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Abstract: This study invesƟgated the spinal neural mechanisms underlying post‐acƟvaƟon potenƟaƟon in ten16healthy young males (21.9 ± 4.8 years). ParƟcipants performed a 10‐second maximal isometric17plantarflexion, aŌer which we measured twitch torque and assessed spinal excitability using the18soleus H‐reflex, D1 presynapƟc inhibiƟon and heteronymous Ia facilitaƟon (HF). High‐density surface19EMG was decomposed to track single motor unit responses. The condiƟoning contracƟon increased20twitch torque by 12.2 Nm (p < 0.001) immediately and returning to baseline within nine minutes. This21mechanical potenƟaƟon was accompanied by a 29% reducƟon in H‐reflex amplitude (p < 0.001),22which recovered within three minutes. Paradoxically, neurophysiological indices of presynapƟc23inhibiƟon, D1 and HF were significantly increased (D1: p<0.017; HF: p<0.001), resulƟng in spinal24facilitaƟon. Single MU analysis revealed increased discharge probability, parƟcularly in higher‐25threshold units indicaƟng overall spinal facilitaƟon. These results demonstrate that post‐acƟvaƟon26potenƟaƟon involves a complex dissociaƟon: H‐reflex pathway inhibiƟon along with facilitaƟon of27presynapƟc spinal mechanisms. This paradox can be explained by either post‐acƟvaƟon depression28(caused by depleƟon of neurotransmiƩer at the Ia–motoneuron synapse) or muscle thixotropy, a29contracƟon history‐dependent decrease in muscle spindle sensiƟvity, which reduces the efficacy of30the Ia afferent volley independently of spinal inhibitory mechanisms. Our findings highlight a31dissociaƟon between spinal presynapƟc facilitaƟon and the decreased H‐reflex, underscoring the32need for future studies to explicitly test the roles of post‐acƟvaƟon depression and muscle thixotropy33aŌer condiƟoning contracƟons.
Keywords: HDsEMG, Ia afference, soleus, heteroniumous Ia facilitation, spinal reflex, muscle contraction, neural mechanisms, performance enhancement
Published in DiRROS: 12.05.2026; Views: 52; Downloads: 26
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Abstract: Background: Sarcopenia, the progressive decline in skeletal muscle mass and function, is a major public health concern linked to falls, hospitalization and loss of independence among older adults. Initially defined by reduced muscle mass, later also by reduced muscle strength and function, it is now recognized that standard diagnostic tools do not fully capture complexity of sarcopenia. Tensiomyography (TMG) is a non-invasive method that assesses skeletal muscle contractile parameters, which undergo change with aging and sarcopenia. The aims of this exploratory study are to determine whether TMG could be a method for contractile parameters assessment in sarcopenia classification and to evaluate the relationship between TMG-derived parameters and sarcopenia classification tests. Methods: We included 654 older adults (70.6% women) and included demographics, sarcopenia classification (EWGSOP2, SDOC), muscle strength (handgrip strength, five sit-to-stand), TMG of three leg muscles, muscle mass (bioimpedance), and physical performance (gait speed, timed up-and-go). MANOVA was used to analyze contractile properties and due to low agreement between classifications, we used both classifications. A partial correlation for each sex was conducted to determine the associations between sarcopenia classification tests and TMG-derived parameters of delay time (Td), contraction time (Tc), radial displacement (Dm) and contraction velocity (Vc), controlling for age. Results: One-way MANOVA confirmed difference between sarcopenic and nonsarcopenic participants according to EWGSOP2 and SDOC classifications in TMG-derived contractile parameters in all three muscles, Td was consistently longer and Dm consistently lower in sarcopenic individuals. Post-hoc univariate tests further demonstrated specific differences due to sarcopenia presence. Ageadjusted partial correlations were weak to moderate, ranging between −0.430 and 0.369. Conclusion: Sarcopenic individuals exhibited longer Td and Tc, and smaller Dm, though not consistently across all muscles. Td was longer in all three muscles, reflecting electromechnical delays linked to aging. Dm was consistently lower, suggesting increased muscle stiffness. Correlations between TMG parameters and sarcopenia classification tests indicated that shorter Td and Tc, higher Dm, and greater Vc were associated with higher muscle volume, muscle strength and performance. The findings indicate that TMG parameters may be associated with neuromuscular degeneration and sarcopenia, supporting further exploration of muscle- and sex-specific differences.
