Trunk Neuromuscular Control Research Articles

The effects of soft vs. rigid back-support exoskeletons on trunk dynamic stability and trunk-pelvis coordination in young and old adults during repetitive lifting

While back-support exoskeletons are increasing in popularity as an ergonomic intervention for manual material handling, they may cause alterations to neuromuscular control required for maintaining spinal stability. This study evaluated the effects of soft and rigid passive exoskeletons on trunk local dynamic stability and trunk-pelvis coordination. Thiry-two young (18–30 years) and old (45–60 years) men and women completed repetitive lifting and lowering tasks using two different exoskeletons and in a control condition. Both exoskeletons significantly reduced the short-term maximum Lyapunov exponent (LyE) of the trunk (p < 0.01), suggesting improved local dynamic stability. There was also a significant main effect of age (p = 0.05): older adults exhibited lower short-term LyE that young adults. Use of the soft exoskeleton significantly increased, while the rigid exoskeleton significantly decreased, long-term LyE, and these changes were more pronounced in the young group compared to the old group. Additionally, exoskeleton use resulted in significant increase (p < 0.001) of mean absolute relative phase (MARP) and deviation phase (DP) by ∼30–60 %, with greater increases due to the rigid than the soft device. Thus, trunk-pelvic coordination and coordination variability were negatively impacted by exoskeleton use. Potential reasons for these findings may include exoskeleton-induced changes in lifting strategy, reduced peak trunk flexion velocity, and cycle-to-cycle variability of trunk velocity. Furthermore, although the soft and rigid devices caused comparable changes in trunk-extensor muscle activity, they exhibited differential effects on long-term maximum Lyapunov exponents as well as trunk-pelvic coordination, indicating that exoskeleton design features can have complex effects on trunk neuromuscular control.

Electromyographic activity of core muscles in isometric pole dance exercises with thigh locks

There is little technical and scientific research on Pole Dancing — an artistic, sensual and sporting activity based on friction and opposition between the body and a bar. The objective of this study is to analyze and compare the electromyographic (EMG) activity of the rectus abdominis (RA), obliquus externus abdominis (OE), and erector spinae (ES) muscles during the execution of different isometric Pole Dance exercises using the thigh lock to fix the body on the bar in the vertical, horizontal and inverted positions (basic seat, plank seat, and inverted seat). Experimental study consisting of a convenience sample of ten female Pole Dance practitioners with more than one year of experience and physically active. The EMG signal obtained during all exercises was quantified in the time domain by root mean square (RMS) and normalized by maximal voluntary isometric contraction (MVIC). Data were collected using simple differential surface electrodes and analyzed using repeated-measures analysis of variance. The results showed a significant difference only for the ES muscle, which was higher for the inverted position when compared to the vertical and horizontal ones. The three exercises produced low to moderate EMG activity in the muscles analyzed. Therefore, these exercises can be prescribed both for Pole Dance training programs — its variations present interesting intensity progression — and for low back pain prevention, as they can improve trunk neuromuscular control.

The Seated Trunk Control Test: Investigation of Reliability and Known-Groups Validity Using Individuals Post-Anterior Cruciate Ligament Reconstruction.

Decreased trunk neuromuscular control is a risk factor for both upper- and lower-extremity injuries, yet there are few reliable and valid clinical tests to identify deficits. The purpose of this study was to determine the reliability and known-groups validity of a novel clinical test, the seated trunk control test (STCT). Cross-sectional reliability and known-groups validity study. Laboratory. 89 unique participants: 34 were 3months postoperative anterior cruciate ligament reconstruction (ACLR) and 55 healthy controls. For the STCT, participants sat on a balance board with their eyes closed for three 30-second trials while investigators counted balance errors. Intraclass correlations (ICCs) were used to assess interrater reliability (N = 20) and test-retest reliability (N = 40). To assess known-groups validity, independent t tests were used to compare STCT errors at 3 months post-ACLR with healthy matched controls (N = 34/group). Area under a receiver operating characteristic curve identified an optimal cutoff for distinguishing between groups. The STCT had perfect interrater reliability (ICC2,3 = 1.00) and good test-retest reliability (ICC3,3 = .79; 95% confidence interval = .61-.89). The ACLR group made significantly more errors on the STCT (mean [SD] = 15.5 [5.4]) than controls (mean [SD] = 8.2 [4.1]; P < .001, Cohen d = 1.52). The STCT's ability to distinguish between groups was excellent (area under a ROC curve = 0.86). A cutoff of 12 errors maximized sensitivity (76%) and specificity (85%). The STCT is reliable between raters and across days. It also has excellent ability to distinguish between individuals with a recent ACLR and healthy matched controls, which provides initial evidence to suggest that the STCT may be clinically useful for identifying deficits in trunk neuromuscular control.

