| Title: | Spinal mechanisms in postactivation potentiation : facilitation of presynaptic inhibition contrasts h-reflex amplitude reduction |
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| Authors: | ID Kalc, Miloš (Author)
ID Holobar, Aleš (Author)
ID Kramberger, Matej (Author)
ID Murks, Nina (Author)
ID Škarabot, Jakob (Author) |
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| Files: |  PDF - Presentation file, download (4,32 MB)
MD5: B749DD3875CFE4D26DC5DEDACBC183A2
 URL - Source URL, visit https://journals.physiology.org/doi/abs/10.1152/jn.00031.2026
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| Language: | English |
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| Typology: | 1.01 - Original Scientific Article |
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| Organization: |  ZRS Koper - Science and Research Centre Koper
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| Abstract: | This study investigated the spinal neural mechanisms underlying postactivation potentiation in 10 healthy young males (21.9 ± 4.8 yr).Participants performed a 10-s maximal isometric plantarflexion, after which we measured twitch torque and assessed spinal excitabilityusing the soleus H-reflex, D1 presynaptic inhibition, and heteronymous Ia facilitation (HF). High-density surface EMG was decomposed totrack single motor unit responses. The conditioning contraction increased twitch torque by 12.2 Nm (P < 0.001) immediately and returnedto baseline within 9 min. This mechanical potentiation was accompanied by a 29% reduction in H-reflex amplitude (P < 0.001), whichrecovered within 3 min. Paradoxically, neurophysiological indices of presynaptic inhibition, D1, and HF were significantly increased (D1:P < 0.017; HF: P < 0.001), resulting in spinal facilitation. Single MU analysis revealed increased discharge probability, particularly inhigher-threshold units, indicating overall spinal facilitation. These results demonstrate that postactivation potentiation involves a complexdissociation; H-reflex pathway inhibition along with facilitation of presynaptic spinal mechanisms. This paradox can be explained by eitherpostactivation depression (caused by depletion of neurotransmitter at the Ia-motoneuron synapse) or muscle thixotropy, a contraction his-tory-dependent decrease in muscle spindle sensitivity, which reduces the efficacy of the Ia afferent volley independently of spinal inhibi-tory mechanisms. Our findings highlight a dissociation between spinal presynaptic facilitation and the decreased H-reflex, underscoringthe need for future studies to explicitly test the roles of postactivation depression and muscle thixotropy after conditioning contractions.NEW & NOTEWORTHY This study provides evidence that postactivation potentiation is accompanied by a reduction in soleusH-reflex amplitude and a concurrent facilitation of presynaptic spinal mechanisms. By combining global EMG and single motorunit analyses extracted from high-density surface EMG, we reveal a dissociation between spinal disinhibition and reflex depres-sion. These findings suggest that acute postcontraction reflex suppression might be mediated by mechanisms other than presyn-aptic inhibition, potentially involving postactivation depression or changes in muscle spindle sensitivity. |
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| Keywords: | HDsEMG, Ia afference, soleus, heteroniumous Ia facilitation, spinal reflex, muscle contraction, neural mechanisms, performance enhancement |
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| Publication status: | Published |
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| Publication version: | Version of Record |
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| Publication date: | 01.01.2026 |
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| Year of publishing: | 2026 |
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| Number of pages: | str. 1437-1517 |
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| Numbering: | Vol. 135, iss. 6 |
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| PID: | 20.500.12556/DiRROS-29360  |
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| UDC: | 612.741 |
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| ISSN on article: | 0022-3077 |
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| DOI: | 10.1152/jn.00031.2026 |
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| COBISS.SI-ID: | 277837059 |
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| Copyright: | © 2026 The Authors. |
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| Note: | Soavtorji: Aleš Holobar, Matej Kramberger, Nina Murks, Jakob Škarabot;
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| Publication date in DiRROS: | 12.05.2026 |
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| Views: | 322 |
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| Downloads: | 348 |
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