{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T17:28:05Z","timestamp":1785432485072,"version":"3.56.0"},"reference-count":41,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2026,4,2]],"date-time":"2026-04-02T00:00:00Z","timestamp":1775088000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Catholic University of Valencia"},{"id":[{"id":"https:\/\/ror.org\/043nxc105","id-type":"ROR","asserted-by":"publisher"}]},{"name":"Catedra Endavant Villarreal CF de l\u2019Esport and Penyagolosa Trails"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Diagnostics"],"abstract":"<jats:p>Background\/Objectives: Understanding how different fatigue contexts influence muscle architecture is essential for optimizing training and recovery strategies in endurance athletes. Ultramarathon running involves prolonged mechanical load and high eccentric demands, which may elicit different acute responses compared to controlled laboratory protocols. This study aimed to examine the effects of time, condition (laboratory vs. race), and muscle on ultrasound-derived muscle architecture in ultratrail runners. Methods: A repeated-measures within-subject design was employed. Forty ultratrail runners completed two fatigue conditions: (1) a standardized laboratory downhill running protocol and (2) an ultramarathon race (CSP 2025; 106 km, +5600 m elevation gain). Muscle thickness and pennation angle of the rectus femoris, vastus lateralis, and medial gastrocnemius were assessed using ultrasound before and after each condition. Linear mixed models were used to evaluate the effects of time, condition, muscle, and their interactions. Results: Forty participants were recruited; 29 completed all assessments. No significant effects of time or condition were observed for muscle thickness, and no interaction effects were detected, indicating that muscle size remained stable across conditions and time points. A significant main effect of muscle was identified (p &lt; 0.001), reflecting inherent morphological differences, with greater thickness in the vastus lateralis compared to the rectus femoris and medial gastrocnemius. In contrast, pennation angle showed a significant main effect of condition (p = 0.031) and a significant condition \u00d7 muscle interaction (p = 0.005), indicating muscle-specific differences between laboratory and race contexts. No significant effect of time was observed for pennation angle. Conclusions: Muscle thickness appears to remain stable following acute fatigue, regardless of the assessment context. In contrast, pennation angle may be more sensitive to condition-specific and muscle-dependent factors. These findings suggest that ultrasound-derived architectural changes observed immediately after exercise likely reflect acute physiological responses rather than true structural adaptations. Therefore, the interpretation of muscle architecture should consider both contextual factors and methodological constraints.<\/jats:p>","DOI":"10.3390\/diagnostics16071080","type":"journal-article","created":{"date-parts":[[2026,4,2]],"date-time":"2026-04-02T14:09:54Z","timestamp":1775138994000},"page":"1080","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Context-Dependent Differences in Muscle Architecture Following Fatigue in Ultramarathon Athletes: A Comparison Between Laboratory and Real Race Settings"],"prefix":"10.3390","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2710-2931","authenticated-orcid":false,"given":"Juan","family":"Vicente-Mampel","sequence":"first","affiliation":[{"name":"Department of Physiotherapy, Medicine and Health Science School, Catholic University of Valencia, 46090 Torrent, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2942-1293","authenticated-orcid":false,"given":"Ignacio","family":"Martinez-Navarro","sequence":"additional","affiliation":[{"name":"Physical Education and Sports Department, University of Valencia, 46010 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8062-4152","authenticated-orcid":false,"given":"Eladio","family":"Collado","sequence":"additional","affiliation":[{"name":"Faculty of Health Sciences, Jaume I University, 12071 Castellon, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4636-7065","authenticated-orcid":false,"given":"Ra\u00fal","family":"Lopez-Grueso","sequence":"additional","affiliation":[{"name":"Department of Education and Specific Didactics, Jaume I University, 12071 Castellon, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1605-3444","authenticated-orcid":false,"given":"Eloy","family":"Jaenada-Carrilero","sequence":"additional","affiliation":[{"name":"Department of Physiotherapy, Medicine and Health Science School, Catholic University of Valencia, 46090 Torrent, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7182-4785","authenticated-orcid":false,"given":"Carlos","family":"Hernando","sequence":"additional","affiliation":[{"name":"Department of Education and Specific Didactics, Jaume I University, 12071 Castellon, Spain"},{"name":"Sport Service, Jaume I University, 12071 Castellon, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"791","DOI":"10.1007\/s40122-025-00721-x","article-title":"Advances in musculoskeletal ultrasound for assistive diagnosis in pain clinics","volume":"14","author":"Zhang","year":"2025","journal-title":"Pain Ther."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1308","DOI":"10.1113\/EP091334","article-title":"Ultrasonographic measurements of fascicle length overestimate adaptations in serial sarcomere number","volume":"108","author":"Hinks","year":"2023","journal-title":"Exp. Physiol."