Trunk Loading Research Articles

Effects of sudden walking perturbations on neuromuscular reflex activity and three-dimensional motion of the trunk in healthy controls and back pain symptomatic subjects.

BackgroundBack pain patients (BPP) show delayed muscle onset, increased co-contractions, and variability as response to quasi-static sudden trunk loading in comparison to healthy controls (H). However, it is unclear whether these results can validly be transferred to suddenly applied walking perturbations, an automated but more functional and complex movement pattern. There is an evident need to develop research-based strategies for the rehabilitation of back pain. Therefore, the investigation of differences in trunk stability between H and BPP in functional movements is of primary interest in order to define suitable intervention regimes. The purpose of this study was to analyse neuromuscular reflex activity as well as three-dimensional trunk kinematics between H and BPP during walking perturbations.MethodsEighty H (31m/49f;29±9yrs;174±10cm;71±13kg) and 14 BPP (6m/8f;30±8yrs;171±10cm;67±14kg) walked (1m/s) on a split-belt treadmill while 15 right-sided perturbations (belt decelerating, 40m/s2, 50ms duration; 200ms after heel contact) were randomly applied. Trunk muscle activity was assessed using a 12-lead EMG set-up. Trunk kinematics were measured using a 3-segment-model consisting of 12 markers (upper thoracic (UTA), lower thoracic (LTA), lumbar area (LA)). EMG-RMS ([%],0-200ms after perturbation) was calculated and normalized to the RMS of unperturbed gait. Latency (TON;ms) and time to maximum activity (TMAX;ms) were analysed. Total motion amplitude (ROM;[°]) and mean angle (Amean;[°]) for extension-flexion, lateral flexion and rotation were calculated (whole stride cycle; 0-200ms after perturbation) for each of the three segments during unperturbed and perturbed gait. For ROM only, perturbed was normalized to unperturbed step [%] for the whole stride as well as the 200ms after perturbation. Data were analysed descriptively followed by a student´s t-test to account for group differences. Co-contraction was analyzed between ventral and dorsal muscles (V:R) as well as side right:side left ratio (Sright:Sleft). The coefficient of variation (CV;%) was calculated (EMG-RMS;ROM) to evaluate variability between the 15 perturbations for all groups. With respect to unequal distribution of participants to groups, an additional matched-group analysis was conducted. Fourteen healthy controls out of group H were sex-, age- and anthropometrically matched (group Hmatched) to the BPP.ResultsNo group differences were observed for EMG-RMS or CV analysis (EMG/ROM) (p>0.025). Co-contraction analysis revealed no differences for V:R and Srigth:Sleft between the groups (p>0.025). BPP showed an increased TON and TMAX, being significant for Mm. rectus abdominus (p = 0.019) and erector spinae T9/L3 (p = 0.005/p = 0.015). ROM analysis over the unperturbed stride cycle revealed no differences between groups (p>0.025). Normalization of perturbed to unperturbed step lead to significant differences for the lumbar segment (LA) in lateral flexion with BPP showing higher normalized ROM compared to Hmatched (p = 0.02). BPP showed a significant higher flexed posture (UTA (p = 0.02); LTA (p = 0.004)) during normal walking (Amean). Trunk posture (Amean) during perturbation showed higher trunk extension values in LTA segments for H/Hmatched compared to BPP (p = 0.003). Matched group (BPP vs. Hmatched) analysis did not show any systematic changes of all results between groups.ConclusionBPP present impaired muscle response times and trunk posture, especially in the sagittal and transversal planes, compared to H. This could indicate reduced trunk stability and higher loading during gait perturbations.

