Effects of warm-up and precooling on endurance
performance in the heat
Sandra U¨ckert, Winfried Joch
............................................................... ............................................................... .....
See end of article for
Dr S U¨ckert, Institute of
Sports Science, University of
Dortmund, Otto-Hahn-Str 3,
44227 Dortmund, Germany;
Accepted 4 December 2006
Published Online First
15 January 2007
Br J Sports Med 2007;41:380–384. doi: 10.1136/bjsm.2006.032292
Objective: To examine the effects of different thermoregulatory preparation procedures (warm-up (WU),
precooling (PC), control (C)) on endurance performance in the heat.
Methods: 20 male subjects completed three treadmill runs to exhaustion (5 days apart). In each session, all
subjects performed an incremental running test after WU (20 min at 70% maximum heart rate (HR)), after PC
(wearing a cooling vest (0˚C–5˚C) for 20 min at rest) or without particular preparation (C). After a 5-min
break, the exercise protocol commenced at a workload of 9 km/h and was increased by 1 km/h every 5 min
until the point of volitional fatigue. Running performance, HR, blood lactate concentration, tympanic
temperature and skin temperature were measured in each trial.
Results: In the PC condition, the running performance (32.5 (5.1) min; mean (SD)) was significantly (p,0.05)
higher than in WU (26.9 (4.6) min) and in C conditions (30.3 (4.3) min). During the first 30 min of testing,
HR, tympanic temperature and skin temperature were significantly (p,0.05) lower after PC than after WU.
There were no significant differences in lactate concentration; however, there was a trend to lower values
Conclusions: The use of an ice-cooling vest for 20 min before exercising improved running performance,
whereas the 20 min WU procedure had a distinctly detrimental effect. Cooling procedures including
additional parts of the body such as the head and the neck might further enhance the effectiveness of PC
30˚C brought about a decrease of 2.3% in the performance of a
10 min exercise bout.2The question, however, as to what
strategies could be applied to compensate for this heat-induced
decrease in performance has been left largely unanswered.
Sufficient fluid intake is a possible answer, and application of
cold provides another one.3 4In the context of endurance in
heat a further question arises—namely, whether warm-up
(WU; including the concomitant increase in core temperature
(CT)) is a sensible measure, taking into consideration the
additional thermal stress.5
For this reason, it is useful to compare the effects of WU and
precooling (PC) to optimise endurance performance. The
practical relevance of the objective lies in the fact that
competitions—for example, the Olympic Games 2008 in
Beijing—will be held in high ambient temperatures, exceeding
30˚C at all times of day, and there is no coherent (systematically
and experimentally tested) position in the literature on the
implications of WU6 7for endurance performance in such
temperatures. Although PC has been discussed more widely
during the last two decades,8–10it has not yet been studied in
comparison with active WU.
t is well established that high ambient temperatures have a
detrimental effect on endurance performance.1 2Compared
with temperate conditions (20˚C), an ambient temperature of
METHODS AND PROCEDURES
Twenty male subjects were tested in this study. They were
physical education students at the University of Muenster,
Muenster, Germany, and regularly practised types of sport with
high endurance and strength components at a high level
(soccer, athletics). All gave their informed consent to partici-
pate in this study after the University of Muenster Human
Ethics Committee had approved of the procedures used. Mean
(SD) values for age, height and weight were 25.6 (3.5) years,
183.4 (7.6) cm and 77.9 (9.5) kg.
After attending a familiarisation session, subjects performed
three testing sessions, five days apart. In every session, subjects
performed the same test, after WU, after PC (with a cooling vest)
or without any thermoregulatory preparation (TPP; control (C)).
The tests were set in randomised order to avoid any order effects.
In each test, subjects performed an incremental running test
on a treadmill until exhaustion. They wore running shoes,
sports socks, shorts and a T-shirt. Subjects were required to
refrain from vigorous exercise for 48 h before testing and to
avoid any food, drink, cigarettes or caffeinated products for 3 h
before the start of a testing session.
The effect of the different TPP procedures was tested using an
incremental step test on a treadmill. Testing commenced at a
pace of 9 km/h, which was increased by 1 km/h every 5 min.
Subjects performed up to the point of volitional fatigue (break-
off or inability to sustain the pace).
