1. Acute effects of orofacial, neck, and shoulder relaxation exercises and chewing on soleus H-reflex and motor unit discharge patternsMarša Magdič, Aleš Holobar, Matej Kramberger, Matjaž Vogrin, Nina Murks, Anita Fekonja, Miloš Kalc, 2025, izvirni znanstveni članek Povzetek: The interconnected nature of orofacial, neck musculature, and the neural system suggests that localised19activities, such as teeth clenching, can influence remote spinal excitability. While stretching exercises are20known to have both local and remote effects, the specific impact of orofacial muscle stretching remains21underexplored. This study investigates the effects of two interventions: 25 guided orofacial and neck22stretching and mobility exercises (Exercises), and chewing six chewing gums for six minutes (Chewing),23on the soleus H-reflex and D1 presynaptic inhibition. Ten volunteers (mean age: 28.75 ± 9 years)24participated, with H-reflex measurements collected using high-density electromyography (HDsEMG)25before and after each intervention. Latency (HLAT ), duration (H DUR ), peak-to-peak (H P2P, D1 PSP ) and positive26peak (H POS ) amplitudes were extracted from unconditioned and conditioned H-reflexes. The ratio27(D1 P2P/H P2P) between conditioned (D1 P2P ) and unconditioned (H P2P ) H-reflex was calculated to study the28D1 presynaptic inhibition mechanisms. Additionally, 8,400 firings from 376 distinct motor units (MUs),29categorised by firing threshold were analysed for latency, firing ratio, and inhibition probability (D1 PROB ).30HP2P, HPOS decreased and HDUR was significantly increased after the Exercise intervention, while the31Chewing intervention had no effect on these parameters. The D1 P2P/H P2P ratio and D1 PROB remained32unchanged, suggesting that the observed drop in H P2P is not mediated by presynaptic inhibition33mechanisms. Single MU analysis confirmed the H-reflex findings. The results of this study suggest that34stretching and mobility exercises targeting the neck and orofacial region can reduce neuromuscular35excitability, offering potential for non-pharmacological management of conditions associated with36motoneuron hyperexcitability and general whole-body relaxation
Ključne besede: high-density electromyography (HDsEMG), remote effect, stretching
Objavljeno v DiRROS: 13.10.2025; Ogledov: 153; Prenosov: 67
 Celotno besedilo (3,20 MB)
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2. Twenty-one days of bed rest alter motor unit properties and neuromuscular junction transmission in young adultsFabio Sarto, Miloš Kalc, Evgeniia Motanova, Martino V. Franchi, Daniel W Stashuk, Nina Murks, Giacomo Valli, Samuele Negro, Tomaž Prašnikar, Mladen Gasparini, Giovanni Martino, Giuseppe De Vito, Aleš Holobar, Boštjan Šimunič, Rado Pišot, Marco Vincenzo Narici, 2025, izvirni znanstveni članek Povzetek: Previous studies showed that properties of higher‐threshold motor units (MUs) and neuromuscular junction (NMJ) function are preserved during short‐term disuse. This study aimed to test how a longer disuse period affects MU properties, NMJ transmission, and NMJ morphology remodeling. Nine young healthy males (age: 18‐29 years) underwent 21 days of horizontal bed rest. Pre‐ (BR0) and post‐bed rest (BR21), quadriceps maximal voluntary contraction (MVC), and size were assessed. We combined intramuscular electromyography (iEMG) and high‐density surface electromyography (HDsEMG) recordings on the vastus lateralis to assess MU properties at 25% and 50% of MVC. Muscle biopsies and blood samples were also collected. Quadriceps MVC and size decreased at BR21. We found alterations in MU properties at both contraction intensities, including reduced discharge rate, MU potential area changes, and increased complexity. NMJ transmission was found to be reduced at BR21 at 25% MVC. This functional NMJ impairment was biochemically corroborated by an increase in serum C‐terminal agrin fragment concentration, a biomarker of NMJ instability. In addition, a direct assessment of NMJ morphology revealed the presence of some denervated NMJs exclusively at BR21. In conclusion, 21‐day bed rest altered MU properties across different contraction intensities and impaired NMJ transmission with initial signs of remodeling/denervation. Disuse duration appears to be a critical factor, as previous shorter studies failed to detect some of these changes. We believe these findings are clinically relevant for disuse after trauma, surgery, or illness, and may support the development of effective countermeasures.
