibrium associated with voluntary arm movements, in people with and without LBP. Summary of background data. When healthy individuals perform rapid voluntary arm movements, small spinal movements (preparatory movement) opposite to the direction of the reactive moments precede voluntary arm movements. Evaluation of trunk movement in people with LBP suggests that this strategy is used infrequently in this population and is associated with an increased spinal displacement following arm flexion. As the preparatory spinal movement was also thought to be an anticipatory mechanism limiting postural perturbation caused by arm movements, we hypothesized that LBP subjects would have compromised control of postural equilibrium following arm flexion.

METHODS

Subjects performed bilateral voluntary rapid arm flexion while standing on support surface of different dimensions with eyes opened or closed.

RESULTS

Results indicated that people with LBP consistently took longer to recover postural equilibrium and made more postural adjustments in different stance conditions. However, there was no increase in the excursion of the COP during the recovery period in the LBP group.

CONCLUSION

These data suggest that while COP is tightly controlled during postural recovery, the finetuning of the control of postural equilibrium is compromised in people with LBP. Postural control dysfunctions should be considered in the management of chronic low back pain.

Changes in lumbar muscle activity because of induced muscle pain evaluated by muscle functional magnetic resonance imaging

STUDY DESIGN

Experimental study of changes in muscle recruitment during trunk extension exercise at 40% of the repetition maximum, because of induced muscle pain.

OBJECTIVE

To investigate the effect of lumbar muscle pain on muscle activity of the trunk muscles using muscle functional magnetic resonance imaging.

SUMMARY OF BACKGROUND DATA

Changed muscle recruitment in patients has an important impact on the etiology and recurrence of low back pain. The mechanisms of these changes in muscle activity are still poorly understood. An experimental study investigating the cause-effect relationship of muscle pain on muscle recruitment patterns can help to clarify these mechanisms.

METHODS

In 15 healthy subjects, the muscle activity of the lumbar multifidus, lumbar erector spinae, and psoas muscles was investigated with muscle functional magnetic resonance imaging. Measurements at rest and after trunk extension exercise at 40% of repetition maximum were performed without and with induced pain.

RESULTS

The lumbar multifidus and lumbar erector spinae were significantly active during the trunk extension exercise, whereas the psoas showed no significant activity. The activity of the lumbar multifidus, lumbar erector spinae, and psoas muscles, was reduced bilaterally and multilevel during the exercise with unilateral low back muscle pain.

CONCLUSION

These data demonstrate that unilateral muscle pain can cause hypoactivity of muscles during trunk extension at 40% of the repetition maximum. The changes were not limited to the side and level of pain. Moreover, the inhibition was not limited to the multifidus muscle; also the lumbar erector spinae and psoas muscles showed decreased activity during the pain condition. Further research has to assess possible compensation mechanisms for this reduced activity in other muscles.

Under-arm partial body weight unloading causes spinal elongation and vibration attenuation during treadmill walking

Whilst exercise is beneficial to those suffering from low back pain (LBP), spinal shrinkage and vibration during walking may aggravate the condition. This study investigates the effects of spinal unloading, by means of body-weight unloading (BWU), on spinal length and vibration response. Under-arm partial BWU (40% of bodyweight) was performed on 8 healthy males whilst walking on a treadmill for 1h, and compared to a control condition in the same participants. Motion analysis was used to track four reflective markers attached to the spine between C7 and the lumbar concavity at 100Hz, in 7s samples at regular intervals during the walk. A quintic polynomial was fitted to the coordinates in the sagittal plane, and sub-sectioned into three regions: the upper thoracic (UT), lower thoracic (LT) and upper lumbar (UL). The lengths of the curves were analysed in the time and frequency domains. The length of the spine increased by 4+/-2% (18mm) during the unloading condition with all regions showing an increase in length. The UL and LT regions lost length in the control condition, thereby exhibiting a significant interaction between unloading and time on region length (both P<0.05). In addition, compared to the control condition, the frequencies of the length changes were attenuated between 3 and 6Hz with unloading. Therefore, under-arm BWU facilitates spinal elongation, attenuates the frequency response of the spine in its resonant frequency regime and thus has potential benefits to the LBP population.

