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

Changes of trunk muscle stiffness in individuals with low back pain: a systematic review with meta-analysis

BACKGROUND

Low back pain (LBP) is one of the most common musculoskeletal conditions. People with LBP often display changes of neuromuscular control and trunk mechanical properties, including trunk stiffness. Although a few individual studies have examined back muscle stiffness in individuals with LBP, a synthesis of the evidence appears to be lacking. Therefore, the aim of this systematic review with meta-analysis was to synthesize and evaluate the available literature investigating back muscle stiffness in association with LBP.

METHODS

We conducted a systematic review of the literature according to the PRISMA guidelines. We searched Pubmed, Scopus, Web of Science and ScienceDirect for studies, that compared back muscle stiffness, measured either by ultrasound-based elastography or myotonometry, between individuals with and without LBP. Pooled data of the included studies were presented descriptively. Additionally, we performed two meta-analyses to calculate the standardized mean difference between the two groups for resting stiffness of the multifidus and erector spinae muscle. For both meta-analyses, the random effect model was used and the weight of individual studies was calculated using the inverse-variance method. The quality of the included studies was assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Analytical Cross-Sectional studies. Furthermore, the certainty of evidence was evaluated using the GRADE approach.

RESULTS

Nine studies were included in our systematic review. Our results suggest that individuals with LBP have higher stiffness of the multifidus (SMD = 0.48, 95% CI: 0.15 - 0.81, p < 0.01; I2 = 48 %, p = 0.11) and erector spinae at rest (SMD = 0.37, 95% CI: 0.11 - 0.62, p < 0.01; I2 = 39 %, p = 0.14) compared to asymptomatic controls. On the other hand, the evidence regarding muscle stiffness during submaximal contractions is somewhat contradictory.

CONCLUSIONS

Based on the findings of this systematic review we conclude that people with LBP may have higher back muscle stiffness compared to asymptomatic controls. Addressing muscle stiffness might represent an important goal of LBP treatment. Nevertheless, our findings should be interpreted with extreme caution due to a limited quality of evidence, small number of included studies and differences in measurement methodology.

Trunk muscle size and function in volleyball players with and without injuries to the head, neck and upper limb

OBJECTIVE

To investigate trunk muscle size and function in elite and community volleyball players with and without a history of head, neck or upper limb injury.

DESIGN

Cross-sectional observational study.

SETTING

Volleyball training camp or training sessions.

PARTICIPANTS

86 volleyball players (elite = 29; community = 57).

MAIN OUTCOME MEASURES

Information regarding history of head, neck or upper limb injuries was collected by self-report questionnaires. Trunk muscle size (multifidus, transversus abdominis, internal oblique and quadratus lumborum) and voluntary contraction (multifidus, transversus abdominis, internal oblique) were assessed using ultrasound imaging.

RESULTS

For trunk muscle size, no significant differences were found between elite and community volleyball players with and without a history of injury (all p > 0.05). A significant difference was found for voluntary contraction of the multifidus and transversus abdominis muscles for elite and community volleyball players with and without a history of injury (all p < 0.05).

CONCLUSION

A difference in trunk muscle contraction but no change in trunk muscle size in players with a history of head, neck or upper limb injuries may represent an altered muscle recruitment pattern rather than a deficiency in trunk muscle strength. Prospective studies are required to determine if these adaptations are compensatory (and protective) or predispose players to further injuries.

The effects of prolonged sitting, standing, and an alternating sit-stand pattern on trunk mechanical stiffness, trunk muscle activation and low back discomfort

