Thermoregulatory responses to ingesting cold and hot drinks in man at seated rest and during cycling exercise

University College London 2006 (2006) Proc Physiol Soc 3, PC127
Poster Communications

Jason KW Lee1, Susan M Shirreffs1, Ronald J Maughan1

1. School of Sport and Exercise Sciences, Loughborough University, Leicestershire, United Kingdom.

The physiological effects of ingesting drinks at different temperatures at rest are unclear (Imms & Lighten, 1989).

During exercise at 50% [vdot]O2peak, the rise in body temperature was similar after ingesting hot or cold drinks (Lee et al. 2004). This study compared thermal responses to ingesting cold and hot drinks at rest and during cycling exercise.

Eight men rested for 75 min (R) or cycled (EX) at 60 ± 1% (Mean ± SD) [vdot]O2peak at 25.3 ± 0.2°C with relative humidity of 56 ± 5%. Subjects ingested 300 ml of cold (C; 4°C) or hot (H; 50°C) flavoured water at 15, 30, 45 and 60 min during each trial. Rectal temperature (Tre), weighted mean skin temperature (Tsk; Ramanathan, 1964), heart rate (HR), skin blood flow (SBF), sweat loss and thermal comfort (TC; adapted from Parsons, 2003) were recorded.

Differences (P<0.05) between trials were assessed using ANOVA followed by Tukey post-hoc and paired t test as appropriate. As there were no differences between trials prior to drinking, the remaining hour was used to assess the effect of drink temperature.

The change in Tre over each trial was different between trials (-0.71 ± 0.24, 0.03 ± 0.07, 0.49 ± 0.17 and 0.74 ± 0.28°C for trials R-C, R-H, EX-C and EX-H, respectively; P<0.05). Tre changed on all trials throughout the 1-h period except on trial R-H.

Mean Tsk was lower with ingestion of cold drinks than with hot drinks at rest (31.44 ± 0.42 and 31.70 ± 0.30°C for trials R-C and R-H, respectively; P<0.05) but not during exercise (32.82 ± 0.64 and 33.05 ± 0.61°C for trials EX-C and EX-H, respectively; P=0.074).

Ingestion of hot drinks resulted in higher HR at rest (58 ± 8 and 64 ± 7 beats/min for trials R-C and R-H, respectively; P<0.01) and during exercise (145 ± 12 and 150 ± 12 beats/min for trials EX-C and EX-H, respectively; P<0.05).

There was no difference between drinks in mean SBF relative to baseline at rest (-20 ± 17 and -7 ± 13% for trials R-C and R-H, respectively; P=0.152) or during exercise (473 ± 184 and 601 ± 283% for trials EX-C and EX-H, respectively; P=0.242).

Sweat loss during exercise was higher when hot drinks were ingested (EX-C = 1.15 ± 0.22 l; EX-H = 1.31 ± 0.25 l; P<0.01).

Ratings of TC were affected by drink temperature (-3.5 ± 1.5, 0.7 ± 0.8, 2.5 ± 1.6 and 3.5 ± 1.3 for trials R-C, R-H, EX-C and EX-H, respectively; P<0.05). The predicted differential in Tre between the cold and hot drinks was 0.99 ± 0.11°C (Nadel & Horvath 1969), but the observed differentials at rest and during exercise were 0.74 ± 0.29 (P<0.01) and 0.24 ± 0.17°C (P<0.01), respectively.

These results show significant thermoregulatory effects of drink temperature. Cold drinks ingested at rest caused a fall in Tre whereas Tre remained stable with hot drinks. The unaccounted differential from the predicted Tre during exercise may be due to a higher evaporative heat loss.