Matching One Sample According to Two Criteria in Observational Studies.

Multivariate matching has two goals: (i) to construct treated and control groups that have similar distributions of observed covariates, and (ii) to produce matched pairs or sets that are homogeneous in a few key covariates. When there are only a few binary covariates, both goals may be achieved by matching exactly for these few covariates. Commonly, however, there are many covariates, so goals (i) and (ii) come apart, and must be achieved by different means. As is also true in a randomized experiment, similar distributions can be achieved for a high-dimensional covariate, but close pairs can be achieved for only a few covariates. We introduce a new polynomial-time method for achieving both goals that substantially generalizes several existing methods; in particular, it can minimize the earthmover distance between two marginal distributions. The method involves minimum cost flow optimization in a network built around a tripartite graph, unlike the usual network built around a bipartite graph. In the tripartite graph, treated subjects appear twice, on the far left and the far right, with controls sandwiched between them, and efforts to balance covariates are represented on the right, while efforts to find close individual pairs are represented on the left. In this way, the two efforts may be pursued simultaneously without conflict. The method is applied to our on-going study in the Medicare population of the relationship between superior nursing and sepsis mortality. The match2C package in R implements the method.

Investigation of hospital discharge cases and SARS-CoV-2 introduction into Lothian care homes.

BACKGROUND: The first epidemic wave of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in Scotland resulted in high case numbers and mortality in care homes. In Lothian, over one-third of care homes reported an outbreak, while there was limited testing of hospital patients discharged to care homes. AIM: To investigate patients discharged from hospitals as a source of SARS-CoV-2 introduction into care homes during the first epidemic wave. METHODS: A clinical review was performed for all patients discharges from hospitals to care homes from 1st March 2020 to 31st May 2020. Episodes were ruled out based on coronavirus disease 2019 (COVID-19) test history, clinical assessment at discharge, whole-genome sequencing (WGS) data and an infectious period of 14 days. Clinical samples were processed for WGS, and consensus genomes generated were used for analysis using Cluster Investigation and Virus Epidemiological Tool software. Patient timelines were obtained using electronic hospital records. FINDINGS: In total, 787 patients discharged from hospitals to care homes were identified. Of these, 776 (99%) were ruled out for subsequent introduction of SARS-CoV-2 into care homes. However, for 10 episodes, the results were inconclusive as there was low genomic diversity in consensus genomes or no sequencing data were available. Only one discharge episode had a genomic, time and location link to positive cases during hospital admission, leading to 10 positive cases in their care home. CONCLUSION: The majority of patients discharged from hospitals were ruled out for introduction of SARS-CoV-2 into care homes, highlighting the importance of screening all new admissions when faced with a novel emerging virus and no available vaccine.

Prenatally diagnosed coronary artery abnormalities in hypoplastic left heart syndrome are associated with a higher probability of heart transplantation.

OBJECTIVE: Coronary artery abnormalities (CA) occur in patients with hypoplastic left heart syndrome (HLHS) and may be associated with higher mortality and heart transplantation (HT). We aimed to determine whether fetuses with HLHS and prenatal CA have a higher risk of death or HT. METHODS: We performed a retrospective review of fetal echocardiograms with HLHS from 2011 to 2018. We excluded fetuses with ventricular septal defects, elective termination, death in utero, planned postnatal non-intervention, or absent follow-up data. Presence or absence of CA was determined by review of serial fetal echocardiograms. Survival analysis was used to evaluate the relationship between prenatal CA and death or HT. RESULTS: Of 86 patients with fetal HLHS, 11 had prenatal diagnosis of CA. Of these, six required HT and five died (one after undergoing HT); only one remains alive without HT. Of those without prenatal CA (n = 75), 25 died and 7 underwent HT. Patients with prenatal diagnosis of HLHS and CA had a significantly increased likelihood of death or HT (p-value <0.05). CONCLUSION: Prenatal diagnosis of CA in our cohort of patients with HLHS was associated with increased risk of death or HT. These data have significance for prenatal counseling and postnatal management.

