Motor unit discharge rate modulation during isometric contractions to failure is intensity- and modality-dependent.

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.

Type selective ablation of postnatal slow and fast fatigue-resistant motor neurons in mice induces late onset kinetic and postural tremor following fiber-type transition and myopathy.

Animals on Earth need to hold postures and execute a series of movements under gravity and atmospheric pressure. VAChT-Cre is a transgenic Cre driver mouse line that expresses Cre recombinase selectively in motor neurons of S-type (slow-twitch fatigue-resistant) and FR-type (fast-twitch fatigue-resistant). Sequential motor unit recruitment is a fundamental principle for fine and smooth locomotion; smaller-diameter motor neurons (S-type, FR-type) first contract low-intensity oxidative type I and type IIa muscle fibers, and thereafter larger-diameter motor neurons (FInt-type, FF-type) are recruited to contract high-intensity glycolytic type IIx and type IIb muscle fibers.

Muscle Recruitment Strategies in a Redundant Task: Age Differences Through Network Analyses.

There are numerous studies comparing young and old adults in terms of muscle coordination in standard tasks (e.g., walking, reaching) and small variations of them.

Motor unit number estimation via MScanFit MUNE in spinal muscular atrophy.

Introduction/aims: MScanFit MUNE (MScanFit) is a novel tool to derive motor unit number estimates (MUNEs) from compound muscle action potential (CMAP) scans. Few studies have explored its utility in 5q spinal muscular atrophy (SMA5q) patients, assessing only the abductor pollicis brevis (APB) muscle. We aimed to assess different distal muscles in pediatric and adult SMA5q patients, further evaluating clinical-electrophysiological correlations.

Short term effects of contralateral tendon vibration on motor unit discharge rate variability and force steadiness in people with Parkinson's disease.

Background: Vibration of one limb affects motor performance of the contralateral limb, and this may have clinical implications for people with lateralized motor impairments through vibration-induced increase in cortical activation, descending neural drive, or spinal excitability.

Objective: The objective of this study was to evaluate the effects of acute biceps brachii tendon vibration on force steadiness and motor unit activity in the contralateral limb of persons with Parkinson's disease.

Methods: Ten participants with mild to moderate Parkinson's disease severity performed a ramp, hold and de-ramp isometric elbow flexion at 5% of maximum voluntary contraction with the more-affected arm while vibration was applied to the distal biceps brachii tendon on the contralateral, less-affected arm.

Prospective Six-Month Analysis of Multiarea Burst Spinal Cord Stimulation: Correlating Intraoperative Neuromonitoring With Postoperative Programming and Clinical Outcomes.

Introduction: DeRidder burst spinal cord stimulation (SCS) has shown superior relief from overall pain to traditional tonic neurostimulation therapies and a reduction in back and leg pain. However, nearly 80% of patients have two or more noncontiguous pain areas. This affects the ability to effectively program stimulation and deliver long-term efficacy of the therapy.

Antagonism of 5-HT receptors attenuates self-sustained firing of human motor units.

5-HT receptors on motoneurones play a critical role in facilitating persistent inward currents (PICs). Although facilitation of PICs can enhance self-sustained firing after periods of excitation, the relationship between 5-HT receptor activity and self-sustained firing in human motor units (MUs) has not been resolved. MU activity was assessed from the tibialis anterior of 10 healthy adults (24.

Developmental changes in motor unit activity patterns: child-adult comparison using discrete motor unit analysis.

Using global surface electromyography (sEMG) and the sEMG threshold it has been suggested that children activate their type-II motor unit (MU) to a lesser extent compared with adults. However, when age-related differences in discrete MU activation are examined using sEMG decomposition this phenomenon is not observed. Furthermore, findings from these studies are inconsistent and conflicting.

How many motor units is enough? An assessment of the influence of the number of motor units on firing rate calculations.

The number of motor units included in calculations of mean firing rates varies widely in the literature. It is unknown how the number of decomposed motor units included in the calculation of firing rate per participant compares to the total number of active motor units in the muscle, and if this is different for males and females. Bootstrapped distributions and confidence intervals (CI) of mean motor unit firing rates decomposed from the tibialis anterior were used to represent the total number of active motor units for individual participants in trials from 20 to 100 % of maximal voluntary contraction.

Prepared for landing: A simple activation strategy scales muscle force to landing height.

Before landing from a jump or fall, animals preactivate muscles to stiffen their limb joints but it is unclear how muscles tune limb stiffness and how collision forcefulness is anticipated. We measured electromyography and force from the lateral gastrocnemius muscle during landings in turkeys, an animal model that allows for direct measurements of muscle force. Many studies of landings in humans and other animals have found the duration of muscle preactivation to be constant, starting approximately 100 ms before impact, irrespective of fall duration.

Quantitative double echo steady state T2 mapping of upper extremity peripheral nerves and muscles.

Introduction: T2 mapping can characterize peripheral neuropathy and muscle denervation due to axonal damage. Three-dimensional double echo steady-state (DESS) can simultaneously provide 3D qualitative information and T2 maps with equivalent spatial resolution. However, insufficient signal-to-noise ratio may bias DESS-T2 values.