Sit-stand desks continue to be a popular intervention for office work. While previous studies have reported changes in subjective measures, there is limited understanding of how sit-stand work differs from prolonged sitting or standing work, from a biomechanical standpoint. The objective of this study was to investigate the effects of prolonged sitting, prolonged standing, and a sit-stand paradigm on changes in trunk stiffness, low back discomfort, and trunk muscle activation. Twelve healthy participants performed 2 h of computer-based tasks in each protocol, on three different days. The sit-stand protocol was associated with a significant increase in trunk stiffness and a decrease in muscle activation of lumbar multifidus and longissimus thoracis pars thoracis, compared to both prolonged sitting and standing. Both sitting and standing were associated with increased low back discomfort. These findings may be worth exploring in more detail, for why alternating sit-stand patterns may help alleviate low back pain. Practitioner summary: We explored changes in objective and subjective measures related to low back discomfort following prolonged sitting, standing, and alternating sit-stand patterns. Alternating sit-stand pattern was associated with increased trunk stiffness and decreased back muscle activity. Hence, sit-stand desks may have benefits in terms of preventing/mitigating low back pain. Abbreviations: DOF: degree of freedom; EMG: electromyogram; ILL: iliocostalis lumborum pars lumborum; LTL: longissimus thoracis pars lumborum; LTT: longissimus thoracis pars thoracis; LBP: low back pain; LM: lumbar multifidus; MVEs: maximum isometric voluntary exertions; RANOVA: repeated-measure analysis of variance; RMS: root mean square.

Directional Dependence of Experimental Trunk Stiffness: Role of Muscle-Stiffness Variation of Nonneural Origin

Trunk stiffness is an important parameter for trunk stability analysis and needs to be evaluated accurately. Discrepancies regarding the dependence of trunk stiffness on the direction of movement in the sagittal plane suggest inherent sources of error that require explanation. In contrast to the common assumption that the muscle stiffness remains constant prior to the induction of a reflex during position perturbations, it is postulated that muscle-stiffness changes of nonneural origin occur and alter the experimental trunk stiffness, causing it to depend on the sagittal direction. This is confirmed through reinterpretation of existing test data for a healthy subject, numerical simulation, and sensitivity analysis using a biomechanical model. The trunk stiffness is determined through a static approach (in forward and backward directions) and compared with the model stiffness for assumed scenarios involving deactivated muscles. The difference in stiffness between the opposite directions reaches 17.5% without a preload and decreases when a moderate vertical preload is applied. The increased muscle activation induced by preloads or electrical stimuli explains the apparent discrepancies observed in previous studies. The experimental stiffness invariably remains between low and high model-stiffness estimates based on extreme scenarios of the postulated losses of muscle activation, thereby confirming our hypothesis.

The effect of sacroiliac chiropractic adjustments on innominate angles

Aim

The aim of this study was to determine whether or not a measurable change in the angle of the innominate bone could be identified after a chiropractic sacroiliac adjustment using a 'PALM PALpation Meter'. Secondly, if a change in the angle of the innominate bone was identified, what was the degree of change in the angle of the innominate bone, induced by the sacroiliac joint (SIJ) adjustment.

Method

This was a true experimental study that consisted of 100 participants who met the inclusion criteria. The participants were randomly allocated to either the treatment or control group. Each group had 50 participants: 25 females and 25 males. Informed consent was obtained from participants prior to commencement of treatment. The treatment group received a chiropractic adjustment based on their specific SIJ dysfunction. The control group was treated with detuned ultrasound therapy (sham treatment).

Procedure

Treatment consisted of a once-off treatment. The angles of the innominate bones were measured bilaterally pre- and post-treatment in both groups. Objective data were collected using the PALM PALpation Meter. Once the dysfunctional SIJ was identified, participants in group 1 were treated with specific chiropractic adjustment techniques based on the restriction. Group 2 participants were treated with detuned ultrasound only.

Results

The results of this study showed that a specific chiropractic adjustment resulted in a measurable change in the angle of the innominate bone (p ≤ 0.001). The change in angle was evident bilaterally; however, the side that was adjusted shows the greatest degree of change. The mean change in angle for the treatment group was 2.25° on the side of dysfunction.

Conclusion

The results of this study showed that a specific chiropractic adjustment can have a positive effect on the angles of the innominate bone, resulting in the tilt of the pelvis levelling into what is considered to be its correct anatomical alignment.