Determination of the

We report the first measurement of the parity-violating elastic electron scattering asymmetry on ^{27}Al. The ^{27}Al elastic asymmetry is A_{PV}=2.16±0.11(stat)±0.16(syst) ppm, and was measured at ⟨Q^{2}⟩=0.02357±0.00010 GeV^{2}, ⟨θ_{lab}⟩=7.61°±0.02°, and ⟨E_{lab}⟩=1.157 GeV with the Q_{weak} apparatus at Jefferson Lab. Predictions using a simple Born approximation as well as more sophisticated distorted-wave calculations are in good agreement with this result. From this asymmetry the ^{27}Al neutron radius R_{n}=2.89±0.12 fm was determined using a many-models correlation technique. The corresponding neutron skin thickness R_{n}-R_{p}=-0.04±0.12 fm is small, as expected for a light nucleus with a neutron excess of only 1. This result thus serves as a successful benchmark for electroweak determinations of neutron radii on heavier nuclei. A tree-level approach was used to extract the ^{27}Al weak radius R_{w}=3.00±0.15 fm, and the weak skin thickness R_{wk}-R_{ch}=-0.04±0.15 fm. The weak form factor at this Q^{2} is F_{wk}=0.39±0.04.

Precision Measurement of the Beam-Normal Single-Spin Asymmetry in Forward-Angle Elastic Electron-Proton Scattering.

A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to the imaginary part of the two-photon exchange process. We report a 2% precision measurement of the beam-normal single-spin asymmetry in elastic electron-proton scattering with a mean scattering angle of θ_{lab}=7.9° and a mean energy of 1.149 GeV. The asymmetry result is B_{n}=-5.194±0.067(stat)±0.082 (syst) ppm. This is the most precise measurement of this quantity available to date and therefore provides a stringent test of two-photon exchange models at far-forward scattering angles (θ_{lab}→0) where they should be most reliable.

The widespread use of topical antimicrobials enriches for resistance in Staphylococcus aureus isolated from patients with atopic dermatitis.

BACKGROUND: Carriage rates of Staphylococcus aureus on affected skin in atopic dermatitis (AD) are approximately 70%. Increasing disease severity during flares and overall disease severity correlate with increased burden of S. aureus. Treatment in AD therefore often targets S. aureus with topical and systemic antimicrobials. OBJECTIVES: To determine whether antimicrobial sensitivities and genetic determinants of resistance differed in S. aureus isolates from the skin of children with AD and healthy child nasal carriers. METHODS: In this case-control study, we compared S. aureus isolates from children with AD (n = 50) attending a hospital dermatology department against nasal carriage isolates from children without skin disease (n = 49) attending a hospital emergency department for noninfective conditions. Using whole genome sequencing we generated a phylogenetic framework for the isolates based on variation in the core genome, then compared antimicrobial resistance phenotypes and genotypes between disease groups. RESULTS: Staphylococcus aureus from cases and controls had on average similar numbers of phenotypic resistances per isolate. Case isolates differed in their resistance patterns, with fusidic acid resistance (FusR ) being significantly more frequent in AD (P = 0·009). The genetic basis of FusR also differentiated the populations, with chromosomal mutations in fusA predominating in AD (P = 0·049). Analysis revealed that FusR evolved multiple times and via multiple mechanism in the population. Carriage of plasmid-derived qac genes, which have been associated with reduced susceptibility to antiseptics, was eight times more frequent in AD (P = 0·016). CONCLUSIONS: The results suggest that strong selective pressure drives the emergence and maintenance of specific resistances in AD.

Evaluation of Staphylococcus aureus eradication therapy in orthopaedic surgery.

