Flat 3-webs of degree one on the projective plane

The aim of this work is to study global $3$-webs with vanishing curvature. We wish to investigate degree $3$ foliations for which their dual web is flat. The main ingredient is the Legendre transform, which is an avatar of classical projective duality in the realm of differential equations. We find a characterization of degree $3$ foliations whose Legendre transform are webs with zero curvature.Comment: 14 page

Measures of neck muscle strength and their measurement properties in adults with chronic neck pain-a systematic review.

Measurement of neck muscle strength is common during the assessment of people with chronic neck pain (CNP). This systematic review evaluates the measurement properties (reliability, validity, and responsiveness) of neck muscle strength measures in people with CNP. This systematic review followed a PROSPERO registered protocol (CRD42021233290). Electronic databases MEDLINE (OVID interface), CINAHL, SPORTDiscuss via (EBSCO interface), EMBASE (OVID interface), and Web of Science were searched from inception to 21 June 2021. Screening, data extraction, and quality assessment (Consensus-based Standards for the selection of Health Measurement Instruments (COSMIN) checklist) were conducted independently by two reviewers. The overall strength of evidence was evaluated using the modified Grading of Recommendations Assessment, Development and Evaluation. From 794 records, nine articles were included in this review which concerned six different neck strength outcome measures. All studies evaluated reliability and one evaluated construct validity. The reliability of neck strength measures ranged from good to excellent. However, the risk of bias was rated as doubtful/inadequate for all except one study and the overall certainty of evidence was rated low/very low for all measures except for the measurement error of a handheld dynamometer. A multitude of measures are used to evaluate neck muscle strength in people with CNP, but their measurement properties have not been fully established. Further methodologically rigorous research is required to increase the overall quality of evidence. [Abstract copyright: © 2023. The Author(s).

Headache features in people with whiplash associated disorders: A scoping review.

Whiplash-associated headache (WAH) is one of the most common symptoms after a whiplash injury, leading to high disability. Nevertheless, the clinical characteristics of WAH have not been well described. To synthesise the existing literature on the clinical characteristics of WAH. Scoping review. The protocol for this scoping review was registered in Open Science Framework and the PRISMA extension for Scoping Reviews tool was used to ensure methodological and reporting quality. A systematic search was conducted in PubMed, EMBASE, CINAHL, Web of Science and Scopus. The search was performed by one author and the screening of articles was conducted by two authors independently. A total of 11363 articles were initially identified and finally 26 studies were included in the review. Headache intensity was the most commonly reported feature. Headache duration, frequency and location were also reported in at least four studies. Few studies reported physical impairments that may be related to the presence of WAH. A differentiation with concussion characteristics was only performed in eight studies. WAH appears to be of mild to moderate intensity, typically with episodes of short duration which is commonly experienced in the occipital region amongst other regions, and with a tendency to reduce in intensity over time. [Abstract copyright: Copyright © 2023. Published by Elsevier Ltd.

Differential motor unit changes after endurance or high-intensity interval training.

PURPOSE: Using a novel technique of high-density surface electromyography (HDEMG) decomposition and motor unit (MU) tracking, we compared changes in the properties of vastus medialis (VM) and vastus lateralis (VL) MUs following endurance (END) and high-intensity interval training (HIIT). METHODS: Sixteen men were assigned to an END or HIIT group (n=8 each) and performed six training sessions over 14 days. Each session consisted of 8-12×60s intervals at 100% peak power output (PPO) separated by 75s of recovery (HIIT) or 90-120min continuous cycling at ~65% VO2peak (END). Pre and post intervention, participants performed: 1) incremental cycling to determine VO2peak and PPO and 2) maximal (MVC), submaximal (10, 30, 50 and 70% MVC) and sustained (until task failure at 30% MVC) isometric knee extensions while HDEMG signals were recorded from the VM and VL. EMG signals were decomposed (submaximal contractions) into individual MUs by convolutive blind source separation. Finally, MUs were tracked across sessions by semi-blind source separation. RESULTS: After training, END and HIIT improved VO2peak similarly (by 5.0 and 6.7%, respectively). The HIIT group showed enhanced maximal knee extension torque by ~7% (p=0.02) and was accompanied by an increase in discharge rate for high-threshold MUs (≥50% knee extension MVC) (p0.05). CONCLUSIONS: HIIT and END induce different adjustments in MU discharge rate despite similar improvements in cardiopulmonary fitness. Moreover, the changes induced by HIIT are specific for high-threshold motor units. For the first time we show that HIIT and END induce specific neuromuscular adaptations, possibly related to differences in exercise load intensity and training volume

Can People with Chronic Neck Pain Recognize Their Own Digital Pain Drawing?

