No Impact of Heat Stress and Dehydration on Short Duration Simulated Motor-Racing Performance

Motor-racing drivers are often exposed to hot environments and may be susceptible to fluid loss and hydration issues, which could influence driving performance. This study assessed the effect of dehydration and heat stress on performance during a short, simulated motor-racing task. Nine healthy males (age: 26.6 ± 7.5 y, body mass: 78.8 ± 12.5 kg, mean ± SD) completed two passive dehydration (sauna) procedures (targeting -1% and -3% body mass loss (BML)) on separate occasions. Driving performance was assessed pre-dehydration (Baseline), immediately post-dehydration (Hot) and following a cooling period (Cool). Measures of driving performance included lap time and sector-time for one section of the track. Subjective ratings of mood, thermal stress and comfort were also collected during trials. Mean lap times were not different between Baseline, Hot, Cool conditions for both 1% (68.44 ± 1.43 s, 68.06 ± 1.17 s, 68.23 ± 1.25 s) and 3% (68.33 ± 1.68 s, 68.01 ± 1.15 s, 68.06 ± 1.26 s) trials respectively. In addition, mean sector times were not different between Baseline, Hot, Cool conditions for both 1% (11.61 ± 0.28 s, 11.55 ± 0.45 s, 11.59 ± 0.35 s) and 3% (11.49 ± 0.33 s, 11.56 ± 0.33 s, 11.63 ± 0.71 s) trials respectively. Changes in participants' subjective ratings (i.e. decreased alertness, concentration and comfort; increased tiredness and light-headedness) were observed at both levels of dehydration (1% and 3% BML), irrespective of heat stress. Thus, fluid loss and heat stress are unlikely to affect driver's motor-racing performance during short duration events. However, the impact of dehydration and heat stress on tasks of longer duration that accurately represent the demands associated with motor-racing requires further consideration.

Tattoos do not affect exercise-induced localised sweat rate or sodium concentration

OBJECTIVES

Skin tattoos have been shown to reduce localised sweat rate and increase sweat sodium concentration ([Na⁺]) when sweating is artificially stimulated. This study investigated whether similar responses are observed with exercise-induced sweating.

DESIGN

Unblinded, within-participant control, single trial.

METHODS

Twenty-two healthy individuals (25.1±4.8 y (Mean±SD), 14 males) with a unilateral tattoo ≥11.4cm² in size, ≥2 months in age, and shaded ≥50% participated in this investigation. Participants undertook 20min of intermittent cycling (4×5min intervals) on a stationary ergometer in a controlled environment (24.6±1.1°C; 64±6% RH). Resultant sweat was collected into absorbent patches applied at two pairs of contralateral skin sites (pair 1: Tattoo vs. Non-Tattoo; pair 2: Control 1 vs. Control 2 (both non-tattooed)), for determination of sweat rate and sweat [Na⁺]. Paired samples t-tests were used to determine differences between contralateral sites.

RESULTS

Tattoo vs. Non-Tattoo: Neither sweat rate (Mean±SD: 0.92±0.37 vs. 0.94±0.43mg·cm^-2·min^-1, respectively; p=0.693) nor sweat [Na⁺] (Median(IQR): 37(32-52) vs. 37(31-45) mM·L^-1, respectively; p=0.827) differed. Control 1 vs. Control 2: Neither sweat rate (Mean±SD: 1.19±0.53 vs. 1.19±0.53mg·cm^-2·min^-1, respectively; p=0.917) nor sweat [Na⁺] (Median(IQR): 29(26-41) vs. 31(25-43)mM·L^-1, respectively; p=0.147) differed. The non-significant differences for sweat rate and [Na⁺] between Tattoo vs. Non-Tattoo were inside the range of the within participant variability (sweat rate CVi=5.4%; sweat [Na⁺] CVi=4.4%).

CONCLUSIONS

Skin tattoos do not appear to alter the rate or [Na⁺] of exercise-induced sweating. The influence of skin tattoos on localised sweat responses may have previously been over-estimated.

Data on experimental investigation of Methyl Ester Sulphonate and nanopolystyrene for rheology improvement and filtration loss control of water-based drilling fluid

Data presented in this article focused on the application of Methyl Ester Sulphonate (MES) surfactant and nanopolystyrene in water based drilling fluid. Data from rheology study using Bingham and Power law models showed that the synergy of MES and nanopolystyrene improved the formulated drilling fluid. Filtration study under LPLT and HPHT conditions showed that MES and nanopolystyrene drilling fluid reduced filtration loss by 50.7% at LPLT and 61.1% at HPHT conditions. These filtration data were validated by filter cake permeability and scanning electron microscope images.

Fluid replacement advice during work in fully encapsulated impermeable chemical protective suits

A major concern for responders to hazardous materials (HazMat) incidents is the heat strain that is caused by fully encapsulated impermeable chemical protective suits. In a research project, funded by the US Department of Defense, the thermal strain experienced when wearing these suits was studied. One particular area of interest was the fluid loss of responders during work in these suits as dehydration may be an additional health concern to the heat strain. 17 City of Raleigh firemen and 24 students were tested at two different labs. Subjects between the ages of 25 and 51 were used for human subject trials in a protocol approved by the local ethical committee. Six different Level A HazMat suits were evaluated in three climates: moderate (24°C, 50% RH, 20°C WBGT), warm-wet (32°C, 60% RH, 30°C WBGT), and hot-dry (45°C, 20% RH, 37°C WBGT, 200 W/m² radiant load) and at three walking speeds: 2.5 km/hr, 4 km/hr, and 5.5 km/hr. 4 km/hr was tested in all three climates and the other two walking speeds were tested in the moderate climate. Weight loss data was collected to determine fluid loss during these experiments. Working time ranged from as low as 20 min in the hot-dry condition to 60 min (the maximum) in the moderate climate, especially common at the lowest walking speed. The overall results from all experiments showed that fluid loss ranged from 0.2-2.2 L during these exposures, with the average fluid loss being 0.8 L, with 56% of the data between 0.5 L and 1 L of fluid loss. Further analysis showed that a suggestion of drinking 0.7 Liter per hour would safely hydrate over 50% of responders after one work-rest cycle. Applying this fluid volume over three work-rest cycles only put 11% of responders at risk of hypohydration vs. the 57% at risk with no fluid intake.