Trunk stiffness decreases and trunk damping increases with experimental low back pain

Movement adaptations to low back pain (LBP) are believed to protect the painful area. Increased trunk stiffness and decreased trunk damping have been shown in people with recurrent LBP. However, no study has examined these properties using external force perturbations to the trunk during acute LBP when protective adaptations might be expected to have most relevance. Adaptations to an acute painful stimulus via unilateral injection of hypertonic saline into the right longissimus muscle were assessed using a trunk force perturbation paradigm and a mass-spring-damper model to describe effective trunk dynamical properties. Equal weights (15% body weight) were connected to the front and back of the trunk via a cable. Either one was dropped at random to perturb the trunk. Effective trunk dynamical properties were estimated in fourteen males (mean (standard deviation) age 25 (6) years) assuming that trunk movement can be modelled as a second order linear system. Effective trunk dynamical properties were compared before, during and after the experimentally induced painful period. Estimates of effective trunk stiffness (K) decreased and damping (B) increased during pain compared to both before ([mean contrast, 95% CI] K: -403 [-651 to -155] Nm^-1, B: 28 [9-50] Nms^-1) and after (K: -324 [-58 to -591] Nm^-1, B: 20 [4-33] Nms^-1) the experimentally induced painful period. We interpret our results to show that, when challenged by a step force perturbation, a healthy system adapts to noxious input by controlling trunk velocity rather than trunk displacement, in contrast to observations during remission from recurrent clinical LBP.

Increased Liveliness of Trunk Muscle Responses in Elite Kayakers and Canoeists

Trunk stability functions play an important role in sport and everyday movements. The aim of this study was to analyze trunk strength, trunk muscles onset of activity, and rate of electromyographic rise (RER) in the case of self-inflicted and unexpected trunk loading. Thirty-two healthy young adults (16 elite kayakers/canoeists and 16 non-athletes) were measured with a multi-purpose diagnostic machine. Trunk strength was assessed in standing position. Trunk muscles onset of activity and RER were assessed through unexpected loading over the hands and rapid shoulder flexion, respectively. In comparison with non-athletes, kayakers/canoeists did not significantly differ in trunk strength and showed lower trunk extension/flexion strength ratio (p = 0.008). In general, trunk muscles onset of activity did not significantly differ between the groups. On the contrary, kayakers/canoeists showed higher RER mean values in all the observed muscles (p < 0.041), except in multifidus muscle during self-inflicted movements. Similarly, higher RER variability was observed in the majority of the observed muscles among kayakers/canoeists. Higher RER among kayakers/canoeists could represent a protective mechanism that ensures spine stability and prevents low back pain.

Reliability of a portable device for quantifying tone and stiffness of quadriceps femoris and patellar tendon at different knee flexion angles

The reliability of MyotonPRO that can monitor the mechanical properties of tissues is still unclear. This study aimed to analyze the within-day inter-operator and between-day intra-operator reliability of MyotonPRO for assessing tone and stiffness of quadriceps femoris and patellar tendon at different knee angles. The tone and stiffness of healthy participants (15 males and 15 females, aged 24.7±1.6 years) in the supine and resting position were measured using the MyotonPRO device. The measurements were quantified at 0°, 30°, 60°, and 90° of knee flexion. The intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimal detectable change (MDC) were calculated and a Bland–Altman analysis was conducted to estimate reliability. The results indicated excellent inter-operator reliability (ICC > 0.78) and good to excellent intra-operator reliability (ICC > 0.41). The inter-operator SEM measurements ranged between 0.1–0.9 Hz and 3.8–37.9 N/m, and intra-operator SEM ranged between 0.5–1.3 Hz and 7.9–52.0 N/m. The inter-operator MDC ranged between 0.3–2.5 Hz and 10.5–105.1 N/m, and intra-operator SEM ranged between 1.1–3.3 Hz and 21.9–144.1 N/m. The agreement of inter-operator was better than that of intra-operator. The study concluded that MyotonPRO is a reliable device to detect the tone and stiffness of quadriceps femoris and patellar tendon.

