2007, Piran, Slovenia

Acute and chronic heat exposure
INTRA-INDIVIDUAL VARIABILITY OF STRAIN DURING
UNCOMPENSABLE HEAT STRESS: A LONGITUDINAL STUDY
Bernhard Kampmann 1 , Georg Bresser 2
1 Division of Applied Physiology, Occupational Medicine & Infectiology, Department of Safety
Engineering, Bergische Universität Wuppertal, Germany
2 Central Mine Rescue Station, Deutsche Steinkohle AG, Herne, Germany
Contact person: kampmann@uni-wuppertal.de
INTRODUCTION
Whenever mean values of physiological strain are recorded for a group of subjects, the intraindividual
variability of the single subjects implicitly is included within the results. To
estimate this contribution to data variability, we decided to carry out a longitudinal study for
two types of training, that had been studied before at the Central Mine Rescue Station for all
mine rescue brigadesmen of a coal mine (52 brigadesmen): for a standard mine rescue
training (SMRT) in a training gallery (with flame protection clothing and SCBA (self
contained breathing apparatus); Kampmann et al., 1997) lasting for two hours, and for a heat
tolerance test (HTT) at ta = 39°C and 88 % relative humidity, treadmill work of 70 Watts
external load, lasting for maximal 30 minutes (Kampmann et al., 1996); only shorts, t-shirt,
socks and safety boots were worn for HTT. Both exposures represented uncompensable heat
stress. The longitudinal study comprised of four brigadesmen of the operational rescue team
of the Central Mine Rescue Station and was extended for 10 years (1990-2000), so additional
information about changes in physiological strain with age could be expected.
METHODS
Before the SMRT started during the late morning, bicycle ergometry was performed, resulting
in a Dynavit ® -score that displays specific fitness (i.e. fitness per body mass). A Dynavit ® -
score of 75 was mandatory for participation in the SMRT that started after a resting period of
about 1.5 hours. The details of the SMRT are given in (Kampmann et al., 1997). From 56
continuous recordings of heart rate and rectal temperature 53 data sets could be evaluated.
During the SMRT the timetable for the training was followed as closely as possible, resulting
in a total duration of 124 ±2 minutes. During the time of investigation, the Central Mine
Rescue Station moved to another location and another training gallery was used; as in both
training facilities no statistical differences were found, the results were analyzed in total.
On different days a HTT according to Stoklossa (Kampmann et al., 1996) was performed after
a resting period around 8:30 and after a further resting period another training took place that
will not be discussed here. Heart rate and body temperatures were monitored continuously.
The exposure was stopped at Tre > 38.5 °C, HR > “220-age” or at request of the subjects.
After it took some time to reinstall the climatic chambers after moving to another location 36
HTTs could be analyzed.
RESULTS
Table 1 gives the anthropometric data of the participating subjects. From these data, body
mass, and the correspondingly Broca-index and BMI, had a significant increase during the
investigation for subjects 1, 3 and 4. The Dynavit-score showed no linear trend with time for
any subjects. No habituation effects were expected during the investigation as all subjects had
participated for several years in mine rescue training (Kampmann and Bresser, 2005)
Table 2 gives heart rates and rectal temperatures at the beginning and end of the SMRT: for
none of the subjects, rectal temperature at the end of SMRT depends significantly on the
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