Poor lumbar spine coordination in acute low back pain predicts persistent long-term pain and disability.

PURPOSE: Sitting balance on an unstable surface requires coordinated out-of-phase lumbar spine and provides sufficient challenge to expose quality of spine control. We investigated whether the quality of spine coordination to maintain balance in acute low back pain (LBP) predicts recovery at 6 months. METHODS: Participants in an acute LBP episode (n = 94) underwent assessment of sitting balance on an unstable surface. Seat, hip and spine (lower lumbar, lumbar, upper lumbar, thoracic) angular motion and force plate data were recorded. Coordination between the seat and hip/spine segments to maintain balance was quantified in the frequency domain to evaluate coordination (coherence) and relative timing (phase angle: in-phase [segments move together]; out-of-phase [segments move opposite]). Center of pressure (CoP) and upper thorax motion assessed overall balance performance. Hip and spine coordination with the seat were compared between those who did not recover (increased/unchanged pain/disability), partially recovered (reduced pain/disability) or recovered (no pain and disability) at 6 months. RESULTS: In both planes, coherence between the seat and lower lumbar spine was lower (and in-phase-unhelpful for balance) at baseline in those who did not recover than those who recovered. Coherence between the seat and hip was higher in partially recovered in both planes, suggesting compensation by the hip. LBP groups had equal overall balance performance (CoP, upper thorax motion), but non-recovery groups used a less optimal strategy that might have consequences for long-term spine health. CONCLUSION: These longitudinal data revealed that individuals with compromised contribution of the lumbar spine to the balance during unstable sitting during acute LBP are less likely to recover.

Trunk postural control during unstable sitting among individuals with and without low back pain: A systematic review with an individual participant data meta-analysis.

INTRODUCTION: Sitting on an unstable surface is a common paradigm to investigate trunk postural control among individuals with low back pain (LBP), by minimizing the influence lower extremities on balance control. Outcomes of many small studies are inconsistent (e.g., some find differences between groups while others do not), potentially due to confounding factors such as age, sex, body mass index [BMI], or clinical presentations. We conducted a systematic review with an individual participant data (IPD) meta-analysis to investigate whether trunk postural control differs between those with and without LBP, and whether the difference between groups is impacted by vision and potential confounding factors. METHODS: We completed this review according to PRISMA-IPD guidelines. The literature was screened (up to 7th September 2023) from five electronic databases: MEDLINE, CINAHL, Embase, Scopus, and Web of Science Core Collection. Outcome measures were extracted that describe unstable seat movements, specifically centre of pressure or seat angle. Our main analyses included: 1) a two-stage IPD meta-analysis to assess the difference between groups and their interaction with age, sex, BMI, and vision on trunk postural control; 2) and a two-stage IPD meta-regression to determine the effects of LBP clinical features (pain intensity, disability, pain catastrophizing, and fear-avoidance beliefs) on trunk postural control. RESULTS: Forty studies (1,821 participants) were included for the descriptive analysis and 24 studies (1,050 participants) were included for the IPD analysis. IPD meta-analyses revealed three main findings: (a) trunk postural control was worse (higher root mean square displacement [RMSdispl], range, and long-term diffusion; lower mean power frequency) among individuals with than without LBP; (b) trunk postural control deteriorated more (higher RMSdispl, short- and long-term diffusion) among individuals with than without LBP when vision was removed; and (c) older age and higher BMI had greater adverse impacts on trunk postural control (higher short-term diffusion; longer time and distance coordinates of the critical point) among individuals with than without LBP. IPD meta-regressions indicated no associations between the limited LBP clinical features that could be considered and trunk postural control. CONCLUSION: Trunk postural control appears to be inferior among individuals with LBP, which was indicated by increased seat movements and some evidence of trunk stiffening. These findings are likely explained by delayed or less accurate corrective responses. SYSTEMATIC REVIEW REGISTRATION: This review has been registered in PROSPERO (registration number: CRD42021124658).