Is balance different in women with and without stress urinary incontinence?

AIMS

This study investigated whether there are differences in center of pressure (COP) displacement, trunk motion, and trunk muscle activity in women with and without stress urinary incontinence (SUI) during static balance tasks when the bladder is empty and moderately full.

METHODS

Subjects stood on a force plate during six static balance conditions: eyes open, eyes closed, standing on foam with eyes open, standing on foam with eyes closed, tandem stance, and standing on a short base. Electromyographic activity (EMG) of the pelvic floor (PF), abdominal, and erector spinae muscles were recorded using surface electrodes. Motion of the lumbar spine, pelvis, and hips was measured with four inclinometers. Trials were performed with the bladder empty, and when the subject reported a sensation of moderate bladder fullness after drinking 250-1,000 ml of water.

RESULTS

Women with SUI had greater COP displacement (range and root mean square), and increased trunk muscle EMG during static balance tests compared to continent women. When tasks were performed with the bladder moderately full, COP displacement and abdominal muscle EMG were increased in both groups.

CONCLUSIONS

This study demonstrates that women with SUI have decreased balance ability compared to continent women. Increased activity of the PF and trunk muscles in women with SUI may impair balance as a result of a reduced contribution of trunk movement to postural correction or compromised proprioceptive acuity. As compromised balance has been linked to falls risk, further research into balance deficits and falls prevalence in this population is warranted.

Failure to use movement in postural strategies leads to increased spinal displacement in low back pain

STUDY DESIGN

Lumbar and hip movements, before and in response to rapid bilateral arm flexion, were evaluated in 10 people with recurrent low back pain (LBP) and 10 matched control subjects when standing on a flat surface or short base.

OBJECTIVE

To evaluate the preparatory movement and resultant displacement of the lumbopelvic region associated with internal perturbation in people with or without LBP.

SUMMARY OF BACKGROUND DATA

Strategies to control the trunk involve movement. Small spinal movements (preparatory movement), opposite to the direction of reactive moments, precede voluntary arm movements in healthy individuals. However, people with LBP often use less spinal movement. We hypothesized that the tendency to reduce spinal motion in LBP may be associated with decreased preparatory motion, and this may counter intuitively lead to increased displacement of the trunk in response to arm movements.

METHODS

Movements at the lumbopelvic region before and in response to rapid bilateral arm flexion were examined using electromagnetic motion sensors when subjects were standing on a flat surface or short base.

RESULTS

In control subjects, preparatory extension of the lumbar spine preceded a resultant flexion of the region in 88% of trials on the flat surface. People with LBP used preparatory extension less frequently (69%, P = 0.027). Consequently, the spinal displacement (resultant flexion) induced by shoulder flexion was significantly greater in the LBP group (3.2 degrees +/- 1.8 degrees) than controls (1.8 degrees +/- 1.6 degrees, P = 0.004). There was a significant correlation (r = 0.47) between preparatory and resultant movement of the lumbar spine in the LBP group, which indicates that subjects with reduced preparatory extension were more likely to have a greater resultant displacement.

CONCLUSION

These data suggest that spinal movement is different in people with LBP, and reduced spinal movement in advance of predictable perturbation may be associated with compromised quality of trunk control.

Delayed trunk muscle reflex responses increase the risk of low back injuries

STUDY DESIGN

Prospective observational study with a 2- to 3-year follow-up.

OBJECTIVES

To determine whether delayed muscle reflex response to sudden trunk loading is a result of or a risk factor for sustaining a low back injury (LBI).

SUMMARY OF BACKGROUND DATA

Differences in motor control have been identified in individuals with chronic low back pain and in athletes with a history of LBI when compared with controls. However, it is not known whether these changes are a risk for or a result of LBI.

