The (in)dependency of blood and sweat sodium, chloride, potassium, ammonia, lactate and glucose concentrations during submaximal exercise.

PURPOSE: To reduce the need for invasive and expensive measures of human biomarkers, sweat is becoming increasingly popular in use as an alternative to blood. Therefore, the (in)dependency of blood and sweat composition has to be explored. METHODS: In an environmental chamber (33 °C, 65% relative humidity; RH), 12 participants completed three subsequent 20-min cycling stages to elicit three different local sweat rates (LSR) while aiming to limit changes in blood composition: at 60% of their maximum heart rate (HRmax), 70% HRmax and 80% HRmax, with 5 min of seated-rest in between. Sweat was collected from the arm and back during each stage and post-exercise. Blood was drawn from a superficial antecubital vein in the middle of each stage. Concentrations of sodium, chloride, potassium, ammonia, lactate and glucose were determined in blood plasma and sweat. RESULTS: With increasing exercise intensity, LSR, sweat sodium, chloride and glucose concentrations increased (P ≤ 0.026), while simultaneously limited changes in blood composition were elicited for these components (P ≥ 0.093). Sweat potassium, lactate and ammonia concentrations decreased (P ≤ 0.006), while blood potassium decreased (P = 0.003), and blood ammonia and lactate concentrations increased with higher exercise intensities (P = 0.005; P = 0.007, respectively). The vast majority of correlations between blood and sweat parameters were non-significant (P > 0.05), with few exceptions. CONCLUSION: The data suggest that sweat composition is at least partly independent of blood composition. This has important consequences when targeting sweat as non-invasive alternative for blood measurements.

Two isothermal challenges yield comparable physiological and subjective responses.

PURPOSE: Ventilated vests are developed to reduce thermal stress by enhancing convective and evaporative cooling from skin tissue underneath the vest. The purpose of this study is to investigate whether thermal stress is equal when a ventilated vest is worn compared to a no-vest situation with similar dry thermal resistance. METHODS: Nine healthy males walked on a treadmill (7 km h-1) for 45 min in a desert climate (34 °C, 20% relative humidity) with and without ventilated vest. Gastrointestinal temperature (Tgi), heart rate (HR), and skin temperature (Tsk) were continuously monitored. Local sweat rate (LSR) was assessed two times on six skin locations. Subjective ratings were assessed every 10 min. RESULTS: Final Tgi (37.6 ± 0.1 °C for vest and 37.6 ± 0.1 °C for no-vest), HR (133 ± 7 bpm and 133 ± 9 bpm) and mean Tsk (34.8 ± 0.7 °C and 34.9 ± 0.6 °C) were not different between conditions (p ≥ 0.163). Scapula skin temperature (Tscapula) under the vest tended to be lower (baseline to final: ΔTscapula = 0.35 ± 0.37 °C) than without vest (ΔTscapula = 0.74 ± 0.62 °C, p = 0.096). LSR at locations outside the vest did not differ with and without vest (p ≥ 0.271). Likewise, subjective responses did not differ between conditions (χ2 ≥ 0.143). CONCLUSIONS: We conclude that two systems with similar dry thermal resistance and, therefore, similar required evaporation, resulted in similar thermal stress during paced walking in a hot-dry environment. Local ventilation did not alter the sweating response on locations outside the vest.