PURPOSE: Despite WHO recommendations, there is currently no national screening and eradication policy for the detection of methicillin-sensitive Staphylococcus aureus (MSSA) in the UK prior to elective orthopaedic surgery. This study aimed to evaluate the effectiveness of current standard methicillin-resistant S. aureus (MRSA) eradication therapies in the context of S. aureus (both MRSA and MSSA) decolonization in an elective orthopaedic population. METHODOLOGY: A total of 100 patients awaiting joint replacement surgery who were positive for S. aureus on PCR nasal screening underwent the current standard MRSA pre-operative decolonization regimen for 5 days. Prior to commencement of the eradication therapy, swabs of the anterior nares, throat and perineum were taken for culture. Further culture swabs were taken at 48-96 h following treatment, at hospital admission for surgery and at hospital discharge. Following the completion of treatment, patients were asked to provide feedback on their experience using Likert rating scales. The primary outcome of this study was S. aureus clearance 48-96 h following eradication treatment.Results/Key Findings. Clearance of S. aureus 48-96 h following treatment was 94 % anterior nares, 66 % throat and 88 % groin. Mean completion with nasal mupirocin was 98 %. There was no statistically significant recolonization effect between the end of the eradication treatment period and the day of surgery (P>0.05) at a median time of 10 days. CONCLUSION: Current MRSA decolonisation regimens are well tolerated and effective for MSSA decolonization for the anterior nares and groin. The decolonization effect is preserved for at least 10 days following treatment.

Underestimation of Staphylococcus aureus (MRSA and MSSA) carriage associated with standard culturing techniques: One third of carriers missed.

OBJECTIVES: Nasal carriers of Staphylococcus (S.) aureus (MRSA and MSSA) have an increased risk for healthcare-associated infections. There are currently limited national screening policies for the detection of S. aureus despite the World Health Organization's recommendations. This study aimed to evaluate the diagnostic performance of molecular and culture techniques in S. aureus screening, determine the cause of any discrepancy between the diagnostic techniques, and model the potential effect of different diagnostic techniques on S. aureus detection in orthopaedic patients. METHODS: Paired nasal swabs for polymerase chain reaction (PCR) assay and culture of S. aureus were collected from a study population of 273 orthopaedic outpatients due to undergo joint arthroplasty surgery. RESULTS: The prevalence of MSSA nasal colonization was found to be between 22.4% to 35.6%. The current standard direct culturing methods for detecting S. aureus significantly underestimated the prevalence (p = 0.005), failing to identify its presence in approximately one-third of patients undergoing joint arthroplasty surgery. CONCLUSION: Modelling these results to national surveillance data, it was estimated that approximately 5000 to 8000 S. aureus surgical site infections could be prevented, and approximately $140 million to $950 million (approximately £110 million to £760 million) saved in treatment costs annually in the United States and United Kingdom combined, by using alternative diagnostic methods to direct culture in preoperative S. aureus screening and eradication programmes.Cite this article: S. T. J. Tsang, M. P. McHugh, D. Guerendiain, P. J. Gwynne, J. Boyd, A. H. R. W. Simpson, T. S. Walsh, I. F. Laurenson, K. E. Templeton. Underestimation of Staphylococcus aureus (MRSA and MSSA) carriage associated with standard culturing techniques: One third of carriers missed. Bone Joint Res 2018;7:79-84. DOI: 10.1302/2046-3758.71.BJR-2017-0175.R1.

The Ultra-High-Risk for psychosis groups: Evidence to maintain the status quo.

Individuals are considered Ultra-High-Risk (UHR) for psychosis if they meet a set of standardised criteria including presumed genetic vulnerability (Trait), or a recent history of Attenuated Psychotic Symptoms (APS) or Brief Limited Intermittent Psychotic Symptoms (BLIPS). Recent calls to revise these criteria have arisen from evidence that Trait, APS and BLIPS groups may transition to psychosis at different rates. Concurrently, it has become clear that the UHR status confers clinical risk beyond transition to psychosis. Specifically, most UHR individuals will not develop psychosis, but will experience high rates of non-psychotic disorders, persistent APS and poor long-term functional outcomes. Rather than focus on transition, the present study investigated whether UHR groups differ in their broader clinical risk profile by examining baseline clinical characteristics and long-term outcomes other than transition to psychosis. Four UHR groups were defined: Trait-only, APS-only, Trait+APS, and any BLIPS. Participants (N=702) were recruited upon entry to early intervention services and followed-up over a period of up to 13years (mean=4.53, SD=3.84). The groups evidenced similar symptom severity (SANS for negative symptoms, BPRS for positive and depression/anxiety symptoms) and psychosocial functioning (SOFAS, GAF, QLS) at baseline and follow-up as well as similar prevalence of non-psychotic disorders at follow-up. Our findings demonstrate that UHR groups evidence a similar clinical risk profile when we expand this beyond transition to psychosis, and consequently support maintaining the existing UHR criteria.