METHODS

Muscle reflex latencies in response to a quick force release in trunk flexion, extension, and lateral bending were measured in 303 college athletes. Information was also obtained regarding their personal data, athletic experience, and history of LBI. The data were entered into a binary logistic regression model to identify the predictors of future LBI. RESULTS.: A total of 292 athletes were used for the final analysis (148 females and 144 males). During the follow-up period, 31 (11%) athletes sustained an LBI. The regression model, consisting of history of LBI, body weight, and the latency of muscles shutting off during flexion and lateral bending load releases, predicted correctly 74% of LBI outcomes. The odds of sustaining LBI increased 2.8-fold when a history of LBI was present and increased by 3% with each millisecond of abdominal muscle shut-off latency. On average, this latency was 14 milliseconds longer for athletes who sustained LBI in comparison to athletes who did not sustain LBI (77 [36] vs. 63 [31]). There were no significant changes in any of the muscle response latencies on retest following the injury.

CONCLUSIONS

The delayed muscle reflex response significantly increases the odds of sustaining an LBI. These delayed latencies appear to be a preexisting risk factor and not the effect of an LBI.

Effect of experimentally induced low back pain on postural sway with breathing

Although breathing perturbs balance, in healthy individuals little sway is detected in ground reaction forces because small movements of the spine and lower limbs compensate for the postural disturbance. When people have chronic low back pain (LBP), sway at the ground is increased, possibly as a result of reduced compensatory motion of the trunk. The aim of this study was to determine whether postural compensation for breathing is reduced during experimentally induced pain. Subjects stood on a force plate with eyes open, eyes closed, and while breathing with hypercapnoea before and after injection of hypertonic saline into the right lumbar longissimus muscle to induce LBP. Motion of the lumbar spine, pelvis, and lower limbs was measured with four inclinometers fixed over bony landmarks. During experimental pain, motion of the trunk in association with breathing was reduced. However, despite this reduction in motion, there was no increase in postural sway with breathing. These data suggest that increased body sway with breathing in people with chronic LBP is not simply because of reduced trunk movement, but instead, indicates changes in coordination by the central nervous system that are not replicated by experimental nociceptor stimulation.

Gait information flow indicates complex motor dysfunction

Gait-related back movements require coordination of multiple extremities including the flexible trunk. Ageing and chronic back pain influence these adjustments. These complex coordinations can advantageously be quantified by information theoretically based communication measures such as the gait information flow (GIF). Nine back pain patients (aged 61+/-10 yr) and 12 controls (aged 38+/-10 yr) were investigated during normal walking across a distance of 300 m. The back movements were measured as distances between characteristic points (cervical spine CS, thoracic spine TS, lumbar spine LS) by the sonoSens Monitor, a system for mobile motion analysis. Gait information flow and regularity indices (RI1: short prediction horizon of 100 ms, RI2: longer prediction horizon of walking period) were assessed as communication characteristics. All indices were non-parametrically tested for group differences. Sensitivity and specificity were assessed by bivariate logistic regression models. We found regularity indices systematically dependent on measurement points, information flow horizon and groups. In the patients RI1 was increased, but RI2 was decreased in comparison to the control group. These results quantitatively characterize the altered complex communication in the patients. We conclude that ageing and/or chronic back pain related dysfunctions of gait can advantageously be monitored by gait information flow characteristics of back movements measured as distances between characteristics points at the back surface.

Isometric force production parameters during normal and experimental low back pain conditions

Background

The control of force and its between-trial variability are often taken as critical determinants of motor performance. Subjects performed isometric trunk flexion and extension forces without and with experiment pain to examine if pain yields changes in the control of trunk forces. The objective of this study is to determine if experimental low back pain modifies trunk isometric force production.

Methods

Ten control subjects participated in this study. They were required to exert 50 and 75% of their isometric maximal trunk flexion and extension torque. In a learning phase preceding the non painful and painful trials, visual and verbal feedbacks were provided. Then, subjects were asked to perform 10 trials without any feedback. Time to peak torque, time to peak torque variability, peak torque variability as well as constant and absolute error in peak torque were calculated. Time to peak and peak dF/dt were computed to determine if the first peak of dF/dt could predict the peak torque achieved.

