Caffeinated Ice Slushy Enhances 1,200 kJ Cycle Time-Trial Performance in the Heat

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.