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Enomoto, S., and Tottori, N. (2025). Muscle morphological adaptations to resistance training and sports participation in children and adolescents: A scoping review. Front. Sports Act. Living, 7.","DOI":"10.3389\/fspor.2025.1646835"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1152\/japplphysiol.00280.2020","article-title":"Differential changes in muscle architecture and neuromuscular fatigability induced by isometric resistance training at short and long muscle\u2013tendon unit lengths","volume":"129","author":"Akagi","year":"2020","journal-title":"J. Appl. Physiol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1640","DOI":"10.1111\/brv.12856","article-title":"From fibre to function: Are we accurately representing muscle architecture and performance?","volume":"97","author":"Charles","year":"2022","journal-title":"Biol. Rev."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2741","DOI":"10.1519\/JSC.0000000000003941","article-title":"Muscle architecture and maturation influences sprint and jump ability in young boys: A multi-study approach","volume":"36","author":"Radnor","year":"2022","journal-title":"J. Strength Cond. Res."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"230","DOI":"10.1016\/j.jbiomech.2019.07.042","article-title":"Development of a finite element musculoskeletal model with the ability to predict contractions of three-dimensional muscles","volume":"94","author":"Li","year":"2019","journal-title":"J. Biomech."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"jeb236679","DOI":"10.1242\/jeb.236679","article-title":"Great power comes at a high locomotor cost: The role of muscle fascicle length in the power versus economy performance trade-off","volume":"224","author":"Cooper","year":"2021","journal-title":"J. Exp. Biol."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Pradas, F., Falc\u00f3n, D., Pe\u00f1arrubia-Lozano, C., Toro-Rom\u00e1n, V., Carrasco, L., and Castellar, C. (2021). Effects of ultratrail running on neuromuscular function, muscle damage and hydration status. Int. J. Environ. Res. Public Health, 18.","DOI":"10.3390\/ijerph18105119"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Constantin-Teodosiu, D., and Constantin, D. (2021). Molecular mechanisms of muscle fatigue. Int. J. Mol. Sci., 22.","DOI":"10.3390\/ijms222111587"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"400","DOI":"10.1080\/15438627.2022.2122826","article-title":"Effects of ibuprofen during 42-km trail running on oxidative stress, muscle fatigue, muscle damage and performance","volume":"32","author":"Ferreira","year":"2024","journal-title":"Res. Sports Med."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1001","DOI":"10.1007\/s00421-024-05656-3","article-title":"Reliability of functional and systemic markers of muscle damage in response to a flywheel squat protocol","volume":"125","author":"Dufner","year":"2025","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"111895","DOI":"10.1016\/j.jbiomech.2023.111895","article-title":"In vivo human medial gastrocnemius fascicle behaviour and belly gear during submaximal eccentric contractions are not affected by concentric fatiguing exercise","volume":"162","author":"Pinto","year":"2024","journal-title":"J. Biomech."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"105526","DOI":"10.1016\/j.jamda.2025.105526","article-title":"Intervention response of muscle architecture and composition markers assessed via ultrasound imaging","volume":"26","author":"Osuka","year":"2025","journal-title":"J. Am. Med. Dir. Assoc."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3349","DOI":"10.1007\/s00421-021-04787-1","article-title":"Cyclic eccentric stretching induces more damage and improved subsequent protection than stretched isometric contractions","volume":"121","author":"Pincheira","year":"2021","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"535","DOI":"10.1007\/s40279-024-02127-9","article-title":"Decoding ultramarathon: Muscle damage as the main impediment to performance","volume":"55","author":"Tiller","year":"2025","journal-title":"Sports Med."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"20","DOI":"10.1186\/s13089-025-00424-6","article-title":"Examiner experience moderates reliability of human lower extremity muscle ultrasound measurement","volume":"17","author":"Warneke","year":"2025","journal-title":"Ultrasound J."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Buffet-Garc\u00eda, J., Plaza-Manzano, G., Varol, U., R\u00edos-Le\u00f3n, M., D\u00edaz-Arribas, M.J., \u00c1lvarez-Gonz\u00e1lez, J., S\u00e1nchez-Jorge, S., and Valera-Calero, J.A. (2024). Reliability of panoramic ultrasound in assessing rectus femoris. Bioengineering, 11.","DOI":"10.3390\/bioengineering11010082"},{"key":"ref_19","unstructured":"World Medical Association (2013). WMA Declaration of Helsinki\u2014Ethical Principles for Medical Research Involving Human Participants, World Medical Association."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"STROBE Initiative (2007). Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. Ann. Intern. Med., 147, 573\u2013577.","DOI":"10.7326\/0003-4819-147-8-200710160-00010"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1135","DOI":"10.1249\/MSS.0000000000002240","article-title":"Trail runners cannot reach VO2max during a maximal incremental downhill test","volume":"52","author":"Lemire","year":"2020","journal-title":"Med. Sci. Sports Exerc."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"78","DOI":"10.1519\/JSC.0000000000002595","article-title":"Absolute reliability and concurrent validity of the Stryd system for assessing running stride kinematics","volume":"35","year":"2021","journal-title":"J. Strength Cond. Res."