Ergogenic effects of precooling with cold water immersion and ice ingestion: A meta-analysis

This review evaluated the effects of precooling via cold water immersion (CWI) and ingestion of ice slurry/slushy or crushed ice (ICE) on endurance performance measures (e.g. time-to-exhaustion and time trials) and psychophysiological parameters (core [T_core] and skin [T_skin] temperatures, whole body sweat [WBS] response, heart rate [HR], thermal sensation [TS], and perceived exertion [RPE]). Twenty-two studies were included in the meta-analysis based on the following criteria: (i) cooling was performed before exercise with ICE or CWI; (ii) exercise longer than 6 min was performed in ambient temperature ≥26°C; and (iii) crossover study design with a non-cooling passive control condition. CWI improved performance measures (weighted average effect size in Hedges' g [95% confidence interval] + 0.53 [0.28; 0.77]) and resulted in greater increase (ΔEX) in T_skin (+4.15 [3.1; 5.21]) during exercise, while lower peak T_core (-0.93 [-1.18; -0.67]), WBS (-0.74 [-1.18; -0.3]), and TS (-0.5 [-0.8; -0.19]) were observed without concomitant changes in ΔEX-T_core (+0.19 [-0.22; 0.6]), peak T_skin (-0.67 [-1.52; 0.18]), peak HR (-0.14 [-0.38; 0.11]), and RPE (-0.14 [-0.39; 0.12]). ICE had no clear effect on performance measures (+0.2 [-0.07; 0.46]) but resulted in greater ΔEX-T_core (+1.02 [0.59; 1.45]) and ΔEX-T_skin (+0.34 [0.02; 0.67]) without concomitant changes in peak T_core (-0.1 [-0.48; 0.28]), peak T_skin (+0.1 [-0.22; 0.41]), peak HR (+0.08 [-0.19; 0.35]), WBS (-0.12 [-0.42; 0.18]), TS (-0.2 [-0.49; 0.1]), and RPE (-0.01 [-0.33; 0.31]). From both ergogenic and thermoregulatory perspectives, CWI may be more effective than ICE as a precooling treatment prior to exercise in the heat.