Barrett, Andrew MSMaunder, Ed2025-12-082025-12-082025-04-29European Journal of Applied Physiology, ISSN: 1439-6319 (Print); 1439-6327 (Online), Springer Science and Business Media LLC, 125(10), 2897-2910. doi: 10.1007/s00421-025-05792-41439-63191439-6327http://hdl.handle.net/10292/20347Aim: To investigate the impact of prolonged running on speed at the moderate-to-heavy intensity transition, and whether increased eccentric load modifies exercise-induced shifts in the moderate-to-heavy intensity transition. Methods: Twelve endurance-trained runners (4 females, 8 males, peak oxygen uptake 51.5 mL kg−1 min−1 in females and 56.1 mL kg−1 min−1 in males) participated. Following trials to assess speed at the first ventilatory threshold (VT1) on a 0% gradient and -10% gradient, participants completed two trials: (i) level trial (LVL): 120-min of running at 0% gradient and (ii) downhill trial (DH): 120-min of running with 90-min at 0% gradient and 6 × 5-min intervals at -10% gradient (DH). Running was conducted at 90% of VT1 speed for respective gradients. Speed at VT1 on 0% gradient, perceived leg muscle soreness, and maximal voluntary isometric knee extensor torque were assessed pre- and post-prolonged exercise. Results: An effect of time was observed for speed at VT1 (∆-6.2 ± 3.6% in LVL and ∆-7.6 ± 3.2% in DH, P < 0.001), with no effect of condition (LVL vs. DH, P = 0.382), or time × condition interaction (P = 0.295). Reduced metabolic energy expenditure (metabolic power) significantly contributed to the reduced speed at VT1 in both trials (P < 0.001), whereas changes in running economy (energetic efficiency) did not (P = 0.228). Conclusion: Prolonged moderate-intensity running reduced speed at the moderate-to-heavy intensity transition, but this was not exacerbated by increased eccentric load. Reduced speed at the moderate-to-heavy intensity transition following prolonged running was primarily attributed to decreased metabolic power.Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.http://creativecommons.org/licenses/by/4.0/DurabilityEccentricEnduranceMarathonRunningThresholds32 Biomedical and Clinical Sciences42 Health Sciences3202 Clinical Sciences4207 Sports Science and ExerciseClinical Trials and Supportive ActivitiesClinical Research6.7 Physical1106 Human Movement and Sports SciencesSport Sciences3202 Clinical sciences3208 Medical physiology4207 Sports science and exerciseHumansRunningMaleFemaleAdultOxygen ConsumptionPhysical EnduranceMuscle, SkeletalMyalgiaYoung AdultMuscle, SkeletalHumansOxygen ConsumptionPhysical EnduranceRunningAdultFemaleMaleYoung AdultMyalgiaHumansRunningMaleFemaleAdultOxygen ConsumptionPhysical EnduranceMuscle, SkeletalMyalgiaYoung AdultJournal ArticleOpenAccess10.1007/s00421-025-05792-4