Clinical prediction rule validity to identify individuals with recurrent low back pain

IntroductionOne set of clinical prediction rules (CPR) can be used clinically to identify patients with low back pain who are likely to benefit from motor control exercise. Individuals with a history of recurrent low back pain during remission (rLBP) still have persisting impaired trunk neuromuscular control. Accordingly, CPR should detect these individuals with rLBP. This study aimed to determine the predictive validity of CPR to identify individuals with rLBP.MethodsOverall, 30 subjects aged less than 40 years (22 subjects with rLBP and 8 subjects without a history of low back pain) were recruited. We used the following criteria as CPR: (1) presence of aberrant movement during active forward bend and (2) passive straight leg raising result greater than 91°. Kappa statistics and the chi-square test were used to determine predictive validity. Diagnostic accuracy was also calculated.ResultsKappa demonstrated substantial agreement (kappa = 0.73), while the chi-square test showed significant association (χ&lt;sup&gt;2&lt;/sup&gt; = 16.28; &lt;i&gt;p&lt;/i&gt; &lt; 0.001) between positive CPR and rLBP. Diagnostic accuracy demonstrated positive likelihood ratio of 3.82, while accuracy equalled 90%.ConclusionsOur findings indicated the predictive validity of CPR to identify individuals with rLBP. The result from this study would help identify those predisposed to recurrent episodes of low back pain who would likely have a positive response to motor control exercise.

Is There a Sex Difference in Trunk Neuromuscular Control among Recreational Athletes during Cutting Maneuvers?

Trunk motion is most likely to influence knee joint injury risk, but little is known about sex-related differences in trunk neuromuscular control during changes of direction. The purpose of the present study was to test whether differences in trunk control between males and females during changes of direction exist. Twelve female and 12 male recreational athletes (with at least 10 years of experience in team sport) performed unanticipated changes of direction with 30° and 60° cut angles, while 3D trunk and leg kinematics, ground reaction forces and trunk muscles electromyography were recorded. Trunk kinematics at the time of peak knee abduction moment and directed co-contraction ratios for trunk muscles during the pre-activation and weight acceptance phases were determined. None of the trunk kinematics and co-contraction ratio variables, nor peak knee abduction moment differed between sexes. Compared to the 30° cut, trunk lateral flexion remained unchanged and trunk external rotation was reduced (p < 0.001; η²p (partial eta squared for effect size) = 0.78), while peak knee abduction moment was increased (p < 0.001; η²p = 0.84) at 60°. The sharper cutting angle induced muscle co-contraction during the pre-activation directed less towards trunk flexors (p < 0.01; η²p = 0.27) but more towards trunk medial flexors and rotators opposite to the movement direction (p < 0.001; η²p > 0.46). However, muscle co-contraction during the weight acceptance phase remained comparable between 30° and 60°. The lack of sex-related differences in trunk control does not explain knee joint injury risk discrepancies between sexes during changes of direction. Trunk neuromuscular strategies during sharper cutting angles revealed the importance of external oblique muscles to maintain trunk lateral flexion at the expense of trunk rotation. This provides new information for trunk strength training purposes for athletes performing changes of direction.

Stability threshold during seated balancing is sensitive to low back pain and safe to assess

Challenging trunk neuromuscular control maximally using a seated balancing task is useful for unmasking impairments that may go unnoticed with traditional postural sway measures and appears to be safe to assess in healthy individuals. This study investigates whether the stability threshold, reflecting the upper limits in trunk neuromuscular control, is sensitive to pain and disability and is safe to assess in low back pain (LBP) patients. Seventy-nine subjects with non-specific LBP balanced on a robotic seat while rotational stiffness was gradually reduced. The critical rotational stiffness, KCrit, that marked the transition between stable and unstable balance was used to quantify the individual’s stability threshold. The effects of current pain, 7-day average pain, and disability on KCrit were assessed, while controlling for age, sex, height, and weight. Adverse events (AEs) recorded at the end of the testing session were used to assess safety. Current pain and 7-day average pain were strongly associated with KCrit (current pain p < 0.001, 7-day pain p = 0.023), reflecting that people experiencing more pain have poorer trunk neuromuscular control. There was no evidence that disability was associated with KCrit, although the limited range in disability scores in subjects may have impacted the analysis. AEs were reported in 13 out of 79 total sessions (AE Severity: 12 mild, 1 moderate; AE Relatedness: 1 possibly, 11 probably, 1 definitely-related to the study). Stability threshold is sensitive to pain and appears safe to assess in people with LBP, suggesting it could be useful for identifying trunk neuromuscular impairments and guiding rehabilitation.