The effect of extensible and non-extensible lumbar belts on trunk muscle activity and lumbar stiffness in subjects with and without low-back pain

BACKGROUND

Lumbar belts have been shown to increase lumbar stiffness, but it is unclear if this is associated with trunk muscle co-contraction, which would increase the compression on the spine. It has been hypothesized that lumbar belts increase lumbar stiffness by increasing intra-abdominal pressure, which would increase spinal stability without increasing the compressive load on the spine.

METHODS

Trunk muscle activity and lumbar stiffness and damping were measured in healthy and low-back pain subjects during three conditions: no lumbar belt; wearing an extensible lumbar belt; wearing a non-extensible lumbar belt. Muscle activity was measured while subjects performed controlled forward and backward 20° trunk sways. Lumbar stiffness and damping were measured by applying random continuous perturbation to the chest.

FINDINGS

External oblique activity was decreased when wearing either lumbar belt during all phases of movement, while rectus abdominis and iliocostalis activity were decreased during the phase of movement where the muscles were maximally active while wearing either belt. Trunk stiffness was greatly increased by wearing either belt. There were no consistent differences in either lumbar stiffness or muscle activity between the two belts. Wearing a lumbar belt had little to no effect on damping. There were no group differences in any of the measures between healthy and low-back pain populations.

INTERPRETATION

The findings are consistent with the hypothesis that lumbar belts can increase spinal stability by increasing intra-abdominal pressure, without any increase in the compressive load on the spine. The findings can also be generalized, for the first time, to subjects with low-back pain.

Quantifying paraspinal muscle tone and stiffness in young adults with chronic low back pain: a reliability study

The reliability of a handheld myotonometer when used in a clinical setting to assess paraspinal muscle mechanical properties is unclear. This study aimed to investigate the between-session intra-rater reliability of a handheld myotonometer in young adults with low back pain (LBP) in a clinical environment. One assessor recorded lumbar paraspinal muscle tone and stiffness in an outpatient department on two occasions. The intraclass correlation coefficient (ICC), standard error of measurement (SEM), smallest real difference (SRD) and Bland-Altman analysis were conducted to assess reliability. The results indicated acceptable between-days intra-rater reliability (ICC > 0.75) for all measurements. The SEM of the muscle tone and stiffness measurements ranged between 0.20–0.66 Hz and 7.91–16.51 N/m, respectively. The SRD was 0.44–1.83 Hz for muscle tone and 21.93–52.87 N/m for muscle stiffness. SEM and SRD at L₁-L₂ were higher than those at other levels. The magnitude of agreement appeared to decrease as muscle tone and stiffness increased. The myotonometer demonstrated acceptable reliability when used in a clinical setting in young adults with chronic LBP. Measurements of the upper lumbar levels were not as reliable as those of the lower lumbar levels. The crural attachment of the diaphragm at L₁ and L₂ may affect paraspinal muscle tone and stiffness during respiratory cycles.

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

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

Evidence of splinting in low back pain? A systematic review of perturbation studies

PURPOSE

The purpose of this systematic review was to assess whether LBP patients demonstrate signs of splinting by evaluating the reactions to unexpected mechanical perturbations in terms of (1) trunk muscle activity, (2) kinetic and (3) kinematic trunk responses and (4) estimated mechanical properties of the trunk.

METHODS

The literature was systematically reviewed to identify studies that compared responses to mechanical trunk perturbations between LBP patients and healthy controls in terms of muscle activation, kinematics, kinetics, and/or mechanical properties. If more than four studies reported an outcome, the results of these studies were pooled.

RESULTS

Nineteen studies were included, of which sixteen reported muscle activation, five kinematic responses, two kinetic responses, and two estimated mechanical trunk properties. We found evidence of a longer response time of muscle activation, which would be in line with splinting behaviour in LBP. No signs of splinting behaviour were found in any of the other outcome measures.

CONCLUSIONS

We conclude that there is currently no convincing evidence for the presence of splinting behaviour in LBP patients, because we found no indications for splinting in terms of kinetic and kinematic responses to perturbation and derived mechanical properties of the trunk. Consistent evidence on delayed onsets of muscle activation in response to perturbations was found, but this may have other causes than splinting behaviour.

