Achieving maximal voluntary contraction of paraspinal muscles requires two tasks: Insight from an EMG study of females with and without adolescent idiopathic scoliosis.

An accurate estimation of maximal voluntary muscle activation is critical for normalisation in scientific studies. Only a handful of studies appropriately normalise muscle activation data when investigating paraspinal muscle activity in populations such as adolescent idiopathic scoliosis (AIS). This neglect compromises the ability to interpret data. The aim of this study was to determine the type of trunk extension task that reliably achieves peak paraspinal muscle activation in participants with and without AIS. Adolescent females with typically developing spines (controls: n = 20, mean[SD] age 13.1[1.8]years), or primary right thoracic AIS (n = 24, age: 13.8[1.5]years, Cobb angle thoracic: 39.5[16.4]°, lumbar: 28.0[11.6]°) performed a series of 3x unresisted and 3x resisted maximal voluntary trunk extensions in prone. Paraspinal muscle activation was recorded bilaterally at two thoracic levels and one lumbar level using surface electromyography (EMG). Muscle activation was highly repeatable within task [ICC 0.77-0.95, all p < 0.01]. At group level, there were no differences in peak muscle activation between tasks irrespective of side (left/right) or vertebral level (Estimate 0.98, 95%CI 0.36 to 2.65, p=0.97). Peak activation was achieved with the unresisted task in 40.5%, and resisted task in 59.5% of the total outcomes (6 recording locations, 44 participants). Individual participant maximum amplitude varied up to 64% (mean[SD]:18[13]%) between the unresisted and resisted tasks. We recommend that both the resisted and unresisted trunk extension tasks are used to increase confidence that a maximum voluntary activation of paraspinal muscles is achieved. Failure to do so could introduce large error in the estimations of muscle activation.

Shear modulus of lower limb muscles in school-aged children with mild hypotonia.

The objective of this study is to compare shear modulus of lower limb muscles between children with hypotonia versus typical development (TD) or developmental disorders associated with altered tone. Nineteen children with mild hypotonia (mean age 9.4 ± 2.3y, 13 male) completed assessment of resting shear modulus of rectus femoris, biceps femoris (BF), tibialis anterior (TA) and gastrocnemius lateralis (GL) at short and long lengths using shear wave elastography. Data was compared with previous data from TD children and a scoping review for children with developmental disorders. Data were collated according to Net-Longitudinal Tension Angle (Net-LTA), which is the muscle length expressed as the net proximal and distal joint angles. Effects of Net-LTA (e.g., short, neutral, long) were examined according to sex, age and body mass index (BMI). In children with hypotonia, shear modulus was: higher at longer versus shorter lengths for four muscles (p < 0.01); correlated with age for BF-short (r = 0.60, p < 0.03) and GL-short (r = -0.54, p < 0.03), with BMI for BF-short (r = 0.71, p < 0.05); and not different between sexes (p > 0.05). The shear modulus values for lower limb muscles for children with mild hypotonia were lower than those for children with Duchenne Muscular Dystrophy (TA-neutral), or Cerebral Palsy (GL-neutral), but not TD children (all four muscles). In conclusion, shear modulus increases with longer muscle length (i.e. higher Net-LTA) in mildly hypotonic children. Children with mild hypotonia have lower shear modulus than children with cerebral palsy and Duchenne muscular dystrophy.

Consensus for experimental design in electromyography (CEDE) project: Application of EMG to estimate muscle force.

Skeletal muscles power movement. Deriving the forces produced by individual muscles has applications across various fields including biomechanics, robotics, and rehabilitation. Since direct in vivo measurement of muscle force in humans is invasive and challenging, its estimation through non-invasive methods such as electromyography (EMG) holds considerable appeal. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, summarizes recommendations on the use of EMG to estimate muscle force. The matrix encompasses the use of bipolar surface EMG, high density surface EMG, and intra-muscular EMG (1) to identify the onset of muscle force during isometric contractions, (2) to identify the offset of muscle force during isometric contractions, (3) to identify force fluctuations during isometric contractions, (4) to estimate force during dynamic contractions, and (5) in combination with musculoskeletal models to estimate force during dynamic contractions. For each application, recommendations on the appropriateness of using EMG to estimate force and justification for each recommendation are provided. The achieved consensus makes clear that there are limited scenarios in which EMG can be used to accurately estimate muscle forces. In most cases, it remains important to consider the activation as well as the muscle state and other biomechanical and physiological factors- such as in the context of a formal mechanical model. This matrix is intended to encourage interdisciplinary discussions regarding the integration of EMG with other experimental techniques and to promote advances in the application of EMG towards developing muscle models and musculoskeletal simulations that can accurately predict muscle forces in healthy and clinical populations.