Athletic background is related to superior trunk proprioceptive ability, postural control, and neuromuscular responses to sudden perturbations

Trunk motor control is essential for athletic performance, and inadequate trunk motor control has been linked to an increased risk of developing low back and lower limb injury in athletes. Research is limited in comparing relationships between trunk neuromuscular control, postural control, and trunk proprioception in athletes from different sporting backgrounds. To test for these relationships, collegiate level long distance runners and golfers, along with non-athletic controls were recruited. Trunk postural control was investigated using a seated balance task. Neuromuscular control in response to sudden trunk loading perturbations was measured using electromyography and kinematics. Proprioceptive ability was examined using active trunk repositioning tasks. Both athlete groups demonstrated greater trunk postural control (less centre of pressure movement) during the seated task compared to controls. Athletes further demonstrated faster trunk muscle activation onsets, higher muscle activation amplitudes, and less lumbar spine angular displacement in response to sudden trunk loading perturbations when compared to controls. Golfers demonstrated less absolute error and variable error in trunk repositioning tasks compared to both runners and controls, suggestive of greater proprioceptive ability. This suggests an interactive relationship between neuromuscular control, postural control, and proprioception in athletes, and that differences exist between athletes of various training backgrounds.

高齢者の脊柱後弯における体幹負荷のモデル解析

高齢者の脊柱後弯における体幹負荷のモデル解析

The Effects of Wearable Resistance Training on Metabolic, Kinematic and Kinetic Variables During Walking, Running, Sprint Running and Jumping: A Systematic Review.

Wearable resistance training (WRT) provides a means of activity- or movement-specific overloading, supposedly resulting in better transference to dynamic sporting performance. The purpose of this review was to quantify the acute and longitudinal metabolic, kinematic and/or kinetic changes that occur with WRT during walking, running, sprint running or jumping movements. PubMed, SPORTDiscus, Web of Science and MEDLINE (EBSCO) were searched using the Boolean phrases (limb OR vest OR trunk) AND (walk* OR run* OR sprint* OR jump* OR bound*) AND (metabolic OR kinetic OR kinematic) AND (load*). A systematic approach was used to evaluate 1185 articles. Articles with injury-free subjects of any age, sex or activity level were included. Thirty-two studies met the inclusion criteria and were retained for analysis. Acute trunk loading reduced velocity during treadmill sprint running, but only significantly when loads of 11% body mass (BM) or greater were used, while over-the-ground sprint running times were significantly reduced with all loads (8-20%BM). Longitudinal trunk loading significantly increased jump performance with all loads (7-30%BM), but did not significantly improve sprint running performance. Acute limb loading significantly increased maximum oxygen consumption and energy cost with all loads (0.3-8.5%BM) in walking and running, while significantly reducing velocity during sprint running. The variation in load magnitude, load orientation, subjects, testing methods and study duration no doubt impact the changes in the variables examined and hence make definitive conclusions problematic. WRT provides a novel training method with potential to improve sporting performance; however, research in this area is still clearly in its infancy, with future research required into the optimum load placement, orientation and magnitude required for adaptation.

Increased spinal height using propped slouched sitting postures: Innovative ways to rehydrate intervertebral discs

Abstract Background Upright and slouched sitting are frequently adopted postures associated with increased intradiscal pressure, spinal height loss and intervertebral disc pathology. Objectives To examine the effects of two sustained propped slouched sitting (PSS) postures on spinal height after a period of trunk loading. Methods Thirty-four participants without a history of low back pain (LBP) were recruited (age 24.4 ± 1.6 years). Subjects sat in (1) PSS without lumbar support and (2) PSS with lumbar support for 10 min, after a period of trunk loading. Spinal height was measured using a stadiometer. Results Mean spinal height increase during PSS without lumbar support was 2.94 ± 3.63 mm and with lumbar support 4.74 ± 3.07 mm. Conclusions Both PSS with and without lumbar support significantly increased spinal height after a period of trunk loading ( p

Trunk Stability, Trunk Strength and Sport Performance Level in Judo.