Comparison of Shoulder Range of Motion Quantified with Mobile Phone Video-Based Skeletal Tracking and 3D Motion Capture-Preliminary Study.

BACKGROUND: The accuracy of human pose tracking using smartphone camera (2D-pose) to quantify shoulder range of motion (RoM) is not determined. METHODS: Twenty healthy individuals were recruited and performed shoulder abduction, adduction, flexion, or extension, captured simultaneously using a smartphone-based human pose estimation algorithm (Apple's vision framework) and using a skin marker-based 3D motion capture system. Validity was assessed by comparing the 2D-pose outcomes against a well-established 3D motion capture protocol. In addition, the impact of iPhone positioning was investigated using three smartphones in multiple vertical and horizontal positions. The relationship and validity were analysed using linear mixed models and Bland-Altman analysis. RESULTS: We found that 2D-pose-based shoulder RoM was consistent with 3D motion capture (linear mixed model: R2 > 0.93) but was somewhat overestimated by the smartphone. Differences were dependent on shoulder movement type and RoM amplitude, with adduction the worst performer among all tested movements. All motion types were described using linear equations. Correction methods are provided to correct potential out-of-plane shoulder movements. CONCLUSIONS: Shoulder RoM estimated using a smartphone camera is consistent with 3D motion-capture-derived RoM; however, differences between the systems were observed and are likely explained by differences in thoracic frame definitions.

Coordination of hip and spine in individuals with acute low back pain during unstable sitting.

BACKGROUND CONTEXT: Trunk postural control differs between individuals with and without chronic low back pain (LBP). Whether this corresponds to differences in hip/spine coordination during the early acute phase of LBP (ALBP) is unclear. PURPOSE: To compare hip/spine coordination in relation to seat movements between individuals with and without ALBP when balancing on an unstable seat and to identify coordination strategies to maintain balance using cluster analysis. STUDY DESIGN/SETTING: Cross-sectional observational study. PATIENT SAMPLE: ALBP (n=130) and pain-free (n=72) individuals. OUTCOME MEASURES: Frequency domain measures to evaluate hip/spine coordination (amplitude spectrum, phase angle, and coherence) and time-series measures to assess overall balance performance (center of pressure [CoP] reflecting the amount of seat movements, upper thorax motion as a surrogate for head motion). METHODS: Participants maintained balance while sitting on a seat fixed to a hemisphere. Seat, hip, and spine (lower lumbar, lumbar, upper lumbar, and thoracic) angular motion and force plate data were recorded. RESULTS: Overall, seat/CoP movements (amplitude spectrum and RMSdisplacement) were greater (in both planes) and sagittal coordination (coherence) between the hip or lower spine and seat movements was lower in ALBP than controls. Cluster analysis using coherence data revealed different coordination strategies to maintain balance. Separate clusters used a "lower lumbar strategy" and "hip strategy" in the sagittal plane, and a "lower and upper lumbar strategy" and "lower lumbar strategy" in the frontal plane. A cluster using a "low coherence strategy" in both planes was also identified. CONCLUSIONS: Hip and lower spine coordination was less in individuals with ALBP in conjunction with a lower quality of overall balance performance. However, interpretation of the relationship between coherence and overall balance performance was not straightforward. Clusters in both the ALBP group and the control group adopted a low coherence strategy, and this was not consistently related to poor overall balance performance. This suggests overall balance performance cannot be inferred from coherence alone and requires consideration of interaction of other different features.

Estimation of human spine orientation with inertial measurement units (IMU) at low sampling rate: How low can we go?