The Volitional Control of Individual Motor Units Is Constrained within Low-Dimensional Neural Manifolds by Common Inputs.

The implementation of low-dimensional movement control by the central nervous system has been debated for decades. In this study, we investigated the dimensionality of the control signals received by spinal motor neurons when controlling either the ankle or knee joint torque. We first identified the low-dimensional latent factors underlying motor unit activity during torque-matched isometric contractions in male participants. Subsequently, we evaluated the extent to which motor units could be independently controlled. To this aim, we used an online control paradigm in which participants received the corresponding motor unit firing rates as visual feedback. We identified two main latent factors, regardless of the muscle group (vastus lateralis-medialis and gastrocnemius lateralis-medialis). The motor units of the gastrocnemius lateralis could be controlled largely independently from those of the gastrocnemius medialis during ankle plantarflexion. This dissociation of motor unit activity imposed similar behavior to the motor units that were not displayed in the feedback. Conversely, it was not possible to dissociate the activity of the motor units between the vastus lateralis and medialis muscles during the knee extension tasks. These results demonstrate that the number of latent factors estimated from linear dimensionality reduction algorithms does not necessarily reflect the dimensionality of volitional control of motor units. Overall, individual motor units were never controlled independently of all others but rather belonged to synergistic groups. Together, these findings provide evidence for a low-dimensional control of motor units constrained by common inputs, with notable differences between muscle groups.

Development of a novel technique to insert intramuscular electromyography electrodes into the deep intrinsic foot muscles via the dorsum of the foot.

This study aimed to develop an insertion technique for intramuscular EMG recording of the oblique head of adductor hallucis (AddH) and first dorsal interosseous (FDI) muscles in humans via the dorsum of the foot, and report feasibility of intramuscular EMG data acquisition during walking in shoes. In eight individuals without musculoskeletal pain or injury (5 males; 32 ± 8 years), intramuscular electrodes were inserted into AddH (oblique head) and FDI through the right foot's dorsum (between metatarsals I-II) with ultrasound guidance. The ultrasound transducer was positioned on the plantar surface. Intramuscular EMG was also recorded from abductor hallucis, tibialis posterior, flexor digitorum longus and peroneus longus. Participants performed six overground walking trials wearing modified shoes, and rated pain associated with the intramuscular electrodes during walking (numerical rating scale, 0-10). High-quality EMG recordings were obtained from intrinsic and extrinsic foot muscles. Analyses of power spectral densities indicated that movement artefacts commonly observed during gait were removed by filtering. Pain associated with AddH/FDI electrodes during walking was low (median[IQR] 1[2]; range 0-4) and similar to other sites. Findings demonstrate that intramuscular EMG recording from AddH (oblique head) and FDI using this insertion technique is feasible and associated with minimal pain when walking in shoes.

Consensus for experimental design in electromyography (CEDE) project: Checklist for reporting and critically appraising studies using EMG (CEDE-Check).

The diversity in electromyography (EMG) techniques and their reporting present significant challenges across multiple disciplines in research and clinical practice, where EMG is commonly used. To address these challenges and augment the reproducibility and interpretation of studies using EMG, the Consensus for Experimental Design in Electromyography (CEDE) project has developed a checklist (CEDE-Check) to assist researchers to thoroughly report their EMG methodologies. Development involved a multi-stage Delphi process with seventeen EMG experts from various disciplines. After two rounds, consensus was achieved. The final CEDE-Check consists of forty items that address four critical areas that demand precise reporting when EMG is employed: the task investigated, electrode placement, recording electrode characteristics, and acquisition and pre-processing of EMG signals. This checklist aims to guide researchers to accurately report and critically appraise EMG studies, thereby promoting a standardised critical evaluation, and greater scientific rigor in research that uses EMG signals. This approach not only aims to facilitate interpretation of study results and comparisons between studies, but it is also expected to contribute to advancing research quality and facilitate clinical and other practical applications of knowledge generated through the use of EMG.