Ključne besede: disuse, unloading, physical inactivity, electrophysiology, electromyography
Objavljeno v DiRROS: 13.05.2025; Ogledov: 594; Prenosov: 257
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3. Neuromuscular junction instability with inactivity : morphological and functional changes after 10 days of bed rest in older adultsStefano Schiaffino, Evgeniia Motanova, Fabio Sarto, Samuele Negro, Marco Pirazzini, Ornella Rossetto, Michela Rigoni, Daniel W Stashuk, Mladen Gasparini, Boštjan Šimunič, Rado Pišot, Marco Vincenzo Narici, 2025, izvirni znanstveni članek Povzetek: The neuromuscular junction (NMJ) plays a key role in modulating muscle contraction,but the impact of short-term disuse on NMJ structure and function, particularly in older humans,remains unclear. This study aimed to investigate NMJ alterations following 10 days of horizontalbed rest in 10 older males (68.5 ± 2.6 years). Before and after bed rest, vastus lateralis musclebiopsies were obtained to evaluate NMJ morphology, intramuscular EMG (iEMG) was recordedto assess NMJ function and blood samples were collected to determine circulating C-terminal agrinfragment (CAF) concentration, a biomarker of NMJ remodelling. In a sub-cohort of six participantswho had NMJs in both pre- and post-bed rest biopsies, we observed altered NMJ morphology,including reduced overlap between NMJ terminals, as well as increased endplate area and peri-meter. CAF concentration was elevated after bed rest, suggesting ongoing NMJ remodelling. iEMGanalysis showed increased motor unit potential complexity and reduced firing rate. In addition,we observed impaired NMJ transmission, inferred from increased near-fibre jiggle and segmentjitter. These findings suggest that older male individuals are susceptible to NMJ remodelling andimpaired transmission with short-term disuse, providing valuable insights into the morphologicaland functional consequences of inactivity in an ageing population. Our study highlights theimportance of developing interventions for mitigating the detrimental consequences of inactivityon neuromuscular health in older adults, which they frequently experience following injury, trauma,illness or surgery.
Ključne besede: ageing, C-terminal agrin, fragment disuse, electromyography, motor unit, NMJ unloading
Objavljeno v DiRROS: 19.03.2025; Ogledov: 697; Prenosov: 431
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4. Inter-person differences in isometric coactivations of triceps surae and tibialis anterior decrease in young, but not in older adults after 14 days of bed restMatjaž Divjak, Gašper Sedej, Nina Murks, Mitja Gerževič, Uroš Marušič, Rado Pišot, Boštjan Šimunič, Aleš Holobar, 2022, izvirni znanstveni članek Povzetek: We examined activation patterns of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), soleus (SO), and tibialis anterior (TA) muscles in eight older (58.4 ± 3.3 years) and seven young (23.1 ± 2.9 years) participants, before and after 14 days of horizontal bed rest. Visual feedback on the exerted muscle torque was provided to the participants. The discharge patterns of individual motor units (MUs) were studied in three repetitions of isometric plantar flexion at 30 and 60% of Maximum Voluntary Contraction (MVC), before, and 1 day after the 14-day bed rest, respectively. In the GL and GM muscles, the older participants demonstrated higher MU discharge rates than the young, regardless of the contraction level, both before and after the bed rest. In the TA and SO muscles, the differences between the older and young participants were less consistent. Detailed analysis revealed person-specific changes in the MU discharge rates after the bed rest. To quantify the coactivation patterns we calculated the correlation coefficients between the cumulative spike trains of identified MUs from each muscle, and measured the root mean square difference of the correlation coefficients between the trials of the same session (intra-session variability) and between different sessions (inter-session variability) in each participant (intra-person comparison) and across participants (inter-person comparison). In the intra-person comparison, the inter-session variability was higher than the intra-session variability, either before or after the bed rest. At 60% MVC torque, the young demonstrated higher inter-person variability of coactivation than the older participants, but this variability decreased significantly after the bed rest. In older participants, inter-person variability was consistently lower at 60% than at 30% MVC torque. In young participants, inter-person variability became lower at 60% than at 30% MVC torque only after the bed rest. Precaution is required when analyzing the MU discharge and coactivation patterns, as individual persons demonstrate individual adaptations to aging or bed rest.
Ključne besede: high density electromyography, muscle disuse, motor units, discharge rate, aging
Objavljeno v DiRROS: 05.09.2022; Ogledov: 1897; Prenosov: 997
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