Influence of Backpack Carriage and Walking Speed on Muscle Synergies in Healthy Children.

Four to five muscle synergies account for children's locomotion and appear to be consistent across alterations in speed and slopes. Backpack carriage induces alterations in gait kinematics in healthy children, raising questions regarding the clinical consequences related to orthopedic and neurological diseases and ergonomics. However, to support clinical decisions and characterize backpack carriage, muscle synergies can help with understanding the alterations induced in this condition at the motor control level.

Residual force depression is not related to positive muscle fascicle work during submaximal voluntary dorsiflexion contractions in humans.

Residual force depression (rFD) following active muscle shortening is assumed to correlate most strongly with muscle work, but this has not been tested during voluntary contractions in humans. Using dynamometry, we compared steady-state ankle joint torques (N = 16) following tibialis anterior (TA) muscle-tendon unit (MTU) lengthening and shortening to the time-matched torque during submaximal voluntary fixed-end dorsiflexion reference contractions (REF) at a matched MTU length and EMG amplitude. Ultrasound revealed significantly reduced (P < 0.

Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females.

Purpose: The purpose of this study was to compare laterality in motor unit firing behavior between females and males.

Methods: Twenty-seven subjects (14 females) were recruited for this study. The participants performed ramp up and hold isometric index finger abduction at 10, 30, and 60% of their maximum voluntary contraction (MVC).

Bruns Garland Syndrome as the first presentation of type 2 diabetes: two case reports and a practical approach to diagnosis.

Background: Diabetes is a global health problem causing a significant burden on the healthcare systems both due to the disease itself and associated complications. Diabetic radiculoplexus neuropathies or Bruns-Garland syndrome constitutes a rare form of microvascular complications, more commonly affecting the lumbosacral plexus and, very rarely, the cervical plexus. We describe two Sri Lankan males who presented with diabetic lumbosacral radiculoplexus neuropathy and diabetic cervical radiculoplexus neuropathy as the initial manifestation of diabetes.

Sex Differences and Physical Activity Status on the Hamstring: Quadriceps Ratio, Activities of Daily Living, and Functional Movement in Older Adults.

The study aimed to investigate sex differences and the effect of physical activity on the hamstring:quadriceps (H:Q) ratio, activities of daily living (ADLs), and the unctional Movement Screen (MS) in older adults. Thirty older adults (72.56 + 6.

Different discrete motor-unit activation patterns in the flexor carpi radialis in boys and men.

Background: Lower activation of higher threshold (type-II) motor units (MUs) has been suggested in children compared with adults. We examined child-adult differences in discrete MU activation of the flexor carpi radialis (FCR).

Methods: Fifteen boys (10.

Blood flow restriction increases necessary muscle excitation of the elbow flexors during a single high-load contraction.

Purpose: To investigate the effects of blood flow restriction (BFR) on electromyographic amplitude (EMG)-force relationships of the biceps brachii (BB) during a single high-load muscle action.

Methods: Twelve recreationally active males and eleven recreationally active females performed maximal voluntary contractions (MVCs), followed by an isometric trapezoidal muscle action of the elbow flexors at 70% MVC. Surface EMG was recorded from the BB during BFR and control (CON) visits.

Unique case study: Impact of single-session neuromuscular biofeedback on motor unit properties following 12 days of Achilles tendon surgical repair.

We explored the first evidence of a single-session neuromuscular biofeedback effect on motor unit properties, neuromuscular activation, and the Achilles tendon (AT) length 12 days after undergoing AT surgical repair. We hypothesized that immediate neuromuscular biofeedback enhances motor unit properties and activation without causing AT lengthening. After 12 days AT surgical repair, Medial Gastrocnemius (MG) motor unit decomposition was performed on a 58-year-old male before and after a neuromuscular biofeedback intervention (surface electromyography (sEMG) and ultrasonography), involving unressited plantar flexion.

Association between physical fitness tests and neuromuscular properties.

Purpose: While various fitness tests have been developed to assess physical performances, it is unclear how these tests are affected by differences, such as, in morphological and neural factors. This study was aimed to investigate associations between individual differences in physical fitness tests and neuromuscular properties.

Methods: One hundred and thirty-three young adults participated in various general physical fitness tests and neuromuscular measurements.

Modified motor unit properties in residual muscle following transtibial amputation.

Neural signals in residual muscles of amputated limbs are frequently decoded to control powered prostheses. Yet myoelectric controllers assume muscle activities of residual muscles are similar to that of intact muscles. This study sought to understand potential changes to motor unit (MU) properties after limb amputation.

Children with developmental coordination disorder have less variable motor unit firing rate characteristics across contractions compared to typically developing children.

Introduction: Understanding the nuances of neuromuscular control is crucial in unravelling the complexities of developmental coordination disorder (DCD), which has been associated with differences in skeletal muscle activity, implying that children with DCD employ distinct strategies for muscle control. However, force generation and control are dependent on both recruitment of motor units and their firing rates and these fine details of motor function have yet to be studied in DCD. The purpose of this study was therefore to compare motor unit characteristics in a small muscle of the hand during low level, handgrip contractions in typically developing (TD) children and children with DCD.