Before the familiarisation session and all three tests, the body
height and weight of the subjects were measured. Before each
testing session, to analyse the heart rate (HR), the HR
transmitter and receiver were adjusted and started in the same
temperate conditions. Subjects then entered the heated
Abbreviations: BL, blood lactate; bpm, beats per minute; C, control;
CT, core temperature; HR, heart rate; PC, precooling; ST, skin temperature;
TPP, thermoregulatory preparation; Tt, tympanic temperature; WU,
laboratory (30˚C–32˚C, 50% relative humidity). These ambient
conditions were chosen to represent typical outdoor environ-
mental conditions at the height of summer.
Before exercising, in an initial 5 min resting period (sitting),
CT, skin temperature (ST) and HR were measured.
In the C test, subjects commenced exercising immediately after
the 5 min resting period, at a pace of 9 km/h on the treadmill.
In the WU test, subjects performed the following WU
procedure on the treadmill: a 5 min run at a self-adjusted pace,
followed by 15 min at 70% of the individual maximum HR
(HRmaxhad been ascertained in a step test outside this study).
During WU, the HR was measured continuously and the CT was
ascertained every 5 min. The blood lactate (BL) concentration
wasmeasuredatthe end of theWU. Between WUandthe start of
the step test, there was a 5 min resting period (sitting).
In the PC test, after the initial resting period, the subjects
remained seated and wore a cooling vest (0–5˚C) against the
skin. The PC procedure lasted for 20 min (identical with the
WU period). HR, CT and ST were measured at the start of
testing and then every 5 min. Before testing, the cooling vests
had been submerged (for 10 min) dried and then cooled down
at 5˚C in a freezer.
Immediately after the 20 min PC procedure, subjects took off
the vests and commenced the step test.
CTwas measured every 2 min andBL was ascertained after 5 min
of exercise and then every 10 min, each time at the end of a pace
step (after 15, 25, 35, and if applicable 45 min). Subjects ran until
exhaustion. Testing could be stopped either by the subjects
Following the step test, there was a 5 min resting period
(sitting) in the heated laboratory while HR and CT were
observed. Subsequently, there was a further 10-min resting
period in temperate conditions (20–22˚C) without measuring.
Measurements and apparatus
Cooling was achieved using an ice-cold cooling vest (Arctic
Heat, Burleigh Heads, Australia) with four integrated cooling
panels (filled with a cooling gel consisting of crystals absorbing
external and internal heat) on the front and three on the back
to avoid cooling the kidney area. To optimise cooling of the
torso, the vest was worn directly on the naked skin. The Arctic
Heat vest weighs only about 1000 g (activated).
Subjects performed on the Kettler Kinetic S3 (Kettler, Ense-
Parsit, Germany) treadmill at the Institute of Sports Science in
Muenster, Germany. The Kinetic S3 uses a non-weight-related
speed-control system driving the belt via a 2.2 kW motor. To
make exercising more convenient, the Kinetic S3 has a
suspension system that automatically adapts to the pace and
weight of the runner. To mimic aerodynamic drag, the treadmill
was adjusted at a gradient angle of 1˚.
The difference in HR between PC and WU increased
progressively during the TPP (generally p(0.05).
HR was measured using the Polar Heart Rate Monitor S810i
(Polar, Kempele, Finland) during the whole testing period. The
electrosensitive chest belt, which was affixed to the subject’s
chest just above the manubrium sterni, transmitted the data to
the watch at the wrist. After testing, the recorded data were
transmitted to a computer and analysed via the Polar Precision
Performance Software (V.4.01.029).
BL concentration was measured using the Roche Accutrend
Lactate system (Roche Diagnostics, Mannheim, Germany) in
combination with BM Lactate Test Stripes and with Softclix
lancets (Roche Diagnostics,).
Tympanic temperature (Tt) was measured by the Braun Pro
3000 ThermoScan thermometer, Type 6014 (Braun, Kronberg,
Germany). The thermometer measured the infrared radiation
generated by the eardrum and the surrounding tissue. To
enhance accuracy, each scan consisted of eight measurements
per second, of which the highest temperature was displayed. The
technical error of measurements amounted to 0.2˚for tempera-
tures in the range 35.5–42.0˚C, and 0.3˚C outside this range.
