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 participate 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 laboratory (30°C–32°C, 50% relative humidity). These ambient conditions were chosen to represent typical outdoor environmental 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 (HRmax had 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 was measured at the end of the WU. Between WU and the 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.
During the running step test, the HR was recorded at 5 s intervals. CT was measured every 2 min and BL 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 themselves via the stop button of the treadmill or by the supervisor.
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
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 temperatures in the range 35.5–42.0°C, and 0.3°C outside this range.
ST was measured using the Ebro TFN 1093 digital thermometer (Ebro, Ingolstadt, Germany), which has a resolution of 0.1°C (measuring range −50°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 −50 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). Post hoc comparisons were used, where appropriate. Significance was set at p<0.05.