Comparison of physiological and behavioral nutrition-related factors in people with and without adolescent idiopathic scoliosis, from cohort data at 8 to 20 years.

Nutrition-related variables including lower body mass index (BMI), lower bone mineral density (BMD), altered body composition and hormone levels have been reported in adolescent idiopathic scoliosis (AIS). The aims of this study were to determine if physiological and behavioral nutrition-related factors differ between people with and without AIS, and to quantify their relationship with AIS, in unbiased cohort sample. BMI, presence of an eating disorder, leptin, adiponectin, BMD, vitamin D, lean mass, and fat mass were compared between those with and without AIS at ages 8, 10, 14, 17, and 20 years, and multiple logistic regression was performed between these variables and AIS. Lower total body BMD (median, 1.0 g/cm2 vs 1.1 g/cm2; p = .03) and lean mass (median, 38.8 kg vs 46.0 kg; p = .04) at age 20 years were observed in those with AIS compared to those without scoliosis. At age 20, the odds of AIS were 3.23 times higher for adolescents with an eating disorder compared to those with no eating disorder (95% CI, 1.02-8.63) when adjusted for BMI. Every 1 kg/m2 increase in BMI decreased the odds of AIS by 0.88 times (95% CI, 0.76-0.98), after adjusting for eating disorder diagnosis. In conclusion, lower BMI in mid-adolescence and presence of eating disorder outcomes, lower BMD, and lower lean mass in late adolescence were associated with the presence of AIS. Current data do not explain the mechanisms for these associations but suggest that serum leptin, adiponectin, and vitamin D are unlikely to be contributing factors. Conclusive determination of the prevalence of eating disorders in AIS will require further studies with larger sample sizes.

Response to letter to editor: The association between hip strength, physical function and dynamic balance in people with unilateral knee osteoarthritis: A cross-sectional study.

We thank the reader for their interest and response to our study investigating the association between clinical measures of hip strength in multiple directions and physical function (including dynamic balance) in people with knee osteoarthritis. Below, we provide a response to their questions, in turn.

Neuromechanical Properties of the Vastus Medialis and Vastus Lateralis in Adolescents With Patellofemoral Pain.

Background: An alteration in the force distribution among quadriceps heads is one possible underlying mechanism of patellofemoral pain. However, this hypothesis cannot be directly tested as there are currently no noninvasive experimental techniques to measure individual muscle force or torque in vivo in humans. In this study, the authors considered a combination of biomechanical and muscle activation measures, which enabled us to estimate the mechanical impact of the vastus medialis (VM) and vastus lateralis (VL) on the patella. Purpose/Hypothesis: The purpose of this study was to determine whether the relative index of torque distribution for the VM and VL differs between adolescents with and without patellofemoral pain. It was hypothesized that, relative to the VL, the VM would contribute less to knee extension torque in adolescents with patellofemoral pain compared with controls. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Twenty adolescents with patellofemoral pain and 20 matched control participants were included (38 female; age, 15.3 ± 1.8 years; weight, 58 ± 13 kg; height, 164 ± 8 cm). Muscle volumes and resting moment arms were quantified from magnetic resonance images, and fascicle lengths were obtained from panoramic B-mode ultrasonography. Muscle activation was estimated using surface electromyography during submaximal isometric tasks (wall-squat and seated tasks). Muscle torque was estimated as the product of muscle physiological cross-sectional area (ie, muscle volume/fascicle length), muscle activation (normalized to maximal activation), and moment arm. Results: Across tasks and force levels, the relative contribution of the VM to the overall medial and lateral vastii torque was 31.0% ± 8.6% for controls and 31.5 ± 7.6% for adolescents with patellofemoral pain (group effect, P > .34). Conclusion: For the tasks and positions investigated in this study, the authors found no evidence of lower VM torque generation (relative to the VL) in adolescents with patellofemoral pain compared with controls.