ST was measured using the Ebro TFN 1093 digital thermo-
meter (Ebro, Ingolstadt, Germany), which has a resolution of
0.1˚C (measuring range 250˚C to +500˚C). The precision of
measurement in the temperature range of our tests was
0.004˚C (manufacturer’s information). The thermometer was
equipped with the Ebro EB 14-N surface probe (measuring range
250 to +500), which has an NiCr-Ni measuring tip 15 mm in
diameter. During the measurements, the probe was pressed onto
the skin of the upper third of the subject’s left scapula.
Statistical analyses were carried out with SPSS V.12.01 for
Windows. Analysis of the means of the data for running
performance, Tt, ST, HR and BL during the tests were
conducted using a one-way analysis of variance with repeated
measurements for thermoregulation preparation (WU, PC, C).
Significance was set at p,0.05.
The cooling vest reduced cardiovascular and thermal strain
during the TPP (figs 1–3). During active WU (20 min), the HR
Heart rate (beats per min) during warm-up (WU) and
Core temperature during warm-up (WU) and precooling (PC).
Effects of warm-up and precooling 381
increased by 61 beats per minute (p,0.001), whereas during
PC, it decreased by 8.9 bpm (p(0.01; fig 1).
Tt rose during WU and during PC. However, the increase during
WU (1˚C; p,0.001) was clearly higher than during PC. During
WU, Tt rose from 36.6˚C (0.5˚C) to 37.6˚C (0.5˚C), whereas
during PC, it increased by 0.54˚C (p,0.001), from 36.6˚C
(0.6˚C) to 37.1˚C (0.4˚C). Thus, the difference between the Tts
in WU and PC was increased during the 20 min of TPP (fig 2).
During WU, ST rose from 34.2˚C (0.9˚C) to 34.7˚C (0.8˚C),
which is an increase of 0.42˚C (p,0.01). By contrast, during PC,
a significant decrease (by 0.69˚C; p,0.001) from 33.6˚C (0.9˚C)
to 32.9˚C (0.7˚C) was observed. Already at the beginning of the
20 min TPP (WU or PC), a significant difference in ST
temperature (0.56˚C (1.08˚C); p(0.05) was observed. At the
end of the preparation period, the difference amounted to
1.67˚C ((0.89˚C); p,0.001). Thus, the different TPPs (WU, PC,
C) caused an inverse behaviour of the ST curves (fig 3), similar
to that of the HR curves.
After the 20 min WU, subjects reached a BL concentration of
2.68 (0.71) mmol/l. Therefore, subjects exercised below the
anaerobic lactate threshold, which indicates that an adequate
WU workload was chosen. Fatigue-related metabolic influences
can be regarded as having been eliminated.
After PC, the running performance was better (by 2.2
(1.94) min) compared with the C test (32.5 (5.1) vs 30.3
(4.3) min; p,0.001; fig 4). Of all 20 subjects, 16 ran more after
PC, 2 ran less (1 min each) and 2 had identical results.
After PC, generally subjects ran longer (32.5 (5.1) min) than
after WU (26.9 (4.6) min). The additional running time after
PC test amounted to 5.6 (2.5) more minutes (p,0.001).
After WU, all subjects ran less compared with the C test.
After WU, the break-off time was 26.9 (4.6) min, whereas in C,
subjects performed for 30.3 (4.6) min. The difference of 3.4
(2.2) min is significant (p,0.001).
Comparing C, PC and WU, the maximum running time was
found after PC, with 2.2 min more than after C and 5.6 min
more than after WU. Thus, the best running performance was
achieved after 20 min of PC.
At the beginning of the step test, the HR was significantly lower
(p(0.05) after PC (80.7 (10.9) bpm) than in C (87.9
(13.7) bpm) or WU (116.2 (10.4) bpm) conditions.
The HRmaxwas higher after PC (192.1 (8.7) bpm) than in C
(189.8 (7.7) bpm), although the difference was not significant
(p.0.05; fig 4). This difference in HR was caused by the
prolonged running times after PC.
Up to the 30th minute of testing, the HR was significantly
lower after PC than after WU (p,0.01). After 35 min of testing,
the difference in HR was no longer significant (p.0.05). The
same applies to the individual HRmaxat the point of volitional
fatigue, with a difference of 0.8 bpm (192.1 (8.6) bpm after PC
and 191.3 (6.5) bpm after WU; p.0.05)).
