Effects of different precooling techniques on repeat sprint ability in team sport athletes

This study aimed to compare the simultaneous use of internal and external precooling methods with singular methods and their effect on repeated sprint cycling in hot/humid conditions. Twelve male team sport players completed four experimental conditions, initially involving a 30-min precooling period consisting of either a cooling jacket (J); ingestion of an ice slushy ice slushy; combination of cooling jacket and ice ingestion (J + ice slushy); or control (CONT). This was followed by 70 min of repeat sprint cycling (in~35°C, 60% relative humidity [RH]), consisting of 2 × 30-min halves, separated by a 10-min half-time period where the same cooling method was again used. Each half comprised 30 × 4 s maximal sprints on 60 s, interspersed with sub-maximal exercise at varying intensities. Total mean power and work performed were significantly higher (p = 0.02) in J + ice slushy (233.6 ± 31.4 W) compared to ice slushy (211.8 ± 34.5 kJ), while moderate effect sizes (ES: d = 0.67) suggested lower core temperatures (TC) in J + ice slushy (36.8 ± 0.3°C) compared to J (37.0 ± 0.3°C) and CONT (37.0 ± 0.3°C) following precooling. A moderate ES (d = 0.57) also indicated lower TC in J + ice slushy (38.2 ± 0.3) compared to ice slushy (38.4 ± 0.4°C) after half-time cooling. Change (Δ) in mean skin temperature over half-time cooling was significantly greater (p = 0.036) for J (1.0 ± 0.4°C) compared to ice slushy (0.5 ± 0.5°C), and ES (d = 0.5-1.10) also suggested a greater Δ for J compared to the other conditions. Sweat loss was significantly greater (p < 0.05) in ice slushy and J + ice slushy compared to J and CONT. In conclusion, a combination of (external and internal) body cooling techniques may enhance repeated sprint performance in the heat compared to individual cooling methods.