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Smith, C.P., Fullerton, E., Walton, L., Funnell, E., Pantazis, D., and Lugo, H. (2022). The validity and reliability of wearable devices for measuring vertical oscillation. PLoS ONE, 17.","DOI":"10.1371\/journal.pone.0277810"},{"key":"ref_24","first-page":"664","article-title":"Architectural anatomy of the human tibialis anterior","volume":"243","author":"Calbet","year":"2023","journal-title":"J. Anat."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"671","DOI":"10.1038\/nmeth.2089","article-title":"NIH Image to ImageJ: 25 years of image analysis","volume":"9","author":"Schneider","year":"2012","journal-title":"Nat. Methods"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Sidiropoulos, G., Strimpakos, N., Kanellopoulos, A.K., Tsekoura, M., Alexiou, K., Papakonstantinou, O., and Dimitriadis, Z. (2025). Measurement Reliability for the Anatomical Characteristics of Cervical Muscles Using Musculoskeletal Ultrasound in Healthy Individuals. Muscles, 4.","DOI":"10.3390\/muscles4030028"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"30186","DOI":"10.1038\/s41598-025-11437-5","article-title":"Estimating vastus lateralis muscle volume from a single ultrasound image","volume":"15","author":"Eggelbusch","year":"2025","journal-title":"Sci. Rep."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"531","DOI":"10.1589\/jpts.27.531","article-title":"Evaluation of muscle damage using ultrasound imaging","volume":"27","author":"Yu","year":"2015","journal-title":"J. Phys. Ther. Sci."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1911","DOI":"10.1007\/s00421-023-05201-8","article-title":"Enhanced skeletal muscle contractile function precedes structural adaptations during resistance training","volume":"123","author":"Wilson","year":"2023","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Wilson, M.T., Ryan, A.M.F., Vallance, S.R., Dias-Dougan, A., Dugdale, J.H., Hunter, A.M., Hamilton, D.L., and Macgregor, L.J. (2019). Tensiomyography-derived parameters reflect architectural adaptations after 6 weeks of training. Front. Physiol., 10.","DOI":"10.3389\/fphys.2019.01493"},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Guerrero, C., Collado-Boira, E., Martinez-Navarro, I., Hernando, B., Hernando, C., Balino, P., and Muriach, M. (2021). Impact of oxidative stress markers on post-race recovery in ultramarathon runners. Antioxidants, 10.","DOI":"10.3390\/antiox10030355"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1016\/j.jcm.2016.02.012","article-title":"A guideline for selecting and reporting ICC for reliability research","volume":"15","author":"Koo","year":"2016","journal-title":"J. Chiropr. Med."},{"key":"ref_33","unstructured":"Rosner, B. (2010). Fundamentals of Biostatistics, Cengage Learning."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"939","DOI":"10.1152\/japplphysiol.00859.2024","article-title":"Eight weeks of eccentric training increases fascicle length","volume":"138","author":"Bizet","year":"2025","journal-title":"J. Appl. Physiol."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1159","DOI":"10.1007\/s00421-021-04608-5","article-title":"Effects of high-volume static stretching on plantar-flexor strength and architecture","volume":"121","author":"Yahata","year":"2021","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1324","DOI":"10.1111\/joa.13750","article-title":"Three-dimensional architecture of human medial gastrocnemius fascicles","volume":"241","author":"Takahashi","year":"2022","journal-title":"J. Anat."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"107401","DOI":"10.1016\/j.ultras.2024.107401","article-title":"Wearable ultrasound devices: An emerging era for biomedicine","volume":"142","author":"Hu","year":"2024","journal-title":"Ultrasonics"},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Taxiarchopoulos, N., Drakonaki, E., Gianniotis, M., Matzaroglou, C., Tsepis, E., and Billis, E. (2023). Real-time diagnostic ultrasound as biofeedback training in low back pain. Healthcare, 11.","DOI":"10.3390\/healthcare11101396"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Lesinski, M., Bashford, G., Markov, A., Risch, L., and Cassel, M. (2024). Reliability of ultrasound and spatial frequency analysis for muscle architecture. Front. Sports Act. Living, 6.","DOI":"10.3389\/fspor.2024.1282031"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"e13609","DOI":"10.7717\/peerj.13609","article-title":"Reliability and accuracy of ultrasound image analyses manually vs. automated","volume":"10","author":"Wohlgemuth","year":"2022","journal-title":"PeerJ"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1140","DOI":"10.1249\/MSS.0000000000003387","article-title":"Running 40 min in heat or temperate environments does not affect operating fascicle length","volume":"56","author":"Mornas","year":"2024","journal-title":"Med. Sci. Sports Exerc."}],"container-title":["Diagnostics"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2075-4418\/16\/7\/1080\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,7]],"date-time":"2026-04-07T08:29:34Z","timestamp":1775550574000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2075-4418\/16\/7\/1080"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,2]]},"references-count":41,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2026,4]]}},"alternative-id":["diagnostics16071080"],"URL":"https:\/\/doi.org\/10.3390\/diagnostics16071080","relation":{},"ISSN":["2075-4418"],"issn-type":[{"value":"2075-4418","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,2]]}}}