After WU, during the first 25 min of testing, the HR was
significantly (p,0.001) higher than in C. After 30 and 35 min,
the differences were not significant (p.0.05). The differences
in the individual HRmaxwere also not significant: after WU, the
individual HRmaxamounted to 191.3 (6.5) bpm compared with
189.8 (7.7) bpm in C, although, in C conditions, subjects ran for
a longer time.
During the step test, the lowest HR values were found after
PC and the highest after WU (fig 5).
During the step test in PC conditions, the HR up to minute 35
was generally lower than in C (p.0.05). Only one subject was
able to run for .40 min in the C test; all the others had to break
off earlier. After PC, three subjects reached the 40 min barrier.
The subject’s HR in C conditions was 176 bpm and the mean
HR of the three subjects in PC conditions amounted to 192
Skin temperature during warm-up (WU) and precooling (PC).
control test and after precooling or warm-up. bpm, beats per minute.
***p,0.001 (heart rate difference).
Running performance (bars) and heart rate (squares) in the
Heart rate (bpm)
10 15 202530 3540
after precooling (PC) or warm-up (WU). bpm, beats per minute.
Heart rate during the step test in the control (C) conditions and
There were no significant differences in lactate concentration
between the different testing conditions (fig 6). However, there
was a trend to lower lactate concentrations after WU compared
with PC and C. Significant differences were observed only in
the beginning. After 5 min, lactate concentrations in the C test
differed significantly from those in PC and WU.
In minute 5, significant (p,0.01) differences were found
between PC (2.79 (0.6) mmol/l) and C (3.56 (1.0) mmol/l).
Between WU (2.82 (1.1) mmol/l) and C (3.56 (1.0) mmol/l),
the differences reached a significance level of p,0.5.
There was a general trend to lower lactate concentrations
after WU compared with C, and there was no significant
difference in lactate concentrations during the step test in WU
and PC conditions.
The individual maximum lactate concentration in the step
test was lowest after WU (5.20 (1.33) mmol/l) (fig 6). This was
even lower than the C value of 6.91 (2.2) mmol/l. The high
maximum value at the point of exhaustion after PC (7.70
(2.06) mmol/l) can be explained by the longer running
During the step test, Tts were significantly higher after WU,
than after PC and in C. At the start of the test, core (tympanic)
temperature (CT) after WU was 0.93˚C (0.72) higher than CT
after C (p,0.001); after 5 min, the difference amounted to
0.66˚C (0.73˚C; p,0.001), after 10 min to 0.59˚C (0.66˚C;
p,0.001), after 15 min to 0.49˚C (0.73˚C; p,0.01), after
20 min to 0.58˚C (0.82˚C; p,0.01), after 25 min to 0.47˚C
(0.75˚C; p,0.01), after 30 min to 0.59˚C (0.74˚C; p(0.05) and
after 35 min to 0.59˚C (1.1˚C; p.0.05) (fig 7).
Tts were also generally higher after WU than after PC: 0.56˚C
(0.67˚C; p,0.001) at the start, 0.45˚C (0.60˚C; p(0.001) after
5 min, 0.51˚C (0.58˚C; p,0.001) after 10 min, 0.49˚C (0.63˚C;
p,0.01) after 15 min, 0.61˚C (0.68; p,0.001) after 20 min,
0.56˚C (0.66; p,0.01) after 25 min, 0.71˚C (0.49˚C; p,0.001)
after 30 min and 0.71˚C (0.65˚C; p.0.05) after 35 min.
Significant differences in Tt between PC and C were found at
the beginning of the step test: 0.38˚C (0.43˚C; p,0.001) at the
start and 0.20˚C (0.43˚C; p(0.05) after 5 min. Over the course
of exercise, CT values were almost identical in the two
conditions. However, towards the end of the test (after
30 min), there was a trend to lower CT values after PC
compared with C, although p.0.05.
A significant (p,0.01) increase in ST was found in all three
testing conditions (fig 8). ST rose in C by 1.92˚C (1.11˚C),
during WU by 1.06˚C (0.82˚C) and during PC by 2.21˚C
Comparing all three testing conditions (C, WU, PC), even at
the beginning, significant differences in ST were found as a
consequence of the different preparation procedures. After PC,
ST (32.95˚C (0.75˚C)) was 0.8˚C (1.1˚C) lower than in C
(33.73˚C (0.89˚C); p,0.01) and 1.67˚C (0.88˚C) lower than after
WU (34.67˚C (0.83˚C); p,0.01).