Studying people in their daily life is important for understanding conditions with multi-faceted aetiology such as chronic low back pain. Inertial measurement units can be used to reconstruct the posture and motion of the body outside of laboratories to enable this research. The battery life of these sensors strongly affects the usability of the system, since recharging them frequently is inconvenient and can lead to additional errors. A major determinant of the battery life for these sensors is sampling rate, but the relationship between sampling rate and accuracy in motion reconstruction is not well documented. We measured the spine of 12 participants using inertial measurement units across a variety of tasks such as sitting, standing, walking, and jogging. The orientation of the spine was reconstructed using several filters, including a novel filter developed specifically for high performance at low sampling frequencies. Benchmarking against optical motion capture, we developed a model showing that the error of all tested filters depends exponentially on the sampling frequency, with the optimal filter gains showing a similar exponential relationship. Using this model of error, we developed a criterion for recommending minimum sampling frequencies for accurate motion estimates for each task, finding frequencies ranging from about 13 to 35 Hz sufficient depending on the task. Although we only studied the spine, these models should provide insight into optimizing sampling rate and filter parameters for inertial measurements in general use.

Comparison of a Wearable Accelerometer/Gyroscopic, Portable Gait Analysis System (LEGSYS+TM) to the Laboratory Standard of Static Motion Capture Camera Analysis.

Examination of gait patterns has been used to determine severity, intervention triage and prognostic measures for many health conditions. Methods that generate detailed gait data for clinical use are typically logistically constrained to a formal gait laboratory setting. This has led to an interest in portable analysis systems for near clinical or community-based assessments. The following study assessed with the wearable accelerometer/gyroscopic, gait analysis system (LEGSYS+TM) and the standard of static motion capture camera (MOCAP) analysis during a treadmill walk at three different walking speeds in healthy participants (n = 15). To compare each speed, 20 strides were selected from the MOCAP data and compared with the LEGSYS+ strides at the same time point. Both scatter and bland-Altman plots with accompanying linear regression analysis for each of the parameters. Each stride parameter showed minimal or a consistent difference between the LEGSYS+ and MOCAP, with the phase parameters showing inconsistencies between the systems. Overall, LEGSYS+ stride parameters can be used in the clinical setting, with the utility of phase parameters needing to be taken with caution.

Postural control of the trunk in individuals with and without low back pain during unstable sitting: A protocol for a systematic review with an individual participant data meta-analysis.

INTRODUCTION: Postural control of the trunk is critical for performance of everyday activities and the health of spinal tissues. Although some studies report that individuals with low back pain (LBP) have poorer/compromised postural control than pain-free individuals when sitting on an unstable surface, others do not. Analyses commonly lack the statistical power to evaluate the relevance of features that could impact the performance of postural control, such as sex, age, anthropometrics, pain intensity or disability. This paper outlines a protocol for a systematic review with an individual participant data (IPD) meta-analysis that aims to synthesise the evidence and evaluate differences of postural control measures between individuals with and without LBP during unstable sitting. METHODS AND ANALYSIS: A systematic review with IPD meta-analysis will be conducted according to PRISMA-IPD guidelines. To identify relevant studies, electronic databases and the reference lists of included articles will be screened. Unstable seat movements are derived from centre of pressure (CoP) data using a force plate or angle of the seat using motion systems/sensors. The comprehensiveness of reporting and methodological quality of included studies will be assessed. Analysis will involve a descriptive analysis to synthesise the findings of all included studies and a quantitative synthesis using two-stage IPD meta-analysis of studies that include both individuals with and without LBP for which IPD set can be obtained from authors. Analyses will include consideration of confounding variables. ETHICS: Exemption from ethical approval was obtained for this review (University of Queensland, ID: 2019003026). SYSTEMATIC REVIEW REGISTRATION: PROSPERO ID: CRD42021124658.

A vision for the future of wearable sensors in spine care and its challenges: narrative review.

