The Effect of Cold and Warm Water Ingestion Prior to and During Passive Heating on Local Sweat Rate

Abstract

BACKGROUNDDuring heat stress, sweating is initiated to mitigate the rise in core temperature. Relative to warm water, previous evidence has demonstrated that cold water ingestion prior to exercise‐induced heat stress in compensable conditions delays the onset of sweating, and produces a reduction in local sweat rate immediately following ingestion. However, it remains unknown whether ingestion of cold water will elicit a similar delay in the onset of sweating and reduction in local sweating during more extreme thermal challenges. It is hypothesized that cold water ingestion prior to and during passive heat stress will result in a delayed onset of sweating and a reduction in local sweat rate in comparison to warm water.METHODSTo date, three male participants (25±4 years, 82±8 kg, 1.9±0.1 m) have completed two passive heating sessions using a water perfused blanket system to increase rectal temperature by 1˚C above baseline. Participants ingested 3.2 ml‧kg‐1 (263±27 mL) of either cold (1.5˚C, CW) or warm (37˚C, WW) water five minutes before passive heating, and following a 0.5˚C and 1.0˚C increase in rectal temperature. Local sweat rate of the forearm and mean skin temperature were measured throughout baseline and passive heating.RESULTSBaseline rectal temperature was not different between CW (37.0±0.2˚C) and WW (36.9±0.1˚C, p=0.17) trials. Mean skin temperature was not different at baseline (CW: 33.5±0.2˚C, WW: 33.1±0.4˚C, p=0.60), and following a 0.5˚C (CW: 38.9±0.5˚C, WW: 38.9±0.6˚C, p = 0.99) and 1.0˚C (CW: 39.3±0.5˚C, WW: 39.2±0.4˚C, p=0.58) increase in rectal temperature. Mean body temperature at the onset of sweating on the forearm was not affected by the water temperature (CW: 37.1±0.2˚C, WW: 37.1±0.3˚C, p=0.79). When compared to the 5‐minutes before 37˚C water ingestion (PRE), mean local sweat rate of the forearm was not different during the 10‐minutes after (POST) at 0.5˚C (PRE: 0.98±0.23 mg‧cm‐2‧min‐1, POST: 1.05±0.36 mg‧cm‐2‧min‐1, p=0.48) and 1.0˚C (PRE: 1.11±0.37 mg‧cm‐2‧min‐1, POST: 1.15±0.49 mg‧cm‐2‧min‐1, p=0.74) increase in rectal temperature. Similarly, mean local sweat rate of the forearm was not different POST compared to PRE ingestion of 1.5˚C water following a 0.5˚C (PRE: 0.89±0.28 mg‧cm‐2‧min‐1, POST: 0.88±0.27 mg‧cm‐2‧min‐1, p=0.74) and 1.0˚C (PRE: 0.93±0.42 mg‧cm‐2‧min‐1, POST: 0.92±0.41 mg‧cm‐2‧min‐1, p=0.71) increase in rectal temperature. However, CW ingestion following a 0.5˚C increase in rectal temperature resulted in a lower local sweat rate of the forearm in comparison to WW for the remainder of heating (p<0.03).CONCLUSIONPreliminary data suggest cold water ingestion may alter the local sweating response in young healthy males during passive heating.