The reporting of study and population characteristics in degenerative cervical myelopathy: A systematic review.

OBJECT: Degenerative cervical myelopathy [DCM] is a disabling and increasingly prevalent condition. Variable reporting in interventional trials of study design and sample characteristics limits the interpretation of pooled outcomes. This is pertinent in DCM where baseline characteristics are known to influence outcome. The present study aims to assess the reporting of the study design and baseline characteristics in DCM as the premise for the development of a standardised reporting set. METHODS: A systematic review of MEDLINE and EMBASE databases, registered with PROSPERO (CRD42015025497) was conducted in accordance with PRISMA guidelines. Full text articles in English, with >50 patients (prospective) or >200 patients (retrospective), reporting outcomes of DCM were deemed to be eligible. RESULTS: A total of 108 studies involving 23,876 patients, conducted world-wide, were identified. 33 (31%) specified a clear primary objective. Study populations often included radiculopathy (51, 47%) but excluded patients who had undergone previous surgery (42, 39%). Diagnositic criteria for myelopathy were often uncertain; MRI assessment was specified in only 67 (62%) of studies. Patient comorbidities were referenced by 37 (34%) studies. Symptom duration was reported by 46 (43%) studies. Multivariate analysis was used to control for baseline characteristics in 33 (31%) of studies. CONCLUSIONS: The reporting of study design and sample characteristics is variable. The development of a consensus minimum dataset for (CODE-DCM) will facilitate future research synthesis in the future.

Multicenter Evaluation of the Cepheid Xpert Hepatitis C Virus Viral Load Assay.

Viral load monitoring for hepatitis C virus (HCV) is necessary to diagnose infection and monitor response to therapy, but the tests involved are currently confined to specialist institutions. There is a need for a fast, accurate assay with limited operator input to enhance the access to viral load monitoring. We evaluated the quantification of HCV RNA in serum and plasma by the Cepheid Xpert HCV Viral Load assay in comparison to the Abbott RealTime HCV assay. Serum and plasma samples were gathered from HCV-infected individuals at four international sites. These were tested with the Xpert HCV Viral Load assay, and results were compared to quantification by the Abbott RealTime HCV assay. An external quality assessment panel of eight samples was also tested. In total, 614 samples were analyzed in the study, and the qualitative results agreed on the two platforms for 588 (95.8%) samples. Further analysis of 396 samples quantified by both tests showed strong correlation (correlation coefficient r = 0.99) across the quantifiable range, with Bland-Altman plot data showing a mean difference (±1.96 standard deviation) of 0.03 ± 0.44 log10 IU/ml. In the external quality assessment panel, the Xpert HCV Viral Load assay results (quantified in log10 IU per milliliter) were within 1 standard deviation of the target value for all but one sample, which was also similarly misquantified by the Abbott RealTime HCV assay. The Xpert HCV Viral Load assay performs well compared to a market-leading HCV viral load test and should be considered for instances where rapid near-to-patient testing is required.

Cannabis-induced attenuated psychotic symptoms: implications for prognosis in young people at ultra-high risk for psychosis.

BACKGROUND: Cannabis use shows a robust dose-dependent relationship with psychosis risk among the general population. Despite this, it has been difficult to link cannabis use with risk for transitioning to a psychotic disorder among individuals at ultra-high risk (UHR) for psychosis. The present study examined UHR transition risk as a function of cannabis use characteristics which vary substantially between individuals including age of first use, cannabis abuse severity and a history of cannabis-induced attenuated psychotic symptoms (APS). METHOD: Participants were 190 UHR individuals (76 males) recruited at entry to treatment between 2000 and 2006. They completed a comprehensive baseline assessment including a survey of cannabis use characteristics during the period of heaviest use. Outcome was transition to a psychotic disorder, with mean time to follow-up of 5.0 years (range 2.4-8.7 years). RESULTS: A history of cannabis abuse was reported in 58% of the sample. Of these, 26% reported a history of cannabis-induced APS. These individuals were 4.90 (95% confidence interval 1.93-12.44) times more likely to transition to a psychotic disorder (p = 0.001). Greater severity of cannabis abuse also predicted transition to psychosis (p = 0.036). However, this effect was mediated by higher abuse severity among individuals with a history of cannabis-induced APS. CONCLUSIONS: Findings suggest that cannabis use poses risk in a subpopulation of UHR individuals who manifest cannabis-induced APS. Whether this reflects underlying genetic vulnerability requires further study. Nevertheless, findings reveal an important early marker of risk with potentially significant prognostic utility for UHR individuals.

Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies.

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

Development of two real-time multiplex PCR assays for the detection and quantification of eight key bacterial pathogens in lower respiratory tract infections.

The frequent lack of a positive and timely microbiological diagnosis in patients with lower respiratory tract infection (LRTI) is an important obstacle to antimicrobial stewardship. Patients are typically prescribed broad-spectrum empirical antibiotics while microbiology results are awaited, but, because these are often slow, negative, or inconclusive, de-escalation to narrow-spectrum agents rarely occurs in clinical practice. The aim of this study was to develop and evaluate two multiplex real-time PCR assays for the sensitive detection and accurate quantification of Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. We found that all eight bacterial targets could be reliably quantified from sputum specimens down to a concentration of 100 CFUs/reaction (8333 CFUs/mL). Furthermore, all 249 positive control isolates were correctly detected with our assay, demonstrating effectiveness on both reference strains and local clinical isolates. The specificity was 98% on a panel of nearly 100 negative control isolates. Bacterial load was quantified accurately when three bacterial targets were present in mixtures of varying concentrations, mimicking likely clinical scenarios in LRTI. Concordance with culture was 100% for culture-positive sputum specimens, and 90% for bronchoalveolar lavage fluid specimens, and additional culture-negative bacterial infections were detected and quantified. In conclusion, a quantitative molecular test for eight key bacterial causes of LRTI has the potential to provide a more sensitive decision-making tool, closer to the time-point of patient admission than current standard methods. This should facilitate de-escalation from broad-spectrum to narrow-spectrum antibiotics, substantially improving patient management and supporting efforts to curtail inappropriate antibiotic use.

Effects of contract-relax vs static stretching on stretch-induced strength loss and length-tension relationship.

The purpose of this study was to determine the acute effects of contract-relax stretching (CRS) vs static stretching (SS) on strength loss and the length-tension relationship. We hypothesized that there would be a greater muscle length-specific effect of CRS vs SS. Isometric hamstring strength was measured in 20 healthy people at four knee joint angles (90°, 70°, 50°, 30°) before and after stretching. One leg received SS, the contralateral received CRS. Both stretching techniques resulted in significant strength loss, which was most apparent at short muscle lengths [SS: P = 0.025; stretching × angle P < 0.001; 11.7% at 90° P < 0.01; 5.6% at 70° nonsignificant (ns); 1.3% at 50° ns; -3.7% at 30° ns. CRS: P < 0.001; stretching × angle P < 0.001; 17.7% at 90°, 13.4% at 70°, 11.4% at 50°, all P < 0.01, 4.3% at 30° ns]. The overall stretch-induced strength loss was greater (P = 0.015) after CRS (11.7%) vs SS (3.7%). The muscle length effect on strength loss was not different between CRS and SS (stretching × angle × stretching technique P = 0.43). Contrary to the hypothesis, CRS did not result in a greater shift in the length-tension relationship, and in fact, resulted in greater overall strength loss compared with SS. These results support the use of SS for stretching the hamstrings.

The role of cherries in exercise and health.

Recently, cherries and cherry products have received growing attention within the literature with regard to their application in both exercise and clinical paradigms. Reported to be high in anti-inflammatory and anti-oxidative capacity, cherries and their constituents are proposed to provide a similar but natural alternative akin to over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) or analgesics. Within exercise paradigms, concern has been raised with regard to the use of products, which inhibit such inflammatory or oxidative actions, because of the possibility of the blunting of physiological training adaptations. Despite this, numerous scenarios exist both within exercise and clinical populations where a goal of optimal recovery time is more important than physiological adaptation. This review critically evaluates and discusses the use of cherries as a supplementation strategy to enhance recovery of muscle function, inhibit exercise-induced inflammation, oxidative stress, and pain primarily; furthermore, the potential application of cherries to clinical populations is discussed.

