The program consisted of three main elements: meditation, exposure to cold, and breathing techniques (see Movie S1 for an impression of the training program).

i)
Meditation, so-called “third eye meditation,” a form of meditation including visualizations aimed at total relaxation.
ii)
During the training, subjects voluntarily exposed themselves to cold in several ways: standing in the snow barefoot for up to 30 min and lying bare chested in the snow for 20 min; daily dipping/swimming in ice-cold water (0–1 °C) for up to several minutes (including complete submersions); and hiking up a snowy mountain (elevation: 1,590 m) bare chested, wearing nothing but shorts and shoes at temperatures ranging from −5 to −12 °C (wind chill: −12 to −27 °C).
iii)
Breathing techniques, consisting of two exercises. In the first exercise subjects were asked to hyperventilate for an average of 30 breaths. Subsequently, the subjects exhaled and held their breath for ∼2–3 min (“retention phase”). The duration of breath retention was entirely at the discretion of the subject himself. Breath retention was followed by a deep inhalation breath, that was held for 10 s. Subsequently a new cycle of hyper/hypoventilation began. The second exercise consisted of deep inhalations and exhalations in which every inhalation and exhalation was followed by breath holding for 10 s, during which the subject tightened all his body muscles. These two breathing exercises were also performed during the endotoxemia experiments. Additional element of the training program consisted of strength exercises (e.g., push-ups and yoga balance techniques).