Cold-Water Immersion Cooling Rates in Football Linemen and Cross-Country Runners With Exercise-Induced Hyperthermia.

CONTEXT:   Ideal and acceptable cooling rates in hyperthermic athletes have been established in average-sized participants. Football linemen (FBs) have a small body surface area (BSA)-to-mass ratio compared with smaller athletes, which hinders heat dissipation.

OBJECTIVE:   To determine cooling rates using cold-water immersion in hyperthermic FBs and cross-country runners (CCs).

DESIGN:   Cohort study.

SETTING:   Controlled university laboratory.

PATIENTS OR OTHER PARTICIPANTS:   Nine FBs (age = 21.7 ± 1.7 years, height = 188.7 ± 4 cm, mass = 128.1 ± 18 kg, body fat = 28.9% ± 7.1%, lean body mass [LBM] = 86.9 ± 19 kg, BSA = 2.54 ± 0.13 m2 , BSA/mass = 201 ± 21.3 cm2 /kg, and BSA/LBM = 276.4 ± 19.7 cm2 /kg) and 7 CCs (age = 20 ± 1.8 years, height = 176 ± 4.1 cm, mass = 68.7 ± 6.5 kg, body fat = 10.2% ± 1.6%, LBM = 61.7 ± 5.3 kg, BSA = 1.84 ± 0.1 m2 , BSA/mass = 268.3 ± 11.7 cm2 /kg, and BSA/LBM = 298.4 ± 11.7 cm2 /kg).

INTERVENTION(S):   Participants ingested an intestinal sensor, exercised in a climatic chamber (39°C, 40% relative humidity) until either target core temperature (Tgi ) was 39.5°C or volitional exhaustion was reached, and were immediately immersed in a 10°C circulated bath until Tgi declined to 37.5°C. A general linear model repeated-measures analysis of variance and independent t tests were calculated, with P < .05.

MAIN OUTCOME MEASURE(S):   Physical characteristics, maximal Tgi , time to reach 37.5°C, and cooling rate.

RESULTS:   Physical characteristics were different between groups. No differences existed in environmental measures or maximal Tgi (FBs = 39.12°C ± 0.39°C, CCs = 39.38°C ± 0.19°C; P = .12). Cooling times required to reach 37.5°C (FBs = 11.4 ± 4 minutes, CCs = 7.7 ± 0.06 minutes; P < .002) and therefore cooling rates (FBs = 0.156°C·min-1 ± 0.06°C·min-1 , CCs = .255°C·min-1 ± 0.05°C·min-1 ; P < .002) were different. Strong correlations were found between cooling rate and body mass (r = -0.76, P < .001), total BSA (r = -0.74, P < .001), BSA/mass (r = 0.73, P < .001), LBM/mass (r = 0.72, P < .002), and LBM (r = -0.72, P < .002).

CONCLUSIONS:   With cold-water immersion, the cooling rate in CCs (0.255°C·min-1 ) was greater than in FBs (0.156°C·min-1 ); however, both were considered ideal (≥0.155°C·min-1 ). Athletic trainers should realize that it likely takes considerably longer to cool large hyperthermic American-football players (>11 minutes) than smaller, leaner athletes (7.7 minutes). Cooling rates varied widely from 0.332°C·min-1 in a small runner to only 0.101°C·min-1 in a lineman, supporting the use of rectal temperature for monitoring during cooling.