Randomized double-blind crossover study of the efficacy of a tart cherry juice blend in treatment of osteoarthritis (OA) of the knee.

OBJECTIVE: To assess the efficacy of tart cherry juice in treating pain and other features of knee osteoarthritis (OA). METHODS: 58 non-diabetic patients with Kellgren grade 2-3 OA were randomized to begin treatment with cherry juice or placebo. Two 8 oz bottles of tart cherry juice or placebo were consumed daily for 6 weeks with a 1 week washout period before switching treatments (crossover design). Western Ontario McMaster Osteoarthritis Index (WOMAC) scores and walking times were recorded prior to and after each treatment period. Additionally, plasma urate, creatinine and high sensitivity C-reactive protein (hsCRP) were recorded at baseline, after the first treatment period and after the second treatment period. Acetaminophen was allowed as a rescue drug and self reported after each treatment period. Treatment effect was examined with repeated measures analysis of variance (ANOVA) using an intention-to-treat (ITT) analysis. RESULTS: There were five withdrawals during the cherry juice treatment (four adverse events (AEs)) and seven withdrawals during the placebo treatment (three AEs). WOMAC scores decreased significantly (P < 0.01) after the cherry juice treatment but not after the placebo treatment (P = 0.46); differences between treatments were not significant (P = 0.16). hsCRP declined during the cherry juice treatment vs placebo (P < 0.01). The decline in hsCRP was associated with WOMAC improvement (P < 0.01). Walking time, acetaminophen use, plasma urate and creatinine were unaffected by treatments. CONCLUSIONS: Tart cherry juice provided symptom relief for patients with mild to moderate knee OA, but this effect was not significantly greater than placebo. Tart cherry juice lowered hsCRP levels and this effect was associated with improved WOMAC scores.

Occurrence of microplastics in the gastrointestinal tract of pelagic and demersal fish from the English Channel.

Microplastics are present in marine habitats worldwide and laboratory studies show this material can be ingested, yet data on abundance in natural populations is limited. This study documents microplastics in 10 species of fish from the English Channel. 504 Fish were examined and plastics found in the gastrointestinal tracts of 36.5%. All five pelagic species and all five demersal species had ingested plastic. Of the 184 fish that had ingested plastic the average number of pieces per fish was 1.90±0.10. A total of 351 pieces of plastic were identified using FT-IR Spectroscopy; polyamide (35.6%) and the semi-synthetic cellulosic material, rayon (57.8%) were most common. There was no significant difference between the abundance of plastic ingested by pelagic and demersal fish. Hence, microplastic ingestion appears to be common, in relatively small quantities, across a range of fish species irrespective of feeding habitat. Further work is needed to establish the potential consequences.

The role of neural tension in hamstring flexibility.

Resistance to stretch, electromyographic (EMG) response to stretch, stretch discomfort and maximum range of motion (ROM) were measured during passive hamstring stretches performed in the slump test position (neural tension stretch) and in the upright position (neutral stretch) in eight healthy subjects. Stretches were performed on an isokinetic dynamometer at 5°/s with the test thigh flexed 40° above the horizontal, and the seat back at 90° to the horizontal. Surface EMG signals were recorded from the medial and lateral hamstrings during stretches. Knees were passively extended to maximum stretch tolerance with test order (neural tension vs neutral) alternated between legs. For neural tension stretches, the cervical and thoracic spine were manually flexed. Maximum ROM was 8° less for the neural tension stretch vs the neutral stretch (P<0.01). Resistance to stretch was 14-15% higher for the neural tension stretch vs the neutral stretch (P<0.001) at common joint angles in the final third of ROM. Stretch discomfort and EMG response were unaffected by neural tension. In conclusion, an increased passive resistance to stretch with the addition of neural tension during passive hamstring stretch despite no change in the EMG response indicates that passive extensibility of neural tissues can limit hamstring flexibility.