The physiological mechanisms determining the progressive decline in the maximal muscle torque production capacity during isometric contractions to task failure are known to depend on task demands. Task-specificity of the associated adjustments in motor unit discharge rate (MUDR), however, remains unclear. This study examined MUDR adjustments during different submaximal isometric knee extension tasks to failure. Participants performed a sustained and an intermittent task at 20% and 50% of maximal voluntary torque (MVT), respectively (Experiment 1). High-density surface EMG signals were recorded from vastus lateralis (VL) and medialis (VM) and decomposed into individual MU discharge timings, with the identified MUs tracked from recruitment to task failure. MUDR was quantified and normalised to intervals of 10% of contraction time (CT). MUDR of both muscles exhibited distinct modulation patterns in each task. During the 20% MVT sustained task, MUDR decreased until ∼50% CT, after which it gradually returned to baseline. Conversely, during the 50% MVT intermittent task, MUDR remained stable until ∼40-50% CT, after which it started to continually increase until task failure. To explore the effect of contraction intensity on the observed patterns, VL and VM MUDR was quantified during sustained contractions at 30% and 50% MVT (Experiment 2). During the 30% MVT sustained task, MUDR remained stable until ∼80-90% CT in both muscles, after which it continually increased until task failure. During the 50% MVT sustained task the increase in MUDR occurred earlier, after ∼70-80% CT. Our results suggest that adjustments in MUDR during submaximal isometric contractions to failure are contraction modality- and intensity-dependent. KEY POINTS: During prolonged muscle contractions a constant motor output can be maintained by recruitment of additional motor units and adjustments in their discharge rate. Whilst contraction-induced decrements in neuromuscular function are known to depend on task demands, task-specificity of motor unit discharge behaviour adjustments is still unclear. In this study, we tracked and compared discharge activity of several concurrently active motor units in the vastii muscles during different submaximal isometric knee extension tasks to failure, including intermittent vs. sustained contraction modalities performed in the same intensity domain (Experiment 1), and two sustained contractions performed at different intensities (Experiment 2). During each task, motor units modulated their discharge rate in a distinct, biphasic manner, with the modulation pattern depending on contraction intensity and modality. These results provide insight into motoneuronal adjustments during contraction tasks posing different demands on the neuromuscular system.
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http://dx.doi.org/10.1113/JP286143 | DOI Listing |
J Clin Ultrasound
December 2024
Department of General Surgery, University of Health Sciences, Van Training and Research Hospital, Van, Turkey.
Background: Ultrasonography (USG), which is used as the first step in the diagnosis of acute appendicitis (AA), sometimes cannot visualize the appendix. The aim of this study was to retrospectively analyze the clinical, imaging, and pathology results of these cases and to provide information to clinicians about the next step to be taken.
Methods: The study was performed retrospectively between January 1, 2021 and December 31, 2021.
J Cardiol
December 2024
Department of Cardiovascular Medicine, Kitasato University School of Medicine, Sagamihara, Japan.
Background: Patients with cardiovascular disease (CVD) are often contending with various comorbidities including cognitive decline. Cognitive decline is a risk marker for adverse outcomes in these patients. On the other hand, cardiovascular rehabilitation (CVR) improves clinical outcomes.
View Article and Find Full Text PDFJ Colloid Interface Sci
December 2024
Key Laboratory of Eco-chemical Engineering, International Science and Technology Cooperation Base of Eco-chemical Engineering and Green Manufacturing, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China. Electronic address:
Despite the ultrahigh theoretical energy density and cost-effectiveness, aprotic lithium-oxygen (Li-O) batteries suffer from slow oxygen redox kinetics at cathodes and large voltage hysteresis. Here, we well-design ultrafine Co nanoparticles supported by N-doped mesoporous hollow carbon nanospindles (Co@HCNs) to serve as efficient electrocatalysts for Li-O battery. Benefiting from strong metal-support interactions, the obtained Co@HCNs manifest high affinity for the LiO intermediate, promoting formation of ultrathin nanosheet-like LiO with low-impedance contact interface on the Co@HCNs cathode surface, which facilitates the reversible decomposition upon charging.
View Article and Find Full Text PDFBackground: Recovery after severe injury may be impacted by a range of psychological factors. This multi-site study investigated the prevalence and impact of anxiety and depression at one year after trauma critical care admission.
Methods: Adult trauma patients admitted to four Level 1 Critical Care Units were prospectively enrolled over 18 months.
Reg Anesth Pain Med
December 2024
Department of Anesthesiology, Michigan Medicine, Ann Arbor, Michigan, USA
Introduction: Previous studies suggest that new persistent opioid use (NPOU) after surgery was associated with larger perioperative opioid prescriptions, but the association between NPOU and postoperative opioid consumption is unknown.
Methods: This retrospective study included opioid naïve individuals aged 18-64 who underwent surgical procedures across 70 Michigan hospitals between July 1, 2018 and November 15, 2021 and were prescribed opioids at discharge. We used clinical and patient-reported opioid consumption data from the Michigan Surgical Quality Collaborative, a statewide surgical registry, linked with the state Prescription Drug Monitoring Program.
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