Thus, in each condition, the highest ST values were measured
after WU, whereas the lowest were found after PC.
At the end of the step test, the differences in ST between the
three testing conditions were not generally significant. ST after
C (35.56˚C (0.95˚C)) and after WU (35.73˚C (0.53˚C)) did not
differ significantly. However, a significant difference in ST was
found between PC and WU conditions. The ST rose to 35.1˚C
(0.88˚C) after PC and to 35.73˚C (0.53˚C) after WU, which is a
difference of 1.67˚C (0.88˚C; p,0.001). Although ST after PC
was also lower than after C (35.65˚C (0.95˚C)), the difference of
0.41˚C (0.97˚C) was not significant (p.0.05).
Thus, the lowest ST (at the end of testing) was found after
PC, although only the differences between PC and WU were
significant. At the point of volitional fatigue, after WU, ST did
not significantly differ from C.
Blood lactate concentration (mmol/l)
control (C) test and after precooling (PC) or warm-up (WU).
Blood lactate concentration (mmol/l) during the step test in the
Core temperature (°C)
510 152025 30 3540
conditions and after precooling (PC) or warm-up (WU).
Core temperature (˚ C) during the step test in the control (C)
the control test (C) and after precooling (PC) or warm-up (WU).
Skin temperature (˚ C) at the beginning and end of the step test in
Effects of warm-up and precooling383
The aim of this study was to investigate whether classic WU
(active) or PC (passive) was able to enhance endurance
performance in the heat.
The effects of WU and PC procedures before an endurance
performance had not yet been compared directly. The results
indicate that there are significant differences between the PC
and WU conditions in measures of running performance, HR,
CT and ST. There were no significant differences in BL
The reduction of CT was regarded as the basis of performance
enhancement by Duffield et al.11However, it could be shown in
this study that there are performance enhancements with no
reduction in CT: after PC with the cooling vest, running
performance was significantly higher than after WU or C,
although the difference in performance between the WU and
the PC condition was, distinctly, the highest.
In addition to CT, ST is the decisive factor in PC: at
significantly lower ST, higher running performances are found.
Unlike what was seen in the previous studies,12 13the CT did
not decrease immediately after the PC procedure, and even
increased by 0.5˚C (p,0.01). This can be regarded as a
compensatory thermoregulatory reaction of the human body.
However, a delayed decrease in CT was found to occur with the
onset of exercising. This phenomenon is known as the after-
drop effect, which can be explained by the reperfusion of cooled
peripheral tissue.14During endurance performance, a distinct
reduction in the rise in CT was measured, supporting the
findings of Duffield et al.11
Therefore, reducing CT during the PC procedure is not a
prerequisite for achieving a performance-enhancing effect in
subsequent running exercises.
In conclusion, the use of a cooling vest for 20 min improved
running performance compared with that after WU and in C
conditions. WU has a negative effect on endurance performance
in heat. During the first 30 min of testing, the values for HR, CT
and ST were significantly lower (p(0.05) after PC than after
Further studies with intensified PC should be conducted. It
would be of particular interest to investigate the effects of
additional cooling of further body parts.
We thank all participants for their support and involvement throughout
the study. In particular, we thank Philipp Oerding for his continued
assistance and Matthias Marckhoff for his support and comments on
earlier drafts of this manuscript. We also acknowledge the financial
support of the Bundesinstitut fu ¨r Sportwissenschaft (BISp), Bonn,
Germany, for this project.
Sandra U¨ckert, Institute of Sports Science, University of Dortmund,
Winfried Joch, Institute of Sports Science, University of Muenster,
Competing interests: None declared.
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What is already known on this topic
N In addition to the lack of warm-up and precooling studies
utilising performance-based test protocols, little was
previously known about on the effect of different
thermoregulatory preparation procedures on endurance
performance in the heat.
What this study adds
N This study has shown that precooling (the use of an ice-
cooling vest for 20 min before exercising) improved
running performance in the heat, whereas the 20-min
warm-up procedure had a detrimental effect.