Objective: This review aimed to: (I) provide a brief overview of some topical areas of current literature regarding applications of wearable sensors in the management of low back pain (LBP); (II) present a vision for a future comprehensive system that integrates wearable sensors to measure multiple parameters in the real world that contributes data to guide treatment selection (aided by artificial intelligence), uses wearables to aid treatment support, adherence and outcome monitoring, and interrogates the response of the individual patient to the prescribed treatment to guide future decision support for other individuals who present with LBP; and (III) consider the challenges that will need to be overcome to make such a system a reality. Background: Advances in wearable sensor technologies are opening new opportunities for the assessment and management of spinal conditions. Although evidence of improvements in outcomes for individuals with LBP from the use of sensors is limited, there is enormous future potential. Methods: Narrative review and literature synthesis. Conclusions: Substantial research is underway by groups internationally to develop and test elements of this system, to design innovative new sensors that enable recording of new data in new ways, and to fuse data from multiple sources to provide rich information about an individual's experience of LBP. Together this system, incorporating data from wearable sensors has potential to personalise care in ways that were hitherto thought impossible. The potential is high but will require concerted effort to develop and ultimately will need to be feasible and more effective than existing management.

Balance control in unstable sitting in individuals with an acute episode of low back pain.

BACKGROUND: Low back pain (LBP) is associated with altered postural control, mostly observed at later stages in the LBP trajectory. It is unclear whether postural control differs in the acute phase of LBP. RESEARCH QUESTION: Is postural control different in the acute phase of LBP (<2 weeks) and do differences depend on pain intensity, psychological features and/or availability of vision to control posture? METHODS: Cross-sectional study design. An unstable sitting paradigm (to reduce the contribution of the legs) assessed postural control of participants with acute LBP (n = 133) and pain-free controls (n = 74). Centre of pressure (CoP) reflected seat movements. Participants balanced with eyes closed, open, or with visual feedback of the anteroposterior CoP position. Balance performance was expressed by CoP displacement and velocity, and stabilogram diffusion analysis. Generalised estimating equations (GEEs) including body mass index, sex, and safety bar touch, tested differences between groups and between balance conditions. Separate GEEs were used to model performance measures and bar touch (yes/no) including pain intensity, disability and psychological features. RESULTS: CoP displacement and critical point coordinates (time and distance where CoP diffusion rate or spread slows) were larger in LBP than pain-free controls independent of balance condition. Long-term diffusion rate was greater in LBP than controls with eyes closed. CoP velocity measures (RMS, short term diffusion rate) were not different between groups. Pain intensity and psychological features were not linearly related to balance performance in participants with acute LBP. Higher pain catastrophizing was associated with touching the safety bar. SIGNIFICANCE: Postural control differs in acute LBP than pain-free controls. Findings might be explained by altered sensory processing, lesser ability to reweight proprioceptive information and/or less accurate trunk muscle control. Although not linearly related to pain-intensity or psychological features in the acute stage, reduced balance performance could potentially have impact on LBP recovery.

Evaluating validity of the Kids-Balance Evaluation Systems Test (Kids-BESTest) Clinical Test of Sensory Integration of Balance (CTSIB) criteria to categorise stance postural control of ambulant children with CP.

PURPOSE: Evaluate the validity of the Clinical Test of Sensory Integration of Balance (CTSIB) scored using Kids-Balance Evaluation Systems Test (Kids-BESTest) criteria compared to laboratory measures of postural control. METHOD: Participants were 58 children, 7-18 years, 17 with ambulant cerebral palsy (CP) (GMFCS I-II), and 41 typically developing (TD). Postural control in standing was assessed using CTSIB items firm and foam surfaces, eyes open (EO) then closed (EC). Face validity was evaluated comparing clinical Kids-BESTest scores between groups. Correlating force plate centre-of-pressure (CoP) data and clinical scores allowed evaluation of concurrent and content validity. RESULTS: Face validity: TD children scored higher for all CTSIB conditions when compared to children with CP. Concurrent validity: the agreement between clinical and CoP derived scores was poor to excellent (Firm-EO = 76%, Firm-EC = 76%, Foam-EO = 59%, Foam-EC = 94%). Clinical scores of "2-unstable" and "3-stable" were not distinguished reliably by force plate measures. Content validity: significant correlations were found between clinical scores and CoP data for the two intermediate conditions (Firm-EC: rs -0.40 to -0.72; Foam-EO: rs -0.12 to -0.50), but not the easier (Firm-EO: rs -0.41 to -0.36) or harder conditions (Foam-EC: rs -0.25 to -0.27). CONCLUSION: Face validity of Kids-BESTest CTSIB criteria was supported. Content and concurrent validity were partially supported. Improved Kids-BESTest scoring terms were recommended to describe postural characteristics of "2-unstable."IMPLICATIONS FOR REHABILITATIONFace validity of the Kids-BESTest criteria for the CTSIB was confirmed.The Kids-BESTest criteria for the CTSIB can identify children with atypical postural control.Concurrent validity and content validity were partially supported, since children with CP resorted to a range of different balance strategies when "unstable."To improve CTSIB Kids-BESTest criteria, new terms were recommended to better describe postural characteristics of "2-unstable."