Although trunk muscle function has been suggested to be a determinant of judo performance, its contribution to high-level performance in this sport has been poorly studied. Therefore, several tests were used to assess the differences in trunk muscle function between 11 international and 14 national level judo practitioners (judokas). Trunk strength and endurance were assessed using isokinetic tests and core stability was assessed using two protocols: 1) sudden loading, to assess trunk responses to unexpected external perturbations; 2) stable and unstable sitting, to assess the participants’ ability to control trunk balance. No differences between groups were found for trunk flexor isokinetic strength, trunk responses against lateral and posterior loading and trunk control while sitting. However, international level judokas showed significantly higher trunk extensor isokinetic strength (p <0.05) and lower trunk angular displacement after anterior trunk loading (p <0.05) than national level judokas. Few and low (r < 0.512) significant correlations were found between strength, endurance and stability parameters, which suggests that trunk strength and endurance are not limiting factors for trunk stability in competitive judokas. These results support the importance of trunk extensor strength and trunk stability against forward perturbations in elite judo performance.

Biomechanical effect of sitting postures on sitting load and feet weight in apparently healthy individuals

Background: Controversies exist about the ideal sitting position. Objective: The present study compared sitting load and feet weight in ischial, sacroischial and ischiofemoral support sitting postures. Methods: Apparently healthy individuals who were asymptomatic of low-back pain for at least 6 months were recruited in the present study. Ischial, sacroischial and ischiofemoral support sitting postures were described based on literature. Assessment of sitting weight was carried out with a standard weighing chair, whereas a bathroom weighing scale was used to assess feet weight. Anthropometric variables were assessed following standard procedures. Data were analysed using descriptive and inferential statistics. Statistical significant level was set at P Results: There were 210 participants comprising 113 males and 97 females, aged 17-35 years. Sacroischial sitting weight of 51.86 (6.57) kg was the highest followed by ischiofemoral sitting weight of 49.52 (6.19) kg and ischial sitting weight of 44.87 (5.99) kg; the differences were statistically significant (P = 0.001). Similarly, ischial feet weight was 19.64 (2.49) kg, followed by ischiofemoral feet weight of 15.92 (2.08) kg and sacroischial feet weight of 12.60 (1.90) kg in sitting positions; the differences were statistically significant (P = 0.000). There was a significant correlation between sitting and feet weights in the different sitting postures and each of height, weight, body mass index (BMI) and femoral length (P Conclusion: The ischial sitting position had the least sitting load, whereas the feet bears the least load in sacroischial sitting. The amount of load experienced in sitting, and the corresponding feet weight was influenced by height, weight, BMI and femoral length. It is implied that sitting position with the highest amount of trunk load has the least amount of feet weight and vice versa.

高齢者における体幹負荷のモデル解析

高齢者における体幹負荷のモデル解析

Comparison between the effectiveness of expiration and abdominal bracing maneuvers in maintaining spinal stability following sudden trunk loading

The purpose of this study was to clarify the effectiveness of expiration and abdominal bracing maneuvers in response to sudden trunk loading in healthy subjects. Fifteen healthy male subjects were anteriorly loaded under different experimental conditions. Tests were conducted at rest and while performing each of the stabilization maneuvers (expiration and abdominal bracing) at 15% of the maximal voluntary isometric contraction of the internal oblique muscle. Subjects had no knowledge of the perturbation timing. An electromyographic biofeedback system was used to control the intensity of internal oblique muscle activation. Muscular pre-activation of three trunk muscles (internal oblique, external oblique, and L3 erector spinae muscles) and lumbar acceleration in response to loading were measured. The expiration and abdominal bracing maneuvers promoted torso co-contraction, reduced the magnitude of lumbar acceleration, and increased spinal stability compared to the resting condition. There were no differences between the expiration and abdominal bracing maneuvers in the pre-activation of the three trunk muscles or in lumbar acceleration in response to loading. It appears that both expiration and abdominal bracing maneuvers are effective in increasing spinal stability in response to sudden anterior loading.