Quantifying Muscle Size Asymmetry in Adolescent Idiopathic Scoliosis Using Three-dimensional Magnetic Resonance Imaging.

STUDY DESIGN: This is a case-control study of prospectively collected data. OBJECTIVE: To quantify paraspinal muscle size asymmetry in adolescent idiopathic scoliosis (AIS) and determine if this asymmetry is (i) greater than observed in adolescent controls with symmetrical spines; and (ii) positively associated with skeletal maturity using Risser grade, scoliosis severity using the Cobb angle, and chronological age in years. SUMMARY OF BACKGROUND DATA: AIS is a three-dimensional deformity of the spine which occurs in 2.5% to 3.7% of the Australian population. There is some evidence of asymmetry in paraspinal muscle activation and morphology in AIS. Asymmetric paraspinal muscle forces may facilitate asymmetric vertebral growth during adolescence. METHODS: An asymmetry index [Ln(concave/convex volume)] of deep and superficial paraspinal muscle volumes, at the level of the major curve apex (Thoracic 8-9 th vertebral level) and lower-end vertebrae ( LEV , Thoracic 10-12 th vertebral level), was determined from three-dimensional Magnetic Resonance Imaging of 25 adolescents with AIS (all right thoracic curves), and 22 healthy controls (convex=left); all female, 10 to 16 years. RESULTS: Asymmetry index of deep paraspinal muscle volumes was greater in AIS (0.16±0.20) than healthy spine controls (-0.06±0.13) at the level of the apex ( P <0.01, linear mixed-effects analysis) but not LEV ( P >0.05). Asymmetry index was positively correlated with Risser grade ( r =0.50, P <0.05) and scoliosis Cobb angle ( r =0.45, P <0.05), but not age ( r =0.34, P >0.05). There was no difference in the asymmetry index of superficial paraspinal muscle volumes between AIS and controls ( P >0.05). CONCLUSIONS: The asymmetry of deep apical paraspinal muscle volume in AIS at the scoliosis apex is greater than that observed at equivalent vertebral levels in controls and may play a role in the pathogenesis of AIS.

Influence of internal muscle properties on muscle shape change and gearing in the human gastrocnemii.

Skeletal muscles bulge when they contract. These three-dimensional shape changes, coupled with fiber rotation, influence a muscle's mechanical performance by uncoupling fiber velocity from muscle belly velocity (i.e., gearing). Muscle shape change and gearing are likely mediated by the interaction between internal muscle properties and contractile forces. Muscles with greater stiffness and intermuscular fat, due to aging or disuse, may limit a muscle's ability to bulge in width, subsequently causing higher gearing. The aim of this study was to determine the influence of internal muscle properties on shape change, fiber rotation, and gearing in the medial (MG) and lateral gastrocnemii (LG) during isometric plantar flexion contractions. Multimodal imaging techniques were used to measure muscle shear modulus, intramuscular fat, and fat-corrected physiological cross-sectional area (PCSA) at rest, as well as synchronous muscle architecture changes during submaximal and maximal contractions in the MG and LG of 20 young (24 ± 3 yr) and 13 older (70 ± 4 yr) participants. Fat-corrected PCSA was positively associated with fiber rotation, gearing, and changes in thickness during submaximal contractions, but it was negatively associated with changes in thickness at maximal contractions. Muscle stiffness and intramuscular fat were related to muscle bulging and reduced fiber rotation, respectively, but only at high forces. Furthermore, the MG and LG had varied internal muscle properties, which may relate to the differing shape changes, fiber rotations, and gearing behaviors observed at each contraction level. These results indicate that internal muscle properties may play an important role in mediating in vivo muscle shape change and gearing, especially during high-force contractions.NEW & NOTEWORTHY Here, we measured internal muscle properties in vivo to determine their influence on the varying shape change and gearing behaviors in the synergistic gastrocnemii muscles. These relationships have previously only been hypothesized or examined within isolated muscles during supramaximal contractions. Our results contribute to a more comprehensive understanding of the factors that influence a muscle's mechanical response to force with implications for preventing or treating muscle deficits associated with aging, disease, and disuse.

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.