Coordination of hip and spine to maintain equilibrium in unstable sitting revealed by spectral analysis.

Unstable sitting paradigms have been used to assess the trunk's contribution to postural control. The coordination of spine or hip with an unstable seat that underpin postural control during this task remain unclear. This study aimed to address this issue using analysis in the frequency domain. Seventy-two healthy pain-free participants maintained balance while sitting on a seat fixed to a hemisphere. Angular motion of seat, spinal regions (lower lumber, lumbar, upper lumbar, and thoracic), and hip was recorded with a three-dimensional (3-D) motion capture system. Coordination between spinal regions and hip with the seat was quantified using cross-spectral analyses. In the sagittal plane, amplitude spectrum of hip and lumbar segments were higher than other segments, coherence between these segments and the seat was high, and their motion was generally opposite in direction to the seat. In the frontal plane, amplitude spectrum of lower lumbar and lumbar segments, but not the hip, were higher than other segments, and coherently moved in the opposite direction to the seat. Segments closest to the seat made a direction-specific and greater contribution to maintenance of equilibrium than upper body segments, which were more limited during unstable sitting. Although eye closure and higher body mass index involved larger amplitude of center of pressure movement, rather than inferring poor control, this was associated with enhanced coordination between segments and seat. Understanding how hip/spine segments are coordinated with the seat is important to interpret postural strategies used to maintain equilibrium and to interpret observations for other populations (e.g., back pain).NEW & NOTEWORTHY This is the first multidirectional spectral analysis of how the hip and spine coordinate during unstable sitting and how different factors impact this coordination. Seat movement was coherently counteracted (out-of-phase) by angular motion of the hip and lower lumbar spine in the sagittal plane and by the lumbar spine in the frontal plane. Although higher BMI and balancing with eyes closed increased movement amplitude, this did not compromise coordination between segments to control balance, instead, coherence increased.

Influence of transducer orientation on shear wave velocity measurements of the iliotibial band.

Tissue anisotropy influences estimation of mechanical properties of connective tissues, such as the iliotibial band (ITB). This study investigated the influence of ultrasound transducer rotation and tilt on shear wave velocity (SWV, an index of stiffness) measurements of the ITB and the intra-rater repeatability of SWV measurements in the longitudinal direction. SWV was measured unilaterally (dominant limb) using ultrasound shear wave elastography in the middle region of the ITB in supine at rest (20-25° knee flexion) in ten healthy volunteers (4 females). A 3-dimensional video system provided real-time feedback of probe orientation with respect to the thigh. Measurements were made at 10° increments of probe rotation, from longitudinal to transverse alignment relative to the approximate direction of ITB fibres, and 5-10° tilts about the longitudinal and sideways axes of the transducer. One-way repeated measures ANOVA compared SWV between angles and tilts. Intraclass correlation coefficients (ICCs) and standard error of measurement (SEM) were used to calculate repeatability for two to five (longitudinal only) repetitions. SWV was greatest when the transducer was aligned to ITB fibres (longitudinal: 10.5 ± 1.7 m/s) and lowest when perpendicular (transverse: 5.8 ± 2.4 m/s). Compared to longitudinal alignment, SWV decreased significantly (p < 0.01) when the transducer was rotated 20° or more. Tilted measurements did not differ between angles. Intra-rater repeatability was excellent with the average of two measurements (ICC = 0.99, 95% CI 0.95, 0.99; SEM = 0.31 m/s). These findings show that SWV changes with orientation relative to fibre direction. Transducer orientation requires careful control to ensure comparable measures.

