The Reliability of Local Sweat Rate Measured Via the Ventilated Capsule Technique: Effects of Measurement Region and Level of Heat Strain

Abstract

Ventilated capsules (i.e. hygrometry) are widely used to measure time dependent changes in local sweat rate. Despite this, understanding of the reliability (consistency) of local sweat rate is limited to the forearm during mild hyperthermia. Further, extensive regional heterogeneity in sweating may render some regions more reliable than others. Knowledge of reliability has important implications for experimental design, statistical analysis and interpretation, yet it is relatively unknown. The purpose of this study was to determine local sweat rate across various regions of the body and the reliability of these responses, during increasing levels of hyperthermia. On three separate instances, fourteen young men (age: 24 [SD 5] years) donned a whole-body water perfusion suit to raise and clamp esopogheal temperature at elicit low (+0.6°C), moderate (+1.2°C) and high (+1.8°C) levels of heat strain. Local sweat rate was measured at the forehead, chest, abdomen, bicep, forearm, hand, quadriceps, calf, and foot via ventilated capsules (3.8 cm2). Absolute reliability was assessed using coefficient of variation (CV%) which quantifies the amount of error in a given measurement. Relative reliability was evaluated via the intraclass correlation coefficient (ICC); the consistency of an individual’s rank within a group during repeated measurements. At low heat strain, most sites demonstrated acceptable relative (ICC ≥0.70), and moderate absolute reliability (CV <25%). At moderate-heat strain, the abdomen, hand, quadriceps, calf and foot had acceptable relative reliability while the forehead, abdomen, forearm, hand and quadriceps had moderate absolute reliability. At high-heat strain, relative reliability was acceptable at the abdomen, quadriceps, calf, foot and absolute reliability was moderate at the chest, abdomen, forearm, hand, quadriceps, calf and foot. Our findings indicate that reliability of local sweat rate is dependent on both measurement site and level of hyperthermia. Researchers should consider this in their experimental design to increase the likelihood of detecting an effect of an intervention if one exists.