Core stability: evaluación y criterios para su entrenamiento

The aim of this study was to review both the characteristics of the tests used to assess core stability and the most important features of trunk stabilization exercise programs. The results of this review suggest that biomechanical methods such as sudden and controlled trunk loading and unloading, unstable sitting paradigm and mathematical modeling, have allowed us to analyze the effect of several factors on spine stability. In addition, field tests commonly used to assess core stability (muscle condition tests, single leg stance balance tests, postural control of lumbar spine and pelvis tests, etc.) have important limitations, mainly due to the absence of studies on the validity of these measurements. Finally, there is a lot of information regarding the effectiveness and safety of the stabilization exercises, but we lack enough information on other training load characteristics.

Study on perceived fatigue evaluating model during simulated load carriage

To establish a perceived fatigue evaluating model during simulated load carriage that is based on objective variables through analyzing the characteristics and trends of shoulder force, shoulder pressure, waist pressure, back pressure, and perceived fatigue, and to provide an analytical technique for research on load carriage. A 50-min simulated walking (at a speed of 5 km/h and a slope of 0%) experiment including 14 healthy male adults was conducted under four levels of backpack payloads (25, 29, 34, 37 kg). Shoulder force and trunk pressure were sampled simultaneously and analyzed with time- and frequency- domain methods. Multivariable linear regression was used to build a perceived fatigue evaluating model during load carriage. The perceived fatigue evaluating model based on shoulder force, trunk pressure distribution ratio, load, and body mass index (BMI) was established. Its adjusted determination coefficient (aR2) was 0.709 and the absolute percentage error (APE) at the end of the experiment was less than 20%. The goodness of fit of the model based on frequency-domain independent variables was much higher compared with the model based on time-domain independent variables. The addition of BMI that represents the individual differences to the model obviously improved the goodness of fit. The perceived fatigue evaluating model established in this study does not rely on the physiological changes of individuals, and thus can be used to establish an evaluation system for human load carriage with dummy as a substitution for human in experiments and to provide a scientific basis for efficient human load carriage.

Lumbopelvic muscle activation patterns in three stances under graded loading conditions: Proposing a tensegrity model for load transfer through the sacroiliac joints

According to the conventional arch model of the pelvis, stability of the sacroiliac joints may require a predominance of form and force closure mechanisms: the greater the vertical shear force at the sacroiliac joints, the greater the reliance on self-bracing by horizontally or obliquely oriented muscles (such as the internal oblique). But what happens to the arch model when a person stands on one leg? In such cases, the pelvis no longer has imposts, leaving both the arch, and the arch model theory, without support. Do lumbopelvic muscle activation patterns in one-legged stances under load suggest compatibility with a different model? This study compares lumbopelvic muscle activation patterns in two-legged and one-legged stances in response to four levels of graded trunk loading in order to further our understanding the stabilization of the sacroiliac joints. Thirty male subjects experienced four levels of trunk loading (0%, 5%, 10% and 15% of body weight) by holding a bucket at one side, at three conditions: 1) two-legged standing with the bucket in the dominant hand, 2) ipsilateral loading: one-legged standing with the bucket in the dominant hand while using the same-side leg, and 3) contralateral loading: one-legged standing using the same leg used in condition 2, but with the bucket in the non-dominant hand. During these tasks, EMG signals from eight lumbopelvic muscles were collected. ANOVA with repeated design was performed on normalized EMG's to test the main effect of load and condition, and interaction effects of load by condition. Latissimus dorsi and erector spinae muscles showed an antagonistic pattern of activity toward the direction of load which may suggest these muscles as lateral trunk stabilizers. Internal oblique muscles showed a co-activation pattern with increasing task demand, which may function to increase lumbopelvic stability (P < 0.05). No unilateral pattern of the internal obliques was observed during all trials. Our results suggest that the lumbopelvic region uses a similar strategy for load transfer in both double and single leg support positions which is not compatible with the arch analogy. Our findings are more consistent with a suspensory system (wire-spoke wheel model). If our proposed model holds true, the pelvic ring can only be integrated by adjusting tension in the spokes and by preserving rim integrity or continuity. Thus, we propose that in order to restore tension integrity throughout the pelvic ring, efforts to unlock restrictions, muscular correction of positional faults and lumbopelvic or even respiratory exercises following sacroiliac joint dysfunctions must be taken into consideration. Our hypothetical model may initiate thinking and act as a guide to future work based on a biomechanical approach to the problem of sacroiliac joint dysfunction.