Cohort profile: why do people keep hurting their back?

OBJECTIVE: Low back pain (LBP) is one of the most disabling and costly conditions worldwide. It remains unclear why many individuals experience persistent and recurrent symptoms after an acute episode whereas others do not. A longitudinal cohort study was established to address this problem. We aimed to; (1) evaluate whether promising and potentially modifiable biological, psychological, social and behavioural factors, along with their possible interactions, predict LBP outcome after an acute episode; (2) compare these factors between individuals with and without acute LBP; and (3) evaluate the time-course of changes in these factors from LBP onset. This paper outlines the methodology and compares baseline characteristics between acute LBP and control, and LBP participants with and without follow-up. RESULTS: 133 individuals with acute LBP and 74 pain-free individuals participated. Bio-psycho-social and behavioural measures were collected at baseline and 3-monthly for 12 months (LBP) or 3 months (control). Pain and disability were recorded fortnightly. Baseline characteristics were mostly similar between those who did and did not return for follow-up. Initial analyses of this cohort have revealed important insights into the pathways involved in acute-to-chronic LBP. These and future findings will provide new targets for treatment and prevention of persistent and recurrent LBP.

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.

Novel insight into pressurization of the male and female urethra through application of a multi-channel fibre-optic pressure transducer: Proof of concept and validation.

PURPOSE: To confirm feasibility of recording pressure along the length of the urethra using a multi-sensor fibre-optic pressure catheter; to identify the spatial and temporal features of changes in pressure along the urethra at sites related to specific striated pelvic floor muscles; and to investigate the relationship between urethral pressures and activation of individual pelvic floor muscles estimated from ultrasound imaging. MATERIALS AND METHODS: Proof-of-concept study including one male (47 years old) and one female (33 years old). A multi-sensor fibre optic pressure catheter (10 mm sensor separation) was inserted into the urethra. Pressure data were recorded simultaneously with trans-perineal ultrasound imaging measures of pelvic floor muscle activity during sub-maximal and maximal voluntary contractions and evoked coughs. RESULTS: Pressure changes along the urethra were recorded in all tasks in both participants. Face validity of interpretation of pressure measures with respect to individual muscles was supported by correlation with ultrasound-measured displacements induced by the relevant muscles. Onset of pressure increase occurred in a distal to proximal sequence in the urethra of the male but not the female during voluntary contraction. Peak urethral pressures varied in location, timing and amplitude between tasks. Evoked cough induced in the greatest urethral pressure increase across all tasks for both participants. CONCLUSIONS: The high spatial resolution pressure catheter provide viable and valid recordings of urethral pressure in a male and female. Data provide preliminary evidence of sex differences in spatial and temporal distribution of urethral pressure changes.

Reliability of recurrence quantification analysis of postural sway data. A comparison of two methods to determine recurrence thresholds.

