Author(s): POFFÉ, C., LAURIKS, W., ROBBERECHTS, R., ENGELBRECHT, L., RAMAEKERS, M., TERBLANCHE, E., KOPPO, K., STALMANS, M., Institution: HASSELT UNIVERSITY, Country: BELGIUM, Abstract-ID: 2374

INTRODUCTION:
We previously showed that ketone ester (KE) ingestion improved endurance performance during a three-week overload training period [1], and enhanced skeletal muscle mitochondrial content following an 8-week training period [2]. However, the precise impact of KE ingestion on mitochondrial function in response to intensified training remains unknown. Therefore, we simulated an 8-day cycling race (RACE) to assess the effects of KE on exercise performance and mitochondrial function.
METHODS:
In a double-blind, placebo-controlled, parallel trial, eighteen well-trained cyclists completed RACE. Immediately following each stage and 30 minutes before sleep, the participants received either 25g KE (n=8) or a taste-matched placebo (n=10, CON). Before (PRE) and after (POST) RACE, exercise performance was evaluated through a 30 minute time-trial, and biopsies were obtained from the m. vastus lateralis to evaluate mitochondrial function using high-resolution respirometry.
RESULTS:
KE intake increased blood [B-hydroxyburate] to 2.6 ± 1.3 mM (p<0.001) within 30 minutes, while blood [B-hydroxybutyrate] remained low (<0.5 mM) in CON. KE was ineffective to counteract the reduction in both time-trial performance (~-3%, p=0.026) and peak heart rate (~-11 bpm, p=0.002) from PRE to POST. Irrespective of KE ingestion, RACE selectively decreased complex I-linked oxidative phosphorylation capacity (p=0.040), and lowered both phosphorylation and substrate control ratios (both p<0.001). Conversely, electron transport system capacity through complexes I and II, as well as leak and coupling control ratios remained stable over time (all p > 0.05).
CONCLUSION:
These data indicate that an 8-day cycling race induces acute fatigue as evidenced by a decrease in endurance performance and lowered peak heart rate. This was accompanied by selective modulation of mitochondrial function. KE ingestion did not mitigate decrements in either exercise performance, nor alterations in mitochondrial function.

[1] Poffé C, Ramaekers M, Van Thienen R, Hespel P. J Physiol. 2019.
[2] Robberechts R, Bekhuis Y, Stalmans M, Lauriks W, Kusters M, Taha K, Rosseel T, Claessen G, Poffé C. J Physiol. 2026.