The influence of load carrying on the energetics and kinematics of terrestrial locomotion in a diving bird

SummaryThe application of artificial loads to mammals and birds has been used to provide insight into the mechanics and energetic cost of terrestrial locomotion. However, only two species of bird have previously been used in loading experiments, the cursorial guinea fowl (Numida meleagris) and the locomotor-generalist barnacle goose (Branta leucopsis). Here, using respirometry and treadmill locomotion, we investigate the energetic cost of carrying trunk loads in a diving bird, the tufted duck (Aythya fuligula). Attachment of back loads equivalent to 10% and 20% of body mass increased the metabolic rate during locomotion (7.94% and 15.92%, respectively) while sternal loads of 5% and 10% had a greater proportional effect than the back loads (metabolic rate increased by 7.19% and 13.99%, respectively). No effect on locomotor kinematics was detected during any load carrying experiments. These results concur with previous reports of load carrying economy in birds, in that there is a less than proportional relationship between increasing load and metabolic rate (found previously in guinea fowl), while application of sternal loads causes an approximate doubling of metabolic rate compared to back loads (reported in an earlier study of barnacle geese). The increase in cost when carrying sternal loads may result from having to move this extra mass dorso-ventrally during respiration. Disparity in load carrying economy between species may arise from anatomical and physiological adaptations to different forms of locomotion, such as the varying uncinate process morphology and hindlimb tendon development in goose, guinea fowl and duck.

Intervening on the Determinants of Mechanical Exposures: The Effects of a Redesigned Production System on Physical Demands and Worker Perceptions

OCCUPATIONAL APPLICATIONS Biomechanical analyses confirmed that workers on an existing production system experienced substantial trunk and shoulder loads. The production system design was a major determinant of these high exposures. To reduce these exposures, workplace stakeholders (including local and corporate management and organized labor) engaged with researchers in a participatory design process. Process elements included biomechanical modeling simulations to develop potential configurations, which were subsequently tested by workers during user trials with mock-ups. Based on stakeholder feedback, a new tilted production system was implemented. Formal analyses following installation of the tilted line demonstrated significant decreases in trunk flexion, spinal compression, and muscle activity for the low back and shoulder regions. Workers perceived that the new tilted line made their work significantly easier, safer, and less tiring. The study indicates that interventions at the production system level, developed using a participatory process, can reduce mechanical exposures while improving worker perceptions of job demands. TECHNICAL ABSTRACT Background: The design of an existing production system (flat line) was identified as the dominant driver of mechanical exposures for the low back and upper limb. A participative process was utilized in designing and implementing a tilted line that allowed workers to adopt more upright postures. Purpose: This study aimed to test the hypotheses that the new tilted production system would (1) decrease physical demands of the low back and shoulder, (2) not increase activity of the wrist musculature, (3) reduce workers’ reports of pain intensity, and (4) be perceived as a positive and beneficial change by the workforce. Methods: Eighteen of 22 tilted line workers volunteered to be videotaped (postures input into a biomechanical model of the upper limb/trunk) and have electromyography from the low back, shoulder, and forearm recorded while they worked at four tilted and flat line positions. Self-report questionnaires were used to compare pain intensity scores from workers on the tilted and flat lines. Results: Working on the tilted line was associated with statistically significant reductions in peak trunk angle (mean difference of 11°), L4/L5 spinal compression (314 N), and peak and mean electromyography for the low back (31% and 29%) and dominant shoulder (11% and 12%). No significant differences in pain scores were observed between the two lines. However, workers perceived that the tilted line made their work significantly easier, safer, less tiring, and assisted with their job. Conclusions: Tilting the production system allowed more upright postures, significantly reducing mechanical exposures for the trunk and upper limb. The participatory design approach may have contributed to workers’ positive perceptions about the newly designed production system. Ergonomic interventions that focus on workplace elements that drive mechanical exposures likely increase change impact and intervention intensity and should be an effective way to decrease musculoskeletal disorder risk factors.