Effects of back-support exoskeleton use on trunk neuromuscular control during repetitive lifting: A dynamical systems analysis

Back-support exoskeletons (BSEs) are a promising ergonomic intervention to mitigate the risk of occupational low back pain. Although growing evidence points to the beneficial effects of BSEs, specifically in reducing low-back physical demands, there is limited understanding of potential unintended consequences of BSE use on neuromuscular control of the trunk during manual material handling (MMH). We quantified the effects of two passive BSEs (BackX™ AC and Laevo™ V2.5) on trunk dynamic stability and movement coordination during a repetitive lifting task. Eighteen participants (gender-balanced) completed four minutes of repetitive lifting in nine different conditions, involving symmetric and asymmetric postures when using the BSEs (along with no BSE as a control condition). Maximum Lyapunov exponents (short-term: λmax-s; long-term: λmax-l) and Floquet multipliers (FMmax) were respectively calculated to quantify the local dynamic and orbital stability of thorax and pelvis trajectories. Thorax-pelvis segmental coordination was also quantified using the continuous relative phase. Wearing the Laevo™ significantly increased λmax-s for the pelvis (by ~ 8%) and FMmax for the thorax and pelvis (by ~ 5–10%). Use of either BSE decreased the in-phase coordination pattern for the thorax-pelvis coupling (by ~ 15%). These results suggest that BSE use can compromise neuromuscular control of the trunk, and caution should thus be used in selecting a suitable BSE for use in a given MMH task. Future work is needed, however, to assess the generalizability of different BSE design approaches in terms of unintended short-term and long-term effects on trunk neuromuscular control.

Effect of a simple core muscle training program on trunk muscle strength and neuromuscular control among pediatric soccer players

PurposeThe purpose of this study was to examine the effect of simple core muscle training (CMT) program on trunk muscle strength and neuromuscular control among pediatric athletes.MethodsForty-nine male soccer players (mean age, 10.8 years) participated. The CMT program had three components (bench, side bench, and Nordic hamstrings) and was performed at least three times weekly for a year. Trunk flexion/extension muscle strength and the K/H ratio (determined by dividing knee separation distance by hip separation distance during drop-jump test and used as an index of lower limb valgus alignment) were measured, and the Y balance test (YBT) was performed before and after intervention. This study did not include the pure control group among the same team. To consider the effect of CMT on trunk muscle strength due to physical growth, we used the data of trunk muscle strength from the local cohort study previously conducted in our institution. One hundred participants who matched the age, height, body weight, and body mass index of the training group was designated as a control group.ResultsIn the training group, the trunk flexion/extension strength significantly increased at 6 months (p < 0.001, p < 0.001, respectively) and 12 months (p < 0.001, p < 0.001, respectively) compared to initial value. The K/H ratio at initial contact and maximum knee flexion phase significantly increased at 6 months (p < 0.001 and p < 0.001, respectively); however, it did not increase at 12 months (p = 0.384 and p = 0.070, respectively) compared to the initial value. In the YBT, the maximized reach distance in each direction significantly increased after intervention on both the dominant and non-dominant sides, except in the posteromedial direction on the non-dominant foot. Compared to the control group, although there was no significant difference in trunk flexion/extension strength at baseline (p = 0.141 and p = 0.390, respectively), the training group showed significantly higher trunk flexion/extension muscle strength at 12 months (p < 0.001 and p < 0.001, respectively).ConclusionThe CMT program increased trunk muscle strength and improved dynamic balance among pediatric male athletes.Level of evidenceLevel II

Comparison between high-velocity low-amplitude manipulation and muscle energy technique on pain and trunk neuromuscular postural control in male workers with chronic low back pain: A randomised crossover trial.