Keywords: tensiomyography, muscle function, older adults, sarcopenia, seniors
Published in DiRROS: 04.02.2026; Views: 604; Downloads: 233
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Abstract: 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
Keywords: high-density electromyography (HDsEMG), remote effect, stretching
Published in DiRROS: 13.10.2025; Views: 459; Downloads: 270
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Abstract: Introduction: Sarcopenia is a multifaceted condition affecting between 10 and 16% of the global population, and although multiple classification algorithms exist, no prevalence has been reported for a representative sample of the Slovenian population. Furthermore, multiple behavioural factors, such as malnutrition, physical inactivity, sedentary lifestyle and lower cognitive function, can contribute to the risk of sarcopenia. This study aims to: a) determine sarcopenia prevalence among Slovenian older adults according to different classification algorithms, b) compare the agreement among the algorithms and c) evaluate the relationship between proposed risk factors and sarcopenia. Methods: 654 participants (≥60 years, 30.4% males) have been classified into sarcopenia groups according to eight algorithms, and agreement (Fleiss K) between them was calculated. Additionally, age, sex, nutritional status, physical activity, sedentary levels and cognitive function were assessed as sarcopenia risk/protective factors. Results: The prevalence of sarcopenia according to EWGSOP2 was 4.1%, ranging from 2.1% to 15.3%, when classified by all eight algorithms. Overall agreement between algorithms was weak (K=.429; 95% CI .414 to .444) with 0.6% of participants classified as sarcopenic by all eight algorithms. Adequate nutrition and physical activity were identified as protective factors, while age, lower cognitive function and sedentary lifestyle were considered risk factors. Conclusion: Sarcopenia prevalence among the Slovenian general population was lower than in the global population. We can conclude that different sarcopenia algorithms lead to a different prevalence of sarcopenia. It is of great importance to be cautious when comparing prevalences among studies and to further validate the classification algorithms.
Keywords: sarcopenia, prevalence, epidemiology, classification algorithms, risk factors
Published in DiRROS: 03.03.2025; Views: 930; Downloads: 547
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Abstract: Pathologies in neck and masticatory muscles affect muscle tone and biomechanical and viscoelastic properties, necessitating precise assessment for treatment. This study evaluated the impact of two guided interventions—relaxing exercises targeting the neck and masticatory muscles (“Exercise”) and heavy chewing using six chewing gums (“Chewing”)—on the masseter and upper trapezius muscles. Twelve participants (aged 19–40 years) underwent myotonometric assessment pre- and post-intervention, measuring tone, stiffness, decrement, relaxation time, and creep. The results showed significant changes in the masseter muscle after exercise, with increased stiffness (14.46%, p < 0.001) and tone (7.03%, p < 0.001) but decreased creep (−9.71%, p < 0.001) and relaxation time (−11.36%, p < 0.001). Conversely, chewing decreased stiffness (−8.82%, p < 0.001) and tone (−5.53%, p < 0.001), while it increased creep (9.68%, p < 0.001) and relaxation time (9.98%, p < 0.001). In the trapezius muscles, tone decreased after both interventions (Exercise: −7.65%, p < 0.001; Chewing: −1.06%, p = 0.003), while relaxation increased (Exercise: 1.78%, p < 0.001; Chewing: 2.82%, p < 0.001). These findings reveal the distinct effects of exercise and chewing on muscle properties, emphasising the complexity of their therapeutic potential and the need for further investigation.
Keywords: muscle tonus, relaxation, masseter muscle, trapezius muscle, intervention studies
Published in DiRROS: 07.01.2025; Views: 987; Downloads: 653
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