Background: Although the reliability of pain drawings (PDs) has been confirmed in people with chronic pain, there is a lack of evidence about the validity of the PD, that is, does the PD accurately represent the pain experience of the patient? Objectives: We investigate whether people with chronic neck pain (CNP) can recognize their own PD to support the validity of the PD in reporting the experience of pain. Moreover, we examined the association between their ability to recognize their own PD with their levels of pain intensity and disability and extent of psychosocial and somatic features. Study Design: Experimental. Setting: University Laboratory. Methods: Individuals with CNP completed their PD on a digital body chart, which was then automatically modified with specific dimensions using a novel software, providing an objective range of distortion and eliminating errors, which could potentially occur in manually controlled visual-subjective based methods. Following a 10-minute break listening to music, a series of 20 PDs were presented to each patient in a random order, with only 2 being their original PD. For each PD, the patients rated its likeliness to their own original PD on a scale from 0 to 100, with 100 representing “this is my pain.” Results: Overall, the patients rated their original PD with a median score of 92% similarity, followed by 91.8% and 89.5% similarity when presented with a PD scaled down to 75% and scaled up by 150% of the original size, respectively; these scores were not significantly different to the ratings given for their original PD. The PD with horizontal translation by 40 pixels (8%) and vertical translation by 70 pixels (12.8%) were rated as the most dissimilar to their original PD; these scores were significantly different to their original PD scores. The Spearman correlation coefficient revealed a significant negative association between their ability to recognize their original PD and their Modified Somatic Perceptions Questionnaire scores. Limitations: The patients in the study presented with relatively mild CNP, and the results may not be generalized to those with more severe symptoms. Conclusions: People with CNP are generally able to identify their own PD but that their ability to recognize their original PD is negatively correlated with the extent of somatic awareness

Non-traumatic chronic shoulder pain is not associated with changes in rotator cuff interval tendon thickness

To determine whether the thickness of the rotator interval tendons is different when comparing both symptomatic and non-symptomatic sides in people with chronic shoulder pain, and to those free of pain. Furthermore, to calculate the level of association between the rotator interval tendon thicknesses and perceived shoulder pain-function. A cross-sectional, observational study. The supraspinatus, subscapularis and biceps brachii tendon thickness of sixty two patients with chronic shoulder pain were determined from standardized ultrasonography measures performed on both shoulders, whereas only the dominant arm was measured for the control subjects. Supraspinatus, subscapularis and biceps brachii tendon thickness was comparable between sides in the symptomatic group and was also comparable between the symptomatic and asymptomatic participants. In addition, the correlation between the tendon thickness and shoulder pain-function was non-significant. Tendon thickness was unaltered in people with chronic shoulder pain. These findings do not rule out the possibility that other changes in the tendon are present such as changes in the elastic properties and cell population and this should be explored in future studies

The relative timing of trunk muscle activation is retained in response to unanticipated postural-perturbations during acute low back pain

The purpose of this study was to assess the activation of the erector spinae (ES) and external oblique (EO) in response to unanticipated, bi-directional postural perturbations before and after the induction of acute low back pain (LBP) in healthy individuals. An experimental session consisted of a baseline, control, and an acute LBP condition. For the control and acute LBP condition, isotonic or hypertonic saline (HS), respectively, was injected into the right ES muscle. In each condition, participants stood on a moveable platform during which 32 randomized postural perturbations (8 repetitions of 4 perturbation types: 8 cm anterior slides, 8 cm posterior slides, 10° anterior tilts, and 10° posterior tilts) with varying inter-perturbation time intervals were performed over a period of 4–5 min. Bilateral surface electromyography (EMG) was recorded from the ES and EO in addition to subjective pain records. During the acute LBP condition: (1) the onset time of the ES and EO was delayed for the forward and backward sliding perturbations (P < 0.05); (2) EMG amplitude was reduced bilaterally for all perturbations (P < 0.05); (3) the order of activation and interval between the onset times of the ES and EO were unaltered and (4) ES, but not EO, activity was adjusted to account for the directional differences between the perturbations. This study revealed that re-establishment of posture and balance was a result of the individuals’ ability to rapidly modulate ES with respect to EO activity and that the bi-directional postural responses, although shifted in time and amplitude, retained temporal features in the presence of acute LBP

