National Geographic : 1974 Jan
Like athletes in training, mine recruits in South Africa go through a rigorous routine to prepare them for the heat and humidity of the depths. For four hours at a stretch in a heated room they step onto a block and down again, starting at 12 steps a minute. In eight days those who complete the regimen are racing at double speed, a sign that they have built up the heat tolerance necessary for working below. Trapped in technology's nightmare, a naked research volunteer coated with black paint is bombarded by light to determine the total area of his body-a crucial factor in measuring the capacity to withstand heat. Results of the experiment will help South African gold-mine managers compute the amount of ventilation needed at different depths to maintain adequate working temperatures.