Acute ketone monoester (KE) supplementation can alter exercise responses, but the performance effect is unclear. The limited and equivocal data to date are likely related to factors including the KE dose, test conditions, and caliber of athletes studied. We tested the hypothesis that mean power output during a 20-min cycling time trial (TT) would be different after KE ingestion compared to a placebo (PL). A sample size of 22 was estimated to provide 80% power to detect an effect size d_z of 0.63 at an alpha level of .05 with a two-tailed paired t test. This determination considered 2.0% as the minimal important difference in performance. Twenty-three trained cyclists (N = 23; peak oxygen uptake: 65 ± 12 ml·kg⁻¹ min⁻¹; M ± SD), who were regularly cycling >5 hr/week, completed a familiarization trial followed by two experimental trials. Participants self-selected and replicated their diet and exercise for ∼24 hr before each trial. Participants ingested either 0.35 g/kg body mass of (R)-3-hydroxybutyl (R)-3-hydroxybutyrate KE or a flavor-matched PL 30 min before exercise in a randomized, triple-blind, crossover manner. Exercise involved a 15-min warm-up followed by the 20-min TT on a cycle ergometer. The only feedback provided was time elapsed. Preexercise venous [β-hydroxybutyrate] was higher after KE versus PL (2.0 ± 0.6 vs. 0.2 ± 0.1 mM, p < .0001). Mean TT power output was 2.4% (0.6% to 4.1%; mean [95% confidence interval]) lower after KE versus PL (255 ± 54 vs. 261 ± 54 W, p < .01; d_z = 0.60). The mechanistic basis for the impaired TT performance after KE ingestion under the present study conditions remains to be determined.

急性酮单酯（KE）补充剂可以改变运动反应，但对运动表现的影响尚不清楚。迄今为止有限且模棱两可的数据可能与 KE 剂量、测试条件和所研究运动员的水平等因素有关。我们测试了这样一个假设：与安慰剂 (PL) 相比，摄入 KE 后 20 分钟循环计时试验 (TT) 期间的平均功率输出会有所不同。使用双尾配对t检验，估计 22 个样本大小可提供 80% 的功效，以在 0.05 的 alpha 水平下检测 0.63 的效应大小d _{z 。}该决定将 2.0% 视为性能的最小重要差异。23 名训练有素的自行车手（N  = 23；峰值摄氧量：65 ± 12 ml·kg ⁻¹分钟^-1 ; M  ±  SD）每周定期骑自行车超过 5 小时，完成了一项熟悉试验，随后进行了两项实验性试验。参与者在每次试验前约 24 小时内自行选择并重复他们的饮食和锻炼。参与者在运动前 30 分钟以随机、三盲、交叉方式摄入 0.35 克/公斤体重的 (R)-3-羟基丁基 (R)-3-羟基丁酸酯 KE 或口味匹配的 PL。锻炼包括 15 分钟的热身，然后在自行车测力计上进行 20 分钟的 TT。提供的唯一反馈是时间流逝。KE 与 PL 后运动前静脉 [β-羟基丁酸] 较高（2.0 ± 0.6 vs. 0.2 ± 0.1 mM，p < .0001)。KE 与 PL 后的平均 TT 功率输出降低 2.4%（0.6% 至 4.1%；平均值 [95% 置信区间]）（255 ± 54 与 261 ± 54 W，p < .01；d z  = 0.60 _）  。在目前的研究条件下摄入 KE 后 TT 性能受损的机制基础仍有待确定。