The association between hip strength, physical function and dynamic balance in people with unilateral knee osteoarthritis: A cross-sectional study.

BACKGROUND: In people with knee osteoarthritis, the association between multidirectional hip strength and physical function or balance is unknown. OBJECTIVE: To determine the relationship between hip flexion, extension, abduction, adduction, external and internal rotation strength and (1) physical function and (2) dynamic balance. DESIGN: Cross-sectional. METHODS: Forty-seven participants (20 men and 27 women, age 66.2 ± 8.2 years) with unilateral knee osteoarthritis were included. Hip strength was assessed with hand-held dynamometry; physical function was assessed with the 40m fast-paced walk test (40mFPWT), 30-s chair-stand test (30sCST), and stair-climb test (SCT); and dynamic balance was assessed in 3 directions using the Star Excursion Balance Test. Multivariable linear regression analysis was used to determine the strength of relationships between measures. RESULTS: Hip strength, in all directions except for internal rotation, was positively associated with better physical function (40mFPWT: R2 = 0.48 to 0.65; SCT: R2 = 0.5 to 0.54; 30sCST: R2 = 0.39 to 0.42), and dynamic balance (anterior: R2 = 0.33 to 0.45; posteromedial: R2 = 0.32 to 0.45; posterolateral: R2 = 0.27 to 0.35). Hip strength, after adjusting for knee extension strength, explained an additional 8%-12% (p < 0.05) and 5%-12% (p < 0.05) reach in the anterior and posteromedial directions of the Star Excursion Balance Test, respectively. CONCLUSIONS: Hip strength in multiple directions is associated with measures of physical function and dynamic balance in people with unilateral knee osteoarthritis. Clinicians are encouraged to consider hip strength in multiple directions in the context of the patients' functional and/or balance goals when developing exercise programs for people with knee osteoarthritis.

Consensus for experimental design in electromyography (CEDE) project: Single motor unit matrix.

The analysis of single motor unit (SMU) activity provides the foundation from which information about the neural strategies underlying the control of muscle force can be identified, due to the one-to-one association between the action potentials generated by an alpha motor neuron and those received by the innervated muscle fibers. Such a powerful assessment has been conventionally performed with invasive electrodes (i.e., intramuscular electromyography (EMG)), however, recent advances in signal processing techniques have enabled the identification of single motor unit (SMU) activity in high-density surface electromyography (HDsEMG) recordings. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, provides recommendations for the recording and analysis of SMU activity with both invasive (needle and fine-wire EMG) and non-invasive (HDsEMG) SMU identification methods, summarizing their advantages and disadvantages when used during different testing conditions. Recommendations for the analysis and reporting of discharge rate and peripheral (i.e., muscle fiber conduction velocity) SMU properties are also provided. The results of the Delphi process to reach consensus are contained in an appendix. This matrix is intended to help researchers to collect, report, and interpret SMU data in the context of both research and clinical applications.

Reproducibility of Hypermobility Assessment Scales for Children When Performed Using Telehealth versus In-Person Modes.

AIMS: Evaluate reproducibility of hypermobility assessments using in-person versus telehealth modes. METHODS: Hypermobility of 20 children (7-12 years) was evaluated using the Beighton Score, Upper Limb Hypermobility Assessment Tool (ULHAT), and Lower Limb Assessment Score (LLAS) via in-person and telehealth modes. Agreement between the two modes was examined using percentage of exact agreement (%EA and %EA ± 2), Limits of Agreement (LoA) and Smallest detectable change (SDC). Reliability was calculated using intra-class correlation coefficients (ICCs). RESULTS: Agreement between modes for total Scores was best for the Beighton (%EA = fair, %EA ± 2 = good), then the ULHAT (%EA = poor, %EA ± 2 = excellent), and LLAS (%EA = poor, %EA ± 2 = fair). Total scores for all scales showed wide LoA, large SDC (25-31%), and fair to good reliability (ICC = 0.54-0.61). Exact agreement for Generalized Joint Hypermobility classification was excellent for the Beighton (≥7/9 threshold) and fair for the ULHAT and LLAS (≥7/12 threshold). Percentage of individual test items with good/excellent agreement was highest for the Beighton (78%, 7/9 items), then the ULHAT (58%, 14/24) and LLAS (42%, 10/24). CONCLUSION: Total Scores of hypermobility scales showed low exact agreement between in-person and telehealth, but fair-excellent agreement within two points. Classification using the Beighton ≥7/9 threshold was excellent. Research is recommended to increase accuracy of online assessments.

