{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T13:07:01Z","timestamp":1784725621593,"version":"3.55.0"},"reference-count":45,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,6,17]],"date-time":"2026-06-17T00:00:00Z","timestamp":1781654400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Physiol."],"abstract":"<jats:p>East African and Norwegian endurance training systems have both produced world-class distance runners, despite substantial differences in how training is organized, regulated, and executed. East African training is commonly characterized by group-based execution, variable pacing, fartlek-style sessions, and internally regulated intensity, often within altitude-associated environments. In contrast, the Norwegian model emphasizes threshold-density training, lactate-guided intensity control, structured interval formats, and repeated moderate-intensity sessions embedded within a high volume of low-intensity work. The purpose of this narrative review was to compare these two endurance training systems, examine their underlying physiological characteristics, and propose a conceptual framework describing distinct pathways to elite endurance performance. The available literature suggests that variability-driven training may favor adaptability, recruitment diversity, and tolerance to pace fluctuations, whereas threshold-density training, embedded within a high volume of low-intensity work, may promote metabolic efficiency, lactate regulation, and steady-state durability. Although these systems differ markedly in training organization, both appear capable of supporting world-class endurance performance. These observations suggest that elite endurance performance does not depend on a single optimal training model but may emerge through different organizational routes to physiological adaptation and performance development.<\/jats:p>","DOI":"10.3389\/fphys.2026.1878492","type":"journal-article","created":{"date-parts":[[2026,6,17]],"date-time":"2026-06-17T04:47:10Z","timestamp":1781671630000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Training variability and threshold density: a conceptual comparison of East African and Norwegian endurance training systems"],"prefix":"10.3389","volume":"17","author":[{"given":"Gerasimos V.","family":"Grivas","sequence":"first","affiliation":[{"name":"Physical Education and Sports, Division of Humanities and Political Sciences, Hellenic Naval Academy","place":["Piraeus, Athens, Greece"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Walaa Jumah","family":"Alkasasbeh","sequence":"additional","affiliation":[{"name":"Department of Physical Education, School of Sports Sciences, The University of Jordan","place":["Amman, Jordan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ioannis","family":"Trigonis","sequence":"additional","affiliation":[{"name":"Department of Physical Education and Sport Science, Democritus University of Thrace","place":["Komotini, Greece"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Konstantinos","family":"Karakatsanis","sequence":"additional","affiliation":[{"name":"Physical Education and Sports, Division of Humanities and Political Sciences, Hellenic Naval Academy","place":["Piraeus, Athens, Greece"]},{"name":"Department of Physical Education and Sport Science, Democritus University of Thrace","place":["Komotini, Greece"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Adam Tawfiq","family":"Amawi","sequence":"additional","affiliation":[{"name":"Department of Movement Sciences and Sports Training, School of Sports Sciences, The University of Jordan","place":["Amman, Jordan"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,6,17]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"639","DOI":"10.1123\/ijspp.8.6.639","article-title":"Effects of different uphill interval-training programs on running economy and performance","volume":"8","author":"Barnes","year":"2013","journal-title":"Int. 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