The ventilated capsule technique is widely used to measure time‐dependent changes in sweating in humans. However, evaluations of its reliability (consistency) have been restricted to the forearm, despite extensive regional heterogeneity in the sweating response. Given the importance of such information for experimental design, statistical analysis and interpretation, we determined the reliability of local sweat rate at nine sites during whole‐body passive (resting) heating. On three separate occasions, a water‐perfused suit was used to increase and clamp oesophageal temperature 0.6, 1.2 and 1.8°C above baseline in 14 young men [24 (SD 5) years of age], while sweat rate was measured at the forehead, chest, abdomen, biceps, forearm, hand, quadriceps, calf and foot using ventilated capsules (3.8 cm2). Absolute and relative reliability were determined via the coefficient of variation (CV) and intraclass correlation coefficient (ICC), respectively. At low heat strain (0.6°C), almost all sites had acceptable relative reliability (ICC ≥ 0.70) and moderate absolute reliability (CV < 25%). At moderate heat strain (1.2°C), only the abdomen, hand, quadriceps and foot had acceptable relative reliability, whereas the forehead, abdomen, forearm, hand and quadriceps had moderate absolute reliability. At high heat strain (1.8°C), relative reliability was acceptable at the abdomen, quadriceps, calf and foot, whereas the chest, abdomen, forearm, hand, quadriceps, calf and foot had moderate absolute reliability. Our findings indicate that the measurement site and level of heat strain impact the consistency of local sweat rate measured via the ventilated capsule technique, and we demonstrate the possible implications for research design and data interpretation.

Laser‐Doppler flowmetry (LDF) is commonly used to assess cutaneous vasodilatation responses, but its reliability (i.e. consistency) during whole‐body passive heating is unknown. We therefore assessed the reliability of LDF‐derived indices of cutaneous vasodilatation during incremental whole‐body heating. Fourteen young men (age: 24 (SD 5) years) completed three identical trials, each separated by 1 week. During each trial, a water‐perfused suit was used to raise and clamp oesophageal temperature at 0.6°C (low‐heat strain; LHS) and 1.2°C (moderate‐heat strain; MHS) above baseline. LDF‐derived skin blood flow (SkBF) was measured at three dorsal mid‐forearm sites, with local skin temperature clamped at 34°C. Data were expressed as absolute cutaneous vascular conductance (CVCabs; SkBF/mean arterial pressure) and normalised to maximal conductance (%CVCmax) achieved via simultaneous local skin heating to 44°C and increasing oesophageal temperature to 1.8°C above baseline. Between‐day reliability was characterised as measurement consistency across trials, while within‐day reliability was characterised as measurement consistency across adjacent skin sites during each trial. Between‐ and within‐day absolute reliability (coefficient of variation) generally improved with increasing heat strain, changing from poor (>25%) at baseline, poor‐to‐moderate (15–34%) at LHS, and moderate (10–25%) at MHS. Generally, these estimates were more consistent when expressed as %CVCmax. Conversely, relative reliability was mostly acceptable (intraclass correlation coefficient ≥0.70) during LHS and when data were expressed as CVCabs. These findings indicate that the consistency of LDF‐derived CVC estimates during heat stress depends on the level of heat strain and method of data expression, which should be considered when designing and interpreting experiments.

Purpose Current occupational heat stress guidelines rely on time-weighted averaging to quantify the metabolic demands of variable-intensity work. However, variable-intensity work may be associated with impairments in whole-body total heat loss (dry + evaporative heat loss), especially in older workers, which exacerbate heat strain relative to constant-intensity work eliciting the same time-weighted average metabolic rate. We, therefore, used direct calorimetry to evaluate whether variable-intensity work would cause decrements in the average rate of whole-body total heat loss that augment body heat storage and core temperature compared with constant-intensity work in young and older men. Methods Eight young (19–31 yr) and eight older (54–65 yr) men completed four trials involving 90 min of work (cycling) eliciting an average metabolic heat production of ~200 W·m−2 in dry-heat (40°C, 20% relative humidity). One trial involved constant-intensity work (CON), whereas the others involved 10-min cycles of variable-intensity work: 5-min low-intensity and 5-min high-intensity (VAR 5:5), 6-min low-intensity and 4-min very high-intensity (VAR 6:4), and 7-min low- and 3-min very, very high-intensity (VAR 7:3). Metabolic heat production, total heat loss, body heat storage (heat production minus total heat loss), and core (rectal) temperature were measured throughout. Results When averaged over each 90-min work period, metabolic heat production, total heat loss, and heat storage were similar between groups and conditions (all P ≥ 0.152). Peak core temperature (average of final 10 min) was also similar between groups and conditions (both P ≥ 0.111). CONCLUSIONS Whole-body total heat loss, heat storage, and core temperature were not significantly influenced by the partitioning of work intensity in young or older men, indicating that time-weighted averaging appears to be appropriate for quantifying the metabolic demands of variable-intensity work to assess occupational heat stress.

Observed individual variability in cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV) is extensive, especially during exposure to stressors such as heat. A large part of the observed variation may be related to the reliability (consistency) of the measurement. We therefore examined the test–retest reliability of cBRS and HRV measurements on three separate occasions in 14 young men (age: 24 (SD 5) years), at rest and during whole‐body heating (water‐perfused suit) to raise and clamp oesophageal temperature 0.6°C, 1.2°C and 1.8°C above baseline. Beat‐to‐beat measurements of RR interval and systolic blood pressure (BP) were obtained for deriving HRV (from RR), and cBRS calculated via (i) the spontaneous method, α coefficients and transfer function analysis at each level of heat strain, and (ii) during forced oscillations via squat–stand manoeuvres (0.1 Hz) before and after heating. Absolute values and changes in all cBRS estimates were variable but generally consistent with reductions in parasympathetic activity. cBRS estimates demonstrated poor absolute reliability (coefficient of variation ≥25%), but relative reliability (intraclass correlation coefficient; ICC) of some frequency estimates was acceptable (ICC ≥0.70) during low‐heat strain (ICC: 0.56–0.74). After heating, forced oscillations in BP demonstrated more favourable responses than spontaneous oscillations (better reliability, lower minimum detectable change). Absolute reliability of HRV estimates were poor, but relative reliability estimates were often acceptable (≥0.70). Our findings illustrate how measurement consistency of cardiac autonomic modulation estimates are altered during heat stress, and we demonstrate the possible implications on research design and data interpretation.