BackgroundA therapeutic recommendation for restoring function in individuals with chronic low back pain (CLBP) is manual therapy through manipulative spinal or muscle energy techniques.ObjectivesTo compare the effectiveness of two osteopathic manipulative techniques on clinical low back symptoms and trunk neuromuscular postural control in male workers with CLBP.MethodTen male workers with CLBP were randomly allocated to two groups: high-velocity low-amplitude (HVLA) manipulation or muscle energy techniques (MET). Each group received one therapy per week for both techniques during 7 weeks of treatment. Pain and function were measured by using the Numeric Pain-Rating Scale, the McGill Pain Questionnaire and the Roland Morris Disability Questionnaire. The lumbar flexibility was assessed by Modified Schober Test. Electromyography (EMG) and force platform measurements were used for evaluation of trunk muscular activation and postural balance, respectively at three different times: baseline, post intervention, and 15 days later.ResultsBoth techniques were effective (p < 0.01) in reducing pain with large clinical differences (-1.8 to -2.8) across immediate and after 15 days. However, no significant effect between groups and times was found for other variables, namely neuromuscular activation and postural balance measures.ConclusionBoth techniques (HVLA thrust manipulation and MET) were effective in reducing back pain immediately and 15 days later. Neither technique changed the trunk neuromuscular activation patterns nor postural balance in male workers with LBP.Clinical implicationsThese results may facilitate clinical decision-making for CLBP management in physiotherapy programs.

Quantifying trunk neuromuscular control using seated balancing and stability threshold

Performance during seated balancing is often used to assess trunk neuromuscular control, including evaluating impairments in back pain populations. Balancing in less challenging environments allows for flexibility in control, which may not depend on health status but instead may reflect personal preferences. To make assessment less ambiguous, trunk neuromuscular control should be maximally challenged. Thirty-four healthy subjects balanced on a robotic seat capable of adjusting rotational stiffness. Subjects balanced while rotational stiffness was gradually reduced. The rotational stiffness at which subjects could no longer maintain balance, defined as critical stiffness (kCrit), was used to quantify the subjects’ trunk neuromuscular control. A higher kCrit reflects poorer control, as subjects require a more stable base to balance. Subjects were tested on three days separated by 24 hours to assess test–retest reliability. Anthropometric (height and weight) and demographic (age and sex) influences on kCrit and its reliability were assessed. Height and age did not affect kCrit; whereas, being heavier (p < 0.001) and female (p = 0.042) significantly increased kCrit. Reliability was also affected by anthropometric and demographic factors, highlighting the potential problem of inflated reliability estimates from non-control related attributes. kCrit measurements appear reliable even after removing anthropometric and demographic influences, with adjusted correlations of 0.612 (95%CI: 0.433–0.766) versus unadjusted correlations of 0.880 (95%CI: 0.797–0.932). Besides assessment, trainers and therapists prescribing exercise could use the seated balance task and kCrit to precisely set difficulty level to a percentage of the subject’s stability threshold to optimize improvements in trunk neuromuscular control and spine health.

Chronic low back pain influences trunk neuromuscular control during unstable sitting among persons with lower-limb loss

BackgroundPersons with unilateral lower-limb loss are at increased risk for developing chronic low back pain. Aberrant trunk and pelvis motor behavior secondary to lower-limb loss potentially alters trunk postural control and increases demands on the trunk musculature for stability. However, it is unclear whether trunk postural control is associated with the presence or chronicity of low back pain within this population. Research questionIs there a potential role of impaired trunk postural control among persons with lower limb loss and chronic low back pain? MethodsTwo groups of males with unilateral lower-limb loss (n = 18 with chronic low back pain; n = 13 without pain) performed an unstable sitting task. Trunk postural control was characterized using traditional and non-linear measures derived from center-of-pressure time series, as well as trunk kinematics and the ratio of lumbar to thoracic erector spinae muscle activations. ResultsTraditional and non-linear center-of-pressure measures and trunk muscle activation ratios were similar between groups, while participants with chronic low back pain demonstrated greater trunk motion and reduced local dynamic stability. SignificanceOur results suggest that persons with both lower-limb loss and chronic low back pain exhibit impaired trunk postural control compared to those with limb loss but without pain. Aberrant trunk motor behavior may be a response to altered functional requirements of walking with a prosthesis. An inability to adequately control the trunk could lead to spinal instability and pain in the presence of repetitive exposure to aberrant motor behavior of these proximal structures during everyday activities.