Results

Absolute and constant errors were higher in the presence of a painful electrical stimulation. Furthermore, peak torque variability for the higher level of force was increased with in the presence of experimental pain. The linear regressions between peak dF/dt, time to peak dF/dt and peak torque were similar for both conditions. Experimental low back pain yielded increased absolute and constant errors as well as a greater peak torque variability for the higher levels of force. The control strategy, however, remained the same between the non painful and painful condition. Cutaneous pain affects some isometric force production parameters but modifications of motor control strategies are not implemented spontaneously.

Conclusions

It is hypothesized that adaptation of motor strategies to low back pain is implemented gradually over time. This would enable LBP patients to perform their daily tasks with presumably less pain and more accuracy.

Effects of experimentally induced pain and fear of pain on trunk coordination and back muscle activity during walking

OBJECTIVE

To examine the effects of experimentally induced pain and fear of pain on trunk coordination and erector spinae EMG activity during gait.

DESIGN

In 12 healthy subjects, hypertonic saline (acute pain) and isotonic saline (fear of pain) were injected into erector spinae muscle, and unpredictable electric shocks (fear of impending pain) were presented during treadmill walking at different velocities, while trunk kinematics and EMG were recorded.

BACKGROUND

Chronic low back pain patients often have disturbed trunk coordination and enhanced erector spinae EMG while walking, which may either be due to the pain itself or to fear of pain, as is suggested by studies on both low back pain patients and healthy subjects.

METHODS

The effects of the aforementioned pain-related manipulations on trunk coordination and EMG were examined. Results. Trunk kinematics was not affected by the manipulations. Induced pain led to an increase in EMG variability and induced fear of pain to a decrease in mean EMG amplitude during double stance.

CONCLUSIONS

Induced pain and fear of pain have subtle effects on erector spinae EMG activity during walking while leaving the global pattern of EMG activity and trunk kinematics unaffected. This suggests that the altered gait observed in low back pain patients is probably a complex evolved consequence of a lasting pain, rather than a simple immediate effect.

RELEVANCE

Variability of EMG data and kinematics may explain pain-dependent alterations of motor control, which in turn might contribute to a further understanding of the development of movement impairments in low back pain.

Knee flexion during stair ambulation is altered in individuals with patellofemoral pain

Reduced knee flexion is a logical gait adaptation for individuals with patellofemoral pain (PFP) to lessen the patellofemoral joint reaction force and minimise pain during stair ambulation. This gait adaptation may be related to the co-ordination of individual vasti components.

PURPOSE

This study investigated the amount of stance-phase knee flexion in individuals with (n=48) and without (n=18) PFP using a cross-sectional design. The relationship between stance-phase knee flexion and onset timing of individual vasti activity was also examined.

METHOD

Stance-phase knee flexion was measured in 2-dimensions using a PEAK movement analysis system during stair ascent and descent. Individuals with PFP were separated into those with synchronous onset of the EMG activity of vastus medialis obliquus (VMO) and vastus lateralis (VL), and those where the onset of VMO EMG activity was delayed relative to the VL.

RESULTS

The amount of knee flexion at heel-strike and peak was less in the individuals with PFP compared with the healthy controls. In addition, there were trends towards individuals with PFP who had a delayed EMG onset of VL having reduced knee flexion during stair descent compared with PFP individuals with simultaneous vasti onsets and the control participants.

CONCLUSION

These results indicate that the amount of stance-phase knee flexion is lower in individuals with PFP and that this may be related to onset timing of the vasti.

Estimation of gait cycle characteristics by trunk accelerometry

This study reports on the novel use of a portable system to measure gait cycle parameters. Measurements were made by a triaxial accelerometer over the lower trunk during timed walking over a range of self-administered speeds. Signals from each trial were transformed to a horizontal-vertical coordinate system and analyzed by an unbiased autocorrelation procedure to obtain cadence, step length, and measures of gait regularity and symmetry. By curvilinear interpolation, speed-dependent gait parameters could be compared at a normalized speed. It was demonstrated that analysis of gait cycle parameters which previously required fixed laboratory equipment and paced walking procedures, now can be made from data obtained by a timing device and a portable sensor at free walking speeds.

