Exercise in warm environments increases thermal/cardiovascular strain and decreases gastrointestinal (GI) integrity and endurance performance. However, laboratory-based studies have provided little to/no facing airflow, potentially exacerbating these effects, particularly for cycling, where convective cooling may be a major contributor to thermal balance. PURPOSE This study investigated the effect of cycling in a warm vs temperate environment with sufficient facing airflow on exogenous glucose use, performance, and GI responses. METHODS Ten trained male cyclists/triathletes (36 ± 6 y; 55 ± 6 mL/kg/min) completed V̇O2peak and familiarisation trials, and two experimental trials in 19 °C (TEMP) and 32 °C (WARM). Experimental trials involved 2 h cycling at ~50% Wpeak (preload) and an ~15 min time trial (TT) with fan-provided airflow covering the cyclist (preload: ~29 km/h, TT: ~35 km/h). A glucose drink containing [U-13C]-glucose was consumed every 20 min during the preload (72 g/h). RESULTS Average 40-120 min (TEMP 0.56 ± 0.13 g/min; WARM 0.48 ± 0.12 g/min; 15%; P = 0.015) and peak (TEMP 0.79 ± 0.18 g/min; WARM 0.68 ± 0.14 g/min; 14%; P = 0.008) exogenous glucose oxidation were reduced in WARM. TT performance was 15% slower in WARM (TEMP 819 ± 47 s; WARM 961 ± 130 s; P = 0.002). GI temperature (P = 0.007), heart rate (P < 0.001), and RPE (P = 0.046) were greater during WARM. GI comfort (P = 0.659) and Intestinal Fatty Acid Binding Protein (IFABP) (P = 0.094) were not different between trials. CONCLUSIONS These data demonstrate that ability to use glucose provided in drinks was impaired during prolonged cycling in WARM. WARM ambient conditions impaired laboratory-based cycling performance, even with facing airflow approximating outdoor conditions, likely via impairments of thermoregulatory, cardiovascular, and metabolic function.

中文翻译：

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温暖的环境会减少外源性葡萄糖氧化，并在面对气流的骑行过程中降低耐力表现。


在温暖的环境中运动会增加热/心血管压力，并降低胃肠道 （GI） 完整性和耐力表现。然而，基于实验室的研究几乎没有提供气流，这可能会加剧这些影响，特别是对于自行车，其中对流冷却可能是热平衡的主要贡献者。目的 本研究调查了在暖温带环境中骑行对外源性葡萄糖使用、性能和胃肠道反应的影响。方法 10 名训练有素的男性自行车手/铁人三项运动员 （36 ± 6 岁;55 ± 6 mL/kg/min） 完成了 V̇O2peak 和熟悉试验，以及 19 °C （TEMP） 和 32 °C （WARM） 的两项实验试验。实验试验包括在 ~50% Wpeak（预载）下循环 2 小时和 ~15 分钟计时赛 （TT），风扇提供的气流覆盖骑车人（预载：~29 km/h，TT：~35 km/h）。在预负荷期间 （72 g/h） 每 20 分钟饮用一次含有 [U-13C]-葡萄糖的葡萄糖饮料。结果 平均 40-120 分钟 （温度 0.56 ± 0.13 g/min;温 0.48 ± 0.12 g/min;15%;P = 0.015）和峰值 （TEMP 0.79 ± 0.18 g/min;温 0.68 ± 0.14 克/分钟;14%;P = 0.008） 外源性葡萄糖氧化在 WARM 中降低。TT 性能在 WARM 中慢 15% （TEMP 819 ± 47 s;暖 961 ± 130 秒;P = 0.002）。WARM 期间 GI 温度 （P = 0.007） 、心率 （P < 0.001） 和 RPE （P = 0.046） 较高。胃肠道舒适度 （P = 0.659） 和肠道脂肪酸结合蛋白 （IFABP） （P = 0.094） 在试验之间没有差异。结论 这些数据表明，在 WARM 中长时间循环期间，使用饮料中提供的葡萄糖的能力受损。 WARM 环境条件损害了基于实验室的骑行表现，即使面对接近室外条件的气流，这可能是由于体温调节、心血管和代谢功能的损害。