Wearing an Inflatable Vest Alters Muscle Activation and Trunk Angle While Paddling a Surfboard

Low back pain is a commonly reported problem among recreational surfers. Some individuals report that wearing a vest with an inflatable bladder that alters trunk angle may help to alleviate pain. The purpose of this study was to determine whether such a vest has an effect on muscle activation and extension of the lower back. Twelve recreational surfers completed 12 paddling trials at 1.1 m/s in a swim flume on both a shortboard and a longboard on 2 separate days. Three conditions of no vest, vest uninflated, and vest inflated were presented to participants in random order. Surface EMG and trunk angle were acquired via wireless sensors placed over the right erector spinae, mid-trapezius, upper trapezius, and latissimus dorsi. Wearing the inflated vest affected muscle activation: erector spinae and mid-trapezius demonstrated a significant decrease in activation relative to wearing no vest (12% and 18% respectively, p < .05). Trunk extension was also significantly reduced when the vest was inflated (18% reduction, p < .05). Results were similar for both the short and longboard, though this effect was greater while paddling the larger board. These results suggest that a properly inflated vest can alter trunk extension and muscle activity while paddling a surfboard in water.

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.

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.

Functional contributors to poor movement and balance control in patients with low back pain: A descriptive analysis

BACKGROUND

Automatic and voluntary body position control is essential for postural stability; however, little is known about individual factors that impair the sensorimotor system associated with low back pain (LBP).

OBJECTIVE

To evaluate automatic and voluntary motor control impairments causing postural instability in patients with LBP.

METHODS

Motor control impairments associated with poor movement and balance control were analyzed prospectively in 32 patients with LBP. Numeric Rating Scale (NRS) for pain assessment, Oswestry Disability Index (ODI) for disability measurement, and computerized dynamic posturography (CDP) for analysis of postural responses were used to measure outcomes of all patients. Computerized dynamic posturography tests including Sensory organization test (SOT), limits of stability test (movement velocity, directional control, endpoint, and maximum excursion), rhythmic weight shift (rhythmic movement speed and directional control), and adaptation test (toes-up and toes-down tests) were performed and the results compared with NeuroCom normative data.

RESULTS

The mean age of the patients was 40.50 ± 12.28 years. Lower equilibrium scores were observed in SOT (p < 0.05). There was a significant increase in reaction time and decrease in movement velocity, directional control, and endpoint excursion (p < 0.05). Speed of rhythmic movement along the anteroposterior direction decreased, while speed increased along the lateral direction (p < 0.05). Poor directional control was recorded in the anteroposterior direction (p < 0.05). Toes-down test showed an increased COG sway in patients compared with that in the controls (p < 0.05).

CONCLUSIONS

LBP causes poor voluntary control of body positioning, a reduction in movement control, delays in movement initiation, and a difficulty to adapt to sudden surface changes.

Age-related differences in trunk intrinsic stiffness

Age-related differences in trunk intrinsic stiffness, as an important potential contributor to spinal stability, were investigated here because of: (1) the role of spinal instability in low back pain (LBP) development; (2) the increasing prevalence of LBP with age, and (3) the increasing population of older people in the workforce. Sixty individuals aged 20-70 years, in five equal-size age groups, completed a series of displacement-controlled perturbation tests in an upright standing posture while holding four different levels of trunk extension efforts. In addition to examining any age-related difference in trunk intrinsic stiffness, the current design assessed the effects of gender, level of effort, and any differences in lower back neuromuscular patterns on trunk intrinsic stiffness. No significant differences in trunk intrinsic stiffness were found between the age groups. However, stiffness was significantly larger among males and increased with the level of extension effort. No influences of differences in neuromuscular pattern were observed. Since the passive contribution of trunk tissues in the upright standing posture is minimal, our values of estimated trunk intrinsic stiffness primarily represent the volitional contribution of the lower back musculoskeletal system to spinal stability. Therefore, it seems unlikely that the alterations in volitional behavior of the lower back musculature, caused by aging (e.g., as reflected in reduced strength), diminish their contributions to the spinal stability.