Passive trunk loading influences muscle activation during dynamic activity

Repetitive loading of the low back tissues induces tension relaxation with a corresponding variation in the myoelectric response of the neuromuscular system, which may influence low back health. The purpose of this study was to observe trunk muscle activities before and after a passive cyclic trunk flexion-extension exercise. Nineteen participants were subjected to sagittal plane loading of the low back tissues. These individuals performed toe-touching before and over 1 hour after load termination. Lumbar paraspinal activity cessation occurred significantly sooner over time during lumbar and pelvic flexion post-loading, as compared with pre-loading. Lumbar paraspinal activity then re-initiated later in lumbar extension. There was no change in peak or average muscle activity during the procedures. It is apparent that passive loading of the viscoelastic lumbar tissues results in a prolonged neuromuscular adaptation, followed by possible neuromuscular compensation sustained within 1 hour of load termination.

Differential activity of regions of the psoas major and quadratus lumborum during submaximal isometric trunk efforts

Controversy exists regarding the function of psoas major (PM) and quadratus lumborum (QL) at the lumbar spine. The functions of discrete regions of PM and QL were studied during trunk loading tasks. Twelve healthy participants performed isometric trunk loading tasks in various directions in upright sitting. Fine-wire electromyography (EMG) electrodes were inserted under ultrasound guidance into PM fascicles arising from the transverse process (PM-t) and vertebral body (PM-v) and the anterior (QL-a) and posterior (QL-p) layers of QL on the right side. Although right PM-t and PM-v were both active during right lateral-flexion trunk efforts, their activity was opposite in the sagittal plane, with greater PM-t towards extension and PM-v towards flexion. QL-a and QL-p were similarly active, though QL-p was active to a greater percentage of MVC during right trunk lateral-flexion efforts. Activity of QL-p was modulated with respiratory phase during the loading tasks with trunk efforts towards the right lateral-flexion/flexion and right lateral-flexion directions. These findings provide novel understanding of the unique activation of discrete regions of PM and QL. These differences must be considered in future EMG studies to better understand the function of these deeply situated trunk muscles in the control of the lumbar spine.

Limitations imposed by wearing armour on Medieval soldiers' locomotor performance

In Medieval Europe, soldiers wore steel plate armour for protection during warfare. Armour design reflected a trade-off between protection and mobility it offered the wearer. By the fifteenth century, a typical suit of field armour weighed between 30 and 50 kg and was distributed over the entire body. How much wearing armour affected Medieval soldiers' locomotor energetics and biomechanics is unknown. We investigated the mechanics and the energetic cost of locomotion in armour, and determined the effects on physical performance. We found that the net cost of locomotion (C(met)) during armoured walking and running is much more energetically expensive than unloaded locomotion. C(met) for locomotion in armour was 2.1-2.3 times higher for walking, and 1.9 times higher for running when compared with C(met) for unloaded locomotion at the same speed. An important component of the increased energy use results from the extra force that must be generated to support the additional mass. However, the energetic cost of locomotion in armour was also much higher than equivalent trunk loading. This additional cost is mostly explained by the increased energy required to swing the limbs and impaired breathing. Our findings can predict age-associated decline in Medieval soldiers' physical performance, and have potential implications in understanding the outcomes of past European military battles.