Ageing affects balance control resulting in a greater amplitude of sway and alterations in structure of the sway time series. Recurrence quantification analysis (RQA) has been used to determine the structure of center-of-pressure (CoP; a measure that reflects standing postural control) data as a means to quantify how CoP repeats itself / recurs below a certain threshold. This study aimed to determine how the method of threshold determination, below which a recurrence is defined, affects the within-session reliability of RQA in an elderly population. Within-session reliability of RQA of CoP motion in the anterior-posterior and mediolateral directions was assessed in 267 individuals (>65 years old) when standing on firm or foam surface with eyes open or closed for each of two recurrence threshold methods. One threshold method sets the recurrence threshold level such that the recurrence rate is fixed to 5%, the other method sets the recurrence threshold based on 27% of the mean distance between all points from which recurrences are quantified. Reliability across four 30-s balance trials within each of four balance conditions (firm vs. foam, eyes open vs. closed) was determined using intra-class correlation, standard error of measurement and minimal detectable change. ICCs were better, the standard error of measurement and minimal detectable change were smaller when the recurrence threshold was set to 5% using the fixed recurrence threshold. Fixing recurrence rate improves the within session reliability of RQA and could increase sensitivity to identify fall risk.

Deep hip muscle activation during squatting in femoroacetabular impingement syndrome.

BACKGROUND: Deep hip muscle retraining is a common objective of non-operative management for femoroacetabular impingement (FAI) syndrome. These muscles are considered to have an important role in hip joint stabilization, however, it is unclear whether their function is altered in the presence of hip pathology. This exploratory study aimed to investigate activation patterns of the hip muscles during two squatting tasks in individuals with and without FAI syndrome. METHODS: Fifteen individuals with FAI syndrome (symptoms, clinical examination and imaging) and 14 age- and sex-comparable healthy controls underwent testing. Intramuscular fine-wire and surface electrodes recorded electromyographic activity of selected deep and superficial hip muscles during the squatting tasks. Activation patterns from individual muscles were compared between-groups using a wavelet-based linear mixed effects model (P < 0.05). FINDINGS: There were no between-group differences for squat depth or speed during descent or ascent for either task. Participants with FAI syndrome exhibited patterns of activation that differed significantly to controls across all muscles (P < 0.05) when squatting using their preferred strategy. Unlike controls, participants with FAI syndrome exhibited a pattern of activation for obturator internus during descent that was similar in amplitude to ascent, despite the contrasting contraction type (i.e. eccentric vs concentric). INTERPRETATION: Individuals with FAI syndrome appear to implement a protective strategy as the hip descends towards the impingement position. Future studies should examine patients prospectively to establish whether these strategies are counterproductive for pathology and warrant rehabilitation.

Task-specific differences in respiration-related activation of deep and superficial pelvic floor muscles.

The female pelvic floor muscles (PFM) are arranged in distinct superficial and deep layers that function to support the pelvic/abdominal organs and maintain continence, but with some potential differences in function. Although general recordings of PFM activity show amplitude modulation in conjunction with fluctuation in intra-abdominal pressure such as that associated with respiration, it is unclear whether the activities of the two PFM layers modulate in a similar manner. This study aimed to investigate the activation of the deep and superficial PFM during a range of respiratory tasks in different postures. Twelve women without pelvic floor dysfunction participated. A custom-built surface electromyography (EMG) electrode was used to record the activation of the superficial and deep PFM during quiet breathing, breathing with increased dead space, coughing, and maximal and submaximal inspiratory and expiratory efforts. As breathing demand increased, the deep PFM layer EMG had greater coherence with respiratory airflow at the frequency of respiration than the superficial PFM (P = 0.038). During cough, the superficial PFM activated earlier than the deep PFM in the sitting position (P = 0.043). In contrast, during maximal and submaximal inspiratory and expiratory efforts, the superficial PFM EMG was greater than that for the deep PFM (P = 0.011). These data show that both layers of PFM are activated during both inspiration and expiration, but with a bias to greater activation in expiratory tasks/phases. Activation of the deep and superficial PFM layers differed in most of the respiratory tasks, but there was no consistent bias to one muscle layer. NEW & NOTEWORTHY Although pelvic floor muscles are generally considered as a single entity, deep and superficial layers have different anatomies and biomechanics. Here we show task-specific differences in recruitment between layers during respiratory tasks in women. The deep layer was more tightly modulated with respiration than the superficial layer, but activation of the superficial layer was greater during maximal/submaximal occluded respiratory efforts and earlier during cough. These data highlight tightly coordinated recruitment of discrete pelvic floor muscles for respiration.

