Passive Warm-up via Hot-Water Immersion Provides Similar Cycling Performance Benefits to Active Warm-up During a 12-Minute Cycling Time Trial.

PURPOSE: To determine whether passive warm-up via lower-limb hot-water immersion (HWI) at 42 °C produces 12-minute cycling time-trial (TT) performance comparable to active warm-up (AWU) in trained cyclists, and whether combining both strategies (HWI + AWU) confers additional benefit. METHODS: Twenty-seven tier 2 to 3 cyclists (20 men and 7 women; age 25 [4] y; training volume 9 [3] h/wk) completed a randomized, crossover trial. Participants performed AWU, HWI (42 °C, 45 min), or HWI + AWU before a 12-minute TT. Power output, heart rate, muscle oxygen saturation, VO2/kg, VCO2/kg, respiratory exchange ratio, blood lactate, and rating of perceived exertion were measured. RESULTS: Power output did not differ between conditions (AWU: 259 [52] W; HWI: 255 [53] W; HWI + AWU: 257 [53] W; P = .308), nor did heart rate, muscle oxygen saturation, VCO2/kg, or respiratory exchange ratio. VO2/kg was lower following HWI than AWU (P < .05), with a blunted response during the first 120 seconds and elevated VCO2/kg during the first 60 seconds, converging thereafter. Pre-TT blood lactate was lower in HWI (1.16 [0.42] mmol/L) than AWU (4.01 [1.63] mmol/L) and HWI + AWU (4.55 [1.75] mmol/L; P < .001). End-trial rating of perceived exertion was higher following HWI than AWU and HWI + AWU (P < .001). CONCLUSIONS: Lower-limb HWI at 42 °C for 45 minutes produces TT performance equivalent to a standardized AWU, with no additive benefit from combining strategies. These findings establish HWI as a viable preparatory alternative for high-intensity endurance cycling, particularly when conventional active preparation is constrained.