Pain and motor control of the lumbopelvic region: effect and possible mechanisms

Many authors report changes in the control of the trunk muscles in people with low back pain (LBP). Although there is considerable disagreement regarding the nature of these changes, we have consistently found differential effects on the deep intrinsic and superficial muscles of the lumbopelvic region. Two issues require consideration; first, the potential mechanisms for these changes in control, and secondly, the effect or outcome of changes in control for lumbopelvic function. Recent data indicate that experimentally induced pain may replicate some of the changes identified in people with LBP. While this does not exclude the possibility that changes in control of the trunk muscles may lead to pain, it does argue that, at least in some cases, pain may cause the changes in control. There are many possible mechanisms, including changes in excitability in the motor pathway, changes in the sensory system, and factors associated with the attention demanding, stressful and fearful aspects of pain. A new hypothesis is presented regarding the outcome from differential effects of pain on the elements of the motor system. Taken together these data argue for strategies of prevention and rehabilitation of LBP.

Influences of nonspecific low back pain on three-dimensional lumbar spine kinematics in locomotion

STUDY DESIGN

A three-dimensional kinematic analysis of lumbar spinal movements with an ultrasonic measuring system was used to distinguish patients with chronic low back pain from those without such pain.

OBJECTIVES

To investigate the effects of chronic low back pain on the three-dimensional movements of the lumbar spine, and to identify variables that would allow discrimination among patients with chronic low back pain and control subjects.

SUMMARY OF BACKGROUND DATA

To the authors' knowledge, no previous studies have described or identified altered spinal and pelvic gait kinematics caused by nonspecific chronic low back pain in all anatomic planes.

METHODS

In this study, 34 participants with chronic low back pain and 22 subjects without such pain were monitored during treadmill gait. Data from the measuring system operating at 30 Hz were low-pass filtered and normalized to a percentage of the gait cycle.

RESULTS

Cross-correlations showed almost identical patterns of pelvic (S1) and thoracic (T12) movement curves in all anatomic planes between groups. No statistical group differences were detected for either pelvic or thoracic oscillation amplitudes. However, Student's t test showed significantly higher coefficients of variation (P < 0.01) in all anatomic planes of patients with chronic low back pain than in healthy control patients.

CONCLUSIONS

The phasic patterns and angular spinal displacements of patients with nonspecific low back pain were shown to be within normal limits. However, the patients demonstrated higher degrees of stride-to-stride variability, representing increased fluctuations in dynamic thoracic and pelvic oscillations. These findings, resulting in less than optimal gait patterns, must be considered in the rehabilitation of patients with chronic low back pain.

Analysis and decomposition of signals obtained by thigh-fixed uni-axial accelerometry during normal walking

The use of piezo-resistive uni-axial accelerometer signals in gait analysis is complicated by the fact that the measured signal is composed of different types of acceleration. The aim of the study is to obtain insight into the signal from a tangential accelerometer attached to the thigh during walking. Six subjects walk with three different speeds. Simultaneous measurements are performed with accelerometers, footswitches and an opto-electronic system. The components of the accelerometer signal are calculated from the opto-electronic system. A clear relationship is found between the measured and calculated accelerometer signals (range RMS: 0.76-3.69 m x s(-2), range rms: 0.22-0.61). The most pronounced feature is a high positive acceleration peak (> 10 m x s(-2)) at the end of the cycle. The gravitational acceleration during one cycle is characterised by a sinusoidal shape, whereas the inertial acceleration contains higher-frequency components (up to 20 Hz). During the major part of the gait cycle, the gravitational and inertial acceleration make opposing contributions to the signal As a result, the gravitational acceleration influences the amplitudes of the measured acceleration signal, the shape and peaks of which are mainly determined by the inertial acceleration. Because the gravitational and inertial accelerations differ in frequency components, the application for gait analysis remains feasible.