Journal Article

Effect of internal and external cooling on high‐intensity intermittent cycling performance and cognitive function in the heat

Cooper, Simon B., Malcolm, Rachel, Cowe, Stacey, Sunderland, Caroline

2025

Overview

We investigated the effect of internal and external cooling on high‐intensity intermittent cycling performance and cognitive function in the heat. Twenty‐nine males completed a control trial (CON) and a cooling trial (ice slurry and ice collar; COOL) in the heat (33°C, 50% relative humidity) involving a 40 min intermittent cycling protocol (two sets of ten 2 min stages, each consisting of 5 s sprint, 105 s active recovery and 10 s rest). A battery of cognitive tests was completed pre‐ and postexercise, with physiological and perceptual responses recorded throughout. No differences in peak or mean power output were found between conditions (all p  > 0.05). Average trial rectal (COOL: 37.39°C ± 0.59°C; CON: 37.59°C ± 0.56°C, p  < 0.001) and neck (COOL: 28.87°C ± 4.87°C; CON: 32.82°C ± 1.43°C, P  < 0.001) temperatures were found to be lower in COOL. Participants reported feeling better and reported lower ratings of thermal sensation and improved comfort in COOL (all p  < 0.05). Response times on the Stroop task complex level were quicker over time in COOL (COOL: −48 ± 23 ms; CON: −11 ± 18 ms, p  = 0.002) and quicker overall on the number level of Sternberg during COOL (COOL: 434 ± 77 ms; CON: 437 ± 84 ms, p  = 0.046). However, over time, the improvement in response times on the number level of Sternberg was greater in CON (COOL: −6 ± 3 ms; CON: −26 ± 2 ms, p  = 0.015). Response times became quicker over time to a greater extent in CON on the visual search complex level (COOL: −15 ± 1 ms; CON: −119 ± 31 ms, p  = 0.009). The combined cooling intervention did not influence sprint performance and had only a minimal influence on some domains of cognitive function but did lead to improvements in physiological and perceptual responses. These findings provide information on a practical combined cooling method that can be implemented in elite sport. What is the central question of this study? The ability to repeatedly perform high‐intensity efforts interspersed with minimal recovery, coupled with optimal cognitive function, is imperative for successful team‐sport performance. However, both components face impairment when core temperatures reach 38.5°C, which can occur commonly when exercising in hot environments. What is the main finding and its importance? The combined cooling intervention was successful at lowering rectal and neck temperature and reducing heart rate. Additionally, the combined cooling intervention elicited lower ratings of thermal sensation, improved comfort and lower perceived exertion. Despite this, no differences were found in sprint performance.