Abstract

High-intensity intermittent exercise (HIIE) can elicit substantial thermal and physiological strain even in temperate environments. We examined whether pre-mid cooling using ice slurry ingestion would attenuate thermal strain and enhance physiological and performance recovery over 48h following HIIE under temperate conditions. Seventeen male team-sport athletes completed two HIIEs (four 22.5-min treadmill running quarters (Q1-4) at 420 km·h⁻¹ interspersed with overground sprints) in a randomized crossover design. Temperate (TEMP; 28°C) or ice slurry (ICE; –1°C) beverages were ingested pre- and mid-HIIE. A 10-s single cycling sprint (SS), repeated cycling sprints (10×6 s), root mean square of successive R-R intervals, muscle soreness, and muscle, cardiac, and inflammatory stress biomarkers were measured at pre- and over 48 h post-HIIE. Rectal temperature (Trec) remained lower in ICE from post-ingestion until pre-Q1 (−0.1 to −0.3 °C; P < 0.01–0.05; d= 0.5–1.1). At Q1, Trec was not significantly different between conditions (P = 0.053; d = 0.51). Trec was similar between conditions in the later quarters (P > 0.1; d ≤ 0.35). Peak SS power (change from baseline) improved in TEMP at 48 h (−0.7 ± 7.8%; P= 0.001; d= 1.20) but not in ICE (−4.8 ± 8.9%, P= 1.0; d= 0.02). MP significantly improved at 48 h in both conditions compared to post-exercise (P = 0.037), reaching 1.4 ± 8.1% in TEMP (d = 0.80) and −1.04 ± 7.1% in ICE (d = 0.15), with no between-condition difference (P = 0.072). Muscle soreness score was greater in TEMP (4.5 ±
0.8) than ICE (3.7 ± 1.1) at 24 h (P= 0.033; d= 0.57). Pre-and mid-exercise ice slurry ingestion may attenuate perceived muscle soreness; however, it may delay cycling power recovery following HIIE. Its use as a cooling strategy therefore warrants caution when performance recovery is a priority.