Shear-wave velocity of the patellar tendon and quadriceps muscle is increased immediately after maximal eccentric exercise.

PURPOSE: To determine whether stiffness of the patellar tendon and quadriceps muscles is altered immediately after and 48 h after a single bout of maximal eccentric exercise of the knee extensor muscles. METHODS: Thirteen healthy individuals [group mean (SD) age 22.4 (3.5) years; 7 female] performed a single bout of maximal eccentric exercise of the non-dominant knee extensors, using an isokinetic dynamometer. Shear-wave velocity (an index of tissue stiffness) was recorded from the patellar tendon, vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL), before, following (post0), and 48 h after (post48) exercise. To investigate features of exercise induced muscle damage, maximal voluntary isometric contraction (MVIC) and self-reported pain and stiffness (numerical rating scales 0 = no pain/stiffness to 100 = worst imaginable pain/stiffness) were measured before, post0, and post48 exercise. Serum creatine kinase (CK) was measured before and post48 exercise. RESULTS: Compared to preexercise, MVIC decreased and self-reported pain and stiffness increased at post0 and post48 and CK levels increased at post48 (all p < 0.01). Compared to preexercise, shear-wave velocity was greater at post0 for the patellar tendon [15.9 (24.6)%, p = 0.01] and RF [23.6 (16.7)%, p < 0.001], each returning to baseline by post48. No significant differences were observed for VL or VM post0 or post48 exercise. CONCLUSION: Maximal eccentric exercise produced an immediate increase in the stiffness of the patellar tendon and RF, resolving by 48 h. As this change was not observed in VL and VM, future studies may explore heterogeneity within synergist muscles following eccentric exercise.

Center of Pressure Motion After Calf Vibration Is More Random in Fallers Than Non-fallers: Prospective Study of Older Individuals.

Aging is associated with changes in balance control and elderly take longer to adapt to changing sensory conditions, which may increase falls risk. Low amplitude calf muscle vibration stimulates local sensory afferents/receptors and affects sense of upright when applied in stance. It has been used to assess the extent the nervous system relies on calf muscle somatosensory information and to rapidly change/perturb part of the somatosensory information causing balance unsteadiness by addition and removal of the vibratory stimulus. This study assessed the effect of addition and removal of calf vibration on balance control (in the absence of vision) in elderly individuals (>65 years, n = 99) who did (n = 41) or did not prospectively report falls (n = 58), and in a group of young individuals (18-25 years, n = 23). Participants stood barefoot and blindfolded on a force plate for 135 s. Vibrators (60 Hz, 1 mm) attached bilaterally over the triceps surae muscles were activated twice for 15 s; after 15 and 75 s (45 s for recovery). Balance measures were applied in a windowed (15 s epoch) manner to compare center-of-pressure (CoP) motion before, during and after removal of calf vibration between groups. In each epoch, CoP motion was quantified using linear measures, and non-linear measures to assess temporal structure of CoP motion [using recurrence quantification analysis (RQA) and detrended fluctuation analysis]. Mean CoP displacement during and after vibration did not differ between groups, which suggests that calf proprioception and/or weighting assigned by the nervous system to calf proprioception was similar for the young and both groups of older individuals. Overall, compared to the elderly, CoP motion of young was more predictable and persistent. Balance measures were not different between fallers and non-fallers before and during vibration. However, non-linear aspects of CoP motion of fallers and non-fallers differed after removal of vibration, when dynamic re-weighting is required. During this period fallers exhibited more random CoP motion, which could result from a reduced ability to control balance and/or a reduced ability to dynamically reweight proprioceptive information. These results show that non-linear measures of balance provide evidence for deficits in balance control in people who go on to fall in the following 12 months.