Hip strength, quadriceps strength and dynamic balance are lower in people with unilateral knee osteoarthritis compared to their non-affected limb and asymptomatic controls.

BACKGROUND: There is insufficient literature on multi-directional hip strength differences and dynamic balance between people with knee osteoarthritis (KOA) and healthy controls. OBJECTIVE: In people with unilateral KOA, determine if hip/knee strength and dynamic balance differs (i) between sides, and (ii) compared to controls. METHODS: Thirty-six participants (17 women; 65.5 ± 8.9 years) with unilateral KOA and 36 age- and sex-matched controls were included in a cross-sectional study. Outcomes included hip strength, quadriceps strength, and dynamic balance (three directions) during the Star Excursion Balance Test. Mixed ANOVA analysis was completed to investigate differences between Limbs and Groups. Mean differences (MD) and 95% confidence intervals (CI) were calculated. RESULTS: Quadriceps and hip adduction strength were 16% (95%CI:10, 22) and 9% [95%CI: 3, 16) lower on the affected compared to non-affected side. Quadriceps and hip abduction, adduction, flexion, and extension strength (MD varying from 16%, 95%CI: 8, 25; to 34%, 95%CI: 17, 50) were weaker bilaterally in individuals with KOA compared to control. Posteromedial balance was 4% (95%CI: 2, 6) lower for affected compared to non-affected limbs in those with KOA and 13% (95%CI: 6, 21) lower in the affected limb compared to controls. Individuals with KOA had lower balance bilaterally in the anterior 11% (95%CI: 7, 15) and posterolateral 21% (95%CI: 13, 30) directions. CONCLUSION: Hip/knee strength (especially in the sagittal and frontal planes) and dynamic balance are lower bilaterally in people with KOA compared to controls. Hip adduction strength is lower on the affected than non-affected limbs of people with KOA. Clinicians should consider that knee extension strength, hip strength, and dynamic balance are lower bilaterally in people with unilateral KOA.

No Difference in Hip Muscle Volumes and Fatty Infiltration in Those With Hip-Related Pain Compared to Controls.

Background: Little is known about muscle morphology in people with hip-related pain, without signs of femoro-acetabular impingement syndrome (FAIS). Identifying changes in hip muscle volume, fatty infiltrate and establishing relationships between muscle volume and strength, may provide insight into potential early treatment strategies. Purposes: To: (i) compare the volumes and fatty infiltrate of gluteus maximus, gluteus medius, gluteus minimis, tensor fascia latae and quadratus femoris between symptomatic and less-symptomatic sides of participants with hip-related pain; (ii) compare the volumes and fatty infiltrate of hip muscles between healthy controls and symptomatic participants; and (iii) explore relationships of hip muscle volumes to muscle strength and patient-reported outcome measures in people with hip-related pain. Study Design: Cross-sectional study. Methods: Muscle volume and fatty infiltrate (from magnetic resonance imaging), hip muscle strength, patient-reported symptoms, function and quality of life (QOL) were determined for 16 participants with hip-related pain (no clinical signs of FAIS; 37±9 years) and 15 controls (31±9 years). Using One Way Analysis of Co-Variance tests, muscle volume and fatty infiltrate was compared between the symptomatic and less-symptomatic sides in participants with hip-related pain as well as between healthy controls and symptomatic participants. In addition, hip muscle volume was correlated with hip muscle strength, hip-reported symptoms, function and QOL. Results: No differences in all the studied muscle volumes or fatty infiltrate were identified between the symptomatic and less-symptomatic hips of people with hip-related pain; or between people with and without hip-related pain. Greater GMED volume on the symptomatic side was associated with less symptoms and better function and QOL (ρ=0.522-0.617) for those with hip-related pain. Larger GMAX volume was associated with greater hip abduction and internal rotation strength, larger GMED volume was associated with greater hip extension strength, and larger QF volume was associated with greater hip abduction strength (rho=0.507-0.638). Conclusion: People with hip-related pain and no clinical signs of FAIS have hip muscle volumes that are not significantly different than those of matched pain-free controls or their less-symptomatic hip. Larger GMED muscle volume was associated with fewer symptoms and greater strength. Level of evidence: Level 3a.