Inter-rater reliability and cross-validation of lumbar stability test

Background: Clinical lumbar stability test can be used to assess individuals’ ability to control their lumbar spine during limb movements. However, inter-rater reliability and validity has not previously been investigated. Therefore, this study aimed to (1) establish inter-rater reliability of lumbar stability test, and (2) cross-validate the lumbar stability test using lab-based equipment as a reference standard.Methods: Twenty-nine healthy university students were recruited. Two fourth year physical therapy students performed lumbar stability test. Lumbar stability levels were used to determine inter-rater reliability using kappa statistics. Then, the participants were asked to perform two trials of 30-s seated balance tests on an unstable chair in eye-open and eye-closed conditions. These trunk neuromuscular control data, including 95% confidence ellipse area (CEA), root-mean-square error along X and Y axes (RMSEx and RMSEy, respectively), were used to cross-validate the lumbar stability test using Spearman’s correlation.Results: Kappa statistics revealed poor to almost perfect agreement (0–1.00). When adjusting for prevalence and bias, inter-rater reliability were fair to almost perfect (0.31–0.59). CEA, RMSEx and RMSEy were greater in eye-closed condition (8.81, 0.30 and 0.48, respectively) comparing with eye-open condition (2.79, 0.16 and 0.26, respectively). Correlation between lumbar stability level and trunk neuromuscular control were fair (r = –0.31–0.34) in eye-open condition and weak (r = –0.14–0.18) in eye-closed condition.Conclusion: Lumbar stability test should be refined to improve inter-rater reliability. Lumbar stability level does not completely represent trunk postural control. Clinicians should use this test with caution.

Trunk postural adjustments: Medium-term reliability and correlation with changes of clinical outcomes following an 8-week lumbar stabilization exercise program

BackgroundLow back pain (LBP) has been previously associated with delayed anticipatory postural adjustments (APAs) determined by trunk muscle activation. Lumbar stabilization exercise programs (LSEP) for patients with LBP may restore the trunk neuromuscular control of the lumbar spine, and normalize APAs. This exploratory study aimed at testing the reliability of EMG and kinematics-based postural adjustment measures over an 8-week interval, assessing their sensitivity to LBP status and treatment and examining their relationship with clinical outcomes. MethodsMuscle activation of 10 trunk muscles, using surface electromyography (EMG), and lumbar angular kinematics were recorded during a rapid arm-raising/lowering task. Patients with LBP were tested before and after an 8-week LSEP. Healthy controls receiving no treatment were assessed over the same interval to determine the reliability of the measures and act as a control group at baseline. Muscle activation onsets and reactive range of motion, range of velocities and accelerations were assessed for between group differences at baseline and pre- to post-treatment effects within patients with LBP using t-tests. Correlations between these dependent variables and the change of clinical outcomes (pain, disability) over treatment were also explored. ResultsKinematic-based measures showed comparable reliability to EMG-based measures. Between-group differences were found in lumbar lateral flexion ROM at baseline (patients < controls). In the patients with LBP, lateral flexion velocity and acceleration significantly increased following the LSEP. Correlational analyses revealed that lumbar angular kinematics were more sensitive to changes in pain intensity following the LSEP compared to EMG measures. These findings are interpreted in from the perspective of guarding behaviors and lumbar stability hypotheses. ConclusionFuture clinical trials are needed to target patients with and without delayed APAs at baseline and to explore the sensitivity of different outcome measures related to APAs. Different tasks more challenging to postural stability may need to be explored to more effectively reveal APA dysfunction.

Trunk muscle activation patterns during walking among persons with lower limb loss: Influences of walking speed

Persons with lower limb amputation (LLA) walk with altered trunk-pelvic motions. The underlying trunk muscle activation patterns associated with these motions may provide insight into neuromuscular control strategies post LLA and the increased incidence of low back pain (LBP). Eight males with unilateral LLA and ten able-bodied controls (CTR) walked over ground at 1.0 m/s, 1.3 m/s, 1.6 m/s, and self-selected speeds. Trunk muscle onsets/offsets were determined from electromyographic activity of bilateral thoracic (TES) and lumbar (LES) erector spinae. Trunk-pelvic kinematics were simultaneously recorded. There were no differences in TES onset times between groups; however, LLA demonstrated a second TES onset during mid-to-terminal swing (not seen in CTR), and activation for a larger percentage of the gait cycle. LLA (vs. CTR) demonstrated an earlier onset of LES and activation for a larger percentage of the gait cycle at most speeds. LLA walked with increased frontal plane trunk ROM, and a more in-phase inter-segmental coordination at all speeds. These data collectively suggest that trunk neuromuscular control strategies secondary to LLA are driven by functional needs to generate torque proximally to advance the affected limb during gait, though this strategy may have unintended deleterious consequences such as increasing LBP risk over time.

