This study aimed to assess the effects of caffeine ingestion incorporated into an ice slushy on cycling time-trial (CTT) performance in hot, humid conditions. Nine moderately trained recreational male cyclists or triathletes ingested 6.8 g/kg crushed ice with either 6% carbohydrate concentration only (CON) or 6% carbohydrate concentration and 3 mg/kg caffeine (CAF) consumed over a 30 min period prior to exercise in a single-blind, counterbalanced design. Postingestion, participants completed a CTT equating 1,200 kJ of work (∼40 km) in a climate-controlled chamber (33 °C and 60% relative humidity). Experimental sessions were separated by 7 days. During each CTT, rectal temperature, cycling time, heart rate, blood lactate, and ratings of perceived exertion and thermal sensation were measured at set intervals of work. The 1,200 kJ CTT was completed faster in CAF (4,716 ± 785 s) compared with CON (4,911 ±755 s) (p < .05); and split times were completed faster in CAF compared with CON from the 800 to 1,200 kJ timepoints of the CTT. Precooling lowered rectal temperature similarly in both CAF (−0.6 ± 0.2 °C) and CON (−0.6 ± 0.1 °C) (p > .05). No differences were observed between CAF and CON for heart rate, rating of perceived exertion, rating of perceived thermal sensation, or blood lactate across the measured time points (p > .05). Precooling with the combination of a carbohydrate-based ice slushy and caffeine resulted in improved CTT performance in hot conditions compared with a carbohydrate-based ice slushy alone. Therefore, the addition of caffeine to ice slushies might be considered by endurance athletes competing in the heat for enhanced performance gains.
Caffeinated Ice Slushy Enhances 1,200 kJ Cycle Time-Trial Performance in the Heat
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Landers https://orcid.org/0000-0002-2679-4342
Zimmermann (matt.zimmermann@uwa.edu.au) is corresponding author, https://orcid.org/0009-0003-3764-3499
Supplementary Materials
- Supplementary Material (PDF 393 KB)
The study investigated the combined effects of ice ingestion (precooling) and caffeine consumption on endurance performance in hot conditions (34 °C). Nine trained male cyclists and triathletes participated in two experimental trials, ingesting either an ice slushy with caffeine or a placebo prior to a 1,200 kJ (∼40 km) cycling time trial. Key findings were: (a) The combination of ice ingestion and caffeine led to a significantly faster completion time of the cycle time trial (4,716 s; 78:36 min) compared with ice ingestion alone (4,911 s; 81:51 min). Specifically, the cycle time trial was completed faster during the latter stages of the cycle time trial (800–1,200 kJ) with the combination of ice ingestion and caffeine. (b) Both conditions resulted in a similar reduction in core body temperature of approximately 0.6 °C due to precooling with 6.8 g/kg of crushed ice consumed within 30 min. This suggested that ice ingestion was effective in cooling the body without compromising performance. (c) While heart rate, perceived exertion, and thermal sensation increased throughout the cycle time trial, there were no significant differences between the caffeine and placebo conditions. This indicates that caffeine may have reduced the perception of effort, enabling increased work output and, therefore, better performance. Conclusions: The findings suggest that the addition of caffeine to precooling with ice ingestion provides further performance benefits compared with ice ingestion alone. This is likely through its effects on reducing perceived effort and enhancing central nervous system function through reduced core temperatures. Overall, athletes can incorporate this combined approach to optimize endurance performance while minimizing risks. Further research is needed to explore variations in precooling techniques, caffeine dosages, and timing for optimal endurance benefits.
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