Core Muscle Response Times and Postural Reactions in Soccer Players and Nonplayers

Decreased core stability has been suggested to be associated with a higher occurrence of lower extremity injuries and low back pain. In a physical contact sport like soccer, direction-specific muscle reflex responses are crucial in maintaining core stability. Delayed core muscle response times repeatedly have been reported in patients with low back pain, but no study has compared core muscle reflex latencies and postural control between soccer players and less active nonplayers. The goal of this study was to investigate whether soccer players will exhibit shorter average core muscle reflex latencies along with less postural sway in response to a sudden trunk perturbation compared with nonplayers. A second goal was to see whether postural control measures are a valid, more practical alternative for the use of surface EMG in measuring reflexive core neuromuscular control. Sudden trunk loading in the frontal and sagittal plane was used in 10 high-level amateur soccer players and 11 less active nonplayers to study core muscle reflex latencies, using surface EMG of six major trunk muscles. Simultaneously, kinematic response data of a balance seat were obtained using gyroscopes measuring seat angular velocity. Soccer players demonstrated shorter reflex latencies compared with nonplayers for the rectus abdominis, erector spinae, and externus obliquus muscles in response to sagittal plane perturbations. These shorter reflex latencies went along with greater seat movement in response to sudden trunk loading, with moderate correlations between the two measures. The results showing shorter reflex latencies and greater balancing movements for soccer players add to the debate whether more postural sway is an appropriate indicator of having less neuromuscular control.

Quantitative Ergonomics Exposure Assessment for Floor Coverers in the Greater Boston Area

Floor Coverers have a high prevalence of knee related injuries. The objective of this study is to quantify whole body ergonomics exposure for Floor Coverers in the greater Boston area. A total of 6213 observations (about 100 hours) were made on 49 Floor Coverers by 7 trained observers in 8 construction sites. Awkward leg postures were common. “Kneeling/Crawling” was observed 61.2% of the time. Non-neutral trunk postures were observed frequently. “Severe Flexion” was observed 36.6% of the time, “Mild Flexion” 12.9%. “Manual Material Handling” was observed most frequently during “Hardwood Floor” (36.1%). Hand tools were used more frequently (32.6%) than power tools (5.2%). “Severe Trunk Flexion” did not always lead to heavy trunk load with kneeling postures. Leg postures should be considered before trunk postures were converted to trunk loads. Awkward leg postures are a big problem for Floor Coverers. A majority of the tasks happened near or on the ground.

People With Recurrent Low Back Pain Respond Differently to Trunk Loading Despite Remission From Symptoms

Cross-sectional design. To compare lumbar multifidus electromyographic activity (EMG) during predictable and unpredictable trunk loading between people with and without recurrent unilateral low back pain (LBP) during symptom remission. Unpredictable loading is a common injury mechanism for LBP. Paraspinal muscle responses to trunk loading differ between people with and without a history of LBP, but whether the response differs between specific regions within the paraspinal muscles is unclear. Differences between deep (DM) and superficial fibers (SM) of multifidus have been implicated in other tasks. It is unknown whether DM and SM EMG differ between people in remission from recurrent LBP and healthy people during trunk loading. DM and SM EMG was recorded bilaterally at L5 with intramuscular electrodes during predictable and unpredictable trunk loading and compared during 10 milliseconds epochs (250 milliseconds before to 150 milliseconds after loading) between sides, loading conditions, and groups. DM EMG increased above baseline before and after predictable load onset, but returned to baseline at the time of impact. Both DM EMG bursts were less in the remission group and less on the non-painful side. Peak SM EMG amplitude on the previously painful side was earlier in the remission group than healthy participants. DM and SM EMG were less after unpredictable load onset in the remission group than healthy participants. Despite symptom remission, DM EMG during predictable loading and DM and SM EMG during unpredictable loading were less in people with recurrent LBP than healthy participants.