Maunder, EdKilding, AndrewHamilton, Kate2023-10-102023-10-102023http://hdl.handle.net/10292/16759Purpose: Physiological characteristics such as power output at the moderate-to-heavy intensity transition degrade during prolonged exercise. Resilience to this has been termed ‘durability’. The relationship between durability and performance has not been well-characterised. Therefore, the purpose of the present investigation was to assess the relationship between durability and the effect of prolonged exercise on severe- intensity performance, and explore intramuscular correlates of durability. Methods: Thirteen well-trained endurance cyclists and triathletes (11 males, 2 females, V̇ O₂peak 57.3 ± 4.8 mL.kg⁻¹.min⁻¹, training volume 12 ± 2.1 h.week⁻¹) performed four laboratory visits. On separate days, an incremental test and 5-min time-trial (TT) was performed to determine power output at the first ventilatory threshold (VT₁) and severe- intensity performance, with (POST) and without (PRE) 150-min of prior moderate- intensity cycling. A resting vastus lateralis microbiopsy was also obtained. Results: Prolonged exercise reduced power output at VT₁ (211 ± 40 W vs. 198 ± 39 W, ∆ -13 ± 16 W, ∆ -6 ± 7%, P = 0.013) and 5-min TT performance (333 ± 75 W vs. 302 ± 63 W, ∆ -31 ± 41 W, ∆ -9 ± 10%, P = 0.017). The reduction in 5-min TT performance was significantly associated with durability of VT1 (rₛ = 0.719, P = 0.007), but not PFO. Durability of VT₁ was not related to vastus lateralis carnosine content, citrate synthase activity, or complex l activity. Conclusion: These data provide the first direct support for the hypothesis that durability of the moderate-to-heavy intensity transition is an important endurance performance parameter.enOpenAccess