The Development of a Seated Clinical Trunk Test to Assess Lower Extremity Injury Risk

Poor neuromuscular control of the trunk is associated with numerous injuries, including anterior cruciate ligament tears. Currently, few reliable methods exist to clinically assess trunk neuromuscular control. The development of such a test could be used to screen individuals who require trunk neuromuscular control training for injury prevention and rehabilitation. PURPOSE: The objective of this study was to assess the between and within session reliability of a new seated clinical trunk control test. METHODS: 10 healthy subjects (10 F, ages 21 ± 1.83, BMI 21.78 ± 3.01) with no prior lower extremity injuries were asked to sit on a wobble board placed on a solid surface on a plinth with their feet approximately 4 inches off the ground. Test length was 30 seconds and subjects had three practice trials followed by 2 test trials with their eyes closed. Performance on the test was measured as the time to the first predefined error and how many errors occurred in 30 seconds for each trial. An error occurred if the subject uncrossed their arms, opened their eyes, or if an edge of the wobble board touched the plinth. Reliability with and between days was assessed with an Intraclass Correlation Coefficient (ICC). RESULTS: Between day reliability for the time to error was good (ICC=0.77) and the reliability for the number of errors was excellent (ICC=0.93). Both the time to error and number of errors had excellent within session rater reliability (ICC <0.99). The average time to error was (day 1: 17.3±9.2 seconds, day 2: 21.5±8.6 seconds), and the average number of errors was (day 1: 1.4±1.8 errors, day 2: 1.2±1.4 errors). The average difference for time to error within the same session was 0.1±0.1 seconds, and there were no differences in the number of errors. CONCLUSION: The seated trunk control test shows good to excellent within and between day reliability for both the number of errors and time to the first error. Furthermore, there were minimal differences between trials, indicating that after the practice trials, there was no additional learning, yielding stable consistent results. These results indicate that the test is a reliable assessment of trunk neuromuscular control. Having established the tests reliability, subsequent studies should assess its ability to differentiate injured versus non-injured individuals.

NEUROMUSCULAR RESPONSES OF THE HAMSTRING MUSCLES DURING UNANTICIPATED TRUNK PERTURBATIONS

BackgroundAnterior cruciate ligament and hamstring strain injuries occur during unanticipated cutting and stopping movements. Previous prospective studies showed that athletes with decreased trunk neuromuscular control are at increased risk of...

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.

Prolonged Intermittent Trunk Flexion Increases Trunk Muscles Reflex Gains and Trunk Stiffness.

The goal of the present study was to determine the effects of prolonged, intermittent flexion on trunk neuromuscular control. Furthermore, the potential beneficial effects of passive upper body support during flexion were investigated. Twenty one healthy young volunteers participated during two separate visits in which they performed 1 hour of intermittent 60 seconds flexion and 30 seconds rest cycles. Flexion was set at 80% lumbar flexion and was performed with or without upper body support. Before and after intermittent flexion exposure, lumbar range of motion was measured using inertial measurement units and trunk stability was assessed during perturbations applied in the forward direction with a force controlled actuator. Closed-loop system identification was used to determine the trunk translational admittance and reflexes as frequency response functions. The admittance describes the actuator displacement as a function of contact force and to assess reflexes muscle activation was related to actuator displacement. Trunk admittance gain decreased after unsupported flexion, while reflex gain and lumbar range of motion increased after both conditions. Significant interaction effects confirmed a larger increase in lumbar range of motion and reflex gains at most frequencies analysed following unsupported flexion in comparison to supported flexion, probably compensating for decreased passive tissue stiffness. In contrast with some previous studies we found that prolonged intermittent flexion decreased trunk admittance, which implies an increase of the lumped intrinsic and reflexive stiffness. This would compensate for decreased stiffness at the cost of an increase in cumulative low back load. Taking into account the differences between conditions it would be preferable to offer upper body support during activities that require prolonged trunk flexion.

