2007, Piran, Slovenia

Occupational Thermal Problems
(Suunto, Finland). Tre was continuously measured by a flexible thermistor probe (YSI 401,
Yellow Springs Instrument Co., USA) at the depth of 10 cm, and skin temperatures (Tsk) were
measured at the shin, hand, scapula and neck (YSI 427, Yellow Springs Instrument Co., USA)
and registered once a minute (Veritec Instrument Type 1400, Canada). Brachial blood
pressure (BP) was measured every 10 minutes of HST, except in the final stages of the test
when it was measured every 5 minutes.
Oxygen consumption was measured three times in 3-5 min (breath by breath, Vmax29,
SensorMedics Corporation, USA). The first collection of respiratory gases was performed
before the subject began the exercise (sitting on a cycle in climatic chamber), the second
sample collection was made after 25 to 35 min of exercise, and the final VO2 analysis was
conducted when it was objectively evaluated that the subject would terminate the test in the
next 5-8 min.
The ratings of perceived exertion (RPE) using Borg scale and subjective evaluations of
thermal comfort and thermal sensation modified from ISO 10551, as well as skin wettedness,
were recorded at 10 minute intervals during the HST. The subjects were allowed to drink
water ad libitum and the amount of water drunk was measured. Nude weight was measured
before and after HST, and sweat loss was determined by the weight change of the subject.
Calculation of physiological variables
Mean skin temperature ( T sk ) was calculated using weighting coefficients (Olesen 1984) and
mean body temperature ( T b)
using the weighting coefficients of 0.9 for Tre and 0.1 for Tsk.
Change in heat storage (∆ S) for heat exposure time was calculated from changes in⎺Tb using
the 0.97 Wh/kg°C for specific heat of the body.
HRV analysis and calculations, as well as calculation of EPOC, which is defined as the excess
oxygen consumed during recovery from exercise as compared to resting oxygen consumption,
were carried out with FirstBeat Pro Softaware (FirstBeat Technologies Ltd, version 1.4.1,
2006, Finland). These variables are calculated individually and reported for the first 5 minutes
(=start), the period between 20 and 25 min into the test (=20−25 min), and the final five
minutes (=end) of HST.
Statistics
Statistical analysis was carried out with SPSS 14.0 (SPSS Inc, Chicago, USA). The normality
of the variables was tested (Shapiro-Wilk test), and the paired sample t-test and a nonparametric
test were used in statistical analysis. Correlation was tested with Pearson
Correlation with the level of significance at p < 0.05 and the level of high significance at
p < 0.01.
RESULTS
Only three subjects completed the full 60 minutes of the test, and the duration of HST varied
between 21 and 60 minutes. With seven subjects, the test was terminated between the 50-60
min of duration. In three cases the test was terminated in less than 40 min.
The external workload remained stable during the test. The average heart rate, however,
increased continuously. During the first 25 min of HST, the average heart rate increased by
20% (p< 0.01). At the termination point, the average heart rate was 27% higher than at the
start of HST (p< 0.01). The average EPOC values increased during the first 25 min of the test
to 31.7 (7.3-72.3) ml/kg from the resting average value. The average end-of-exercise EPOC
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