Motor Unit Recruitment is Altered When Acute Experimental Pain is Induced at a Site Distant to the Contracting Muscle.

Acute pain alters motor unit discharge properties in muscles that are painful or influence loading of painful structures. Less is known about the changes in discharge when pain is induced in distant tissues that are unable or have limited capacity to modify the load of the contracting muscle. We aimed to determine whether acute experimental pain alters quadriceps motor unit discharge when pain is induced in; (i) a muscle that is unlikely to be mechanically influenced by modified quadriceps activity (tibialis anterior: TA), or (ii) the antagonist muscle (biceps femoris: BF). Using a within-subject design, 16 adults performed force-matched isometric knee extension during pain-free control conditions, and trials after painful hypertonic saline injections into TA or BF. Surface and intramuscular electromyography recordings were made. Despite maintained force, discharge rate of quadriceps motor units was lower during Pain than Control conditions for TA and BF trials (both P < 0.001). Redistribution of motor unit activity was observed; some units were recruited in control or pain but not both. As modified quadriceps motor unit discharge has limited/no potential to modify load in the painful tissue to protect the painful part, the findings might support an alternative hypothesis that activity is redistributed to larger motor units.

Adolescent perspectives on participating in a feasibility trial investigating shoe inserts for patellofemoral pain.

BACKGROUND: Patellofemoral pain (PFP) affects one-quarter of adolescents, yet there are few evidence-informed recommendations to treat PFP in this population. HAPPi Kneecaps! is a randomised, controlled, participant- and assessor-blind, parallel-group feasibility trial of shoe inserts for adolescents with PFP. The aim of this qualitative study was to explore adolescents' perspectives of participating in HAPPi Kneecaps!. METHODS: All 36 adolescents with PFP from the HAPPi Kneecaps! study were invited to participate in semi-structured interviews. We used a descriptive qualitative methodology underpinned by a relativist framework to investigate adolescents' perspectives on participating in the trial. Inductive thematic analysis was used to examine patterns regarding how each adolescent experienced the HAPPi Kneecaps! study within their social, cultural, and historical contexts. RESULTS: 14 out of 36 HAPPi Kneecaps! participants provided consent and participated in interviews (12 females; mean [SD] age 14.9 [2.4] years). Overall, most adolescents responded positively when discussing their experience, such as improvements in their knee pain and satisfaction with how the study was run. Major themes that were generated from the analysis and feedback were: (1) shoe inserts require little effort to use; (2) perceptions of the program were generally positive; (3) participation in the trial could be made easier; (4) warm weather matters; and (5) life happens. CONCLUSION: Adolescents with PFP who participated in the HAPPi Kneecaps! study found that shoe inserts were easy to wear. Most adolescents experienced an improvement in their symptoms and enhanced participation in sport and exercise. Adolescents with PFP prefer an option for warmer climates (e.g. flip flops or sandals), access to online logbooks, and clinicians who are easily accessible. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12619000957190 . Date registered: 8/07/2019.

Consensus for experimental design in electromyography (CEDE) project: High-density surface electromyography matrix.

High-density surface electromyography (HDsEMG) can be used to measure the spatial distribution of electrical muscle activity over the skin. As this distribution is associated with the generation and propagation of muscle fiber action potentials, HDsEMG is processed to extract information on regional muscle activation, muscle fiber characteristics and behaviour of individual motor units. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, summarizes recommendations on the use of HDsEMG in experimental studies. For each application, recommendations are included regarding electrode montage, electrode type and configuration, electrode location and orientation, data analysis, and interpretation. Cautions and reporting standards are also included. The steps of the Delphi process to reach consensus are contained in an appendix. This matrix is intended to help researchers when collecting, reporting, and interpreting HDsEMG data. It is hoped that this document will be used to generate new empirical evidence to improve how HDsEMG is used in research and in clinical applications.