Differences In Core Stability Between Collegiate Football Players With And Without Shoulder Pain

Evidence suggests that poor core stability is a risk factor for extremity injury in athletes. Diminished core stability may alter force generation and dissipation in the extremities during tasks that require force transfer through the trunk. However, limited evidence exists to support this relationship with upper extremity injuries. PURPOSE: The purpose of this study was to determine differences in core stability between collegiate football players with and without non-traumatic shoulder pain. METHODS: 20 collegiate football players (10 with pain; No Pain/Pain -mean height (cm): 181 ± 5/182 ± 5; mean weight (kg): 97 ± 17/99 ± 17; BMI matched) completed tests of core stability (trunk neuromuscular control and muscle capacity). Isolated trunk control was assessed via an unstable chair placed on a force plate. Static control was assessed by center of pressure (COP) movement during seated balance using 95% confidence ellipse area (CEA; mm2) and mean velocity (MVEL; mm/s). Dynamic control was assessed during a speed and accuracy target acquisition task (targets displayed on a monitor). Directional control (DC; mm; COP path to target) and precision control (movement around target prior to acquisition (PC; CEA mm2)) were measured. Variables were averaged across 3 trials. Trunk muscle capacity was assessed by trunk flexor (FLEX; s) and extensor endurance (EXT; s) and double-leg lowering (DLL; °). MANOVA (effect size Eta) and t-tests (effect size Cohen’s d) were used to assess group differences, p < .05 considered significant. RESULTS: Core stability was not significantly different between groups. Data presented as mean ± stdev (No Pain/Pain), p-value, effect size: Static control- CEA 183 ± 129/131 ± 85 and MVEL 5.7 ± 3.0/6.4 ± 2.6, p = 0.38, Eta =.33; Dynamic Control- DC 49± 9/46 ± 6, p = 0.49, d =.39 and PC 143 ± 72/93± 25, p = 0.051, d = 0.93; Muscle Capacity: FLEX 77 ± 38/99 ± 32, EXT 74 ± 22/69± 28, p = 0.22, Eta= .40 and DLLT 14 ± 10/15 ± 11, p = 0.92, d =.05. CONCLUSIONS: Our data do not provide clear evidence of diminished core stability in collegiate football players with a non-traumatic shoulder injury. There is a trend toward differences in PC; however mean group differences do not exceed our MDC90 (73 mm2). This may be because players were from the same D1 university football team and adhered to the same strength and conditioning program.

The Effects of Vibration and Muscle Fatigue on Trunk Sensorimotor Control in Low Back Pain Patients.

IntroductionChanges in sensorimotor function and increased trunk muscle fatigability have been identified in patients with chronic low back pain (cLBP). This study assessed the control of trunk force production in conditions with and without local erector spinae muscle vibration and evaluated the influence of muscle fatigue on trunk sensorimotor control.MethodsTwenty non-specific cLBP patients and 20 healthy participants were asked to perform submaximal isometric trunk extension torque with and without local vibration stimulation, before and after a trunk extensor muscle fatigue protocol. Constant error (CE), variable error (VE) as well as absolute error (AE) in peak torque were computed and compared across conditions. Trunk extensor muscle activation during isometric contractions and during the fatigue protocol was measured using surface electromyography (sEMG).ResultsForce reproduction accuracy of the trunk was significantly lower in the patient group (CE = 9.81 ± 2.23 Nm; AE = 18.16 ± 3.97 Nm) than in healthy participants (CE = 4.44 ± 1.68 Nm; AE = 12.23 ± 2.44 Nm). Local erector spinae vibration induced a significant reduction in CE (4.33 ± 2.14 Nm) and AE (13.71 ± 3.45 Nm) mean scores in the patient group. Healthy participants conversely showed a significant increase in CE (8.17 ± 2.10 Nm) and AE (16.29 ± 2.82 Nm) mean scores under vibration conditions. The fatigue protocol induced erector spinae muscle fatigue as illustrated by a significant decrease in sEMG median time-frequency slopes. Following the fatigue protocol, patients with cLBP showed significant decrease in sEMG root mean square activity at L4-5 level and responded in similar manner with and without vibration stimulation in regard to CE mean scores.ConclusionsPatients with cLBP have a less accurate force reproduction sense than healthy participants. Local muscle vibration led to significant trunk neuromuscular control improvements in the cLBP patients before and after a muscle fatigue protocol. Muscle vibration stimulation during motor control exercises is likely to influence motor adaptation and could be considered in the treatment of cLBP. Further work is needed to clearly identify at what levels of the sensorimotor system these gains are achievable.