Shear wave elastography investigation of multifidus stiffness in individuals with low back pain

© 2019 Elsevier Ltd The purpose of this study was to investigate differences in passive muscular stiffness between the superficial multifidus (SM)and deep multifidus (DM), and to compare their passive and active stiffness in individuals with low back pain (LBP) and asymptomatic individuals. Fifteen LBP individuals and 15 asymptomatic individuals were recruited. Passive stiffness of the SM and DM was measured bilaterally using sheer wave elastography (SWE) with participants lying prone. Active stiffness was measured for the SM during trunk extension, and the contraction ratio was calculated. DM displayed higher passive muscular stiffness than SM in both the asymptomatic and LBP groups (14.41 ± 2.62 and 15.40 ± 2.77 kPa respectively; t = 7.765 and t = 3.864, p < 0.05). Individuals with LBP exhibited higher passive muscular stiffness of SM (LBP: 10.15 ± 4.21, asymptomatic: 6.84 ± 1.69 kPa; t = 3.002, p < 0.05)and a lower contraction ratio (LBP: 1.54 ± 0.47, asymptomatic: 2.65 ± 1.36 kPa; p < 0.05) compared to the asymptomatic group. The findings support a differentiation in passive muscular stiffness between SM and DM and provide evidence for an alteration in muscular stiffness at rest in individuals with LBP. The lower increase of muscular stiffness with contraction observed for those with LBP may reflect a deficit in activation of the multifidus

Tracking motor units longitudinally across experimental sessions with high-density surface electromyography.

KEY POINTS: Classic motor unit (MU) recording and analysis methods do not allow the same MUs to be tracked across different experimental sessions, and therefore, there is limited experimental evidence on the adjustments in MU properties following training or during the progression of neuromuscular disorders. We propose a new processing method to track the same MUs across experimental sessions (separated by weeks) by using high-density surface electromyography. The application of the proposed method in two experiments showed that individual MUs can be identified reliably in measurements separated by weeks and that changes in properties of the tracked MUs across experimental sessions can be identified with high sensitivity. These results indicate that the behaviour and properties of the same MUs can be monitored across multiple testing sessions. The proposed method opens new possibilities in the understanding of adjustments in motor unit properties due to training interventions or the progression of pathologies. ABSTRACT: A new method is proposed for tracking individual motor units (MUs) across multiple experimental sessions on different days. The technique is based on a novel decomposition approach for high-density surface electromyography and was tested with two experimental studies for reliability and sensitivity. Experiment I (reliability): ten participants performed isometric knee extensions at 10, 30, 50 and 70% of their maximum voluntary contraction (MVC) force in three sessions, each separated by 1 week. Experiment II (sensitivity): seven participants performed 2 weeks of endurance training (cycling) and were tested pre-post intervention during isometric knee extensions at 10 and 30% MVC. The reliability (Experiment I) and sensitivity (Experiment II) of the measured MU properties were compared for the MUs tracked across sessions, with respect to all MUs identified in each session. In Experiment I, on average 38.3% and 40.1% of the identified MUs could be tracked across two sessions (1 and 2 weeks apart), for the vastus medialis and vastus lateralis, respectively. Moreover, the properties of the tracked MUs were more reliable across sessions than those of the full set of identified MUs (intra-class correlation coefficients ranged between 0.63-0.99 and 0.39-0.95, respectively). In Experiment II, ∼40% of the MUs could be tracked before and after the training intervention and training-induced changes in MU conduction velocity had an effect size of 2.1 (tracked MUs) and 1.5 (group of all identified motor units). These results show the possibility of monitoring MU properties longitudinally to document the effect of interventions or the progression of neuromuscular disorders